CEA Task Force Report on Grid Interactive Solar PV_Jan'10

REPORT OF TASK FORCE

ON

INTEGRATION OF SOLAR SYSTEMS WITH

THERMAL/ HYDRO POWER STATIONS

AND

CONNECTIVITY OF SOLAR ROOF TOP

SYSTEMS WITH GRID

CENTRAL ELECTRICITY AUTHORITYNew Delhi – 110066

January’ 2010

Report of the Task Force to examine technical issues relating to feasibility of integrating solar power plants with thermal/hydro-electric power plants and connectivity of solar roof top systems with grid

Central Electricity Authority January 2010

CONTENTS

Section-1 Report of the Task Force

Section-2 Report of Subgroup -I - Grid Interactive Rooftop Solar PV

System

Section-3 Report of Sub-Group –II & III - Integration of Solar Systems

with Thermal/Hydro Power Stations

SECTION - 1


Central Electricity Authority. January 2010 Page 1 of 7

1 Background

1.1 A Task Force was set up by the Ministry of New & Renewable Energy (MNRE) under the chairmanship of Chairperson CEA, vide O.M. No. 32/61/2009-10/PVSE dated 28th May 2009, to examine technical issues relating to feasibility of integrating solar power plants with thermal/hydro-electric power plants and connectivity of solar roof top systems with grid. Composition of the Task Force is given at enclosed Annexure-I. The Terms of Reference of the task force were as under:-

In regard to thermal/hydro electric plants i) To examine feasibility of integrating solar based plants with

Thermal (Coal and gas)/Hydro-electric power plants including issues relating to availability of land and effect of fugitive ash in coal based plants.

ii) To suggest the feasible options for type of solar plants (PV solar cells, solar thermal plants) for installation at thermal/hydro-electric power plants.

iii) To examine the feasibility of hybrid solar power systems in thermal power plants including use of secondary fuel firing or heat storage devices during the period when solar power is not available.

iv) To suggest scheme for connecting solar based plants with the station electric supply system for thermal/hydro electric power plants.

v) To suggest arrangements for metering and accounting for energy supplied by the solar based plants.

vi) To suggest modalities of implementation for solar based plants at thermal/hydro electric power plants including preparation of project report

In regard to solar roof top systems i) To suggest schemes for connecting solar roof top systems with the

grid. ii) To suggest arrangements for metering for accounting of energy

supplied by the solar roof tops.

1.2 As a part of efforts to rapidly add solar generation capacity under the

National Solar Mission., it is envisaged to identify and set up solar based capacity in vacant land in thermal and hydro plants and this Task Force has been constituted by the Ministry of New and Renewable Energy (MNRE) to work out the modalities of integrating such solar plants with the



thermal and hydro-electric plants and also the technical issues related to interconnection of solar rooftop systems with the grid

1.3 The first meeting of the Task Force was held in CEA office on 18th June,

2009. During the meeting three sub-groups were formed as follows:-

Sub-group – I Grid interactive rooftop solar PV systems Sub-group – II Integration of solar systems with thermal power stations Sub-group –III Integration of solar systems with hydro power stations

1.4 The details of the tasks assigned to the sub-groups, and their composition is as under:-

Sub-Group-I: Grid interactive rooftop solar PV systems

This Sub-group was assigned the task of bringing out guidelines on interconnection of solar rooftop systems; one each for a commercial building and an independent house; to the grid including preparation of connection scheme, bill of material, specifications, metering as well as safety aspects. The Sub-group was also asked to look into to voltage, frequency, harmonics, reliability, islanding and other related issues with regard to solar generation.

The composition of this Sub-group is as under:

i) Sh. S.M. Dhiman, Member (GO&D), CEA - Chairman

ii) Sh Puneet Goel, Director, Ministry of Power

iii) Sh. M.K. Raina, ED(T&RE), NHPC

iv) Shri Jitender Sood, BEE

v) Shri CVSN Murthy, AGM BHEL , Bangalore

vi) Sh. S.K. Sangal, ED, CEL

vii) Sh. S. Ramesh, Chief Engineer, KPCL

viii) Sh. Vivek Singla, GM NDPL

ix) Sh. Alok Gupta, Chief Engineer (DPD), CEA – Member-Secretary

Sub-Group-II: Integration of solar plants with existing thermal plants

This Sub-group was assigned the task of studying the issues related to integration of solar plants with existing CCGT stations and coal based



stations including issues of space availability, type of solar system, connectivity and metering. The composition of this Sub-group is as under:

i) Shri S. Seshadri, Member (Thermal), CEA - Chairman

ii) Dr. Ashvini Kumar, Director, MNRE

iii) Shri Lalit Kapur, Director, MOEF

iv) Shri A.K Gupta,. G.M, NTPC

v) Shri R.K. Sikri, GM, NTPC

vi) Shri Vishnu Gupta, G.M(I/C), BHEL

vii) Shri M. M Vijayvergia Executive Director RRECL

viii) Shri N.M. Mathur, Chief Engineer, RRVUNL

ix) Sh. Sanjay Sharma, Director, CEA – Member-Secretary

Sub-Group-III: Integration of solar plants with existing hydro plants

This Sub-group was assigned the task of studying the issues related to integration of solar plants with existing hydro-electric stations including issues of space availability, type of solar system, and feasibility report for one of the stations of BBMB. The composition of this Sub-group is as under:

i) Shri Suresh Chander, Chief Engineer (TE&TD), CEA - Chairman

ii) Dr. Ashvini Kumar, Director, MNRE.

iii) Dr. S. Bhowmik Addl. Director, MOE&F

iv) Shri Vishnu Gupta, G.M (I/C), BHEL

v) Sh. M.K. Raina, ED(T&RE), NHPC

vi) Shri Ashok Thapar Director BBMB

vii) Shri Moti Lal Director , Hydro, CEA – Member-Secretary

2 Deliberations of the Task Force

2.1 The task force in its first meeting held on 18th June 2009, constituted the sub-groups as referred above and discussed the broad modalities to be followed by the sub-groups. The report of sub-group I was discussed in the second meeting of the task force held on 29th October 2009 and approved by the task force. The third meeting of the task force was held on 8th January 2010 wherein the report of sub-group II &III was discussed by the task force and approved.



2.2 The record notes of discussion of the meetings are placed at Annex-II. The

reports of the sub-group I and sub-group II & III have been placed at section- 2 and section- 3 of this report. The salient details of the issues covered in the reports of the sub-groups are discussed as under:-

3 Sub-group I Grid Interactive roof top systems

3.1 The report covers details of the solar roof top systems including equipment to be used, functional description, type of schemes metering arrangements, software and control requirements, selection of cables, earthing requirements, technical particulars of meters, schematic diagrams, voltage levels, power quality issues such as harmonics & ripples, compliance to regulations, capacity, area coverage, implementation mechanism, islanding protection etc.

3.2 Various technologies for Solar PV systems, their relative costs and

efficiency were studied by the sub-group. It is seen that crystalline silicon is the frontrunner technology having about 92 % market share. The efficiency of this technology is about 15 to 23 %. Thin film technology presently has a low market share of about 8 % . Various types of thin film technologies exist with efficiency ranging from 6% to 12%. The cost of thin film technologies is lower at about 6o% of the cost of crystalline silicon technologies.

3.3 The report also gives the bill of material for typical ratings from few kW to

50kW systems. A model technical specification has also been prepared (volume-II) which can be readily used by DISCOM/consumer.

3.4 The various types of metering and tariff philosophies prevalent in the world

were studied by the Sub-group. It is gathered that under solar power mission Generation Based Incentive(GBI) based on entire solar generation is being considered irrespective of what consumer consumes .This generation would be treated as deemed export to the grid. With this consideration metering arrangements have been finalized and it has been proposed that wherever the battery is used two inverter scheme would be better solution.

3.5 The report also indicates a sample calculation to arrive at the capacity of

the roof top solar PV system, battery and inverter.

3.6 A group comprising of officers from CEA, BHEL and NHPC has been entrusted the task of preparing a feasibility report and identifying sites for installation of solar PV plant at Leh and Kargil. Feasibility report is under preparation and shall be submitted separately.



3.7 The Sub-group has also prepared a detailed project report for a 25 kW roof

top solar system to be installed in Sewa Bhawan as a demonstration project. The DPR is available at CEA website http://cea.nic.in .

4 Sub-group II & II Integration of solar systems with thermal/hydro Power stations

4.1 The report covers feasible options for installing solar systems in thermal and hydro power plants including the technology options and the possible areas of installation of the solar systems in the power stations. The pre-requisites for installing solar systems and the existing facilities in the power stations required to be shared with solar systems have also been discussed. The feasibility of integrating the solar system with thermal stations on the steam side and electrical side have also been discussed in detail. A brief summary of Feasibility Study for Solar Thermal Plant in NTPC -Anta CCGT station has also been annexed with the report for reference

4.2 The issues related to solar radiations in general and source of data for

solar radiation etc have been discussed in detail. Various solar thermal technologies have been discussed bringing out their International status of development, operating plants and relative costs and land and other inputs required. It is seen that solar trough and solar tower are the only two proven and matured technologies available and either of them can be adopted depending on the plant size proposed and site specific factors- land availability, its orientation, aspect ratio etc.

4.3 The options for solar generation at any power station would depend upon

the following: i) Adequate solar irradiation ii) Availability of land iii) Availability of water (for solar thermal)

Adequate direct normal component of solar irradiation is necessary for solar thermal plants. Normally a solar irradiation (DNI) of 1800 kWh/m2 is considered necessary for solar thermal plants. Solar PV plants can, however, utilize global radiations including diffused components. Thus solar irradiations available at a location is the prime consideration for selection of technology

4.4 About 5-7 acres/MW land is required for solar thermal plants. Thus availability of large tract of continuous flat land would be required if solar



thermal is to be considered. When land is available in several scattered patches, rather than a contiguous piece, then Solar photovoltaic plants could be considered. Solar thermal plants require water for cooling tower blow down and DM make up. Usually water requirement is 4 M3/MWh. Additionally, some water is also required for washing of mirror panels and requirement varies with location depending on dust levels.

4.5 In hydro stations large tract of continuous land are generally not available.

Also the hydro stations have no facilities for supplying warm up steam etc to solar thermal power plant. Thus solar PV systems may be the only choice for hydro stations.

4.6 Providing thermal storage systems involves additional solar field for

storage systems. It is not only expensive but would also require additional land for the storage system itself and also for additional solar field. Thus in the context of power stations, storage systems are not considered necessary.

4.7 The choice of areas for solar plants in existing Thermal Power Stations

could be:-

• Open land areas not intended for any future expansion • Abandoned ash ponds in coal fired stations • Areas in existing green belt subject to MOE&F approval • Roof top of turbine hall (for PV systems) • Roof top in administrative building, guest houses, and large

buildings (for PV systems) 4.8 Integration of solar plants on the steam side to the existing station is

expected to be too cumbersome. This may also disturb the existing thermodynamic cycle and involve issues of performance reliability of the existing station. Thus, the solar plants in existing TPS may be considered as a stand alone plant without any inter-connection to the steam side of the station. However, integrated solar plants with gas plants could be considered for new stations depending on site specific factors for which site specific techno-economics and feasibility studies would be required.

4.9 It may not be advisable to integrate solar plant with new coal based plants

since turbine-generators in coal based plants are of standard rating and there would be no increase in the power output by solar thermal energy.

4.10 Typical station facilities required to be shared in case of solar thermal

plants are as under:-

• DM Water • Circulating water make up



• Auxiliary steam • Auxiliary electricity supply • Fire fighting system

4.11 Various options available for integration of solar thermal power with

electrical system of existing gas based plant have been discussed in the report and electrical integration with the option of additional switch yard bay comes out to be the most suitable amongst all the options. However, site specific studies are required regarding the interconnection before finalizing the scheme.

4.12 All thermal and hydro generating utilities should explore the potential of

installing solar plants in vacant land of their existing stations. Detailed Project Report for the specific project would be required to be developed by a consultant to study the feasibility of the solar power plant, technology to be employed, generation projections, cost estimates etc.

****

SECTION - 2

REPORT OF SUBGROUP-I ON

GRID INTERACTIVE ROOFTOP SOLAR PV SYSTEM

1111

Grid Connected PV SystemsGrid Connected PV SystemsGrid-connected PV systems are connected to utility grid. Energy generated by

the array is fed directly to the grid.

PCU

TO LOAD

+

GRID SUPPLY

SOLAR PVARRAY

AC B

US

• Inverter • Load voltage conditioning• Data logger• Local & Remote monitoring

Central Electricity Authority New Delhi

December 2009

ii

C O N T E N T S S.No. TOPICS Page No.

1 BACKGROUND 1 2 CONSTITUTION OF SUB-GROUP-I: 2 3 TERM OF REFERENCE OF SUBGROUP-I 2 4 PROCEEDINGS OF SUB-GROUP-I 3 5 SCOPE 3 6 TYPE OF TECHNOLOGY FOR SOLAR CELLS 3 7 EQUIPMENTS REQUIRED FOR GRID INTERACTIVE ROOF

TOP SOLAR PV SYSTEM 7

8 FUNCTIONAL DESCRIPTION 7 9 PROTECTIONS AND CONTROL 12 10 CAPACITY CALCULATIONS FOR PV SYSTEMS 13 11 TYPE OF SCHEMES AND COINNECTION ARRANGEMENTS 13 12 METERING PHILOSOPHY AND REQUIREMENTS 17 13 VOLTAGE LEVELS 20 14 COMPLIANCE TO REGULATIONS ON METERING AND GRID

CONNECTIVITY 21

15 POWER QUALITY REQUIREMENTS 21 16 COMMUNICATION INTERFACE 23 17 MOUNTING STRUCTURES 24 18 POWER AND CONTROLCABLES 24 19 EARTHING MATERIAL 25 20 JUNCTIONS BOXES OR COMBINERS 26 21 ACCEPTANCE OF SYSTEMS AND PERFORMANCE

EVALUATION 26

22 SYSTEM DOCUMENTATION 26 23 TECHNICAL PARTICULARS, SPECIFICATION AND BILL OF

MATERIAL 26

LIST OF ANNEXURES AND EXHIBITS TO REPORT OF SUBGROUP-I A. ANNEXURES:

Sl No Annexure No Particulars Page No.

1. Annexure-I Minutes of 1st Meeting of Sub-Group - I held on 15.7.09. 27 2. Annexure-II Calculation for PV solar system capacity for individual

consumer house 32

3. Annexure-III Technical particulars of single phase 10-60 or 18-20 amp energy meters

34

4. Annexure-IV Typ ica l techn ica l pa r t i cu la rs o f So la r Modu les (160 and 80 wat ts )

38

5. Annexure-V Technical particulars of solar PV system-0.5 -50 kWp 39

iii

B. EXHIBITS: Sl No Schemes Description Page No.1 Scheme-I Grid interactive Solar PV

System without Battery. 40

2 Scheme-II Grid interactive Solar PV System with full load Battery backup.

41

3 Scheme-III Grid interactive Solar PV System with Partial load Battery backup

42

4 Scheme-IV Grid Interactive Solar PV System With Full Load DG Backup

43

5 Scheme-V Grid Interactive Solar PV System With Partial Load DG Backup

44

6 Scheme-VI Grid Interactive Solar PV System With Full Load Battery and DG Backup

45

7 Scheme-VII Grid Interactive Solar PV System With Partial Load Battery and DG Backup

46

iv

EXECUTIVE SUMMARY

1. A Task force was constituted by MNRE under the chairmanship of Chairperson CEA to look into the technical issues related to feasibility of the integration of solar power plant with thermal/hydro and interconnectivity of rooftop solar PV system with the grid. This task force in its meeting held on 18-06-2009 constituted a Subgroup-I to look into metering and interconnectivity of roof top solar PV system with the grid. The Subgroup-I comprised of the following members.

i) Shri SM Dhiman, Member(GO&D), CEA -Chairman ii) Shri Puneet Goel, Director, Ministry of Power iii) Shri MK Raina, ED, NHPC iv) Shri Jitendra Sood, Energy Economist, BEE v) Shri CVSN Murthy, AGM, BHEL, Bangalore. vi) Shri SK Sangal, ED, CEL vii) Shri S Ramesh, Chief Engineer, KPCL viii) Shri Vivek Singla, GM, NDPL ix) Shri Alok Gupta, Chief Engineer(DP&D), CEA-Member Secretary

2. The sub-group met on 15th July, 2009 in CEA and deliberated upon the metering and interconnectivity issues.

3. The report is prepared with an aim to provide ready solutions for roof

top solar PV systems for commercial, industrial and residential complex installations and individual consumer houses to feed full or part of the house load. However these can be extended for non-roof top solar photovoltaic systems as well.

4. The following type of modules of grid interactive roof top Solar PV

system have been considered by the sub-group for various applications depending upon grid supply availability and the redundancy the consumer needs.

Sl No

Schemes Description

1 Scheme-I Grid interactive Solar PV System without Battery. 2 Scheme-II Grid interactive Solar PV System with full load

Battery backup. (Two inverter scheme)

3 Scheme-III Grid interactive Solar PV System with Partial load

v

Battery backup (Two inverter scheme) 4 Scheme-IV Grid Interactive Solar PV System With Full Load

DG Backup 5 Scheme-V Grid Interactive Solar PV System With Partial Load

DG Backup 6 Scheme-VI Grid Interactive Solar PV System With Full Load

Battery and DG Backup (Two inverter scheme) 7 Scheme-VII Grid Interactive Solar PV System With Partial Load

Battery and DG Backup (Two inverter scheme)

5. The report covers equipment to be used, functional description, type of schemes metering arrangements, software and control requirements, selection of cables, earthing requirements, technical particular of meters, schematic diagrams, voltage levels, power quality issues such as harmonics , ripples, compliance to regulations, capacity, area coverage, implementation mechanism, islanding protection etc. The report also gives the bill of material for typical ratings from few kW to 50kW systems as also a model technical specification (volume-II) which can be readily used by DISCOM/consumer.

6. The various types of metering and tariff philosophies prevalent in the

world were studied by the Sub-group. It is gathered that under solar power mission Generation Based Incentive(GBI) based on entire solar generation is being considered irrespective of what consumer consumes .This generation would be treated as deemed export to the grid. With this consideration metering arrangements have been finalized and it is proposed that wherever the battery is used two inverter scheme would be better solution.

7. The report also indicates a sample calculation to arrive at the capacity

of the roof top solar PV system, battery and inverter.

8. A group comprising of officers from CEA, BHEL and NHPC has been entrusted the task of preparing a feasibility report and identifying sites for installation of solar PV plant at Leh and Kargil. Feasibility report is under preparation and shall be submitted separately.

9. The Sub-group has also prepared a detailed project report for roof top

solar system to be installed in Sewa Bhawan as a demonstration project which is also enclosed.

1

REPORT OF SUBGROUP -I

ON GRID TIED ROOFTOP SOLAR PV SYSTEM

1 BACKGROUND: 1.1 Several cities and towns in the country are experiencing a substantial growth in

their peak electricity demand. Municipal Corporations and the electricity utilities are finding it difficult to cope with this rapid rise in demand and as a result most of the cities/towns are facing severe electricity shortages. Various industries and commercial establishments e.g. Malls, Hotels, Hospitals, Nursing homes etc housing complexes developed by the builders and developers in cities and towns use diesel generators for back-up power even during the day time. These generators capacities vary from a few kilowatts to a couple of MWs. Generally, in a single establishment more than one generators are installed; one to cater the minimum load required for lighting and computers/ other emergency operations during load shedding and the others for running ACs and other operations such as lifts/ other power applications. Under such conditions use of grid tied roof top Solar Photovoltaic systems seem to be feasible solutions. Similar solar PV system can be employed in rural areas on vacant land to feed cluster of households where space is not a constraint and grid connectivity is not feasible as on today. The implementation of standalone system in such rural areas would give an opening to setting up of small scale industries.

1.2 In order to supplement ambitious capacity addition programme of Government of

India solar power is being encouraged in our country. This will also reduce green house gas emission. The National Solar Mission envisages solar generation capacity addition of 20000 MW by the year 2020. The main objective of installing solar photovoltaic device system in urban areas, industries and rural areas will be as follows:-

i) To reduce the burden on conventional electricity in cities/towns facing

shortage of power. ii) To provide access to electricity to all rural households especially where

grid connectivity is not a cost effective solution.

iii) To create awareness and demonstrate effective alternate solutions for community/institutional solar based systems in urban areas and industry.

iv) To save highly subsidized diesel in institutions and other commercial

establishments including industry facing huge power cuts especially during day time.

2

v) To reduce the burden on depleting fossil fuel resources such as coal and to reduce carbon emission.

vi) To provide a clean and environment friendly energy generation.

1.3 Accordingly a task force was constituted by MNRE under the chairmanship of Chairperson, CEA, to examine the technical issues related to feasibility of integrating solar power plants with thermal/hydro power plant and interconnectivity of solar rooftop system with the grid. The task force comprises of members from CEA, Ministry of Power, Ministry of Environment and Forest, MNRE, BEE, NTPC, NHPC, BHEL, CEL, RCEL, RRVUNL, GEDA etc. The first meeting of the task force was held on 18th June, 2009 at CEA office, New Delhi. During the meeting three sub-groups were formed to look after interconnectivity of solar rooftop system with the grid, integration of solar power plant with the existing thermal power plant and integration of solar power plant with the existing hydro plant respectively.

2 CONSTITUTION OF SUB-GROUP-I: 2.1 The constitution of Subgroup-I on Grid Tied Roof Top Solar PV System:

is as follows:-

1. Shri SM Dhiman, Member(GO&D), CEA-Chairman 2. Shri Puneet Goel, Director, Ministry of Power 3. Shri MK Raina, ED, NHPC 4. Shri Jitendra Sood, Energy Economist, BEE 5. Shri CVSN Murthy, AGM, BHEL, Bangalore. 6. Shri SK Sangal, ED, CEL 7. Shri S Ramesh, Chief Engineer, KPCL 8. Shri Vivek Singla, GM, NDPL 9. Shri Alok Gupta, Chief Engineer(DP&D), CEA-Member Secretary

3 TERM OF REFERENCE OF SUBGROUP-I: 3.1 To bring out guidelines on interconnection of roof top solar PV system one each

for a commercial building and an independent house to the grid which shall include scheme, bill of material, specification, metering as well as safety aspects.

3.2 To look at voltage, frequency, harmonics, reliability, islanding and other related

issues with regard to solar generation. 3.3 To prepare a Feasibility Report for installing solar plant in Leh and Sewa Bhawan.

3

4 PROCEEDINGS OF SUB-GROUP-I: 4.1 The First meeting of the Subgroup-1 was held on 15th July 2009 in CEA office. The

Minutes of first meeting of the Sub-Group I held during the meeting are enclosed at Annexure-I. The draft report prepared was also circulated to various members of subgroup as also to members of task force. The comments received were discussed and report was finalized accordingly.

5 SCOPE: 5.1 These guidelines are prepared with an aim to provide ready solutions for roof top

systems for commercial, industrial and residential complex installations and individual consumer houses to feed full or part of the house load. However these can be extended for non-roof top solar photovoltaic systems as well.

5.2 These guidelines are prepared to give an insight of the solar photo voltaic system

and are not a comprehensive technical or economic guide on photovoltaic systems. The consumers are required to consult photovoltaic system designer, retailer or supplier before procuring and installing any solar photovoltaic system.

5.3 These guidelines cover type of PV system to be used, functional description,

connectivity, equipment used, harmonics, schematic diagrams, voltage levels, compliance to regulations, capacity, area coverage, implementation mechanism, islanding protection, safety and reliability etc

6 TYPE OF TECHNOLOGY FOR SOLAR CELLS: 6.1 The solar PV system shall be designed with either mono/ poly crystalline silicon

modules or using thin film photovoltaic cells or any other superior technology having higher efficiency.

6.2 Three key elements in a solar cell form the basis of their manufacturing

technology. The first is the semiconductor, which absorbs light and converts it into electron-hole pairs. The second is the semiconductor junction, which separates the photo-generated carriers (electrons and holes), and the third is the contacts on the front and back of the cell that allow the current to flow to the external circuit. The two main categories of technology are defined by the choice of the semiconductor: either crystalline silicon in a wafer form or thin films of other materials.

6.3 Crystalline Technology

i. Crystalline silicon (c-Si) has been used as the light-absorbing semiconductor in most solar cells, even though it is a relatively poor absorber of light and requires a considerable thickness (several hundred microns) of material. Nevertheless, it has proved convenient because it

4

yields stable solar cells with good efficiencies and uses process technology developed from the huge knowledge base of the industry.

ii. Two types of crystalline silicon are used in industry. The first is mono

crystalline, produced by slicing wafers (up to 150mm diameter and 350 microns thick) from a high-purity single crystal boule.

iii. The second is multi crystalline silicon, made by sawing a cast block of

silicon first into bars and then wafers. The main trend in crystalline silicon cell manufacture is toward multi crystalline technology.

iv. For both mono- and multi crystalline Si, a semiconductor homo junction is

formed by diffusing phosphorus (an n-type dopant) into the top surface of the boron doped (p-type) Si wafer. Screen-printed contacts are applied to the front and rear of the cell, with the front contact pattern specially designed to allow maximum light exposure of the Si material with minimum electrical (resistive) losses in the cell.

v. The most efficient production cells use mono crystalline c-Si with laser

grooved, buried grid contacts for maximum light absorption and current collection.

vi. Some companies are using technologies that by-pass some of the

inefficiencies of the crystal growth/casting and wafer sawing route. One route is to grow a ribbon of silicon, either as a plain two-dimensional strip or as an octagonal column, by pulling it from a silicon melt. Another is to melt silicon powder on a cheap conducting substrate. These processes may bring with them other issues of lower growth/pulling rates and poorer uniformity and surface roughness.

6.4 Thin film Technology

i. The selected materials are all strong light absorbers and only need to be about 1micron thick, so materials costs are significantly reduced. The most common materials are amorphous silicon (a-Si, still silicon, but in a different form), or the polycrystalline materials: cadmium telluride (CdTe) and copper indium (gallium) diselenide (CIS or CIGS).

ii. Each of these three is amenable to large area deposition (on to

substrates of about 1 meter dimensions) and hence high volume manufacturing. The thin film semiconductor layers are deposited on to either coated glass or stainless steel sheet.

iii. The semiconductor junctions are formed in different ways, either as a p-i-

n device in amorphous silicon, or as a hetero-junction (e.g. with a thin cadmium sulphide layer) for CdTe and CIS. A transparent conducting

5

oxide layer (such as tin oxide) forms the front electrical contact of the cell, and a metal layer forms the rear contact.

iv. Amorphous silicon is the most well developed of the thin film

technologies. In its simplest form, the cell structure has a single sequence of p-i-n layers. Such cells suffer from significant degradation in their power output (in the range 15-35%) when exposed to the sun.

v. Better stability requires the use of thinner layers in order to increase the

electric field strength across the material. However, this reduces light absorption and hence cell efficiency.

vi. This has led the industry to develop tandem and even triple layer devices

that contain p-i-n cells stacked one on top of the other. In the cell at the base of the structure, a-Si is sometimes alloyed with germanium to reduce its band gap and further improve light absorption. All this added complexity has a downside though; the processes are more complex and process yields are likely to be lower.

vii. In order to build up a practically useful voltage from thin film cells, their

manufacture usually includes a laser scribing sequence that enables the front and back of adjacent cells to be directly interconnected in series, with no need for further solder connection between cells.

viii. As before, thin film cells are laminated to produce a weather resistant and

environmentally robust module. Although they are less efficient (production modules range from 5 to 8%), thin films are potentially cheaper than c-Si because of their lower materials costs and larger substrate size.

ix. However, some thin film materials have shown degradation of

performance over time and stabilized efficiencies can be 15-35% lower than initial values. Many thin film technologies have demonstrated best cell efficiencies at research scale above 13%, and best prototype module efficiencies above 10%. The technology that is most successful in achieving low manufacturing costs in the long run is likely to be the one that can deliver the highest stable efficiencies (probably at least 10%) with the highest process yields.

x. Amorphous silicon is the most well-developed thin film technology to-date

and has an interesting avenue of further development through the use of "microcrystalline" silicon which seeks to combine the stable high efficiencies of crystalline Si technology with the simpler and cheaper large area deposition technology of amorphous silicon.

6

xi. However, conventional c-Si manufacturing technology has continued its steady improvement year by year and its production costs are still falling too.

xii. The emerging thin films technologies are starting to make significant in-

roads in to grid connect markets, particularly in Germany, but crystalline technologies still dominate the market. Thin films have long held a niche position in low power (<50W) and consumer electronics applications, and may offer particular design options for building integrated applications.

6.5 It would be seen from the table given below that crystalline solar modules are

costlier but much more efficient than thin film modules and therefore have 92% share in the market. Typical cost of solar cell technologies are as follows, however the cost are further coming down worldwide.

6.6 Approximate cost of Technologies

Technology type

Current conversion efficiency (%)

Manufacturing cost ($ per watt)

Market share (%)

A. Crystalline silicon

92

A.1 Mono crystalline

17-23 2.40 -

A-2 Poly crystalline

15-18 2.15

B. Thin film 8 B.1 Amorphous

silicon 6 1.35 -

B.2 Tandem micro crystalline

8.5 1.35 -

B.3 Cadmium telluride

11 1.15 -

B.4 Copper indium gallium diselenide

12 1.75 -

(Source : Power line vol.13-No.8-April, 2009)

7

7 EQUIPMENTS REQUIRED FOR GRID TIED ROOF TOP SOLAR PV SYSTEM: 7.1 The grid tied roof top solar PV system generally comprises the following

equipment.

i. SPV Power Source ii. Inverter iii. Grid Charger(only with system with batteries) iv. Charge Controller (only with system with batteries) v. Batteries(Optional) vi. Mounting Structure vii. AC and DC Cables viii. Earthing equipment /material ix. Junction Boxes or combiners x. Instruments and protection equipments

7.2 The functions of inverter, Charge controller and Grid charger can be built in one

unit called power conditioning unit (PCU). Similarly inverter and charger can also be built in one unit. All control logics are built in inverter or PCU.

8 FUNCTIONAL DESCRIPTION 8.1 SOLAR PV POWER SOURCE

i. Photovoltaic solar system use the light available from the sun to generate electricity and feed this into the main electricity grid or load as the case may be. The PV panels convert the light reaching them into DC power. The amount of power they produce is roughly proportional to the intensity and the angle of the light reaching them. They are therefore positioned to take maximum advantage of available sunlight within siting constraints. Maximum power is obtained when the panels are able to 'track' the sun's movements during the day and the various seasons. However, these tracking mechanisms tend to add a fair bit to the cost of the system, so a most of installations either have fixed panels or compromise by incorporating some limited manual adjustments, which take into account the different 'elevations' of the sun at various times of the year. The best elevations vary with the latitude of the load location.

ii. The power generating capacity of a photovoltaic system is denoted in Kilowatt

peak (measured at standard test conditions of solar radiation of 1000 W per m2). A common rule of thumb is that average power is equal to 20% of peak power, so that each peak kilowatt of solar array output power corresponds to energy production of 4.8 kWh per day (24 hours x 1 kW x 20% = 4.8 kWh)

iii. Solar photovoltaic modules can be developed in various combinations

depending upon the requirements of the voltage and power output to be taken

8

from the solar plant. No. of cells and modules may vary depending upon the manufacturer prudent practice.

iv. The capacity and rating of Roof top SPV Power Source will depend on the

load to be fed by it. The basic building block of PV technology is the solar “cell”. Numbers of cells are wired in series to provide one PV “module”. Many modules are linked together to form a PV “array”. Many arrays are then wired to form a solar PV system to give the desired output. Roof top PV modules are sold commercially in the range of 10 watts to 100 watts power output.

v. For the purpose of grid tied roof top solar PV system of 0.5kW to 50 kW

considered in the report, two PV modules of 160 watts and 80 watts consisting of 72 cells and 36 cells respectively have been considered. These modules of sizes other than above are also available in the market and can be used. These modules can be connected in series parallel combination to form PV arrays and PV systems.

vi. As a rule of thumb, the roof top solar PV modules will cover a maximum area

in the range of 8m2 to 18m2 per kWp depending on the type of technology used and also depending upon the space available. The orientation would be generally towards south and inclination angle shall be as per latitude of the location of the installation.

vii. The power delivered by an SPV power source will depend on PV module

rating and isolation level of the location and environmental factors like dust, wind, velocity and temperature of the location. Knowing the rating of the SPV system (power source) only vis-a-vis load does not guarantee the deliverance of full power of the load. Some of the features of SPV technology & environmental factors which influence the performance of the power source are I-V Curve, Voltage of the SPV power source, Irradiance or light intensity, Temperature of the cells, Response of the light spectrum, and Orientation of the panel/array, Full Sun hours or Isolation /day. (isolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed In the case of photovoltaic it is commonly measured as kWh/(kWp·y) (kilowatt hours per year per kilowatt peak rating).

viii. With a view to encourage technology development and reduction in the cost of

the PV power plant projects, the PV power project developers shall make effort to utilize the state of the art technology to set up the plants. They are expected to use large capacity and higher power output PV modules available for the specific technology used in setting up the power plant.

ix. I-V Curve

The suppliers of the SPV power source shall provide the I-V Curve at standard condition of 1000W/m

2 solar intensity at 25 Degree Centigrade and Air Mass

9

(thickness of the atmosphere)) of 1.5. By looking at the I-V curve it shall be possible to know about the optimum power to be delivered by the SPV panel/array/source. In addition the peak hour behavior of current and voltage can also be estimated from the curve. A module which is rated at 17 volts will produce less than its rated power when used in a battery system. This is because the working voltage will be between 12 and 15 volts. As wattage (power) is the product of volts times amps, the module output will be reduced. For example: a 50 watt module working at 13.0 volts will produce 39.0 watts (13.0 volts x 3.0 amps = 39.0 watts).This is important to remember when sizing a PV system. An I-V curve is simply all of a module’s possible operating points, (voltage/current combinations) at a given cell temperature and light.

x. SPV Voltage:

The voltage of the SPV power source is an important factor that affects the battery charging in case of system with battery. The voltage of the SPV Cell/Module/Panel decreases with the rise of its temperature, which increases or decreases @ 0.0024V/cell/degree Celsius. To charge a battery fully the voltage of the power source shall be better than 2.5V/cell. Considering this fact, the Voltage of the SPV panel at optimum power shall be such that the voltage delivered by it at the battery terminals shall be about 2.25V/cell.

xi. Irradiance or Light intensity

In actual field condition the irradiance may be different than the standard irradiance. The SPV modules or panels are designed at a standard irradiance of 1000 watts per meter square at 25° Celsius and AM (air mass) 1.5, which is called “ONE SUN” or peak irradiance. The current delivered by the SPV power source will decrease or increase but there would be no variation in the system voltage.

xii. Solar PV modules shall comply with the requirement of Bureau of Indian

Standards (BIS) or IEC 61215 or other international standards and MNRE approved test centers.

xiii. The PV power project developers are required to optimize generation of

electricity in terms of kWh generated per kWp of PV capacity installed vis-à-vis available solar radiation at the site. This may be achieved through use of efficient electronics, lower cable losses, maximization of power transfer from PV modules to electronics and the grid, maximization of power generation by enhancing incident radiation by optional methods like seasonally changing tilt angles etc.

xiv. Before installing the PV solar system it shall be ensured that sun path is clear

and not shaded by trees, roof gables, chimneys, buildings or other features of

10

home such as cable antenna and the surrounding landscape. Roof top must be shake proof, flat concrete tiles and mission tiles roof.

xv. As a rule of thumb 15% generation may be deducted if system is to be located

within 50 km. of the coast and 7% may be deducted if PV system is located in valley regions subject to fog conditions.

xvi. Ideally, grid tied systems do not require battery back up as the grid acts as

the back-up for absorbing excess solar power and feeding the customer load in case of shortfall. However, to enhance the performance reliability of the overall systems, a minimum battery-back of one hr of load capacity could also be considered where grid supply is not reliable and erratic.

8.2 INVERTER

i. The DC power produced is fed to inverter for conversion into AC. In a grid tied

system AC power is fed to the grid at 11 KV three phase systems or to a 415V three phases or 220/240 V single phase system line depending on the system installed at institution/commercial establishment or residential complex or single house consumer and load requirement. Power generated from the solar system during the daytime is utilized fully by powering the captive loads and feeding excess power to the grid as long as grid is available. In cases, where solar power is not sufficient due to cloud cover etc. the captive loads are served by drawing power from the grid. The inverter should always give preference to the Solar Power and will use Grid/DG power only when the Solar Power is insufficient to meet the load requirement.

ii. The output of the inverter must synchronize automatically its AC output to the exact AC voltage and frequency of the grid.

iii. In a solar PV system without battery or with battery the inverter continuously

monitors the condition of the grid and in the event of grid failure; the inverter automatically switches to off-grid supply within 20-50 milliseconds. The solar system is resynchronized with the grid within two minutes after the restoration of grid. Grid voltage is continuously monitored and in the event of voltage going below a preset value and above a preset value, the solar system shall be disconnected from the grid within the set time. Both over voltage and under voltage relays shall have adjustable voltage (50% to 130%) and time settings (0 to 5 seconds).

iv. Over-voltage protection shall be provided by using Metal Oxide Varistors

(MOVs) on DC and AC side the inverter.

v. The inverter shall be so designed so as to operate the PV system near its maximum Power Point (MPP), the operating point where the combined values

11

of the current and voltage of the solar modules result in a maximum power output.

vi. The inverter shall be a true sine way inverter for a grid interactive PV

system.

vii. In case of system with battery, inverter also monitors the, state of Battery Voltage, and performs switching operations to ensure that battery is charged continuously.

viii. The degree of protection of the indoor inverter panel shall be at least IP 31

and that of outdoor at least IP-55 8.3 CHARGE CONTROLLER

i. Normally in a solar PV system with battery, battery is first charged from solar system through Charge Controller. A charge controller monitors the battery's state-of-charge to insure that when the battery needs charge-current it gets it, and also insures the battery isn't over-charged. Connecting a solar panel to a battery without a regulator seriously risks damaging the battery and potentially causing a safety concern.

ii. Charge controllers (or often called charge regulator) are rated based on

the amount of amperage they can process from a solar array. If a controller is rated at 20 amps it means that you can connect up to 20 amps of solar panel output current to this one controller. The most advanced charge controllers utilize a charging principal referred to as Pulse-Width-Modulation (PWM) - which insures the most efficient battery charging and extends the life of the battery. Even more advanced controllers also include Maximum Power Point Tracking (MPPT) which maximizes the amount of current going into the battery from the solar array by lowering the panel's output voltage, which increases the charging amps to the battery - because if a panel can produce 60 watts with 17.2 volts and 3.5 amps, then if the voltage is lowered to say 14 volts then the amperage increases to 4.28 (14v X 4.28 amps = 60 watts) resulting in a 19% increase in charging amps for this example.

iii. Many charge controllers also offer Low Voltage Disconnect (LVD) and

Battery Temperature Compensation (BTC) as an optional feature. The LVD feature permits connecting loads to the LVD terminals which are then voltage sensitive. If the battery voltage drops too far the loads are disconnected - preventing potential damage to both the battery and the loads. BTC adjusts the charge rate based on the temperature of the battery since batteries are sensitive to temperature variations above and below about 75 F degrees.

12

8.4 GRID CHARGER

In a grid tied solar PV system with battery, a grid charger can also provided which charges the battery taking AC power from the Grid/DG in case solar power is not sufficient to charge the battery or battery voltage is very low. This may happen during the continuous cloudy days.

8.5 BATTERIES

For the purpose of making this report battery system is not considered in view of reliability of grid power supply and has been kept as optional item. In case battery system is also envisaged generally low maintenance. Lead Acid batteries are provided wherever required. Generally, the batteries are provided are of 2V cells connected in series to reach the system voltage. Battery shall be suitable for charging from SPV system as well as from the grid in case of grid interactive system and with SPV system alone in case of stand alone system.

9 PROTECTIONS AND CONTROL 9.1 In addition to disconnection from the grid (islanding protection ) on no supply,

under and over voltage conditions , PV systems shall be provided with adequate rating fuses, fuses on inverter input side (DC) as well as output side (AC) side for overload and short circuit protection and disconnecting switches to isolate the DC and AC system for maintenance.

9.2 Fuses of adequate rating shall also be provided in each solar array module to

protect them against short circuit.

9.3 There could always be possibility of something being wrong with the inverter and it continues to put electricity to the grid in the event of grid failure. In such case to avoid any accident, a manual disconnect switch beside automatic disconnection to grid would have to be provided to isolate the grid connection by the utility personal to carry out any maintenance. This switch shall be locked by the utility personal.

9.4 Following protections shall also be provided to ensure safe and efficient operation

and shall include the following:

• Avoiding Battery overcharging (in case of SPV system with battery) • Avoiding Battery over discharge(in case of SPV system with

battery) • Battery over load protection(in case of SPV system with battery) • Ground fault protection system.

13

• Any other protection as per manufacturer’s prudent practice for safe and efficient protection.

10 CAPACITY CALCULATIONS FOR PV SYSTEMS:

Sample calculation for A sample calculation to arrive at capacity of PV system, Battery and inverter is placed at Annexure-II

11 TYPE OF SCHEMES AND CONNECTION ARRANGEMENTS: 11.1 The rooftop solar system can be a standalone system as well as grid tied system.

In this report the Sub-Group has considered only the grid tied system. In the grid tied system also there can be a number of schemes depending upon the reliability of supply the consumer needs.

11.2 Wherever the battery is not envisaged, the solar system can be directly connected

to consumer AC bus and the total energy of the solar system will be supplied to consumer/grid depending upon the requirement of the consumer. The scheme for grid tied rooftop solar system is shown in Scheme-I.

11.3 In case where battery is also envisaged, the scheme of connection for solar PV

system will depend upon the way the battery is charged. There are two possible ways of charging battery. First one is where there is AC coupling i.e. first the DC produced by solar is converted into AC and battery is connected through a charger which converts AC into DC. This arrangement is shown in Configuration-A. In this arrangement as long as grid is available the solar system, consumer, and battery system will be tied up with grid. In case of grid failure solar system, battery system and consumer load would be disconnected form grid and solar will be connected to battery and AC loads through another route. This arrangement has been finalized with the premise that normally consumer and battery system will take supply from gird. This scheme is envisaged in Europe where feed in tariff is employed. However the only difference proposed here is regarding the positioning of the solar meter(SM). In the scheme in vogue in Europe for feed in tariff the SM is towards the grid side and does not record the energy drawn by the consumer /battery during grid failure. In the suggested scheme as per configuration-A, during grid failure also it measures the solar generation including the energy drawn by battery and the consumer load.

11.4 In the second arrangement, solar system directly charges the battery through

charge controller i.e. DC coupling (Configuration-B). In this arrangement the AC system is not involved to charge the battery and battery will always be connected to solar system. In case, battery is discharged due to any reason whatsoever solar system will first charge the battery and the excess generation from the solar will be fed into grid. This scheme would not reflect the true gross generation produced by the solar PV system.

14

11.5 In case battery system is envisaged, it is proposed to adopt Configuration A.

8

CONFIGURATION –A

Solar PVInverter

Consumer

Battery

InverterCum Charger

GrId

GM

CM

SM

Normally solar is tied with the grid. When grid fails inverter controlled switch S1 ,located in inverter, will open within 20-50 m sec and S2 will close

S1

S1S2

SM-Solar Meter

GM-Grid Meter

CM-consumer Meter

SI

SEGI

GE

CI

CE

SE+GI+CE=GE+CI+SI

SW

SW –Manual Lockable switch for grid maintenance

9

CONFIGURATION B

Solar PVCharge controller

Consumer

Battery

InverterCum Charger

GrIdGM

CM

SM

Normally solar is tied with the grid. When grid fails switch S located in inverter will open within 20-50 m sec

S

SM-Solar Meter

GM-Grid Meter

CM-consumer Meter

Battery Charging is through DC Bus so SM always measures Net Solar generation ie. Gross excluding battery Charging

SE+GI+CE=GE+CI+SI

GI

GE

SI

SE

CI

CE

15

11.6 Based on above two configurations following schemes of grid tied roof top Solar

PV system has been considered by the sub-group for various applications depending upon grid supply availability and the redundancy the consumer needs.

Sl No

Schemes Description

1 Scheme-I Grid tied Solar PV System without Battery. 2 Scheme-II Grid tied Solar PV System with full load Battery backup. 3 Scheme-III Grid tied Solar PV System with Partial load Battery

backup 4 Scheme-IV Grid Tied Solar PV System With Full Load DG Backup 5 Scheme-V Grid Tied Solar PV System With Partial Load DG Backup 6 Scheme-VI Grid Tied Solar PV System With Full Load Battery and

DG Backup 7 Scheme-VII Grid Tied Solar PV System With Partial Load Battery and

DG Backup 11.7 The above schemes are briefly discussed

i. Scheme-I : Grid tied roof top solar PV system without battery

This is a simplest scheme of the grid tied rooftop solar system. In this arrangement inverter which is heart of the entire solar system continuously supervises the grid condition and in the event of grid failure or under voltage or over voltage, the solar system is disconnected by the circuit breaker /auto switch provided in the inverter. Since there is no back up in the solar system, it cannot supply the consumer load in the event of grid failure because the load is continuously varying in nature. Block diagram of the scheme is shown in scheme-I

ii. Scheme-II: Grid tied roof top solar PV system with full load Battery back up (based on Configuration-A)

In this scheme when the grid is available consumer loads will be fed from grid side and solar system is connected to grid through its inverter. Solar is continuously feeding the grid. In this arrangement battery and inverter cum charger (which may be available in the consumer house) is also shown. The DC generated form solar is first converted to AC and than it is connected to other equipments/grid. When grid fails automatic disconnection from the grid side takes place and solar is connected to battery system and AC consumer load directly through another switch which operates after a time delay. Block diagram of the scheme is shown in Scheme-II.

16

iii. Scheme-III: Grid tied roof top solar PV system with partial load Battery back up (Based on Configuration-A)

Under this scheme also, the basic operation will be same as given in for

scheme-II but bus splitting is necessary in the even of grid failure so as to supply critical loads as battery back up is not sufficient to feed the entire consumer load. In the event of grid failure or under voltage or over voltage, inverter will disconnect the grid supply and connect the inverter with emergency panel. Battery system shall supply the emergent loads and battery will be charged depending on availability of solar power. Block diagram of the scheme is shown in Scheme-III.

iv. Scheme-IV: Grid tied roof top solar PV system with full load

DG backup system

All the equipment envisaged in the Scheme-I would be provided in this scheme as well, however, in addition there is second line of defense and DG set is also envisaged because in some parts of the country, the grid supply is not very reliable and is erratic. The operation of this scheme would be similar to module A but in addition provision is kept for consumer DG set. In case the failure of utility grid the solar PV system shall be disconnected form the grid and DG shall start. Once DG is started the solar system shall also be connected to the AC bus after synchronization with the DG set. DG set will be automatically disconnected in the event of grid supply is restored. Block diagram of the scheme is shown in Scheme-IV.

v. Scheme-V: Grid tied roof top solar PV system with partial load DG

Backup system

Under this scheme also, the basic operation will be similar to that under Scheme-VI. Only AC bus segregation in the consumer premises would be necessary to supply critical loads during grid failure. Block diagram of the scheme is shown in Scheme-V.

vi. Scheme-VI: Grid tied roof top solar PV system with full load Battery and DG backup system(based on Configuration-A)

In this arrangement solar PV system will remain tied up with the utility grid as long as supply from the grid is available. In the event of supply failure or low voltage or over voltage solar system will be disconnected from the grid and DG system will start. Once the DG set is started and solar generation is possible the solar system shall be again connected to the system. In the event of restoration of grid supply the solar system shall be again connected to main grid. All the control operations shall be performed by the inverter connected to solar system. Block diagram of the scheme is shown in Scheme-VI.

17

vii. Scheme-VII :Grid tied roof top solar PV system with partial load

Battery and DG backup system(based on Configuration-A)

The scheme will be similar to Scheme-VIII. Only AC load segregation will be done in case of grid failure. Block diagram of the scheme is shown in Scheme-VII

11.8 In Europe where feed into tariff based on gross energy generated by solar system

is envisaged, the first scheme is more popular. In USA and Canada the metering arrangement is based on net metering and the second scheme is generally envisaged The Committee has suggested that we should adopt. Configuration – A where battery system is envisaged.

11.9 The above schemes have been considered with the premise that solar system is

installed by individual consumer. There can be a case where solar company or a service provider implements a solar system and makes contract with the distribution utility and supplies number of consumers. In that case solar system shall be connected to utility bus instead of consumer bus. The connection point shall be utility bus. The metering arrangement for the same will be similar otherwise.

11.10 The control scheme for sequence of operations of various equipments is a matter

of detail engineering and can be prepared in consultation with the supplier of the solar PV module and inverter.

11.11 The DG and its associated equipments shall not in scope of supplier ,however in

case DG system is envisaged by the consumer necessary hardware and controls to disconnect and connect DG set shall be provided in inverter and wiring shall be done by the solar PV supplier.

11.12 Block diagram has been made to illustrate the connection diagram and metering

arrangement and does not show all wires, breakers, fuses, disconnecting switches and lightening arrestors which are required to be provided for safe and efficient operation by supplier of PV system.

12 METERING PHILOSOPHY AND REQUIREMENTS: 12.1 Metering is required to measure the following energy transactions besides

measurement of DC battery voltages, DC current, AC system voltages and currents , frequency etc

a. Solar Gross Generation b. Consumer load consumption c. Export of energy to the Grid d. Import of energy from the Grid

18

e. Export from DG to Grid

12.2 There are two basic philosophies of metering prevalent in the world when utility grid is connected with solar generating source and feed the load.

• Net metering or Market rate net metering • Feed in tariff metering

12.3 Net Metering:

i. Net metering is an electricity policy for consumers who own (generally small) renewable energy facilities, such as wind, solar power or home fuel cells. Net metering means measurement of net energy consumption by the load from a system. If a consumer load is connected to two generating sources and one is infinite grid and other is a small generating source such as solar described above their may be following options depending upon the size of the small source and time of use

ii. Generated power by the small source is in excess of the load at a particular

moment. In this case surplus power from this source will be fed into the grid if it is a grid interactive system.

iii. Generated power by the small source is less than the power required by the

load. In this case the extra power to meet the consumer load will be taken from grid.

iv. At the end of month the billing of the consumer by the distribution company is

done based on the net energy import from the grid. Under net metering, a distribution company receives credit for net energy supplied to the consumer load in case it is import and pays to the developer of the small source if there is net export to the grid.

v. In this case the tariff has to be same for export as well as import of energy

as the billing is done on net energy basis. vi. In some parts of USA and Canada, credit for the export is adjusted on

predefined period of say six months or year and adjusted in running bills. No incentive is given for net export beyond the defined period. However it is learnt that gradually they are also shifting towards feed in tariff.

12.4 Feed in tariff Metering

i. It is a different method of providing power to the electricity grid that does not offer the price symmetry of net metering, making this system a lot less profitable for home users of small renewable energy systems.

19

ii. Under this arrangement, practice is to have two uni-directional meters are installed—one records electricity drawn from the grid and the other records excess electricity generated and fed back into the grid. The above functionality can also be achieved with having one meter having separate export and import recording registers.

iii. The user pays retail rate for the electricity they use, and the power provider

purchases their excess generation at its avoided cost (wholesale rate). There may be a significant difference between the retail rate the user pays and the power provider's avoided cost.

iv. Germany and Spain, on the other hand, have adopted a price schedule, or

Feed-in Tariff (FIT), whereby customers get paid for any electricity they generate from renewable energy on their premises. The actual electricity being generated is counted on a separate meter, not just the surplus they feed back to the grid.

v. In Germany, for the solar power generated, a feed-in tariff of more than 3

times the retail rate per kWh for residential customers is being paid in order to boost solar power (figure from 2006). Wind energy, in contrast, only receives around a third of the retail rate because the German system pays what each source costs.

vi. Feed in tariff is in vogue except in some parts of USA and Canada

12.5 Metering arrangement in Indian Context:

i. The various type of metering and tariff philosophies prevalent in the world were studied by the group and it was considered that Generation Based Incentive (GBI) based on entire solar generation would be appropriate to encourage consumer to implement roof top solar PV systems. Under this arrangement, both on the solar power consumed by the operator and solar power fed into the grid feed in tariff be provided. The two inverter based scheme (Configuration A) as described above is recommended for systems where battery is envisaged as in configuration-B the solar meter(export) measures net generation i.e. gross generation minus battery charging by solar. In cases where battery is not envisaged the scheme-I would be applicable.

ii. Suggested metering scheme for solar PV systems is shown in block diagram

of each schemes annexed herewith. Meters would have to install as per above.

iii. Metering scheme indicated herewith is only for guideline purpose and

applicable scheme would be as per the metering scheme finalised by the appropriate Electricity Regulatory Commission.

20

iv. Metering requirements shall be as per Regulations on “Installation and

Operation of Meters“.

v. If the tariff is different for different time slots in a day, the Time of Use metering arrangement would be required to be provided and facility for recording export and import in the meter for each time slot shall be required.

vi. Technical particulars of meters are given in Annexure-III.

13 VOLTAGE LEVELS:

i. Though rooftop systems shall be generally connected on LV supply, large solar PV system may have to be connected to 11 kV system. Following criteria have been suggested for selection of voltage level in the distribution system for ready reference of the solar suppliers.

a Up to 10 KW PV system supply Low Voltage single phase supply

shall be provided. b Thereafter up to a level of 100 kW PV system, three phases low

voltage supply shall be provided. c In case load is more than 100 kW and does not exceed 1.5 MW, SPV

system connection can be made at 11 kV level. d In case load is more than 1.5 MW PV system and does not exceed 5

MW, SPV system connection can be made at 11kV/33 kV/66kv level or as per the site condition.

ii. Utilities may have voltage levels other than above, DISCOMS may be

consulted before finalization of the voltage level and specification be made accordingly.

iii. The voltage variation in various power supply systems shall be ±10% iv. The solar PV system for above 11 kV systems is not considered in these

guidelines because the same may not be feasible on roof top due to space limitation and operational problems.

v. In the roof top solar system, the grid interconnection is generally made to

low voltage single phase or three phase system. For large PV system for commercial installation having large load, the solar power can be generated at low voltage levels and stepped up to 11 kV level through the step up transformer. The transformers and associated switchgear would require to be provided by the SPV supplier.

21

14 COMPLIANCE TO REGULATIONS ON METERING AND GRID CONNECTIVITY: CEA has notified regulations on “Installation and Operation of Meters”, grid connectivity and technical standards of grid connectivity which stipulates the various technical requirements such as accuracy class of meters, level of harmonics and other requirements. The developer of solar power shall ensure that requirement of these Regulations shall be complied with. Non-compliance to these regulations will be dealt with requisite provisions of the ACT.

15 POWER QUALITY REQUIREMENTS: 15.1 DC INJECTION INTO GRID:

i. The injection of DC power into the grid shall be avoided by using an isolation transformer at the output of the inverter.

ii. Various standards and guidelines define the maximum DC component that

feed-in electricity from grid-feeding inverters may possess. The following is the practice followed by few countries.

Standard designated as:

Standard applicable in: threshold values

IEC 61727 Thailand 1% (of rated AC current) IEEE 1547 USA 0.5% (of rated AC

current) EN 50438 Europe Not specified IEEE 929 Thailand (until 2008) 0.5% (of rated AC

current) UL 1741 USA 0.5% (of rated AC

current) AS 4777 Australia 0.5% (of rated AC

current) VDE 0126-1-1 Germany 1 A Synergrid C10/11 Belgium 1% (of rated AC current) DK5940 Italy 0.5% (of rated AC

current) G83 United Kingdom 20 mA (recommended)

iii. BIS is aligned to IEC standards as such it is suggested that IEC 61727 may

be followed in Indian environment. It is also proposed by the committee that CEA may approach BIS to develop standards for solar systems covering power quality requirements for solar systems.

22

15.2 RIPPLE CONTENT ON DC SIDE

i. The most common meaning of ripple in electrical science, is the small unwanted residual periodic variation of the direct current (dc) output of a power supply which has been derived from an alternating current (ac) source. This ripple is due to incomplete suppression of the alternating waveform within the power supply.

ii. PV modules shall produces Pure DC Voltage and Current without any ripple.

The inverter operation will influence the voltage on the DC side, so will have a backlash on the PV generator voltage. Depending on the inverter topology and with or without transformer, the ripple on the DC side may appear very different. Even an old style transformer inverter has some very low AC 2x50Hz ripple on the DC side. That's due to the energy flow in the inverter.

iii. A transformer-less inverter has no galvanic separation between AC and DC

side. The voltage to ground is influenced by AC and depending on the topology of the inverter even full AC sin wave on the DC side (on top of DC voltage level - measured to earth) or for other topologies, there will be no AC ripple on DC side.

iv. There is no standard available for ripple control, it is proposed that the ripple

content must not exceed 3% based on products literature. 15.3 HARMONICS ON AC SIDE:

i. Harmonic distortion is caused principally by non-linear load such as rectifiers and arc furnaces and can affect the operation of a supply system and can cause overloading of equipments such as capacitors, or even resonance with the system leading to overstressing (excessive voltage & current). Other effects are interference with telephone circuits and broadcasting, metering errors, overheating of rotating machines due to increased iron losses (eddy current effects), overheating of delta connected winding of transformer due to excessive third harmonics or excessive exciting current.

ii. The limits for harmonics shall be as stipulated in the CEA Regulations on

grid connectivity which are as follows:

a. Total Voltage harmonic Distortion= 5% b. Individual Voltage harmonics Distortion=3% c. Total Current harmonic Distortion=8%

iii. Utilities must procure sufficient number of harmonic measuring

instruments for carrying out measurements at regular intervals near the source of harmonics generation.

23

15.4 VOLTAGE UNBALANCE

The Voltage Unbalance at 33 kV and above shall not exceed 3.0%

15.5 VOLTAGE FLUCTUATIONS

(i) The permissible limit of voltage fluctuation for step changes which may occur repetitively is 1.5%.

(ii) For occasional fluctuations other than step changes the maximum permissible limits is 3%.

(iii) The limits prescribed in (i) and (ii) above shall come into force not later than five years from the date of publication of these regulations in the Official Gazette.

16 COMMUNICATION INTERFACE:

16.1 The communication must be able to support

• Real time data logging • Event logging • Supervisory control • Operational modes • Set point editing

16.2 The following parameters shall also be measured and and displayed continuously.

a. Solar system temperature b. Ambient temperature c.Solar irradiation/isolation d.DC current and Voltages e.DC injection into the grid (one time measurement at the time of installation) f.Efficiency of the inverter g.Solar system efficiency h.Display of I-V curve of the solar system i.Any other parameter considered necessary by supplier of the solar PV system based on prudent practice.

16.3 Data logger system must record these parameters for study of effect of various

environmental & grid parameters on energy generated by the solar system and various analysis would be required to be provided through bar charts, curves, tables, which shall be finalized during approval of drawings.

24

16.4 The communication interface shall be an integral part of inverter and shall be suitable to be connected to local computer and also remotely via the Web using either a standard modem or a GSM / WIFI modem.

16.5 The bidder must supply all the required hardware to have this web based SCADA

operational such that the system can be monitored via the web from distribution company office. Full fledged SCADA is recommended for Solar PV plants above 25 kW.

17 MOUNTING STRUCTURES: 17.1 Hot dip galvanized iron mounting structures may be used for mounting the

modules/ panels/arrays. These mounting structures must be suitable to mount the SPV modules/panels/arrays on the roof top, on the ground or on the poles/masts, at an angle of tilt with the horizontal in accordance with the latitude of the place of installation.

17.2 The following may be ensured about the mounting structure :

i The Mounting structure shall be so designed to withstand the speed for the wind

zone of the location where a PV system is proposed to be installed (Delhi-wind speed of 150 kM/ hour). It may be ensured that the design has been certified by a recognized Lab/ Institution in this regard.

ii The mounting structure steel shall be as per latest IS 2062: 1992 and

galvanization of the mounting structure shall be in compliance of latest IS 4759.

18 POWER AND CONTROL CABLES: 18.1 Power Cables of adequate rating shall be required for interconnection of :

- Modules/panels within array - Array & Charge Controller - Charge Controller & Battery - Charge controller & Loads Including Inverter (if used) & between load &

inverter.

18.2 The cable shall be 1.1 grade, heavy duty, stranded copper/aluminium conductor, PVC type A insulated, galvanized steel wire/strip armoured, flame retardant low smoke (FRLS) extruded PVC type ST-1 outer sheathed. The cables shall, in general conform to IS-1554 P+I & other relevant standards.

18.3 The minimum size of 11 kV power cables shall be chosen taking into account Fault level contribution to the system and full load current. However, power cables size for 415 V systems shall be chosen taking into account the full load current & voltage drop. The allowable voltage drop at terminal of the connected equipment

25

shall be max. 2.5% at full load. The derating factors viz. group duration of temp. duration shall also be considered while choosing the conductor size.

18.4 Control Cables

The cable shall be 1.1 grades, heavy duty, stranded copper conductor, PVC type A insulated, galvanized steel wire/strip armoured, flame retardant low smoke (FRLS) extruded PVC type ST-1 outer sheathed. The cables shall, in general conform to IS-1554 P+I & other relevant standards.

18.5 The permissible voltage drop from the SPV Generator to the Charge controller shall not be more than 2% of peak power voltage of the SPV power source (generating system). In the light of this fact the cross-sectional area of the cable chosen is such that the voltage drop introduced by it shall be within 2% of the system voltage at peak power.

18.6 All connections should be properly terminated, soldered and/or sealed from

outdoor and indoor elements. Relevant codes and operating manuals must be followed. Extensive wiring and terminations (connection points) for all PV components is needed along with electrical connection to lighting loads.

19 EARTHING MATERIAL: 19.1 Earthing is essential for the protection of the equipment & manpower. Two main

grounds used in the power equipments are :

a. System earth b. Equipment earth

19.2 System earth is earth which is used to ground one leg of the circuit. For example in AC circuits the Neutral is earthed while in DC supply +ve is earthed.

19.3 In case of equipment earth all the non-current carrying metal parts are bonded

together and connected to earth to prevent shock to the man power & also the protection of the equipment in case of any accidental contact.

19.4 To prevent the damage due to lightning the one terminal of the lightning protection

arrangement is also earthed. The provision for lightning & surge protection of the SPV power source & Charge controller is required to be made.

19.5 In case the SPV Array can not be installed close to the equipment to be powered

& a separate earth has been provided for SPV System, it shall be ensured that all the earths are bonded together to prevent the development of potential difference between ant two earths.

26

19.6 Earth resistance shall not be more than 5 ohms. It shall be ensured that all the earths are bonded together to make them at the same potential.

19.7 The earthing conductor shall be rated for the maximum short circuit current. &

shall be 1.56 times the short circuit current. The area of cross-section shall not be less than 1.6 sq mm in any case.

20 JUNCTIONS BOXES OR COMBINERS

Dust, water and vermin proof junction boxes of adequate rating and adequate terminal facility made of fire resistant Plastic (FRP) shall be provided for wiring. Each solar shall be provided with fuses of adequate rating to protect the solar arrays from accidental short circuit.

21 ACCEPTANCE OF SYSTEMS AND PERFORMANCE EVALUATION 21.1 The installer must verify that the system has been installed according to the

manufacturer’s procedures. A checkout procedure should be developed to ensure an efficient and complete installation.

21.2 A system can be checked with some common test equipment to verify proper

installation and performance. A key to keeping the system testing simple is to do the tests on cloudless days. Clouds can cause fluctuations that confound evaluation of the results.

22 SYSTEM DOCUMENTATION: It is essential that the owner have complete documentation on the system. System documentation should include an owner’s manual and copies of relevant drawings for whatever system maintenance might be required in the future. 23 TECHNICAL PARTICULARS, SPECIFICATION AND BILL OF MATERIAL: 23.1 Two PV modules are considered here one comprising cells forming a 160 watt

module and another 80 watt module. Technical particular of module Type-160 (160 watts) and Module Type-80 (80 watts) are indicated in Annexure-IV.

23.2 Bill of material for suggested ratings (0.5kW to 100 kW) of Roof top PV system is

indicated in Annexure-V. 23.3 Typical Technical specification of a rooftop solar system is enclosed as volume –II

of this report.

27

ANNEXURE-I

MINUTES OF THE FIRST MEETING OF SUB GROUP I – INTERCONNECTIVITY OF SOLAR PHOTO VOLTAIC ROOF TOP SYSTEMS WITH THE GRID HELD ON 15-07-2009.

First meeting of the Sub Group-I regarding Interconnectivity of Solar Photo Voltaic Roof Top System with the Grid was taken by Member (GO&D), CEA at 10.30 hours on 15th July, 2009 at CEA, Sewa Bhawan, R.K. Puram, New Delhi. List of participants is enclosed. 2. Member (GO&D), CEA, welcomed the participants to the meeting and stated that a National Solar Mission has been envisaged to ensure rapid and large scale diffusion of solar energy technologies in the country. National Solar Mission envisages setting up of grid inter active solar capacity of about 20,000 MW by 2020 & about 1 lakh MW by 2030. Among various applications, grid interactive Solar Power generation will be one of the important applications. A Task Force has been constituted under the Chairperson, CEA to examine inter-alia, technical issues relating to feasibility of integrating solar based plants with thermal/hydro electric power plants and connectivity of Solar rooftop systems and other Solar Plants with grid. In the first meeting of Task Force held on 18th June, 2009, three Sub Groups were constituted to look into various aspects related to setting up of solar power plants in India. The terms of reference of the Sub Group- I headed by Member (GO&D) CEA is to bring out guidelines on interconnection of Solar roof top system for the commercial and domestic buildings to the grid which would include scheme, bill of material, specification, metering as well as safety aspect. This Sub Group would also look at voltage, frequency, harmonics, reliability, islanding and other related issued with regard to solar generation. Member (GO&D), CEA has also been requested to prepare a feasibility report for installing solar plant in Leh & Ladakh Region. 4. Subsequently M/s. BHEL and M/s. CEL made presentations regarding their experience of setting up of Solar Power Plants in the country covering all aspects including manufacturing, installation and operation etc. During the presentation it was seen that M/s. BHEL has implemented solar PV System at the following places-

• Lakshadweep - aggregating capacity of 1 MWp at various islands

(8x100 + 1x150 +2x50 KW)

• Andaman & Nicobar - (2x50 KW )

• Sunderaban (WB)- 490 kWp at six Islands & 55 kWp under progress,

• Ranchi - 620 kWp (2.2 to 5.5 kW packages fo tribal school & hostels)

• Punjab - 200 No. SPV each of 1800 Wp for water pumps

• Chattisgarh- 220 kWp village electrification system ranging from 1 to 6 kWp

28

• APTRANSCO- Vidyut Soudha-Hyderabad – 100 kWp

M/s. BHEL indicated that synchronization of SPV with grid needs to be with digital phased locked type to ensure continuous tracking and better loop response. Inverter output needs to be for larger window so far as voltage (330 V to 460 V, L-L) and frequency (47Hz to 52 Hz). M/s. BHEL indicated that meter must record both the export and import from the grid and has to be very accurate. It was indicated that output DC voltage can vary from 48 V DC to 800 V DC depending upon peak power rating of the array. The junction box for field cable termination needs to be IP 65 rated. The SCADA must be able to support

• Real time data logging • Event logging • Supervisory control • Operational modes • Set point editing

M/s. CEL in their presentation intimated that they have installed number of solar PV Plants both off and grid tied of various capacities and they are pioneer in the implementation of solar PV system. They have got accredition from various agencies. M/s. CEL indicated that inverter efficiency of about 94% - 98% available in the market and Grid Tied solar PV system must have the following features:

• Maximum power Point Tracking (MPPT) • Balancing of 3 phases • Automatic sleep mode operation at night to minimize unnecessary losses. • On Board data logging & LCD DISPLAY • Remote access facility via telephone network.

M/s. CEL also indicated scheme arrangement for 1 MW solar PV Plant which can generate 16 MU (16 million units) per year, improve the grid voltage and will meet the peak load as well. M/s CEL indicated that both bi-directional meter (1 meter) and unidirectional (2 meter) may be installed. M/s. NDPL also shared their experience on their two solar plants one 14.85 KW and another 3.96 KW which they have installed in their training institute at CENPEID at Rithala. M/s. NDPL also intimated that they are planning to install 1 MW plant at Keshav Puram which is sent for DERC approval.

NDPL indicated that it intends to add 50 MW of grid tied SPV Power Plants at consumer rooftops for 10,000 consumers @ 5 KW per consumer. The space requirement will be 700-800 Sq. feet each. For this, a policy incentive is required and suggested the following regulatory policy support –

• Capex subsidy of 50% on grid tied roof top system

29

• Long term loan at 8% to the end consumer (say 10-20 years) • 100% tax rebate on income for export of solar energy to the grid. • Energy buy back by utility at a cost of Rs. 6.37 per unit.

Chief Engineer (DP&D) intimated that metering is not a very complicated issue. CEA regulation on metering takes care of metering from such system and can be finalized by the appropriate electricity regulators. However, the metering scheme shall be formulated in the report of Sub-Group-I. 4 The following emerged from the discussion :

1 A number of grid tied Solar Photo Voltaic (SPV) Power Plants have been operational in the country for more than 10 years successfully.

2 Grid tied SPV PPs of capacities 200 KW and less are normally tied to the grid on

low voltage whereas capacities more than 200 KW are tied to the grid at 11 KV through a step up transformer however there are no fixed norms.

3 In the case of small DG Grid, the capacity of the SPV should not be more than

one third of the size of the grid for stable operation of grid. Installation of batteries for storage and back up is advisable for better regulation of frequency and quality of power.

4 The cost of procurement and installation of SPV Power Plants in the last 5 years

has come down significantly to about Rs. 16-19 Crores per MW from the earlier cost of Rs. 25 Crore per MW. The cost is likely to come down further with increase in the demand for SPV Power Plants.

5 Normally the cost break up of SPV Power Plant is of the order of:

• SPV Module 60% • Inverter 10% • Balance Equipments 30%

6 In case of use of batteries, the cost of the power plant will increase by 30-40%. The cost of battery is avoidable in case of connection with the infinite grid and the grid supply is reliable.

7 There are only few companies manufacturing inverters to suite the application in

the country and therefore, generally inverters are being imported by the manufacturer of SPV.

8 The SPV Power Plants are supplied with state of the art SCADA and various protection along with monitoring of the entire SPV system.

9 The level of total harmonic generation from the SPV Power Plant must be limited

to 3% only.

30

10 In place of single inverter, a number of inverters can be used to avoid the higher size cable and to improve the redundancy in the system.

11 The representative of Indian Semiconductor Association (ISA) informed that

there is shortage of silicon material and Indian manufactures are importing almost all of the silicon material being used in India. A total of about 400-500 MW capacity for manufacturing SPV Cells is available in India. We have to augment the manufacturing capacity in next 5 years to achieve the target of 1000 MW generation from SPV Plants.

12 A small group comprising of following officers to study the system of Leh and

Laddakh for installation of SPV Plants and to bring out a feasibility report was formed:

• Shri Puneet Goel, Director, MoP • SE, RE, J&K • Shri C.V.S.N Murthy, AGM, BHEL • Shri Y.K. Khanduja, DM, NHPC • Shri R.K. Verma – Director, CEA This group would meet frequently to finalize SPV system for Leh and Ladakh and

submit feasibility report to sub group I. This would be a part of the report of the sub group I. Shri R.K. Verma, Director would coordinate the activities of sub group.

13. The representative from J&K requested to install off grid SPV Power Plants at

following locations which would also be looked into by the above group: • Nyoma • Zamskar • Nobra • Darass

14. Member (GO&D), CEA stated that separate guidelines may be prepared for

various capacities of SPV Power Plants such as for capacities upto 1 kW, for capacities between 1 and 10 kW & for capacities more than 10 kW.

15. It was decided that BHEL / CEL/ NDPL/ ISA would provide the draft

specifications for all the items of SPV Power Plants including safety aspects to CEA as per above for finalizing the specifications of the SPV Plant within a week time.

The meeting ended with vote of thanks to the chair.

31

List of Participants Central Electricity Authority 1. Shri S.M. Dhiman, Member (GO&D) In chair 2 Shri Alok Gupta, Chief Engineer (DP&D) 3 Shri R.K. Verma, Director (DP&D) 4 Shri T.K. Saha, Director (DP&D) 5 Shri Vivek Goel, Dy. Director (DP&D) 6 Shri M.S. Sodhi, AD (DP&D) 7 Shri Raghbar Singh, AD (DP&D) 8 Shri Praveen Kamal, AD (DP&D) Ministry of Power Shri Puneet Goel, Director N.H.P.C. 1 Shri M.K. Raina, ED 2 Shri Y.K. Khanduja, DM B.E.E. Shri Jitendra Sood, Energy Economist NDPL

Shri Vivek Singla, GM C.E.L. Shri S.K. Sangal, ED Shri R.K. Jain, AGM K.P.C.L. 1 Dr. Tandan, MD 2 Shri Murli Dhar Rao, TD 3 Shri S. Ramesh, CE 4 Shri S.M. Jaandar 5 Shri T. Sannappa, Resident Engineer BHEL Shri CVSN Murthy,AGM J&K 1 Shri A. Matir, CPE 2 Shri Shiv Kumar, EE ISA Shri Rajiv Jain, AD

32

Annexure-II

CALCULATION FOR PV SOLAR SYSTEM CAPACITY FOR INDIVIDUAL CONSUMER HOUSE Total consumption(Units) per month= Consumption (Units) per day= Net power generation(units) required per day= Net power generation(watts hour) required per day= Approximate power generation losses(%) with good inverter (12/24 V DC to 230 V AC or high frequency CFL output) Minimum Required Gross Power Generation= Suns insolation factor in India for Solar P.V. (Photo Voltaic) Panel Requirement= (total Watt Hour requirement/insolation Factor) (Normal SPV Panels are available in 10W, 18W, 37W and 74 W) Number of Panels required (panels of 74 watts)= Battery requirement Normal autonomy of the system, minimum 1 day Total Watt requirement of the system (Multiply with 2 for getting 1 day no sun autonomy Minimum safety factor of the Battery= Total power requirement in the battery(watt Hour)=

Batteries are available in Ampere Hour rating with voltage rating of 6/12/24 V DC.

converting watt Hour into Ampere Hour (Ah), divide by the battery voltage rating

Battery Voltage Battery Ampere hours required = Normally batteries are available in Ah range of 40, 60, 80, 100 and 200. Capacity of One battery(AH) Number of batteries= Say Inverter Selection For every 1000 Watts, 1.1 KVA inverter is required. A normal house peak load will be 2000 to 2500 watts only. For Example a) 4 Tube lights for 4 hours-watts hour =4 nos. x 40 watts x 4 hours b) 2 CFL lamps for 4 hours-watts hour =4 nos. x 15 watts x 4 hours c) 1 Fan for 8 hours-watt hours =1 nos. x 60 watts x 8 hours d) 2 Fans for 4 hours-watt hours =2 nos. x 60 watts x 4 hours

33

e) 1 Refrigerator for 24 hours =1 no. x 600 watts x 24 hours x 20%

If operated carefully, a good refrigerator motor will be on for only 20% of the time f) 1 T.V for 6 hours-watt hours =1 no. x 60 watts x 6 hours g) 1 Mixie for 10 minutes-watt hours =1 no. x 750 watts x 10/60 hours h) 1 Washing machine for ? Hour =1 no.x 750 watts x 1/2 hour i) 1 water pump for ? Hour =1 no. x 375 watts x ? Hour Total Day's consumption(kwh) =a+b+c+d+e+f+g+h+i or kWh Total month's consumption =5.88 x 30 Or Peak load for the Day(watts) Refrigerator + 3 Fans + 4 Tuble lights + 1 TV =600+180+160+60 For every 1000 Watts, 1.1 KVA inverter is recommended

Hence the inverter requirement

34

Annexure-III

TECHNICAL PARTICULARS OF SINGLE PHASE 10-60 or 20-80 Amp ENERGY METERS

1.0 FUNCTIONAL SPECIFICATION: 1.1 Applicable IS IS 13779 or IS 14679 depending upon accuracy

of meters. 1.2 Regulations CEA Regulations on “ Installation and Operation

of Meters:” ,2006 1.3 Accuracy Class Index 1.0 or better up to 650 V 1.4 Voltage 415 Volt(P-P), +20% to -40% Vref, however the

meter should withstand the maximum system voltage i.e. 440 volts continuously.

1.5 Display a) LCD (Six digits),pin type 1.6 Power factor range Zero lag –unity- zero lead 1.7 Display parameters a) Display parameters :

LCD test, KWH import, KWH export, MD in KW export, MD in KW import, Date & Time, AC current and voltages and power factor (Cumulative KWH will be indicated continuously by default & other parameters through push-button) b) Display order shall be as per Annexure-A

1.8 Power Consumption Less than 1 Watt & 4VA in Voltage circuit and 2 VA for Current circuit

1.9 Starting current 0.2 % of Ib 1.10 Frequency 50 Hz with + / - 5% variation 1.11 Test Output Device Flashing LED visible from the front 1.12 Billing data a) Meter serial number, Date and time, KWH

import, KWH export, MD in KW (both export and import), History of KWH import and export, & MD(both export & import) for last 6 billing cycles along with TOD readings. b) All these data shall be accessible for reading, recording and spot billing by downloading through optical port on MRI or Laptop computers at site.

1.13 MD Registration a) Meter shall store MD in every 30 min. period along with date & time. At the end of every 30 min, new MD shall be compared with previous MD and store whichever is higher and the same shall be displayed. b) It should be possible to reset MD automatically

35

at the defined date (or period) or through MRI. c) Manual MD resetting using sealable push button is an optional.

1.14 Auto Reset of MD Auto reset date for MD shall be indicated at the time of finalizing GTP and provision shall be made to change MD reset date through MRI even after installation of meter on site.

1.15 TOD metering Meter shall be capable of Time of use metering for KWH, and MD in KW with 8 time zones (programmable on site through CMRI)

1.16 Security feature Programmable facility to restrict the access to the information recorded at different security level such as read communication, communication write etc

1.17 Memory Non volatile memory independent of battery backup, memory should be retained up to 10 year in case of power failure

1.18 Software & communication compatibility

a) Optical port with RS 232 compatible to transfer the data locally through CMRI & remote through PSTN / Optical fiber / GSM / CDMA / RF / any other technology to the main computer. b) The Supplier shall supply Software required for CMRI & for the connectivity to AMR modules. The supplier shall also provide training for the use of software. The software should be compatible to Microsoft Windows systems (Windows 98 system). The software should have polling feature with optional selection of parameters to be downloaded for AMR application. c) Copy of operation manual shall be supplied. d) The data transfer (from meter to CMRI / AMR equipment) rate should be minimum 1200 bps. e) The Supplier shall provide meter reading protocols.

1.19 Climatic conditions a) Refer IS: 13779 or IS: 14697 for climatic conditions. b)The meter should function satisfactorily in India with high end temperature as 60ºC and humidity up to 96%.

1.20 Meter Sealing As per CEA Regulations, Supplier shall affix one Utility /buyer seal on side of Meter body as advised and record should be forwarded to Buyer.

1.21 Guarantee / Warranty

10 Years.

1.22 Insulation A meter shall withstand an insulation test of 4 KV

36

and impulse test at 8 KV 1.23 Resistance of

heat and fire The terminal block and Meter case shall have safety against the spread of fire. They shall not be ignited by thermal overload of live parts in contact with them as per the relevant IS.

1.24 Battery Lithium with guaranteed life of 15 Years 1.25 RTC & Micro

controller The accuracy of RTC shall be as per relevant IEC / IS standards

1.26 P.C.B. Glass Epoxy, fire resistance grade FR4, with minimum thickness 1.6 mm

1.27 Power ON/Off hrs: Along with billing history parameters, meter shall log monthly ON/ Off hrs as history.

1.28 Tamper Logging Last 200 events of Magnetic tamper; single wire tamper and top cover tamper shall be logged in memory along with Occurrence and restoration event data. Logic of defining tamper and OBIS code shall be agreed before supply of meter.

1.29 Protection against HV spark:

Meter shall continue to record energy or log the event, incase it is disturbed externally using a 35KV spark gun/ ignition coil.

2. TAMPER & ANTI-FRAUD DETECTION/EVIDENCE FEATURES

The meter shall not get affected by any remote control device & shall continue recording energy at least under any one or combinations of the following conditions:

2.1 I/C & O/G Interchanged Meter should record forward energy 2.2 Phase & Neutral Interchanged Meter should record forward energy 2.3 I/C Neutral Disconnected,

O/G Neutral & Load Connected to Earth.

Meter should record forward energy

2.4 I/C Neutral disconnected, O/G Neutral Connected To Earth Through Resistor & Load Connected To Earth.


2.5 I/C Neutral connected, O/G Neutral Connected To Earth Through Resistor & Load Connected To Earth.


2.6 I/C (Phase & Neutral) Interchanged, Load Connected To Earth.


37

2.7 I/C & O/G (Phase or Neutral) Disconnected, Load Connected To Earth.


3.0 INFLUENCE PARAMETERS The meter shall work satisfactorily with guaranteed accuracy limit under the presence of the following influence quantities. a) External magnetic field – 0.5 Tesla. b) Electromagnetic field induction, c) Radio frequency interference, d) Vibration etc, e) Waveform 10% of 3rd harmonics, f) Voltage variation, g) Electro magnetic H.F. Field, h) D.C. immunity test,

ANNEXURE A DISPLAY SEQUENCE FOR THE PARAMETERS A Default Display: Cumulative KWH to be displayed continuously without decimal B On-demand Display: After using pushbutton the following parameters should be displayed. 1. LCD test 2. Date 3. Real Time 4. Current MD in kW 5. Current kW generated by solar system 5. Last month billing Date 6. Last month billing KWH reading 7. Last month billing Maximum Demand in KW 8. Last month billing Maximum Demand in KW occurrence Date 9. Last month billing Maximum Demand in KW occurrence Time 10. Instantaneous AC Current and Voltages Note: The meter display should return to Default Display mode (mentioned above) if the ‘push button’ is not operated for more than 6 seconds.

Annexure-IV TY PI CAL TE CHNI CAL P AR TI CULAR S OF S O LAR MODULES ( 160 AND 80 WATTS) Electrical Parameters Module-160 Module-80 Maximum Power Rating Pmax. (Wp)* 160.0 80.0Minimum Power Rating Pmin (Wp)* 150.0 75.0Rated Current IMPP (A)

4.45 4.45

Rated Voltage VMPP (V) 36.0 18.0Short Circuit Current Isc (A) 5.00 5.00Open Circuit Voltage Voc (V) 44.0 22.0 Physical Parameters No. of Cells(Nos) 72 36 Physical Dimension (mm) (L x W x T) 1580 x 805 x

42 1200 x 550 x 35

Weight (Kg) 14.2 7.4 Environmental Rating Nominal Operating Cell Temperature (NOCT ** (0C) 49 ±2 Maximum permitted module temperature (0C) -40 to + 85 Maximum permissible system voltage (V) 1000 Relative Humidity at 850C (%) 85 Temp. Co-efficient of the short-circuit current + .0004/K Temp. Co-efficient of the open-circuit voltage - .0034/K * Under Standard Test Conditions (STC): Air Mass : AM 1.5 Irradiance : 1000 W/m2 Cell Temperature : 250C ** Nominal Operating Cell Temperature (NOCT) at : Wind Speed :1m/s Irradiance : 800 W/m2 Ambient Temperature : 200C

39

Annexure-V Technical Particulars of Solar PV System-0.5 kWp to 50 kWp

Note: Manufactures may offer module of different size than 160 watt in that case the

configuration may differ slightly.

DC output of PV Array (KWp) 0.5 1 3 5 10 25 50 Area required (square feet) 75 150 450 750 1500 3750 7500 No. of cells in one PV module 36 36 72 72 72 72 72 DC rating of one module (WP) 80 80 160 160 160 160 160 Connection configuration Cells are connected in series to form one PV module. Rated DC current of one module 4.45 4.45 4.45 4.45 4.45 4.45 4.45 Rated DC voltage of one module (Vmpp)

18 18 36 36 36 36 36

No. of PV module in one array (all in series)

2 2 5 5 5 10 10

Max. DC output voltage of Array (Volt)

36 36 180 180 180 360 360

No. of Arrays 4 7 4 7 14 16 32 Rating of inverter(KVA) 0.6 1.1 4 6 12 30 60 Nominal AC output voltage(volt) 240 240 240 240 440 440 440 Variation In Output Voltage ±1% ±1% ±1% ±1% ±1% ±1% ±1% Nominal frequency(Hz) 50 50 50 50 50 50 50 Grid Frequency variation ±3% ±3% ±3% ±3% ±3% ±3% ±3% No. of phases/ wire ½ ½ ½ ½ ¾ ¾ ¾ AC output voltage range(Grid) -20% to 15% Power Factor Range 0.8 lag to unity Minimum Efficiency of Inverter (%) 94 94 94 94 94 94 94 No load Losses of Inverter(max) 1% 1% 1% 1% 1% 1% 1% DC Injection into Grid(max) 1% 1% 1% 1% 1% 1% 1% Ripple content on DC side 3% 3% 3% 3% 3% 3% 3% Total Voltage harmonic Distortion(AC side)

5% 5% 5% 5% 5% 5% 5%

Individual Voltage harmonic Distortion(AC side)

3% 3% 3% 3% 3% 3% 3%

Total Current harmonic Distortion(AC side)

8% 8% 8% 8% 8% 8% 8%

No. of AC& DC distribution board

1 1 1 1 1 1 1

No. of AC distribution Board

1 1 1 1 1 1 1

. 15

SCHEME-I

GRID INTERACTIVE SOLAR PV SYSTEM WITHOUT BATTERY

Utility AC BUS

SOLAR

~ ±

Consumer ACLoad

SM

GM

MAIN CONSUMER PANEL

CM

Inverter

SESI

GIGE

CI

SW

SM-Solar Meter

GM-Grid Meter

CM-consumer Meter

S

1. Switch S (built in Inverter) will open out automatically in grid failure and closes on its restoration after a time delay 2. Tariff for operators of solar roof top devices shall be

based on feed tariff fixed by Regulator, both on solar power consumed by operator and the solar power fed into the grid i.e SE

3. CI=Consumer Import, GI/GE=Grid Import & Export, SE/SI=Solar export and Import, SW –Manual

Lockable switch for grid maintenance

41

16

Utility AC BUS

Battery Solar

~ ±Charger Cum inverter

SM

Main Consumer Panel

Inverter

GE GI

SE SI

CMCI

Consumer AC loads

S

GM

SW

S1 S

SM-Solar Meter

GM-Grid Meter

CM-Consumer Meter

SCHEME-IIGRID INTERACTIVE SOLAR PV SYSTEM WITH FULL LOAD BATTERY BACKUP

(Based on Configuration-A)





42

17

EXHIBIT-C1MODULE C1: SOLAR PV SYSTEM WITH PARTIAL LOAD BATTERY BACKUP

(Two inverter scheme)Utility AC BUS

Inverter cum Charger

BatterySolar

NON EMERGENCY AC LOADS

SM

GM

Main Consumer Panel

CM

AC EMERGENCYLOADS

EMERGENCY LOAD AC PANEL

GE GI

SISE

CI

SW

S

InverterS1

S

S1S

SCHEME-IIIGRID INTERACTIVE SOLAR PV SYSTEM WITH PARTIAL LOAD BATTERY

BACKUP (Based on Configuration-A)





43

18

SCHEME-IV

GRID INTERACTIVE SOLAR PV SYSTEM WITH FULL LOAD DG BACKUP

Utility AC BUS

SOLAR

~ ±

Consumer ACLoad

SM

GM

MAIN CONSUMER PANEL

CM

Inverter

SESI

GIGE

CI

SW

SM-Solar Meter

GM-Grid Meter

CM-consumer MeterS

DG

S1

DG BUS

DM DE





44

19

SCHEME-VGRID INTERACTIVE SOLAR PV SYSTEM WITH PARTIAL LOAD DG BACKUP

Utility AC BUS

Inverter

Solar

AC

NON EMERGENCY AC LOADS

SM

UM

Main Consumer Panel

CM

AC EMERGENCYLOADS


GE GI

SISE

CI

SW

S

S

S1

DG

S2

SM-Solar Meter

GM-Grid Meter

CM-Consumer Meter

DM DE



3. CI=Consumer Import, ,GI/GE=Grid Import & Export, SE/SI=Solar export and Import, SW –Manual


45

20

Utility AC BUS

Inverter Cum Charger

SolarBattery

~ ±AC LOADS

SM

GM

MAIN CONSUMER PANEL

CM

DG

DG BUS

CI

GEGI

SI

DM

SE

DE

S2

SW

S

SM-Solar Meter

GM-Grid Meter

CM-Consumer Meter

S1

S

inverter

SCHEME-VIGRID INTERACTIVE SOLAR PV SYSTEM WITH FULL LOAD BATTERY BACKUP

AND DG (Based on Configuration Type-A)



3. CI=Consumer Import, ,GI/GE=Grid Import & Export, SE/SI=Solar export and Import, SW –Manual


46

21

Utility AC BUS

Inverter cum charger

SolarBattery

~ ±NON EMERGENCY AC LOADS

SM

GM

Main Consumer Panel

CM

InverterAC EMERGENCYLOADS


GE GI

SI

CI S1

DG

DG BUS

DM

DE

S2

S1

SW

S

S

SE

SCHEME-VIIGRID INTERACTIVE SOLAR PV SYSTEM WITH PARTIAL LOAD BATTERY

BACKUP AND DG (Based on configuration-A)



3. CI=Consumer Import, GI/GE=Grid Import & Export, SE/SI=Solar export and Import, SW –Manual Lockable

switch for grid maintenance.

SECTION - 3

REPORT OF SUB-GROUP II III

ON



&


January’ 2010

REPORT OF SUB-GROUP II III

ON



&


January’ 2010

Report of Sub-group II & III on “Integration of Solar Systems with Thermal / Hydro Power Stations”

Central Electricity Authority January-2010 Page 1 of 24

CONTENTS

Sl. No. CONTENT Page No. 1 Background 2 2 About Solar Irradiation 4 3 Solar Generation Technologies 5 4 Solar Options for Power Stations 10 Technology Options 10 Possible Areas of Installation of Solar Plants 11 Integration with Thermal Stations on Steam Side 12 Sharing of Existing Facilities 14 Electrical Interconnection between Solar Thermal

and Conventional Stations 15

Electrical Interconnection between Solar PV systems and Conventional Stations

19

Metering 20 5 Solar Power Plants in Hydro Power Stations 20 6 Tariff Projections – CERC Regulations 21 7 Conclusions 21 Annexure Annexure -1 Composition of Sub-Group 23 Appendices Appendix – I Solar Maps Appendix – II Excerpts from Feasibility Study

for Solar Thermal Plant in NTPC – Anta CCGT Station

Appendix – III Salient Features of 140 MW Integrated Solar Combined Cycle Power Plant

Appendix – IV Assumptions for generic levelised tariff for solar power plants as per CERC



REPORT OF SUB-GROUP –II & III ON

“ INTEGRATION OF SOLAR SYSTEMS WITH

THERMAL/HYDRO POWER STATIONS”

1 Background

1.1 A Task Force was set up by the Ministry of New & Renewable Energy (MNRE) under the chairmanship of Chairperson CEA, vide O.M. No. 32/61/2009-10/PVSE dated 28th May 2009, to examine technical issues relating to feasibility of integrating solar power plants with thermal/hydro-electric power plants and connectivity of solar roof top systems with grid. Composition of the Task Force is given at enclosed Annexure-I.

The first meeting of the Task Force was held in CEA office on 18th June, 2009. During the meeting three sub-groups were formed as follows:-

Sub-group – I Grid interactive rooftop solar PV systems Sub-group – II Integration of solar systems with thermal power stations Sub-group –III Integration of solar systems with hydro power stations

This report covers the salient issues relevant for installation of solar power plants in existing thermal and hydro power stations as referred to Sub-Group-II and III. Report of Sub-Group-I on “Grid interactive rooftop solar PV systems” has been issued separately.

1.2 The Terms of Reference of the sub-group –II and III are as follows:-

i) To examine feasibility of integrating solar based plants with Thermal (Coal and gas)/Hydro-electric power plants including issues relating to availability of land and effect of fugitive ash in coal based plants.

ii) To suggest the feasible options for type of solar plants (PV solar cells, solar thermal plants) for installation at thermal/hydro-electric power plants.

iii) To examine the feasibility of hybrid solar power systems in thermal power plants including use of secondary fuel firing or heat storage devices during the period when solar power is not available.

iv) To suggest scheme for connecting solar based plants with the station electric supply system for thermal/hydro electric power plants.

v) To suggest arrangements for metering and accounting for energy supplied by the solar based plants.

vi) To suggest modalities of implementation for solar based plants at thermal/hydro electric power plants including preparation of project report



1.3 The composition of the sub-groups is given below:

Sub-group-II

i) Shri S. Seshadri, Member (Thermal), CEA - Chairman

ii) Dr. Ashvini Kumar, Director, MNRE

iii) Shri Lalit Kapur, Director, MOEF

iv) Shri A.K Gupta,. G.M, NTPC

v) Shri R.K. Sikri, GM, NTPC

vi) Shri Vishnu Gupta, G.M(I/C), BHEL

vii) Shri M. M Vijayvergia Executive Director RRECL

viii) Shri N.M. Mathur, Chief Engineer, RRVUNL

ix) Sh. Sanjay Sharma, Director, CEA – Member-Secretary

Sub-group –III

i) Shri Suresh Chander, Chief Engineer (TE&TD), CEA - Chairman

ii) Dr. Ashvini Kumar, Director, MNRE.

iii) Dr. S. Bhowmik Addl. Director, MOE&F

iv) Shri Vishnu Gupta, G.M (I/C), BHEL

v) Sh. M.K. Raina, ED(T&RE), NHPC

vi) Shri Ashok Thapar Director BBMB

vii) Shri Moti Lal Director , Hydro, CEA – Member-Secretary

1.4 Deliberations of Sub-groups –II & III

i) The sub-groups had three meetings on 16th July 2009, 6th August

2009 and 25th September 2009. Presentations on solar technologies were made by various Indian suppliers developing solar technologies in the second meeting of the sub-group on 6th August ’09. In the third meeting held on 25th September ’09, presentations were made by NTPC on the feasibility studies made for installation of a solar plant at their Anta Combined Cycle Gas Turbine station. Visit was also made to Bhakra hydro stations on 21.08.2009 for study of potential for installation of solar power plant.

ii) This report of the sub-group –II & III has been prepared based on the

deliberations held in the meetings of the sub-group and various presentations made.



2 About Solar Irradiation

2.1 Extraterrestrial solar irradiation follows in a direct line from the sun to the earth. Upon entering the earth’s atmosphere, global irradiation is divided into two components – direct normal component and diffused component. The solar irradiation diffused by air, water molecules and dust within the atmosphere is known as diffused component. The direct normal irradiation component represents that portion of solar radiation reaching the surface of the earth that has not been scattered or absorbed by the atmosphere. The Direct Normal Irradiation (DNI) is the integral value of direct normal irradiance over a certain time interval and its unit is J/m² or kWh/m². Concentrating Solar Power (CSP) or solar thermal technologies can only use the direct irradiation. The second part, the diffused irradiation cannot be converted into beam radiation and is thus not useful for CSP. Generally sites with annual sum of DNI larger than 1800 kWh/m² are considered as potential sites for CSP. The solar photo-voltaic (SPV) technologies, however, utilize both direct and diffused irradiation for electricity generation.

The DNI available at a certain site may be interpreted as “fuel-resource” for a CSP plant and the annual sum of DNI as well as the seasonal and daily distribution is very important for solar field layout and plant performance. However, irradiance measurements are not common for meteorological stations today and particularly long term measurements from the past are hardly available. The main problem with DNI data from any source is the accuracy, which is hard to determine. The validation can only be done by a cross check of the data from different sources. Some sources from where DNI data can be accessed are given below:

i) DLR has developed methods to derive DNI data from satellite

measurements. These services are offered under the name SOLEMI (http://www.solemi.de/) at a cost.

ii) NASA Website (http://eosweb.larc.NASA.gov/sse/) where data tables

for a certain location and plots for a whole region are available free of charge. The main differences between this NASA data and the DLR satellite data are the different temporal and spatial resolution. The NASA data contains only mean daily values for each month whereas the DLR satellite data contains mean values for every hour of each year. The NASA satellite data is derived from a pixel size of 30km×30km whereas the DLR satellite data is derived from a pixel size of 3km×4km.

iii) The third source of irradiation data is a software tool called

METEONORM 6.0 (http://www.meteonorm.com/) which provides a method for the calculation of solar radiation on arbitrarily orientated



surfaces and other meteorological data at any desired location with hourly resolution.

iv) The National Renewable Energy Laboratory (NREL), Golden

Colorado, USA has prepared a DNI map of Asia with a 40km resolution for SWERA (http://swera.unep.net). This map does not provide specific information but it may be used for further investigation of potential CSP sites in India.

2.2 A few solar maps are appended at Appendix- I for reference. These

include global solar map of India for global radiations (source: TERI) and DNI maps for Asia and North-west India by NREL.

3 Solar Generation Technologies

3.1 Solar power generation technologies can be broadly classified into two broad types as under:-

i) Solar Photovoltaic technologies ii) Concentrated Solar Power (CSP) technologies

3.2 The Solar Photovoltaic technologies convert sunlight falling on to a photovoltaic (PV) cell directly into D.C. electricity which is then converted into AC by inverters. This technology has several variants based on the type of photovoltaic materials used. Tracking and concentrating systems are also used to focus sunlight on to the PV modules to improve the system efficacy and enhance generation. Application of PV systems is generally limited to rooftops on residential and commercial buildings, though utility scale plants are also possible.

The Solar Photovoltaic (SPV) technologies have been covered in detail in Report of Sub-Group-I on “Grid interactive rooftop solar PV systems”.

3.3 In Concentrated Solar Power (CSP) plants, also known as Solar Thermal plants, solar energy is focused through various types of mirrors to heat a working fluid and produce steam (directly or indirectly through an intermediate heating fluid). Steam is then used to rotate a turbine or power an engine to drive a generator and produce electricity as in a conventional power block. CSP technology are better suited for utility scale power plants as compared to SPV technologies.

These technologies are of following four types, characterised by the type of mirror used to collect solar energy. A brief description of these technologies is given below and their comparison is drawn in Table-I.



Parabolic trough is well established and most proven CSP technology and commercial plants upto 80 MW size are in operation.

Parabolic trough shaped mirrors collect and reflect the solar energy onto receiver tubes positioned along the focal line of parabolic mirrors. Troughs are made to rotate on a north-south axis to track the sun from east to west. Heat transfer fluid (synthetic oil), suitable for temperatures upto 400 deg C, flowing through these receiver tubes is used to generate steam through steam generators and drive turbine to generate electricity.

Solar Towers deploy numerous large number of flat sun tracking mirrors, known as heliostats, to focus sunlight onto a fixed receiver mounted on a tower. The heliostats tack the sun on two axes. The central receiver can achieve very high concentrations of solar irradiation thus resulting in extremely high temperature for the operating fluid. Most of the concepts for solar tower utilize a Rankine cycle as power conversion process. Heat of the absorber coolant is transferred in separate heat exchangers to a water/steam cycle as in conventional steam power plants. Direct steam generation, without any intermediate fluid, is also possible. Steam parameters upto 100 bars and 560 deg C are achievable. Brayton cycle is the focus of development to increase efficiency levels.



Spain has several solar tower systems operating or under construction. Maximum size in operation is 20 MW. Most of the realized pilot and demo solar tower facilities have thermal storage facility incorporated to improve the dispatchability of the plant. Nevertheless these storage solutions have the drawback of higher initial investment costs and higher land requirements.

Linear Fresnel Reflectors technology uses a reflector made of several slices of mirrors with small curvature approximating a parabola. Mirrors are mounted on trackers and configured to reflect sunlight onto a receiver tube fixed in space above these mirrors. These Fresnel reflectors offer direct steam generation and thus omit intermediate high transfer fluid.



These systems have lower investment costs and also lower optical performance as compared to parabolic trough collectors. This technology is in developmental stage and some small experimental systems have been realised.

Solar Dish The parabolic shaped dish tracks the sun, through a two axis movement, continuously to gather the solar energy and point focuses the same onto a thermal receiver (mounted at the focal point) to heat up the fluid. Heat from the thermal receiver is used to produce electricity through Stirling Engine.

Dish technology is modular and produces relatively small amount of electricity compared to other CSP technologies – typically in the range of 10 to 25 kW which results in high capital costs. Distributed dish concept with common power conversion unit was also adopted in eighties but is not the focus of development any more due to heat loss during heat transportation over long distances.



TABLE-I : COMPARISON OF CSP TECHNPLOGIES Solar Thermal (CSP ) Technologies Parameter

Parabolic Trough Solar Tower Fresnel Reflector (CFLR)

Solar Dish

Site Solar Characteristics/ Solar radiation required

Generally sites with annual sum of DNI larger than 1800 kWh/m²

Land Requirement Typically 5-7 acres/MW

Typical shape of solar plant Rectangle Sector of a circle/ Rectangle

Rectangle Rectangle

Water Requirement Typically 4m3/MWhr No water requirement

Maximum Temperature 400 deg C 270 deg C Possible upto 560 deg C

400 deg C 800 deg C

Efficiency ~ 14% ~17% Possible upto 22%

- ~ 22-24%

Typical CUF Typically 22-25%

Plant cost Lower than parabolic trough Lower than parabolic trough Very High

Largest plant size 80 MW 20 MW 5 MW

Development Status Most proven Mature Demonstration Demonstration

Plants installed -9 SEGS plants (14 MW to 80 MW) in California built from 1985 to 1991 – Total capacity : 354 MW - Nevada Solar One (64 MW) started in 2007

-Planta Solar 10 and Planta Solar 20 are in operation with capacities of 11 and 20 MW in Seille Spain -Sierra Sun Tower USA 5 MW - Solar Two plant (10 MWe) with molten salt storage- demo plant

- 9MWth used for FW heating in 2000 MW coal fired Liddell Power plant (Australia) - Two small capacity experimental plants in Spain in 2007 - 1.4 MWe at Murcia, Spain in 2009

Small operational plants with unit size of 10-25 kW

Technology Providers Sener Solar Millenium Abengoa ACS-Cobra Acciona Solel

Abengoa eSolar Sener BrightSource Torresol Solarreserve

Austra MAN Ferrostaal

Stirling Energy Systems



4 Solar options for Power Stations

Technology Options

4.1 From the discussions in the foregoing para, it may be seen that the

options for solar generation at any power station would depend upon the following: i) Adequate solar irradiation ii) Availability of land iii) Availability of water (for solar thermal)

4.2 As mentioned above, adequate direct normal component of solar

irradiation is necessary for solar thermal plants. Normally a solar irradiation (DNI) of 1800 kWh/m2 is considered necessary for solar thermal plants. Solar PV plants can, however, utilize global radiations including diffused components. Thus solar irradiations available at a location is the prime consideration for selection of technology.

4.3 About 5-7 acres/MW land is required for solar thermal plants. Thus

availability of large tract of continuous flat land would be required if solar thermal is to be considered. When land is available in several scattered patches, rather than a contiguous piece, then Solar photovoltaic plants could be considered. Following considerations should also be kept in view regarding land:

i) Land should be flat with 1-3% gradient or less. ii) North- south orientation is preferred. iii) Aspect ratio of land should be commensurate with the technology

Economy of solar thermal improves with scale of plant. For sites suitable for higher size solar thermal plants, presently parabolic trough technology is the most proven and widely deployed technology. For this technology, 50 MW plant would be ideal from techno-economics point of view though lower sizes (10-20 MW) can be considered depending on availability of land. NTPC have prepared feasibility report for a 15 MW plant at Anta CCGT plant based on parabolic trough technology. For solar tower technology, maximum 20 MW plant is operational. This technology is available in 2.5 MW modules also. Fresnel reflector and dish technologies are at demonstration stage and, if considered, can be deployed for still lower sizes.

4.4 Solar thermal plants require water for cooling tower blowdown and DM

make up. Usually water requirement is 4 M3/MWh. Additionally, some water is also required for washing of mirror panels and requirement varies with location depending on dust levels.



4.5 In hydro stations large tract of continuous land are generally not available. Also the hydro stations have no facilities for supplying warm up steam etc to solar thermal power plant. Thus solar PV systems may be the only choice for hydro stations. Details of solar PV technology are covered in the Report of Sub-Group-I on “Grid interactive rooftop solar PV systems”.

4.6 Solar thermal plants are sometimes provided with heat storage systems

to improve the despatchability. For this purpose, additional solar field is provided to cater for storage which can then be used for generation during off-sun hours; else storage systems can only facilitate shifting solar generation from on-sun to off-sun period for peaking purposes etc. Providing additional solar field for storage systems is not only expensive; it would also require additional land for the storage system itself and also for additional solar field. Storage systems constitute major cost of the solar thermal plants, accounting for almost 70-80 % of the total plant costs.

In the context of power stations, storage systems are obviously not necessary. The limited objective of keeping the solar power generation equipment in hot condition can be met by supplying steam to the solar power plant from the auxiliary steam supply of the thermal station.

4.7 Hybrid plant operation has also been adopted to increase capacity utilization of solar plant even without storage systems. The solar thermal plants in California employ gas fired boilers to supplement power generation during off-sun hours. Such an arrangement appears to have been provided as a means to improve quantum and reliability of power supply to the grid as these are large solar plants. One solar tower based system has been commissioned in Kibbutz Samar in Israel which has 30 different heliostats tracking the sun and directing solar energy to the top of a 30m tall tower. The tower also houses a micro-turbine that can be run on solar thermal, as well as bio-diesel, natural gas or biogas, particularly when the sun goes down.

Possible areas of installation of solar plants

4.8 The choice of areas for solar plants in existing Thermal Power Stations

could be:-

• Open land areas not intended for any future expansion

• Abandoned ash ponds in coal fired stations

• Areas in existing green belt subject to MOE&F approval

• Roof top of turbine hall (for PV systems)

• Roof top in administrative building, guest houses, and large buildings (for PV systems)



4.9 The land chosen should be away from high dust areas like coal and ash handling plants and their fugitive emissions. In case of abandoned ash pond lands, suitable surface improvement may be required to prevent ash carry over and deposition on solar field. Washing arrangement for solar field would have to be provided commensurate with the expected dust levels in the vicinity.

4.10 Land availability would vary at each plant. Land availability at two thermal

plants is indicated below as an example:

- 1000x700 M2 at Anta CCGT plant of NTPC - Two plots of 1200 mtrX200 mtr and 600 mtrX 200 mtr at Suratgarh

Thermal power plant of RRVUNL.

NTPC have assessed the solar capacity of 15 MW at Anta CCGT plant in 70 hectare plot. Per MW area requirement is high because of gas pipeline passing through the plant which cannot be relocated. It is estimated that about 15 MW capacity can be installed in 36 hectare area available at Suratgarh TPP.

Integration with Thermal Stations on steam side

4.11 Solar thermal plants generate steam from solar heat and thus

conceptually it should be feasible to utilize the solar heat (steam) in existing thermal cycles of the coal or gas based stations to achieve fuel savings and reduced CO2 emissions. This type of integration can result in a) elimination of power conversion equipment (steam turbine generator etc) for the solar plant thus reducing the cost of solar thermal plants and b) increase the efficiency of solar thermal plant due to higher efficiency of higher size steam-turbine generator.

4.12 Some plants of Integrated Solar Combined Cycle Systems (ISCCS) i.e. a

combination of solar field and fossil fuel fired combined cycle power plants, are under construction but none is under operation. These include:

i) 30 MWe parabolic trough field (130000 m² collector area) integrated

into a146 MWe CCPP at Kuraymat, Egypt. ii) 20 MWe parabolic trough field (183000 m² collector area) integrated

into a 472 MWe CCPP at Ain-Beni-Mathar, Morocco. iii) 25 MWe parabolic trough field (180000 m² collector area) integrated

into a 150 MWe CCPP at Hassi-R'mel, Algeria.. It is also feasible to integrate solar thermal with coal fired power plants. One example of this integration, also the only one, is Fresnel reflector technology based 9MW solar thermal plant integrated with 2000 MW Liddle coal fired plant in Australia.



4.13 The possible areas of integration with thermal stations on steam side can

be identified as

i) Using solar steam for feed water heating ii) Mixing solar steam with main steam inside boiler/HRSG or in pipe

en-route to turbine. iii) Injecting solar steam directly in turbine at some intermediate stage. iv) Separate back pressure turbine for solar steam and exhaust to

existing plant condenser.

Using solar steam for Feed Water (FW) heating may appear to be least cumbersome as solar steam would not be fed to the turbine. However, in coal fired plants, feed water heating is done partially in the regenerative cycle and then the FW is fed to the economizer. Replacing or supplementing regenerative cycle feed water heating with solar heating would involve taking the existing FW heaters out by closing their extractions and the adverse thermodynamic impact on the turbine cycle heat rate would have to studied. Further, even physically installing the solar steam based FW heaters in the turbine hall area and routing solar steam pipes to the turbine hall from the solar field may pose severe space constraints in view of compact and optimized turbine hall layout. Also the additional pressure drops in FW circuit may necessitate installation of additional FW pumps or augmenting boiler feed pumps which may not be possible.

Heating FW after the regenerative cycle so as to have higher than design FW temperature at entry to boiler thus reducing the economizer duty may also not serve much purpose as in existing boilers it will only increase the flue gas exit temperature thus increasing the flue gas losses and not leading to any fuel savings. Besides, the physical constraints of installing solar FW heaters and problem of meeting additional pressure drop in FW circuit would remain. Similar issues are likely in using solar steam for FW heating in CCGT stations.

Mixing solar steam to Main Steam would require special mixing arrangement due to difference in temperature of solar steam and Main steam. Also variation in solar irradiation over the day and during various seasons may involve large variations in the solar steam quantity and parameters thus leading to changes in aggregate steam quality to the turbine. Fluctuating steam flow to the turbine and large variation in steam parameters may involve stress implications on the Steam Turbine and will have to be examined in consultation with turbine manufacturer.



Injecting solar steam in turbine intermediate stages is virtually ruled out in existing turbines as the turbines have very little flow margins available, primarily for operational degradations.

4.14 The feasibility of integrating solar power plant with existing station on the

steam side were also examined in the Feasibility study for solar plant at Anta CCGT station got conducted by NTPC through Evonic, Germany. The salient extracts of possible integrating options examined and findings are given at Appendix-II. As may be seen, integration options involved:-

• Issues of mismatch of steam parameters of solar and conventional power station steam, (especially under fluctuation of flow and parameters of solar steam due to fluctuation in solar conditions) and sub-optimal steam use

• Margins available in existing equipment to accommodate additional steam flow from solar field

• Concerns about impact on existing performance of the stations

It was finally decided to go for standalone 15 MW solar thermal plant.

4.15 Thus, integration on the steam side to the existing station is expected to be too cumbersome. This may also disturb the existing cycle and involve issues of performance reliability of the existing station. Thus, the solar plants in existing TPS may be considered as a stand alone plant without any inter-connection to the steam side of the station.

However, integrated solar plants with gas plants could be considered for new stations depending on site specific factors for which site specific techno-economics and feasibility studies would be required. It may not be advisable to integrate solar plant with new coal based plants since turbine-generators in coal based plants are of standard rating and there would be no increase in the power output by solar thermal energy. It may be mentioned here that a 140 MW Integrated Solar Combined Cycle Power Power Plant with solar component of 35 MW and gas turbine component of 105 MW was conceived at Mathania, Rajasthan. CEA had given its techno-economic clearance to the plant in the year 1999. However, the plant could not materialize due to high prices of Naphtha, non-availability of gas and some other reasons. Details of this plant are given in enclosed Appendix – III.

Sharing of Existing Facilities

4.16 Even for a standalone solar thermal plant, the existing station facilities

would require to be shared with the solar power plant and it needs to be ensured that appropriate provisions exist for the same in the existing



station systems. Typical station facilities required to be shared in case of solar thermal plants are as under:-

• DM Water

• Circulating water make up

• Auxiliary steam

• Auxiliary electricity supply

• Fire fighting system

i) Solar thermal plants need DM water for the power cycle initial filling as well as cycle make up. The typical make up quantity can be taken similar to the conventional power cycle at about 3% of the cycle flow. In addition, if the solar field washing is also required to be done by DM water, the water requirement for same would also have to be considered. Frequency of washing, quality and quantity of water for washing would have to be ascertained from suppliers of solar field.

ii) In all probabilities, separate cooling tower would have to be installed

for solar thermal power plant. However, the circulating water requirement would have to be met from the existing station CW system.

iii) The solar thermal plant may need auxiliary steam supply for initial

warm up of the power plant island so as to enable faster start up of solar plant.

iv) The existing fire fighting system would required to be extended to

cover the solar thermal plant also.

v) The issue related to auxiliary supply is discussed subsequently.

Electrical Interconnection between Solar Thermal and conventional Stations

4.17 Following options are available for integration of solar thermal power with

electrical system of existing plant.

� Solar power connected to Generator bus of existing plant (Option-I) � Solar power connected to plant 6.6kV unit/ station bus (Option-II) � Solar power evacuation to grid through new switchyard bay

(Option-III)

The site specific interconnection scheme may be required depending on the techno-economics of various options.

i) Solar power connected to Generator bus of existing plant (Option-I)

Generator voltage of solar thermal plant is likely to differ from that of existing plant. Either solar generator is required to be customized as per



existing generator bus voltage level or is to be stepped up by a transformer. Further, size of existing generator-transformer may not have adequate margin to take up solar power also. In addition, following issues will also need to be considered, if this option is to be deployed:

a) Feasibility of connection to generator bus from point of view of

availability of space. b) Operation of solar plant in the event of tripping of existing unit

The scheme is shown in Exihibit-I.

Unit tap-off

415V Station Bus

Unit loads

Solar Gen

Station loads

Station Trans

Gen Trans

Gen

Switchyard Bus

Unit Tran

M1

6.6kV Unit Bus 6.6kV Station Bus

OPTION - I

EXHIBIT - I

Trans

Aux. load solar

thermal

Station loads

Trans

M2 Note: M1 – Main Meter M2 – Aux. Consumption Meter M3 – Check Meter M1 – M2 = Net Solar Energy generated

M3



ii) Solar power connected to plant 11/ 6.6kV unit/ station bus (Option-II)

In this option, solar power will be used to meet part of the auxiliary power consumption of the existing plant. It is preferable to connect solar power to station bus so that it would be possible to evacuate solar power in the event of tripping of one of the units. An auxiliary transformer would be required to match the solar power with the voltage level of the unit/ station bus. The following aspects need to be studied before deciding for implementation of this option: a) Solar power should be less than the load on unit/ station bus b) With the addition of solar generation, the fault level of the existing

switchgears will increase and the existing switchgear, bus duct etc. may or may not be adequate to meet the new fault level.

c) Feasibility of connection from point of view of availability of space d) Changes required in present protection scheme, logic of operation

etc.

The scheme is shown below

Station loads

Station Trans

Gen Trans

Gen

Switchyard Bus

Unit Trans

11/ 6.6kV Unit Bus

11/ 6.6kV Station Bus

Unit loads

OPTION - II

EXHIBIT - II

Solar Gen

M1

Trans

Aux. load solar

thermal

M2

415V Station Bus

Station loads

Note: M1 – Main Meter M2 – Aux. Consumption Meter M3 – Check Meter M1 – M2 = Net Solar Energy generated

M3



iii) Solar power evacuation to grid through additional switchyard bay

(Option-III) In this option, generated voltage by solar plant will be stepped up to switchyard voltage level through transformer and connected to the grid. No modification/ augmentation are envisaged in the electrical system of the plant. Since additional bay will have to be added, the availability of space in the existing switchyard need to be studied before deciding for implementation of this option. The scheme is shown in Exihibit-III.

Auxiliary Power requirement of Solar Thermal Plant

4.18 Solar thermal plant requires auxiliary power of about 8% when solar plant

is in operation and about 1% during off sun hours. Besides, solar thermal plant will daily require start up power. It is preferred to tap off feeder from

Main Bus - II Existing/ New Switchyard Bus

OPTION - III

EXHIBIT - III

By-pass Bus

Main Bus - I

Note: 1) Switching schemes may be one other than the ‘Two mains and By-pass bus’ arrangements shown here. 2) M1 – Main Meter 3) M2 – Aux. Consumption Meter 4) M3 – Check Meter 5) M1 – M2 = Net Solar Energy generated

Solar Gen

M1

Trans

Aux. load solar

thermal

M2

415V Station Bus (Existing plant)

Station loads

M3



existing station switchgear for auxiliary power/start up power requirement of solar plant at required voltage level.

Electrical Interconnection between Solar PV system and conventional Stations

4.19 Generally, in an existing plant vacant space is available in scattered areas

and also on the roof-top of buildings. In case the space available is shadow free, independent Solar Photovoltaic system may be installed to generate electricity and power may be fed into the respective switchgear nearby at 3 ph 415V or higher voltage levels. SPV output of the inverter shall be synchronized automatically to the exact AC voltage and frequency of the system. Typical schematic diagram is illustrated the sketch below:

Following suggested criteria shall be considered for selection of voltage level of Solar PV system:

i. Up to 10kW solar PV system : 1 phase, 240V supply ii. Above 10kW and upto 100kW solar PV system,: 3 phase, 415V supply iii. Above 100kW and upto 1.5MW: 6.6/ 11kV level. iv. Above 1.5MW and upto 5 MW: 11/ 33/ 66kV level or as per the site

condition

SWITCHGEAR

M1

SW

S

Inverter

Solar PV Array

Load

Notes: Normally solar PV system is tied with switchgear. In case of failure, switch ‘S’ in inverter will open automatically within 20 - 30 msec.

SOLAR PV SYSTEM (SPV)

SW - Manual lockable switch M1 - Solar Energy Meter



For further details regarding connectivity of solar PV systems, Report of Sub-Group-I on “Grid interactive rooftop solar PV systems” “may be referred.

Metering 4.20 As shown in the Exihibits I-III above, three nos. meters shall be provided

– two (one main meter and one check meter) for metering solar energy generated and another for auxiliary power consumed by the solar thermal plant. Tariff for solar generation shall be provided for the net energy generated after deducting auxiliary power consumed. Meters shall interface type complying with the requirements of CEA Regulations on “Installation and Operation of Meters“.

5 Solar Power Plants in Hydro Power Stations

5.1 The sub-group made a visit to Bhakra hydro stations to ascertain the feasibility of installing solar plants. It is seen that areas around the dam have a hilly terrain with dense vegetation. Such topography is not considered suitable for installing solar power plants. The spillway slope could have been considered but is facing north and thus not suitable. However depending on suitable direction, such areas could be possible choice for installing solar plants.

5.2 Roof tops in Ganguwal and Kotla power houses and fore-bay areas

measuring about 2580 m2 were found suitable for solar PV systems. These areas can support solar PV of about 150 kW capacity. In addition rooftop of Nangal Dam workshop Building and vacant land near guest house were also identified for solar PV systems. The dimensions/area available and possible solar plant capacity are being worked out by BBMB. BBMB also proposed to install floating solar panels on the canal downstream of the Kotla and Ganguwal power houses. Specific studies may be required to examine the feasibility of floating systems.

5.3 From the visit it is seen that large tract of continuous land are generally

not available in hydro stations; also the hydro stations have no facilities for supplying warm up steam etc to solar thermal power plant. Thus solar PV systems may only be considered for hydro stations. The possible areas of installation could be power house roof tops, fore-bays, colony roof tops, open grounds etc. Floating solar PV panels if found feasible can also be considered in canals or dam areas.

5.4 For such solar PV systems in Hydro stations, Report of Sub-Group-I on

“Grid interactive rooftop solar PV systems” may be referred to.



6 Tariff Projections – CERC Regulations

6.1 CERC has notified Central Electricity Regulatory Commission (Terms and Conditions for Tariff determination from Renewable Energy Sources) Regulations, 2009 and also issued orders for the generic tariffs for the financial year 2009-10 for renewable energy sources including solar PV and solar thermal based power projects. As per these orders, generic levellised tariff has been worked out as under by CERC:

Figs (Rs./kWh)

Parametric Assumptions for the above levelised tariff are given in Appendix-IV.

7 Conclusion

7.1 The options for solar generation at any power station would depend upon the following: i) Adequate solar irradiation ii) Availability of land iii) Availability of water (for solar thermal)

7.2 Adequate direct normal component of solar irradiation is necessary for

solar thermal plants. Normally a solar irradiation (DNI) of 1800 kWh/m2 is considered necessary for solar thermal plants. Solar PV plants can, however, utilize global radiations including diffused component. Thus solar irradiations available at a location is the prime consideration for selection of technology.

About 5-7 acres/MW land is required for solar thermal plants. Thus availability of large tract of continuous flat land would be required if solar thermal is to be considered. Further in case solar thermal plant is envisaged, water availability of approx. 4 m3/MWh has to be ensured.

7.3 When continuous tract of land are not available to suit solar thermal

plants, and land is available in several scattered patches, then Solar photovoltaic plants could be considered. For hydro stations solar PV systems would only be feasible. As a rule of thumb these plants require about 20 m2 for each kW of installed capacity and assessment of feasible capacity can be made based on total land/rooftop areas available.

Parameter Solar PV Solar Thermal

Levelised Tariff 18.44 13.45



7.4 In case of solar power plant in coal based stations, location should be away from high dust areas like vicinity of coal and ash handling plants. Also washing requirements of solar field/solar panels would have to be ascertained from the suppliers.

7.5 Integration of solar thermal plants on the steam side to the existing

station is a cumbersome proposition. Thus, the solar plants in existing TPS may be considered as a stand alone plant without any inter-connection to the steam side of the station. However, integrated solar plants with conventional gas based plants could be considered for new stations depending on site specific factors for which site specific techno-economics and feasibility studies would be required.

7.6 Various options available for integration of solar thermal power with

electrical system of existing gas based plant have been discussed in the report and as brought out, electrical integration with the option of additional switch yard bay comes out to be the most suitable amongst all the options. However, site specific studies are required regarding the interconnection before finalizing the scheme.

7.7 Considering the high tariff of solar power, two meters (one main and one

check meter) may be provided for solar electricity generated. Suitable metering arrangements would also be required for measurement of auxiliary power consumption of the solar thermal plant from the existing station electric supply.

7.8 All thermal and hydro generating utilities should explore the potential of

installing solar plants in vacant land of their existing stations. Detailed Project Report for the specific project would be required to be developed by a consultant to study the feasibility of the solar power plant, technology to be employed, generation projections, cost estimates etc. A brief summary of Feasibility Study for Solar Thermal Plant in NTPC -Anta CCGT station is enclosed at Appendix-II for reference.

***



Annexure-I composition of subgroup




Central Electricity Authority January-2010

APPENDICES Appendix –I Solar Maps

Appendix-II

Excerpts from Feasibility Study for Solar Thermal Plant in NTPC -Anta CCGT station

Appendix-III Salient features of 140 MW Integrated Solar Combined Cycle Power Plant

Appendix –IV Assumptions for generic levelised tariff for solar power plants as per CERC



Appendix-I Solar Maps

Global Solar Radiation Map of India Source TERI





DNI Map of North- west India



Appendix-II

Feasibility Study for Solar Thermal Plant in NTPC -Anta CCGT station 1. Anta Gas Power Plant is a Combined Cycle Power Plant (CCPP) owned

and operated by NTPC, which consists of three gas turbines of 88.7 MW capacity each and a condensing steam turbine of 153.28 MW having a peak load capacity of 164.14 MW. Thus, the total installed capacity is 419.38 MW. Feasibility Study for installation of solar generation at Anta CCGT station has been done by NTPC. The study was done by Evonik Energy Services, Germany through KFW, Germany.

2. Anta site was chosen due to good solar irradiation. The direct normal

irradiation (DNI) at Anta is 2090 kWh/m2 which is comparable with southern part of Spain where number of solar thermal plants are under construction.

3. Anta TPS has 175 acres of vacant land on which the proposed solar plant

would be installed. Area available for solar field would be 1000 m x 700 m. The available land at Anta is considered suitable for supporting 15 MW solar power plant. More compact solar field is possible. However, this would require relocating the gas pipe line which is running in the centre of the plot and is not considered desirable by NTPC. Thus the solar field has been divided into two parts which appropriate clearance for the pipeline. The solar field would generate steam at 30 bar, 370 deg C.

4. Possibilities of connecting the solar plant to the existing CCGT station on

the steam side were examined but not found feasible due to fluctuating steam output from the solar plant and large difference in the steam parameters from the solar field and CCGT station. Hence, standalone plant of 15 MW capacity is proposed. Such integration may, however, be possible in new CCGT stations where initial designs itself could incorporate the requirements of the solar integration

5. Parabolic trough technology has been chosen as several plants of this

technology are operating in California for more than 20 years. Other technologies considered were Fresnel collector, solar tower and parabolic dish collectors which are stated to be in demonstration phase.

6. Net solar generation of 32163 MWh per year has been estimated

considering 10% discount on DNI and plant availability of 96%. This works out to capacity utilization factor of 24.5%. The Auxiliary load for solar plant is estimated to be 1.7 MW when the plant is in service and 0.2 MW when the plant is not in service

7. The water requirements are estimated as under:-

DM water consumption – 10,000 m3 per year



CW water consumption – 183,000 m3 per year Total water consumption- 193,000 m3 per yr

Thus the total water requirement works out to be about 6m3/MWh. The water requirement would be met from existing plant. Also adequate provisions for cooling water system, raw water storage, DM water exist in the existing CCGT station.

8. Various options for integrating the solar plant with the existing pant on the

electrical side were also considered. Options to connect the proposed solar plant to the existing generator bus ducts, 6.6 KV station supply and 220 KV Switchyard were studied. The brief findings in regard to interconnection options are as under:-

Option-I Interconnection to existing generator bus ducts

• The fault current rating of existing IPB is exceeded.

• Layout constraints for tap-off connection to new Solar Generator

• Load sharing between two generators of dissimilar ratings and circulating current through their grounding system is considered undesirable

Option-II Interconnection to 6.6 KV station supply

• The fault level with 10 MW solar generation increases to 22KA(rms), which is beyond the present capacity requiring complete replacement of complete HT switchgear.

Option-III Interconnection to 220 kV switchyard

• Addition of one no. 220 kV bay required along with equipments and protection.

• Modification of bus bar protection system required.

• Step up Transformer required GenV/220 kV (12.5 MVA)

Finally the option of Interconnection to 220 kV switchyard was adopted.

9. Operation and Financial parameters considered :–

Plant output 15 MW Plant availability 96% Total capital cost with IDC Rs. 367.5 Crores Cost per MW Rs. 24.5 Crore Debt : Equity ratio 70:30

Euro grant from KFW 5 million Euro Interest rate on Kfw loan 3.5%



Interest rate on Rupee loan 12% Repayment period Kfw loan 12 years and grace of 3

years Foreign exchange variation Not considered O&M cost Rs. 43.8 lakh per MW

O&M escalation factor NIL Contingency for solar panel cost 10% Contingency for other plant cost 5% Levelised cost of Generation Base case Rs.8.47 per kWh With 5 million Euro grant Rs. 8.29 per kWh

With 5 million Euro grant + CDM Benefits

Rs. 8.29 per kWh

Base case + consultancy cost of 1 million Euro

Rs. 8.63 per kWh

10. The above study could serve as a typical reference/bench mark for

guidance. However specific studies would be required for each site to establish the feasible solar field configurations, solar outputs, equipment efficiency and cost of generation.

Study of Integration of Solar Power Plant with Existing CCGT Station

11. The original aim of the Anta study was to assess the feasibility and economy of an extension by a solar collector field to increase generation capacity of the existing steam turbine at Anta. The peak load capacity of individual GT at Anta is 94.17 MW each and STG of 164.14 MW. Thus the existing steam turbine had margin available for taking solar steam and this originally led to the idea to analyze the extension of the CCPP by a solar collector field by integrating solar generated steam into the existing CCPP with the possibility of raising the output of the steam turbine.

12. Several potential integration concepts with variations were evaluated during

the study. The integration options considered were:-

12.1. To integrate the solar steam into the HP-drums of the existing HRSGs

12.2. To integrate the solar steam between two super heaters of the

existing HRSGs 12.3. To integrate the solar steam of 370°C into the main steam (of

485°C) pipe via new mixing arrangement. 12.4. To superheat the solar steam of 370°C in a separate fired

superheater to bring it to 485°C before integrating it into the main steam (of 485°C) pipe.



12.5. Solar steam to be used in a new Back-pressure Turbine Generator and exhaust of the BPST to be mixed with LP steam at LPT inlet.

12.6. Solar steam to be used in a new Condensing Turbine Generator

and exhaust of the CST to be connected to condenser of the existing power plant

13. The option to integrate the solar steam into the HP-drums could not be

adopted due to the following reasons:-

• Solar steam would have required to be de-superheated to match the steam temperature inside drum thus leading to loss in efficiency

• Solar steam piping need to be connected to each of the three drums so that solar plant operates even when one of the gas turbine is working. This would have involved lot of complex pipe work

• Steam would be required to be injected in each drum in proportion of the gas turbine load needing complex control logics.

• Shut down of the entire plant for integration work would be required leading to loss in revenue.

14. The option to integrate the solar steam between two super heaters of the

existing HRSGs was not considered in detail due to the fact that the super heaters of the HRSGs are difficult to access for modification, A major modification of 20 years old HRSGs was not considered desirable.

15. The option to integrate the solar steam of 370°C into the main steam (of

485°C) pipe via new mixing arrangement was considered in detail. However it could not be adopted due to the following reasons:-

• It involved a temperature difference of around 100°C between HP Main steam and Solar Steam and thus required special mixing arrangement.

• Stress implications on the Steam Turbine due to frequent changes in main steam temperature.

• Lower HP steam temperature at turbine inlet due to mixing of solar steam would lead to higher mass flow for the turbine. Thus the margin available in the turbine was getting further reduced.

• Due to implications on the turbine OEM consultation was felt necessary for this option

16. The option to superheat the solar steam of 370°C in a separate fired

superheater to bring it to 485°C was considered in detail. However it could not be adopted due to the following reasons:-

• Superheating the solar steam at 370°C in a separate fired superheater was required to bring it to 485°C before integrating into the main steam (at 485°C) pipe.



• Separate fired superheater would have needed supplemental heating by gas-fired burners thus increasing gas consumption.

• Also the new gas fired superheater would have a low efficiency compared to the CCPP.

• Also it would have been difficult to separate the electrical output from the solar side and the conventional leading to possible problems with the regulators.

17. Using Solar steam in a new Back-pressure Turbine Generator with exhaust

of the BPST to be mixed with LP steam at LPT inlet of existing steam turbine involved partially unloading the GTs as otherwise the max flow rate of LP turbine was getting exceeded.

18. Installing a new Condensing Turbine Generator for Solar steam and

connecting exhaust of the CST to condenser of the existing power plant involved serious installation difficulties it required construction of new pedestal close to the existing STG which might have posed be a serious problem. Also it would not have ben possible to inject CST steam from the new condensing turbine into the existing condenser via a new opening in condenser neck.

19. Thus the integration options could not be considered and it was decided to

install a stand alone solar power plant of 15 MW capacity.

****



Appendix-III

Salient features of 140 MW Integrated Solar Combined Cycle Power Plant 1. A 140 MW Integrated Solar Combined Cycle Power Plant was proposed at

Mathania Rajasthan. Salient details are given below:

Plant capacity 140 MW with solar component of 35 MW and non-solar component of 105 MW

Configuration Solar + 2 nos. GTGs + 2 nos. HRSG +1 No. STG

Solar Plant Capacity 35 MW Annual solar share 9% (operation without auxiliary firing

at night) 6% (operation with auxilisry firing at night)

Solar field area 600,000 m2 Solar technology Parabolic trough DNI (25 yr average) at site 2177 kWh/m2 Solar heat input 94.5 MW Feed water inlet temperature 245 deg C Live steam pressure/ temperature 105 kg /cm2, 370 deg C Live steam flow 50 kg/S Solar heat interconnection with CCGT cycle

The heat transfer fluid (HTF) is circulated through the solar field where it is heated. The solar heated HTF generates superheated steam in heat exchangers. The superheated steam is then fed to the high pressure (HP) casing of steam turbine. The spent steam is condensed in conventional steam condenser and returned to heat exchangers via condensate and feed water pumps. Provision also made for auxiliary firing in HRSG in the evening and night to make up for low or no insolation.

Report of Sub-group II & III on “Integration of Solar Systems with Thermal / Hydro Power Stations


Appendix-IV

Assumptions for generic levelised tariff for solar power plants as per CERC

Report of Sub-group II & III on “Integration of Solar Systems with Thermal / Hydro Power Stations


Documents

CEA Task Force Report on Grid Interactive Solar PV_Jan'10