Potential for conversion of classical PSP to variable speed ......ENERGY.2011.7.3 STORAGE-2 AND BALANCING VARIABLE ELECTRICITY SUPPLY DEMAND / ESTORAGE EXTRACT of eStorage D4.1 Potential

European Commission – Directorate General for Research

S E V E N T H F R A M E W O R K P R O G R A M M E

T H E M E 5 - E N E R G Y

Project acronym : eSTORAGE

Project full title : Solution for cost-effective integration of renewable intermittent generation by demonstrating the feasibility of flexible large-scale energy storage with innovative market and grid control approach.

Grant agreement no.: 295367

Collaborative project / Demonstration Project

Number of deliverable: Extracts of D4.1

Dissemination level (PU, PP, RE, CO, RUE, CUE, SUE) : PU

Date of preparation of the deliverable (latest version): 05/04/2016

Date of approval of the deliverable by the Commission: dd/mm/yyyy

Potential for conversion of classical PSP to

variable speed units in EU15, Norway and

Switzerland (EXTRACTS)

ENERGY.2011.7.3-2- STORAGE AND BALANCING VARIABLE ELECTRICITY SUPPLY AND DEMAND / ESTORAGE

EXTRACT of eStorage D4.1 Potential for conversion of classical PSP to variable speed units.doc 28/04/2016 2/42

R E V I S I O N C H A R T A N D H I S T O R Y L O G

V E R S I O N S

Version number When Organization name Comments

v1 28/04/2016 AHF Extract from D4.1 validated by reviewers to be

published on the eStorage website

D E L I V E R A B L E Q U A L I T Y R E V I E W

Quality check Status Date Comments

Reviewer 1 (EDF) 21/04/2016

Reviewer 2 (ICL) 27/04/2016

Quality Manager 28/04/2016

PC 28/04/2016



T A B L E O F C O N T E N T S

1 INTRODUCTION ................................................................................................................................ 9

1.1. BACKGROUND OF THE STUDY ........................................................................................................................ 9

1.2. OBJECTIVES .............................................................................................................................................. 10

2 METHODOLOGY ............................................................................................................................. 11

2.1. RESEARCH APPROACH ............................................................................................................................... 11

2.2. DATA COLLECTION .................................................................................................................................... 12

3 PUMPED-HYDRO: A PROVEN ENERGY STORAGE TECHNOLOGY ..................................................................... 12

3.1. DESCRIPTION ........................................................................................................................................... 12

3.2. CHARACTERISTICS ..................................................................................................................................... 14

3.3. FUTURE DEVELOPMENT ............................................................................................................................. 15

3.4. COST DEVELOPMENT ................................................................................................................................. 16

4 RESULTS AND ANALYSIS .................................................................................................................... 16

4.1. GENERAL OVERVIEW OF EUROPEAN ELECTRICITY SYSTEM ................................................................................. 16

4.2. POTENTIAL FOR VARIABLE SPEED DEPLOYMENT .............................................................................................. 18

4.2.1. Needed Modifications ............................................................................................................. 18

4.2.2. Estimation of the Potential for Conversion ............................................................................. 22

4.2.3. Identification of case studies ................................................................................................... 23

5 CONCLUSIONS ................................................................................................................................ 26

REFERENCES ......................................................................................................................................... 26

APPENDICES: COUNTRY FILES ...................................................................................................................... 28

AUSTRIA .............................................................................................................................................. 29

BELGIUM ............................................................................................................................................. 30

GERMANY ............................................................................................................................................ 31

SPAIN .................................................................................................................................................. 32

FRANCE................................................................................................................................................ 33

UNITED KINGDOM .................................................................................................................................... 34

GREECE ................................................................................................................................................ 35

IRELAND .............................................................................................................................................. 36

ITALY ................................................................................................................................................... 37



LUXEMBOURG ..................................................................................................................................... 38

PORTUGAL ........................................................................................................................................... 39

SWEDEN .............................................................................................................................................. 40

NORWAY ............................................................................................................................................. 41

SWITZERLAND ...................................................................................................................................... 42



L I S T O F F I G U R E S

Figure 1: Overview of the installed PSP capacity in the EU-15 + Norway + Switzerland ................................ 11

Figure 2: Scheme of a Pumped-Storage Power Plant (Alstom, 2012) ............................................................. 13

Figure 3: Overview of installed capacity in 2012 and newly added capacity for period 2013-2017 (Alstom,

2012) ................................................................................................................................................................ 13

Figure 4: Power mix capacity (Source: EIA, 2013) ........................................................................................... 16

Figure 5: Renewables production in 2010 (Eurelectric, 2012) ........................................................................ 17

Figure 6: Market development for PSP in the EU-15 = Norway + Switzerland (Alstom, 2013) ....................... 18

Figure 7: The different steps to determine if a conversion is possible or not (Alstom, 2013) ........................ 19

Figure 8: Comparison between a variable speed generator (left) and a conventional generator (right)

(Alstom, 2013) ................................................................................................................................................. 21

Figure 9: Age of units in 2013 for the EU-15 + Norway + Switzerland (Alstom, 2013) ................................... 23

Figure 10 Share of unit axis depending on the unit power output (MW) (Alstom, 2013) .............................. 24

Figure 11: Unit power output in generator mode (MVA) in function of speed (rpm) (Alstom, 2013)............ 24



L I S T O F T A B L E S

Table 1 : Typical PSP operating parameters (Alstom, 2012) ........................................................................... 14

Table 2 : Breakdown of the installed PSP capacity (Alstom, 2013) ................................................................. 17

Table 3 : Selected case studies Vs Installed capacity ...................................................................................... 25



Ancillary services Ancillary services enable to maintain frequency and voltage at appropriate levels while managing balance and congestion

BOP Balance of plant: essentially all equipment in a plant that are neither the turbine or the generator

DFIM - Double fed induction machine

Variable speed unit with a power converter located between the generator rotor and the grid. Only a part of the full active power of the generator is transferred through the power converter

ENTSO-E European Network of Transmission System Operators for Electricity

EU European Union

FRT Fault Ride Through - capability of electric generators to stay connected in short periods of lower electric network voltage

Fully fed machine Variable speed unit with a power converter located between the generator stator and the grid. The full active power of the generator is transferred through the power converter

GW Gigawatt

Head Difference in elevation between the upper reservoir water level and the lower reservoir water level

Horizontal machine Unit arrangement where the shaft connecting the turbine and the generator is horizontal

IVC Inverter controller

MV Medium voltage

MVA Megavolt Ampere

MW Megawatt

Partial load Turbine operation below its rated power.

PSP Pumped hydro Storage Plant

RAM Reliability, Availability, Maintainability

Reversible machine A same turbine that generate powers when rotating in one direction and pumps water up when rotating in the other direction.

TEG Turbine electronic governor

Ternary machine Unit arrangement with a pump and a separated turbine installed on a single shaft connecting them to the motor generator

TWh Terawatt hour

Vertical machine Unit arrangement where the shaft connecting the turbine and the generator is vertical

VSI Voltage Source inverter. Power electronics or frequency converter used to feed DFIM rotors.

G L O S S A R Y



P A R T I C I P A N T O R G A N I S A T I O N S

Participant organization name Short name Country

ALSTOM HYDRO FRANCE AHF France

ELECTRICITE DE FRANCE S.A. EDF France

ELIA SYSTEM OPERATOR ELI Belgium

ALSTOM GRID SAS AGR France

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE ICL United Kingdom

DNV GL KEM The Netherlands

ALGOE ALG France



1 INTRODUCTION

1.1. Background of the Study

The European Union (EU) has decided to take a proactive position concerning the issue of global warming

by enacting its 20-20-20 package. This aims at raising the share of the EU energy consumption produced

from renewable resources to 20%, reducing by 20% the EU greenhouse gases emissions level of 1990, and

improving by 20% the EU’s energy efficiency.

New renewables such as solar or wind power have been widely deployed. However one major challenge of

new renewable energy consists in it being intermittent while the grid needs to be balanced at any moment.

Concretely, this means that the current EU electricity system will need to be more flexible to allow the full

utilisation of renewables. Thus, while wind is blowing but demand for power is low, the grid frequency may

become unstable, increasing the risk of outages. Therefore, in certain countries power production has to be

reduced. The choice is made by grid operators to disconnect wind turbines from the grid – as it is less

constraining than stopping an inflexible base-load power plant – cutting off a source of carbon-free energy.

Today, beyond interconnection development, the only solution that exists to avoid curtailing intermittent

renewable generation and also happens to be available on a large-scale is Pumped Hydro Storage Plants

(PSP). PSP are able to store energy when there is a surplus in the energy system and therefore constitute a

vitally important part of the new low-carbon electricity system the EU wants to achieve.

However, conventional PSPs can only regulate their power in generation mode, while their operation in

pumping mode is typically much less flexible; new technologies are therefore under development to enable

greater operational flexibility of PSPs. In that context, the variable speed technology for PSP can bring the

additional flexibility in pumping mode as well. This could lead to a better integration of renewables in the

electricity system, by serving a dual purpose as the surplus of intermittent renewable energy could be

absorbed at any time of the day while at the same time allowing services to be balanced. Developing

technically and economically feasible solutions to upgrade existing plants to variable speed within the

eStorage project will allow upgrading a significant part of European PSP capacity, all at a much lower cost

than developing new plants.

The goal of eStorage Work Package 4 (WP4) is to draft a plan to replicate the variable speed PSP technology

development of work package 1 (WP1) throughout Europe. Within WP1, a detailed study has been

conducted to upgrade one unit of Le Cheylas PSP into variable speed. One of the main challenges is

represented by the physical space that is available, as the variable speed motor-generator requires a much

larger volume in the powerhouse. Before finding new locations for developing variable speed PSPs from

scratch, it is crucial to survey the installed PSP base in Europe. The survey will help determine the issues

that have to be resolved in order to allow a large-scale deployment of the variable speed technology.

The European PSP installed base is indeed quite diverse. It includes several different unit types, depending

first on the difference in elevation between the upper and lower reservoirs and also on the design choices

made by the plant owners. The improvement in performance and services, as well as the cost of modifying

the units varies significantly with the type of unit. The number of hours of operation, and thus the services

provided by the units depends upon the size of the reservoirs. All of these parameters can have a significant



impact on the feasibility of upgrading the existing plant into variable speed hence the need for it to be

carefully studied.

The potential for conversion to the variable speed technology will be therefore assessed through a

comprehensive survey of the European PSP fleet, which is the primary objective of this report.

1.2. Objectives

This report presents the comprehensive EU-wide survey on the possible upgrade of conventional PSPs in

operation into variable speed that has been performed in eStorage project.

Upgrading conventional PSP into variable speed presents several challenges: variable speed motor

generators require larger volume in the powerhouse and have more restrictive limitations in terms of

rotational speed and unit power due to the higher level of stress in variable speed rotors. The starting

sequence can also be quite different. It is therefore important to survey the currently installed PSP base to

comprehensively determine the issues that need to be solved in order to maximize the uptake of the

upgrade technology, given that the unit configuration and initial design choice will also have an impact on

the upgrade cost.

Key objectives of the report include:

Collect data on the existing European installed PSP base to survey different plant arrangements and

installed type of machines,

Propose a comprehensive overview and segmentation of all existing PSP sites that are eligible for

variable speed conversion in the EU-151 countries, Norway and Switzerland, including details on

necessary modifications to the plants and an estimate of the additional regulation capacity achievable

through variable speed conversions,

Identify and select the plants that are representative of different PSP clusters and have distinctly

different plant arrangements, machine axis positions (horizontal or vertical) or other hydraulic,

electrical and mechanical constraints. These plants will be further examined through detailed case

studies.

This report is structured into five parts: the methodology of this survey is presented in the first part while

the second part focuses on the pumped-hydro storage technology. The third part is presenting the results

of the survey and provides a detailed analysis of the PSP fleet for each country. The fourth part presents

the results of the 5 case studies that were performed to identify detailed technology gaps. Finally,

conclusions are closing the report.

1 EU-15 countries are Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the

Netherlands, Portugal, Spain, Sweden and the United Kingdom



2 METHODOLOGY

2.1. Research Approach

This study adopts two complementary research approaches: exploratory and descriptive research. The

analysis started with an exploratory research, focusing on determining and understanding the issues

related to the conversion of a conventional PSP into variable speed. It mainly consisted of collecting data

and having discussions with PSP and variable speed experts. The result of this first phase of research

created the right avenue to proceed to the second phase, the descriptive research.

The descriptive research for this study was the most important part of the work. It aimed at describing the

European PSP installed base and dividing it into different segments according to common characteristics

such as plant arrangements, machine axis etc. The first task has been to list which plant characteristics

needs to be collected.

The scope of this research is limited to the EU-15 countries, Norway and Switzerland. The rationale

behind this choice is that these countries include the bulk of the European PSP installed capacity (81.7 % of

the PSP capacity in Europe). Our estimate is that these countries account for approximately 42.7 GW out of

the 50.9 GW of PSP capacity in EU-272 countries, Norway and Switzerland.

Figure 1: Overview of the installed PSP capacity in the EU-15 + Norway + Switzerland

2 EU-27 Member States include: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,

Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovak Republic, Slovenia, Spain, Sweden and the United Kingdom.



2.2. Data Collection

The definition of plant characteristics to be collected has been performed through 27 interviews conducted

with experts from Alstom Hydro and EDF. The goal was to determine the most important criteria when

considering an upgrade from conventional PSP to variable speed. The data gathering task also included

collecting feedback on the Le Cheylas PSP upgrade to variable speed, which is used for the case study

assessment. This phase brought to light more than 200 parameters that were used to survey the PSP units

in operation in the EU-15 + Norway + Switzerland. These parameters were classified into four principal

categories:

General information about the power plant (e.g. year of commissioning, country, operator...)

Information on the reservoirs (e.g. size, levels…)

Information on the plant production (e.g. when, how much…)

Information on the unit (e.g. type of axis, power in pumping and turbine modes…)

Actual plant parameters collected in the second phase included values of the parameters identified through

the exploratory research. A variety of sources of proven reliability were employed which included: internal

data from eStorage partners, an internal database, on-site visits and specialized publications and journals

on hydroelectricity. The websites of different European plant operators have been referenced as well to

benefit from the information available online.

3 PUMPED-HYDRO: A PROVEN ENERGY STORAGE TECHNOLOGY

Energy production and consumption levels have become an issue of growing importance in order to

guarantee the stability of electrical networks. Pumped storage hydroelectricity is currently the only

economic and flexible means of storing large amounts of excess energy that have been deployed on a large

scale, helping the power systems to successfully and efficiently balance supply and demand. This is

becoming even more important as more and more countries are increasing their renewable capacities.

3.1. Description

The key components of a Pumped Storage Plant are two water reservoirs (an upper and a lower one), a

penstock, which transports the water from one reservoir to another, and an underground power station.

The latter contains the “energy conversion” part of the PSP: the pump turbine and the motor generators.

Most modern PSPs are equipped with reversible units meaning that the same turbine is able to either pump

water or to drive the generators to produce electricity, depending on its rotational direction.



Figure 2: Scheme of a Pumped-Storage Power Plant (Alstom, 2012)

PSP is considered as a mature technology. This has been a standard solution for peak shifting in Western

Europe, where low-cost nuclear power is used to supply base load demand and to pump water to the upper

reservoir during low demand periods. Nowadays it is becoming increasingly common to manage the

fluctuations in the supply of wind and solar power in North Western Europe using PSPs.

Figure 3 shows the installed pump storage capacity in MW per country in EU-15 + Switzerland + Norway.

Figure 3: Overview of installed capacity in 2012 and newly added capacity for period 2013-2017 (Alstom, 2012)



3.2. Characteristics

Maximum power generation is determined by the maximum flow of water from the upper to the lower

storage reservoir and the height difference between the reservoirs (e.g. the head). The amount of

electricity that can be stored is determined by the head and the size of the (smallest of the two) reservoirs.

The cycle efficiency of a modern PSP is around 80% or more; cycle losses arise from the losses in pumping,

generating and water evaporation.

When connected to the grid, a PSP is normally used to provide energy during peak-hours. When electricity

demand is low (or there is excessive supply from intermittent renewable generators), pumped-storage

turbines pump water into the upper reservoir and store it (pumping mode). When demand and prices peak,

the water is released through turbines to the lower reservoir (production mode) and the electricity is

produced. PSPs further allow utilities to reap financial benefits from storing the intermittent renewable

output that might otherwise be lost due to surplus supply in the system.

KEY DATA PERFORMANCE

General

Performances

50 to 500 MW

150 to 300 MW

Per unit Output/Input

Most typical values

> 8 hours full load Storage capacity

10 to 1,200 m Head Range

> 80% Cycle efficiency

Reaction Time

~ 15 s

~ 2 min

~ 5 min

~ 10 min

50% to 100% Generation

0% to 100% Generation

0% to 100% Pumping

100% Generation to 100% Pumping

Ancillary Services

40% to 100%

70% to 100%

Reactive Power

Black Start capability

Production adjustment range

Pumping power adjustment range (Variable speed machines only)

Table 1 : Typical PSP operating parameters (Alstom, 2012)

The large storage size (lengthy discharge time) of PSPs makes them useful for bulk energy applications, such

as load/time shifting. Furthermore, PSPs can respond quickly to sudden changes in supply-demand balance,

making it a useful tool to balance the variability of electricity demand from consumers or unplanned

outages of other power plants. Combined with the fast ramp rates, PSP can thus support renewable

integration by providing ancillary services such as network frequency and voltage regulation, capacity

reservation, black start capabilities, as well as reactive power production.



3.3. Future Development

Three main areas for future improvements in the PSP technology have been identified as:

Increasing the capability to install PSPs everywhere (e.g. on islands using sea water, or using

existing underground reservoirs while minimising the potential negative impact on the

environment )

Increasing PSP flexibility and efficiency (e.g. by enabling power regulation in both modes through

the development of variable speed technology, shortening the start-up and transition time,

improving design and resistance to cavitation).

Non-technical issues (e.g. develop business models that include pumped storage plants, grid

connections and market models, develop remuneration systems that compensate flexibility and

storage capabilities).

The eStorage project focuses on the development of variable speed technology. Variable speed pumped

hydro storage provides additional flexibility in pump/storage mode. Conventional pumped hydro storage

plants do not allow variations in pump load. Variable speed pumped hydro storage has a faster response

and is able to regulate the pump load, enabling frequency support during pumping mode. Retrofitting a

conventional PSP with a variable speed generator could increase the power capacity by 15 to 20% and the

general plant efficiency by 1%.

Unlike conventional hydropower plants, variable speed pumped storage plants use asynchronous motor-

generators that allow the pump rotational speed to be adjusted. As a result, variable speed pumped

storage plants benefit from high levels of additional flexibility including:

Regulation of the amount of energy absorbed in pumping mode. This facilitates storing energy

when prices of electricity are low, reduces the number of starts and stops, and allows the sale of

grid regulation service (network frequency and voltage) while in pumping mode.

Operating closer to the turbine’s optimal efficiency point, resulting in a significant increase in

global plant efficiency.

Smoother operation (for example at partial load), elimination of operation modes prone to

hydraulic instability or cavitation. This would result in improved reliability, reduced maintenance

and an increased lifespan. It also results in the reduction of pump turbine submergence level,

reducing civil engineering costs.

Operating over a wider head range, increasing the availability of the plant. For pumped storage

plants on sites characterised by wide head variations, variable speed increases the partial load

operation range to 33% of rated power in turbine mode and thus increases the generation

flexibility.

Instantaneous power output adjustment helps to rectify sudden voltage disruptions/variations

caused by network problems. These benefits result in improved profitability for pumped storage

plant owners, and allow network operators to improve the reliability of the grid as well as the

quality of the power supplied to end consumers.

Today, the most prominent PSP with variable speed units in operation is Goldisthal in Germany. Other

projects based on variable speed units are currently under construction: the first unit of 4x250MW Linthal

2015 plant (Switzerland) will be commissioned during spring 2016. The 3 other units will each be



commissioned later within a three month interval. Vendanova III (Portugal) first unit is planned to be

commissioned by end of 2016. Nant de Drance (Switzerland) first units will be commissioned in 2018

3.4. Cost Development

Given that PSP is a mature form of storage technology, no future cost reductions are expected.

4 RESULTS AND ANALYSIS

4.1. General overview of European electricity system

Net electricity generation output in the EU-15 + Norway + Switzerland amounted approximately to

2,870 TWh in 2012. Accounting for 16 % of that figure, hydro represents the largest source of renewable

power generation. The 157 PSP plants currently in operation in the EU-15 + Norway + Switzerland with an

installed capacity of 42.7 GW enable generating 63.7 TWh of power.

Figure 4: Power mix capacity (Source: EIA, 2013)



Figure 5: Renewables production in 2010 (Eurelectric, 2012)

The PSP portfolio in the EU-15 + Norway + Switzerland is mainly composed of low power output units, with

almost half of the installed fleet represented by machines below 50 MW. The fleet is also ageing, with the

majority of its machines having been commissioned before 1990.

Table 2 : Breakdown of the installed PSP capacity (Alstom, 2013)

I N S T A L L E D C A P A C I T Y

( E U - 1 5 + N O R W A Y + S W I T Z E R L A N D )

SIZE

INSTALLED CAPACITY BUILT BEFORE 1990

Units % in MW Units % in MW

< 50 MW 281 15 % 262 17 %

50 – 105 MW 148 26 % 133 28 %

105 – 200 MW 100 34 % 87 35 %

200 – 300 MW 32 17 % 22 14 %

300 – 400 MW 11 8 % 7 6 %

TOTAL 572 100 % 511 100 %



The market for Pumped-Storage has seen a significant expansion during the period 1960 – 1990,with an

annual average growth of 30% resulting in an average of 1.1 GW of new capacity added each year (see

figure 7). This development followed the development of the European nuclear power plant fleet. Though

the market in Europe for PSP is already considered ripe, the European Union’s 20-20-20 vision further

reinforces the potential of this “segment” given that this technology is viewed as the only reliable option

available to match up the required scale of storing large volumes of surplus intermittent renewable power.

There is therefore great potential for PSPs to propel the EU in reaching their energy policy goals 20-20-20

package. These insights and developments have encouraged countries such as Portugal, Switzerland or

Austria to approve a certain number of new PSP projects. By 2020, the European installed capacity is

expected to reach the level of 47.8 GW, a rise of almost 16 % in 10 years.

Figure 6: Market development for PSP in the EU-15 = Norway + Switzerland (Alstom, 2013)

A detailed analysis per country is included in the appendix.

4.2. Potential for Variable Speed deployment

The study of the potential for variable speed deployment is conducted in three phases. Firstly, the variable

speed deployment is analyzed from a technical perspective, in order to respond to questions such as:

Which modifications are needed on an existing unit?

What needs to be taken into account in order to determine if a conversion is possible or not?

Then, the second phase consists in assessing the potential for conversion in terms of additional power

flexibility that could be brought onto the grid, and to determine the number of plants that could be

converted. Finally, the third phase involves the selection of business cases, which will be based on different

technical solutions for conversion given the diversity of the European installed PSP fleet.

4.2.1. Needed Modifications

PSP with variable speed units create new challenges for manufacturers with respect to the design,

manufacturing and assembly of the machine. For an optimized solution the hydraulic machine, the motor

generator and its excitation system as well as the balance of plant components have to be customized for

each power station.



Two technologies are proposed for an upgrade to variable speed:

1. Keeping a synchronous motor generator connected to a full power supply frequency converter

(fully fed machine), which is suitable for units with low power output, or

2. Replacing the synchronous motor generator by a double fed induction machine (DFIM) connected

to a reduced power supply frequency converter on the rotor, suitable for large power output (> 100

MW).

When studying the feasibility of converting a conventional machine to variable speed, it is necessary to

conduct a variety of studies in order to assess whether there is an economic case for the conversion of the

unit and the power plant. The scheme below summarizes the major steps to follow in order to conclude

whether the conversion to variable speed for a conventional machine is of interest. These steps have been

identified through interviews with variable speed experts as well as from experience from the upgrade of

Le Cheylas unit 2.

Figure 7: The different steps to determine if a conversion is possible or not (Alstom, 2013)

Defining systems’ needs

The first step consists in defining the needs of the wider system, i.e. the plant operator expectations:

1. Is it important to improve the performance of the machine?

2. Is the plant required to provide more ancillary services to the grid?

3. What are the key drivers in the cost/benefit analysis?

4. What level of reactive power provision is required?

These questions help to identify the requirements and objectives of the plant operator with respect to the

conversion. This will condition the perspective in which the feasibility studies will be realized and later help

explore the economics behind the plant conversion.



Hydraulic studies

Once the reasons for conversion have been established, the turbine manufacturer will conduct the first

feasibility study on hydraulics, looking at the level of efficiency the new machine needs to reach in order to

fulfil the objectives of the conversion. This also takes into account the power of the existing unit and how it

deals with harmonics. External factors such as the temperature, humidity or the variation of the water flow

in pumping mode also need to be taken into account as they will impact the performance of the future

variable speed machine. This step helps to answer the three main questions:

1. Is active power variation in pumping mode possible?

2. Does the plant arrangement allow a possible upgrade?

3. What is the feasibility of adding a variable speed generator?

If power variation in pumping mode is possible, a second hydraulic study will define which level of speed

variation can be obtained, and which equipment needs to be modified to enable that variation level. Some

basic parameters of hydraulic components such as the runner diameter or the shaft length are assessed in

order to decide whether to continue with the conversion study. During this analysis, the pump design is

also assessed. The manufacturer will face two key challenges when converting to variable speed: the need

for improving the stability and the cavitation limits. The stability limit is the maximum limit that the

machine should not exceed to avoid operating in an unstable domain, risking damage. If the plant operator

wishes to increase the range of power variation, this limit needs to be shifted further away from operating

area. In addition, the risk of cavitation is increased with variable speed machines, as the existing machine

has a fixed elevation and cannot be set deeper beyond that point: if the plant operator wants to increase

the machine performance, the cavitation performance of the turbine also needs to be improved.

If after this step the conversion is successful for the plant owner and the plant operator, an economic

assessment will be conducted to compare the cost of conversion and the benefit of more improved

performance. The cost-benefit analysis allows the plant owner and operator to establish the economic

feasibility of the upgrade to variable speed.

Realizing the electrical study

The final steps will assess the electrical machine, i.e. generators, converters and other equipment such as

the civil engineering structure or the cooling system. A variable speed motor generator includes several

components that differ from a conventional one.



Figure 8: Comparison between a variable speed generator (left) and a conventional generator (right) (Alstom, 2013)

The Rotor of a double-fed induction machine is significantly different from the one in a conventional

synchronous machine. Its weight is therefore 30 to 50% higher than that of a rotor of a salient pole

machine. Consequently, specific design studies have to be realised. In the case of variable speed upgrade,

the rotor is completely redesigned. It consists of a three-phase rotor winding wound onto a cylindrical

rotor. In addition, the frequency converter, an additional piece of equipment needs to be installed in the

plant. It actually replaces the existing static frequency converter used to start the unit in pump mode, and is

used as the AC excitation system instead of the existing DC excitation system for the synchronous machine.

The stator also needs to be oversized since it is in a sub-synchronous mode; power is transferred from the

rotor to the stator. The balance of the plant must therefore be suitably adapted: a generator circuit breaker

and starting braking short circuit breakers. In certain cases, phase reversal disconnectors and isolated

phase bus ducts have also to be replaced. The main constraint on the variable speed upgrade is to integrate

the stator and the rotor in the motor-generator pit. The pit dimension can be a limiting factor, as the

variable speed machine is heavier and has greater volume. The shaft line behaviour is also impacted by this

additional weight.

Structural design of the electrical machine has to support the new weight of the rotor. One of the critical

parameter for the shaft line dimensioning is the natural bending frequency, a phenomenon that represents

a risk to damage the machine. The difficulty can be partially overcome by the rearrangement of the unit

layout. For a variable speed conversion, the shaft line and the thrust bearing need to be redesigned with a

higher capacity to support the supplement of the unit axial load which comes mainly from the new rotor.

Finally the concrete structure has to be able to carry the new thrust bearing, : in some cases, if it is not

possible to keep the redesigned thrust bearing in its original arrangement, the thrust bearing can be moved



onto the turbine head cover. A modification may also be needed in the lifting system as the new rotor is

heavier and the capacity of the crane might not be able to support it. Different options are available to

resolve these civil engineering issues: reinforcing the cranes with metallic structures, procuring specific

lifting equipment dedicated to the DFIM rotor and stator, or assembling the rotor directly in the pit.

Adapting control systems

Control systems also need to be adapted during a variable speed conversion. In a conventional PSP there

are essentially two controllers for each unit. On the electrical side, the excitation controller mainly

regulates the voltage or the power factor of the machine. On the hydraulic side, the turbine governor

regulates the power and the speed of the machine during start-up and synchronization. In contrast, the

control system of variable speed units consists of three components: variable speed controller, turbine

governor (TEG) and inverter controller (IVC). The variable speed controller defines the optimum speed

based on the current head and the desired power in normal operation. It also handles all mode changes

and the synchronization process. It is linking the TEG and the IVC to the unit control system. It handles all

signals to be exchanged between the unit and the unit control system.

The structure of the control system will therefore be more complex compared to conventional units and

therefore needs to be adapted.

With the introduction of the ENTSO-E transmission code, Europe is preparing for more severe grid

conditions and consequently more demanding connection rules for power stations, in order to be prepared

for the future requirements of the transmission system. The new grid code has an impact on control and

protection schemes of all power-stations, and particularly on variable speed PSPs. In order to obtain

permission to connect to the grid, power stations need to prove the so-called Fault Ride Through (FRT)

capability. In short, a power station must remain connected to the grid if a three-phase short circuit occur

at the connection point in the duration of 150 ms. The challenge for the protection system is to detect a

FRT situation and not to disconnect the unit in such a case. Consequently, each protection function needs

to be checked separately to avoid undesired tripping during FRT.

Furthermore, the entire PSP will need to be upgraded to deliver all necessary functionalities similar to

conventional units, such as the start-up of the units and the level of harmonics.

With respect to the balance of plant, the need to replace the existing transformer is evaluated considering

the necessary maximum power as well as the condition of the transformer.. The new converters, used to

start the variable speed unit in pumping mode, also require more space. If the available space is limited and

represents a constraint for the upgrade, it is possible to install new converters outside the power plant.

To conclude, one of the key limiting factors to determine the potential for conversion is the physical space

available in the power plant.

4.2.2. Estimation of the Potential for Conversion

Due to a high number of mode changes, motor-generators are generally ageing faster than base load hydro

generators, particularly considering the recent operational requirements of 10-20 starts and stops per day.

Adding variable speed technology to a conventional PSP will increase plant efficiency and flexibility by

allowing power regulation in both turbine and pumping mode. It will enable electric utilities harness surplus

power from intermittent sources such as wind to fill pumped hydro storage plants’ upper reservoirs faster,

storing the surplus energy for later use when demand is high or when no wind energy is available.



Considering a typical 30-year lifespan for a motor generator, it means that 34.9 GW of PSP generators for

the area EU-15 + Norway + Switzerland will need to be refurbished by 2020. This represents 84 % of the

existing 42.7 GW of installed PSP capacity in the area. The marginal cost of enabling additional regulation

capability could therefore be potentially reduced if it is carried out at the same time as the standard

generator refurbishment.

Figure 9: Age of units in 2013 for the EU-15 + Norway + Switzerland (Alstom, 2013)

The power absorbed in pumping mode by a variable speed unit can vary by 30 %, compared to a

conventional PSP unit. Thus, converting 100 MW of conventional PSP into variable speed will provide

around 30 MW of regulation capability while in pumping mode. This means that if the 34.9 GW of

conventional generators older than 30 years are converted into variable speed, 10.47 GW of additional

frequency regulation capability in pumping mode are obtainable. Such capability would typically be used to

provide frequency regulation that will be increasingly required in systems with high wind penetration.

4.2.3. Identification of case studies

To complete this survey, different case studies have been analysed in order to identify the main

technological gaps associated with upgrading existing European PSP units to variable. The main objective of

these case studies is to develop a feasibility and predesign study that comprises a technical and cost

evaluation

The case studies need to efficiently reflect the entire existing PSP installed base. As a result, the plants that

are selected for case study assessment need to differ in their structures and limitations to represent the

diversity of the European PSP fleet. It is thus imperative that the case studies include horizontal and vertical

machines (respectively 29% and 71% of the fleet) as well as reversible and ternary units (respectively 46%

and 54% of the fleet), and represent the power and speed ranges that comprise the units currently

operating on the European market. Those were the parameters that were therefore analysed for the PSP

installed base.

The type of unit axis (i.e. whether the turbine and the generator are coupled on a vertical or horizontal axis)

was therefore studied as a function of unit power output, in order to provide a more detailed overview.

This is an important parameter to take into account, as one of the major issues with variable speed

conversion is the available space as some replaced components are larger and heavier. Proportion of units



with different axis arrangements is presented in the figure below. It can be observed that the majority of

PSP machines in Europe are vertical, but as the graph shows the share of horizontal machines is non-

negligible, especially at lower levels of power output. This confirms that the upgrade of this type of

machines also needs to be studied; therefore, at least one horizontal machine will be chosen to figure

among the business cases.

Figure 10 Share of unit axis depending on the unit power output (MW) (Alstom, 2013)

The second analysis conducted was considering the generator output power (in MVA) and the unit rated

speed (in rpm), while taking into account the machine axis arrangement. This resulted in the figure below.

Figure 11: Unit power output in generator mode (MVA) in function of speed (rpm) (Alstom, 2013)



The five plants thus selected are representative of the different types of units in operation today: high-

speed low power output, low speed-low power output, low speed-high power output and high speed-high

power output. It was also ensured that vertical and horizontal machines as well as reversible ternary units

were present among the selected business cases.

Looking at installed capacity table below, we notice that our selection of case studies covers well the

existing diversity of arrangements and power ratings.

SIZE

Units % in MW Units % in MW

< 50 MW 281 15% 262 17%

50 - 105 MW 148 26% 133 28%

150 - 300 MW 132 51% 109 49%

301 - 400 MW 11 8% 7 6%

TOTAL 572 100% 511 100%

INSTALLED CAPACITY

(EU - 15 + NORWAY + SWITZERLAND)

INSTALLED CAPACITY BUILD BEFORE 1990

1

2

3

4 5

Table 3 : Selected case studies Vs Installed capacity

For the 5 business cases, a predesign of the upgrade has been effectuated. This enabled the consortium to:

Receive an in-depth analysis of the additional benefits that could be realized by upgrading these units to variable speed.

Perform a technology gap analysis.

The most important gaps have been identified and related R&D programs have been accordingly defined.

Essentially, the consortium has identified all major hindrances associated with upgrading 75% of the

European PSP fleet to variable speed.

The R&D program that is expected to be implemented within eStorage project should aim at overcoming all

identified technical barriers.

The detailed results of the business cases and the technical gaps remain proprietary and confidential and

only the primary conclusions can be shared in this publication.



5 CONCLUSIONS

The objective of Task 4.1.1 was to perform a global survey of the European PSP fleet in order to identify

gaps in technology. The result of this analysis will then provide an input to WP1 to allow prioritizing the

actions to prepare a new variable speed rotor guide.

The survey estimated the installed PSP capacity in EU15, Norway and Switzerland at 42.7 GW of turbine

power. Not surprisingly, most of the fleet is located in the mountainous region of the Alps and the Pyrenees

with very few plants in lowland regions such as the Netherland or North Germany. The survey also allowed

defining 5 typical configurations that were further studied in order to highlight the necessary modifications

associated with variable speed conversion.

The upgrade of existing fixed speed units to variable speed has attracted significant interest in Europe, and

the consortium has had the opportunity to involve real plant operators in the study. The names of these

operators remain confidential, but the work performed for them has encouraged further interest

evidenced by the fact that ,currently at least two other operators are conducting feasibility studies for plant

upgrades with expected commissioning dates from 2020 onwards. T4.1.1 has therefore been successful not

only in terms of the identification of gaps but also from the aspect of participating in eStorage

dissemination actions.

REFERENCES



ALSTOM POWER. (2012). Hydro Pumped-Storage Power Plants. Paris.

EASE. (2013). Pumped-Hydro Storage.

eStorage. (2013). Technology Development Report.

EUROPEAN WIND ASSOCIATION. (2013). Wind in power - 2012 Statistics.

EUROSTATS. (2012, November). Electricity production and supply statistics. Retrieved November 4th,

2013, from eurostats:

http://epp.eurostat.ec.europa.eu/statistics_explained/index.php/Electricity_production_and_supply_st

atistics

GIMENO-GUTIERREZ, M., & LACAL-ARANTEGUI, R. (2013). Assessment of the European potential for

pumped hydropower energy storage. Luxembourg: Publications Office of the European Union.

HENRY, J.-M., HOUDELINE, J.-B., RUIZ, S., & KUNZ, T. (n.d.). How reversible pump-turbines can support

grid variability. The variable speed approach.

HENRY, J.-M., MAURER, F., DROMMI, J.-L., & SAUTEREAU, T. (2013). Upgrading an Existing Pumped

Storage Power Plant into a Variable Speed. Hydrovision 2013.

INTERNATIONAL ENERGY AGENCY. (2012). Technology Rooadmap: Hydropower. Paris: International

Energy Agency.

KUNZ, T., SCHWERY, A., & SARI, G. (2012, July 17-20). Adjustable speed pumped storage plants -

Innovation challenges and feedback of experience from recent projects. Hydrovision International.

TELLER, O., KAELIN, B., GOUTARD, E., & KUNZ, T. (2012, July 17-20). Upgrading PSP into variable speed

coupled with efficient Energy and Market Management Solutions: a key opportunity. HydroVision

International.

US Department of Energy. (2013). International Energy Statistics. Retrieved November 15th, 2013, from

US Energy Information Administration:

http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=44&pid=44&aid=1#



APPENDICES: COUNTRY FILES



Net electricity production 67,3 78,5 90,3

Net natural hydro production 41 51 56,2

Net production from PSP 13,4 17,8 20,3

Net production from wind 2,2 6,4 8,7

Net production from solar 0 0,5 3,8

Total variable RES electricity 2,2 6,9 12,5

PSP storage capacity tbd tbd tbd

% PSP possible varspeed upgrade tbd tbd tbd

% storage of variable RES possible tbd tbd tbd

[TWh](Source: Eurelectric, 2012)

2010 2020 2030

Units % in MW

< 105 MW 55 49%

105 - 200 MW 7 30%

200 - 300 MW 3 21%

300 - 400 MW 0 0%

Total 65 100%

SizeInstalled Capacity

AUSTRIA

General Data

PSP Data




Net natural hydro production 1,7 1,7 1,7



Net production from solar 0,6 0,7 0,8






2010 2020 2030

Units % in MW

< 105 MW 4 12%

105 - 200 MW 3 36%

200 - 300 MW 3 52%

300 - 400 MW 0 0%

Total 10 100%


BELGIUM

General Data

PSP Data




Net natural hydro production 27 30,5 32,5

Net production from PSP 6,3 9,5 11

Net production from wind 37,79 90 116

Net production from solar 11,68 33 37

Total variable RES electricity 49,47 123 153





2010 2020 2030

Units % in MW

< 105 MW 83 44%

105 - 200 MW 7 17%

200 - 300 MW 6 20%

300 - 400 MW 4 19%

Total 100 100%


GERMANY

General Data

PSP Data



Net electricity production 290,7 355 355

Net natural hydro production 44,9 41 42

Net production from PSP 4,4 5 5


Net production from solar 8,14 14 20






2010 2020 2030

Units % in MW

< 105 MW 51 41%

105 - 200 MW 18 32%

200 - 300 MW 9 27%

300 - 400 MW 0 0%

Total 78 100%


SPAIN

General Data

PSP Data





Net production from PSP 5,6 ? ?

Net production from wind 9,7 31 58,2

Net production from solar 0,6 8,8 22






2010 2020 2030

Units % in MW

< 105 MW 23 22%

105 - 200 MW 16 49%

200 - 300 MW 6 28%

300 - 400 MW 0 0%

Total 45 100%


FRANCE

General Data

PSP Data



Net electricity production 366,2 329 374,7


Net production from PSP 3,1 3 3








2010 2020 2030

Units % in MW

< 105 MW 4 12%

105 - 200 MW 6 24%

200 - 300 MW 0 0%

300 - 400 MW 6 64%

Total 16 100%


UNITED KINGDOM

General Data

PSP Data



Net electricity production 53,5 61,8 ?

Net natural hydro production 7,5 6,1 ?

Net production from PSP 0,0 0,9 ?

Net production from wind 2,7 14,7 ?

Net production from solar 0,2 3,6 ?

Total variable RES electricity 2,9 18,3 0





2010 2020 2030

Units % in MW

< 105 MW 3 49%

105 - 200 MW 3 51%

200 - 300 MW 0 0%

300 - 400 MW 0 0%

Total 6 100%


GREECE

General Data

PSP Data





Net production from PSP 0 0,4 0,4


Net production from solar 0 0 0






2010 2020 2030

Units % in MW

< 105 MW 4 100%

105 - 200 MW 0 0%

200 - 300 MW 0 0%

300 - 400 MW 0 0%

Total 4 100%

Installed CapacitySize

IRELAND

General Data

PSP Data



Net electricity production 290,7 ? ?

Net natural hydro production 54,4 ? ?

Net production from PSP 3,3 ? ?

Net production from wind 9 ? ?

Net production from solar 1,9 ? ?






2010 2020 2030

Units % in MW

< 105 MW 84 33%

105 - 200 MW 32 55%

200 - 300 MW 4 12%

300 - 400 MW 0 0%

Total 120 100%


ITALY

General Data

PSP Data













2010 2020 2030

Units % in MW

< 105 MW 13 80%

105 - 200 MW 0 0%

200 - 300 MW 1 20%

300 - 400 MW 0 0%

Total 14 100%


LUXEMBOURG

General Data

PSP Data




Net natural hydro production 16,4 14 14,3









2010 2020 2030

Units % in MW

< 105 MW 14 70%

105 - 200 MW 3 30%

200 - 300 MW 0 0%

300 - 400 MW 0 0%

Total 17 100%


PORTUGAL

General Data

PSP Data





Net production from PSP 0 0 0

Net production from wind 3,502 12,5 21


Total variable RES electricity 3,502 12,5 21





2010 2020 2030

Units % in MW

< 105 MW 4 27%

105 - 200 MW 0 0%

200 - 300 MW 0 0%

300 - 400 MW 1 73%

Total 5 100%


SWEDEN

General Data

PSP Data



Net electricity production 124,4 143 145

Net natural hydro production 118,4 134 135

Net production from PSP 0 0 0








2010 2020 2030

NORWAY

General Data

PSP Data

Units % in MW

< 105 MW 20 45%

105 - 200 MW 6 55%

200 - 300 MW

300 - 400 MW

Total 26 100%

Installed CapacitySize




Net natural hydro production 37,5 41,2 42

Net production from PSP ? 5,8 6


Net production from solar 0 0,3 0,8






2010 2020 2030

Units % in MW

< 105 MW 64 100%

105 - 200 MW 0 0%

200 - 300 MW 0 0%

300 - 400 MW 0 0%

Total 64 100%


SWITZERLAND

General Data

PSP Data

Documents

Potential for conversion of classical PSP to variable speed ......ENERGY.2011.7.3 STORAGE-2 AND BALANCING VARIABLE ELECTRICITY SUPPLY DEMAND / ESTORAGE EXTRACT of eStorage D4.1 Potential