TRAINING FOR OLADE`S MEMBER COUNTRIES COURSE CAPEV 14 2011 By César Angeles-Camacho Instituto de Ingenieria, UNAM [email protected] DESIGN AND IMPLEMENTATION

TRAINING FOR OLADE`S MEMBER COUNTRIES COURSE CAPEV 14 2011

By César Angeles-CamachoInstituto de Ingenieria, [email protected]

DESIGN AND IMPLEMENTATION OF COMBINED HYBRID SYSTEMS (ADVANCES IN TECHNOLOGY AND REGULATION)

Octubre 2011

Lecturer: PhD. César Angeles-CamachoContact Details:

Instituto de Ingeniería, Edificio Bernardo Quintana (12), Room 202 (Cord. De Eléctrica y Computación)

Telephone: 56-23-36-00 ext. 8810

Email: [email protected]

Power Electronic Equipment Principles and its Applications in Electric Power Systems, Generation, Transmission and Distribution

Wind Generation – Impact on the Power Networks, Transmission and Distribution System

Modelling and Simulation of Large-scale Power Systems with FACTS Equipment

Areas of Expertise/Research

Session 4 Chapter 5: Wind – PV- Diesel hybrid

systems

Contact Details: PhD. César Angeles Camacho

Instituto de Ingeniería, Edificio Bernardo Quintana (12), Room 202 (Cord. De Eléctrica y Computación)

Telephone: 56-23-36-00 ext. 8810

Email: [email protected]

a. Introduction.

b. Design and configuration of a Wind-PV – Diesel system.

c. Sizing.

d. Optimization of Wind-PV-Diesel system.

e. Environmental impact of Wind-PV-Diesel system.

Wind-PV hybrid systems with diesel generator backup.

Wind and Solar are naturally complementary in terms of both resources being well suited to hybrid systems.

The rapid growth of the solar photovoltaics (PV) industry has contributed to the demand for small wind turbines, as the two technologies are often market complements.

Hybrid electric systems combine wind and PV systems to make the most of the area's seasonal wind and solar resources;

with wind relatively more available in winter months and at night time,

and solar relatively more available in summer months and during winter's sunlit days.

Introduction

Introduction

These hybrid systems provide a more consistent year-round output than either wind-only or PV-only systems and can be designed to achieve desired attributes at the lowest possible cost.

These systems can be grid connected, but they are also often stand-alone, distributed energy generators.

Introduction

Introduction

A drawback, common to solar and wind power generations, is their unpredictable nature and dependence on weather and climatic changes.

Both of these would have to be oversized to make their stand alone systems completely reliable.

For the times when neither system is producing enough electric power, most hybrid systems have backup power through batteries

and/or an engine generator powered by conventional fuels, such as diesel.

Introduction

Therefore, depending on the requirement and the availability of energy sources, more than two sources maybe combined, such as solar-wind-Diesel system.

This kind of hybrid system can attenuate individual fluctuations, increase overall energy output and reduce energy storage

requirements significantly.

Introduction

Various hybrid energy systems have been installed in many countries over the last decade, resulting in the development of systems that can compete with conventional, fuel based remote area power supplies in many applications.

With the wide spread introduction of net-metering, the use of small isolated or grid connected hybrid energy systems is expected to grow tremendously in the near future, both in industrialized and developing countries.

Introduction

However, with the increased complexity, the optimum design of hybrid system becomes complicated through

uncertain renewable energy supplies

Uncertain load demand,

non-linear characteristics of the components,

and the fact that optimum configuration and optimum control strategy of the system are interdependent.

Design and configuration of a wind-PV system

Typical stand-alone hybrid solar-wind-diesel power generation system consists of three types of power generation facilities:

i. PV array,

ii. wind turbine,

iii. diesel generator,

And other componets like,

inverter, rectifier,

Battery bank. serve for the storage of the natural energies

controller,

and other accessory devices and cables.


In stan-along systems the storage Batteries are installed to ease the fluctuations of power generation output normally happened in case of

renewable energy source.


Various combinations of diesel generator, wind turbine, PV array, battery, and power converter modules can be taken into account towards identifying an economically viable solution that would meet the required load.

For commissioning a hybrid system it is initially assume that the site selected is exposed to reasonable wind speeds as well as good solar irradiation.

It is also essential to know the energy demand at that site.

This allowed for the design of a suitable hybrid power system that would meet the demands of load at best.


Climatic conditions determine the availability and magnitude of wind and solar energy at particular site.

Pre-feasibility studies are based on weather data (wind speed, solar insolation) and load requirements for specific site.

In order to calculate the performance of an existing system, or to predict energy consumption or energy generated from a system in the design stage, appropriate weather data is required

Feasibility of hybrid PV/wind energy system strongly depends on solar radiation and wind energy potential available at the

site


Various feasibility and performance studies are reported to evaluate option of hybrid PV/wind energy systems

Photovoltaic array area, number of wind machines, and battery storage capacity play an important role in operation of hybrid

PV/wind–diesel system while satisfying load

The collected data of the various energy sources is analysed in order to plan for the structure of the system

Simulations and modelling were carried out over a period of time, allowing the statistical information about local weather to be truly representative.


The recent state of art hybrid energy system technological development is the result of activities in a number of research areas, such as

Advances in electrical power conversion through the availability of new power electronic semiconductor devices, have led to improved efficiency, system quality and reliability.

Development of versatile hybrid energy system simulation software; continuing advances in the manufacturing process and improve efficiency of photovoltaic modules.


The development of customized, automatic controllers, which improve the operation of hybrid energy systems and reduce maintenance requirements.

Development of improved, deep-cycle, lead-acid batteries for renewable energy systems.

Availability of more efficient and reliable AC and DC appliances, which can recover their additional cost over their extended operating lifetime.

The task for the hybrid energy system controller is to control the interaction of various system components and control power flow

within the system to provide a stable and reliable source of energy.

Sizing

After pre-feasibility study the selection of proper sizing of equipment is made based on weather data and maximum capacity.

The unit sizing of integrated power system plays an important role in deciding the reliability and economy of the system.

Open literature show wide Studies by the different researchers discussing different methods to determining the wind generator capacity and the number of PV panels, number and size of wind turbines and number and capacity of battery needed for the stand-alone system.

Sizing

Some methods to determinate the size of the Wind-PV-Diesel Systems are,

linear programming techniques to minimize the average production cost of electricity while meeting the load requirements in a reliable manner, and takes environmental factors into consideration both in the design and operation phases are used.

Using the measured data of solar and wind energy at a given location, research's employ a simple graphical construction to determine the optimum configuration of the two generators that satisfies the energy demand of the user throughout the year.

Presented some methodologies for optimal sizing of stand-alone WG-P-Diesel systems are using genetic algorithms.

Sizing

Optimum size of hybrid PV/wind energy system can be calculated on an hourly basis or on the basis of daily average power per month, the day of minimum PV power per month, and the day of minimum wind power per month.

National Renewable Energy Laboratory (NREL)’s, Hybrid Optimization Model for Electric Renewable (HOMER , www.homerenergy.com) has been used as the sizing and optimization software tool.

HOMER contains a number of energy component models and evaluates suitable technology options based on cost and availability of resources.

Sizing

Analysis with HOMER requires information on

a) resources,

b) economic constraints,

c) and control methods.

It also requires inputs on component types,

their numbers,

costs, efficiency,

longevity,

etc.

Sizing

HOMER Optimization and Sensitivity analysis could be done with variables having a range of values instead of a specific number.

HOMER's optimization and sensitivity analysis algorithms allow the user to evaluate the economic and technical feasibility of a large number of technology options and to account for uncertainty in

technology costs,

energy resource availability,

and other variables

Considering the combine resources W-PV-Diesel, it is important that an optimum solution is found based on the local needs and resources

available.

Optimization of Wind-PV-Diesel system

In order to predict the hybrid system performance, individual components need to be modelled first and then their mix can be evaluated to meet the load demand.

The solar array or panel is defined as a group of several modules electrically connected in series-parallel combinations to generate the required current and voltage.

In order to predict the hybrid system performance, individual components need to be modelled first and then their mix can be evaluated to meet the load demand.

PV module modelling


The ideal equivalent circuit of a solar cell consists of a current source in parallel with a diode.

Equivalent Electrical Circuit

The complex physics of the PV cell can be represented by the equivalent electrical circuit shown

The output terminals of the circuit are connected to the load.

Iph is equal to the light-generated current Ii less the diode-current ID and the shunt-leakage current Ip

Internal resistance

Rp is inversely related with leakage current to the ground


Equivalent Electrical CircuitThe open circuit voltage Voc of the cell is obtained when the load current is zero,

where ID = the saturation current of the diodeQ = electron charge = 1.6 · 10 –19 CoulombsA = curve fitting constantK = Boltzmann constant = 1.38 · 10–23 Joule/°KT = temperature on absolute scale °K

The load current is therefore given by the expression:


PV module can be seen as a black box that with two connectors, producing a current, I, at a voltage, V.

If the array is operating at voltage V and current I, the power generation is

P = V · I watts.

The power–voltage (P–V) characteristic of a photovoltaic module

operating at a standard irradiance of 1000 W/m and temperature of 25

°C is show


A simplified simulation PV model is used to estimate the actual performance of PV modules under varying operating conditions.


PV modules represent the fundamental power conversion unit of a PV system, but a single PV module has limited potential to provide power at high voltage or high current levels.

It’s then mandatory to connect PV modules in series and in parallel in order to scale-up the voltage and current to tailor the PV array output. If a matrix of Ns×Np PV modules is considered, the maximum power output of the PV system can be calculated by:


Wind Turbine Performance Model: The wind turbine power output can be simulated by:

Modelling of Wind turbine

A complex mathematical modelling of wind energy conversion system includes, wind turbine dynamics and generator modelling.

However a simplex model can be used.


Modelling of diesel generator

To attenuate shortfalls in energy production during periods of poor sunshine, and poor wind speed a backup diesel generator is used for increased system availability and minimum storage requirements.

The choice of diesel generator depends on type and nature of the load.



To determine rated capacity of the engine generator to be installed, following two cases should be considered:

1. If the diesel generator is directly connected to load, then the rated capacity of the generator must be at least equal to the maximum load,

2. If the diesel generator is used as a battery charger, then the current produced by the generator should not be greater than CAh/5 A, (CAh is the ampere hour capacity of the battery).



Overall efficiency of diesel generator is given by

ŋhover-all = ŋbreakthermal X ŋgenerator

Here ŋbreakthermal is brake thermal efficiency of diesel-engine

For the studied system, the diesel generator is started at times when the battery SOC falls below a certain level (diesel generator starting

point), and then the diesel generator runs at full power (or at a rate not exceeding the maximum current that batteries are capable of

absorbing) to charge the batteries with any surplus power until the battery SOC reach the diesel generator stopping point.


Battery Performance Model: Most battery models focus on three different characteristics.

i. The first and most commonly used model mainly focuses on the battery state of charge (SOC).

ii. The second type of model is the voltage model, which is employed to model the terminal voltage.

iii. The third type of model is the lifetime model used for assessing the expected lifetime of the battery.

Modelling of Batteries bank


Minimization of the objective function (ACS) can be realized using different optimization techniques.

The flow chart of the optimization process to obtain the optimum configuration and control strategies, implemented employing Genetic Algorithm (GA), is illustrated in Figure


Based on Genetic Algorithm (GA), which has the ability to attain the global optimum with relative computational simplicity,

GA as a sizing method for hybrid WG-PV-DG system can be used to calculate the system optimum configuration that satisfies the load demand with minimum annualized cost of system.

Minimization of the system cost is achieved not only by selecting an appropriate system configuration, but also by finding a suitable control strategy.

The decision variables included in the optimization process are the PV module number, PV module slope angle, wind turbine number, wind turbine installation height, battery number, diesel generator (DG) type, DG starting and stopping points.

Environmental impacts

Environmental evaluation of the Diesel generator only

Petroleum-based products are one of the main causes of anthropogenic carbon dioxide(CO2) emissions to the atmosphere.

Indeed the combustion of each litter of diesel produced 2.7 kg of CO2.

For example, during the life cycle of a conventional Diesel Generator used in medium size WG-PV-Diesel system, the diesel oil which will be consumed is 1,244,286.28 l leading to about 3360 tonnes of CO2 released in the nature.


Environmental evaluation of PV generator only

The mayor drawback with this scenario is there cycling of batteries at the end of their life time.

In fact, there is no policy concerning recycling of batteries in some countries or regions and this particular aspect represents a considerable environmental concern.

In the case studied, over the life time of the system, for a total capacity of 41,037.5 Ah, it is 411 batteries of 100 Ah (12 V) which will be probably thrown in the nature.


From environmental point of view, from the present hybrid system, Diesel Generator is the only released in the nature of CO2 gases during its operation, whereas the hybrid system enabled to save CO2 emission compared to the sue of Diesel Generator only.

It is also important to noted that in some countries batteries will be thrown in the nature against zero battery released when considering the diesel generator only system scenario.

Further more, if the diesel generator is fuelled by biofuels more tonnes of CO2 emission which will be saved.

Indeed, the use of pure biodiesel lowers the emission of CO2 by 80%.


The potential emission reduction could also be used to generate income through carbon trading.

In order for any remote area energy system to be sustainable, it is imperative that there are locally trained technicians available.

Moreover, the consumers must be able to pay a regular user fee to pay for any maintenance required and procures spare parts.


We can conclude that from economic and environmental point of view, the hybrid system Wind/PV/diesel presents many benefits compared to the Diesel Generation only and the Wind or PV generator only.

However, this hybrid system design and management must be improved to bring the energy more and more cheaper for remote areas.

Recommended reading : Ngan MS, Tan CW. Assessment of economic viability for PV/wind/diesel hybrid energy system in southern Peninsular Malaysia. Renew Sustain Energy Rev (2011), doi:10.1016/j.rser.2011.08.028

Questions ?

PhD César Angeles-Camacho, MIET & MIEEEUniversidad Nacional Autónoma de MéxicoInstituto de IngenieríaEdif. Bernardo QuintanaCircuito Exterior, Ciudad UniversitariaCP 04510, México, D.F.Tel. +52 (55) 5623-3600 Ext. 8810email: [email protected]

Documents

TRAINING FOR OLADE`S MEMBER COUNTRIES COURSE CAPEV 14 2011 By César Angeles-Camacho Instituto de Ingenieria, UNAM [email protected] DESIGN AND IMPLEMENTATION