References

Electric Energy Its Generation, Transmission and Use, McGraw-Hill, Maidenhead, 1980. 2 'Ancillary service provision from distributed generation', DTI report, Contract No. DG CG 00030 00 00, URN No. 04 1738, UK. 3 'National Grid Seven Year Statement', available from 4 'The costs and impacts of intermittency', Report by UKERC, Imperial College, London, March 2006. 5 Farmer, E.D., Newman, V.G. and Ashmole, P.H. 'Economic and operational implications of a...

The UK Electricity Supply Industry ESI

The State-Owned Central Electricity Generating Board Before 1990, the entire UK ESI was in the state sector and was centrally planned and operated by the Central Electricity Generating Board (CEGB). The remit of the CEGB was to provide a secure supply of electricity to its consumers. All generating plant, transmission lines, distribution lines, substations and metering were owned and operated by the CEGB as a monopoly. During the days of the CEGB, electricity was supplied to consumers through...

Dynamic Demand Control

A scheme is being investigated that uses the already existing stored energy in millions of consumer appliances and requires the installation of dynamic demand control (DDC). These monitor system frequency and switch the appliance on or off, striking a compromise between the needs of the appliance and the grid. Initially fridges and freezer applications have been investigated. Refrigerators are 'on' in all seasons, throughout the day and night, and are therefore available to participate in...

Renewables

Figure 1.10 provides an overview of the earth's main energy paths that can be tapped to generate sustainable electricity. The main source of easily accessible renewable energy Figure 1.9 Geological storage options for CO2. (Source World Coal Institute) Figure 1.9 Geological storage options for CO2. (Source World Coal Institute) Figure 1.10 Renewable energy flow paths Figure 1.10 Renewable energy flow paths is the sun. On average the rate of solar radiation intercepted by the earth's surface is...

Introduction

This chapter reviews the economics of renewable power generation and the electricity market, which is increasingly the mechanism that determines what generation is used and when. At the outset a comparison is made between the capital and running costs of renewable and conventional forms of generation. Consideration is then given to how the economics change if external costs are taken into account along with the benefits costs of small scale embedded renewable energy generation. A description is...

Limits of Penetration from Nondispatchable Sources

Early on in the development of renewables, the UK's Central Electricity Generating Board (CEGB) carried out a number of extensive simulation studies to estimate the impact of large Figure 3.17 CEGB simulation study of large penetration. (From Grubb, M.J., IEE Proceedings C, V. 138(2), March 1991, reproduced with permission of IET) Figure 3.17 CEGB simulation study of large penetration. (From Grubb, M.J., IEE Proceedings C, V. 138(2), March 1991, reproduced with permission of IET) penetrations...

Active and Reactive Power from Renewable Energy Generators

As mentioned earlier, the large generators of conventional power systems have their individual AVRs set to maintain the generator bus voltage virtually constant. Generators fed from renewable energy sources are substantially smaller in rating and are, in general, connected to the distribution rather than the transmission network. For these reasons, conventional generator control schemes have not been considered appropriate for small embedded renewable energy supplied generators. For example, a...

Harmonics Distortion

Both loads and generators can cause distortion of network voltages, and such distortion is usually expressed in terms of harmonics. A common source of harmonics is the widespread use of cheap power supplies found in computers, televisions and other appliances. The voltage waveform in a modern office building or in a residential distribution network can be badly distorted by harmonics created by such loads, long before any distributed generators are even contemplated. The distortion of the...

Building Integrated Wind Turbines

There has been considerable interest of late, particularly in Northern Europe, in the possibility of fitting small wind turbines on the roof tops of individual houses. Enthusiasts for this approach claim that small wind turbines sited within the urban environment have the potential to make a significant contribution to the reduction of CO2 levels. A typical wind turbine of this type is illustrated in Figure 8.4. The difficulties facing the designers and manufacturers of such machines are...

Example Load Flow

Node Load Flow

As discussed already, renewable energy generation can affect both line loadings and voltages throughout the system. Load flow is a technique that allows the flows of real and reactive current throughout the network to be calculated, based on the location of the loads and sources and the line impedances. The network of Figure 6.1 is used here to illustrate the way in which load flow analysis is applied at a distribution level to assess the effect of connecting a renewable energy generator at a...

Capacity Factor and Capacity Credit [

When renewables displace significant amounts of conventional generation plant, an extra conventional plant capacity margin is required to maintain system supply reliability. It is important to recognize that an additional plant margin will only be required at times of low electricity demand and high input from variable sources. At other times an additional margin will not be required as there will be sufficient conventional plant available to meet demand irrespective of the contribution from...

Power Transfer Equations

There is interest in exploring the mechanism by which power is injected into the grid by a synchronous generator. This can be done by means of the concept of complex power developed in Appendix A. The grid connected synchronous generator of Figure 4.7 will be considered. The complex power at end B of the line is given by Then 1B is expressed as a function of the line voltages using Kirchoff's voltage law, Substituting Equation 4.7 into Equation 4.6 gives I lt -jf - j e-5 Sb - y1 sin 5 j X Vb -...

Applications to Renewable Energy Generators

Direct Drive Enercon Diagram

All PV systems generate direct current and so power electronic converters, known as inverters, are required to connect them to power systems. As described in Chapter 2, PV modules have an I-V characteristic that depends on incident radiation intensity and to a lesser extent the solar spectrum and module temperature. Different types of PV have different shapes of I-V curve, characterized in simple terms by a fill factor, as explained in Chapter 2 . To maximise the output of any PV module, or...

The Synchronous Generator Equivalent Circuit

Generator Equivalent Circuit

To analyse the power flows in electrical systems, component representations are required that can be incorporated into network or circuit models. To use the available circuit analysis tools described in Chapter 5 , it is necessary to build up these representations from basic circuit elements, namely resistors, inductors, capacitors and voltage or current sources Appendix A . Electrical power engineers over the years have developed a range of what are known as equivalent circuits for network...

Small Hydro

A small-scale hydro is commonly defined as being smaller than 5 MW. At even lower powers lt 100 kW , the so-called microhydro is subdivided into dammed and run of the river schemes in which there is no storage a further distinction is into high and low head. It is estimated that the world potential of small microhydro is around 500GW of which roughly only one-fifth has been exploited to date. A particular attraction of small microhydro is that the resource is often located in remote rural...

The Transmission System [

Figure 1.12 in Chapter 1 gave a pictorial view of a typical power system and the desirability of using various voltage levels for transmission were explained. Overhead lines, supported Renewable Energy in Power Systems Leon Freris and David Infield 2008 John Wiley amp Sons, Ltd Figure 5.1 Overhead lines at four different voltage levels. Courtesy of Murray Thomson Figure 5.1 Overhead lines at four different voltage levels. Courtesy of Murray Thomson on steel towers pylons , concrete towers or...

Wind Turbines

Vestas V90 Power Curve

The power in the wind than can be extracted by a wind turbine is proportional to the cube of the wind speed and is given in watts by Figure 2.6 The Vestas V9G, Systems A S 3MW wind turbine. Reproduced with permission of Vestas Wind where p is the air density, A is the rotor swept area, U is the wind speed and Cp is the power coefficient that represents the aerodynamic efficiency of the rotor. The variability in power output from one wind turbine would therefore be expected to substantially...

Reactive Power Management

Reactive Power Management

The principle of conservation of reactive power described in Section A.13 requires that reactive power is scheduled so that as the consumer demand of Q varies over a day, appropriate Q resources are available to provide it. In Chapter 3 it was explained that a discrepancy between demand and supply of active power is manifested by rises or falls in frequency, a parameter that is common to the whole interconnected power system. In contrast, reactive power deficits or excesses manifest themselves...

Fault Level Increase

As noted previously, fault level can be used as a measure of grid strength and can be compared with proposed generator capacity to give an indication of likely effects on line voltage. However, as shown in Figure 6.6, the fault level can itself be increased by the connection of embedded generators, particularly where synchronous machines are involved. This does not invalidate the previous comments on voltage effects, but it does represent another factor to be considered in the connection of a...

Offshore Wind Farm Development

An offshore installation has advantages over and above the reduction in turbine costs from the resulting economies of scale. The marine environment is windier resulting in an increased energy yield, and the winds are more persistent and less turbulent making system-wide integration easier. Very large wind turbines that might cause an unacceptable visual intrusion onshore may well be acceptable if sited away from the shore. Additionally, the transportation of exceptionally large or heavy items...

Transformer Basics

Transformer Basics

The transformer is an indispensable part of any power system operating at a range of voltages. The transformer mode of operation is included here as it provides a useful aid to the under- Figure 4.9 The Transformer. Reproduced from Reference 1 with permission of John Wiley amp Sons, Inc. Figure 4.9 The Transformer. Reproduced from Reference 1 with permission of John Wiley amp Sons, Inc. standing of the mode of operation of induction generators which are used extensively in wind turbines. The...

Connection Voltage

The distribution system in the UK includes 400 V, 11 kV, 33kV and 132kV other countries have similar voltage levels. As mentioned in Section 5.7.4, the fault level at the point of connection which is a measure of network strength, is an important design parameter, not only for predicting currents under fault conditions, but also for predicting performance under normal operating conditions and in particular, voltage rise. The fault level at the PCC is very important when considering connecting a...

Structure of the Electrical Power System

Electricity is widely used because it is a supremely flexible form of energy. It can be readily and efficiently transported and is easily converted to other forms of energy. Mechanical energy can be provided by very efficient motors, light energy by increasingly efficient light Figure 1.12 Pictorial view of the components of a large power system Figure 1.12 Pictorial view of the components of a large power system fittings, heat energy by 100 efficient resistive elements, and power supply to...

Optimum Economic Dispatch

The aim is to load generating sets in response to demand changes so as to minimize the cost of supply. This is known as optimum economic dispatch OED and over the years sophisticated OED methods have been developed to identify the minimum cost solution and at the same time satisfy numerous engineering and operational requirements and constraints. Here the basic ideas that provide guidance in the task of adjusting the load on individual conventional or RE generators will be investigated in order...

Load Flow and Power System Simulation [

Power System Flow

Section 5.4 looked at the maths describing an individual overhead line or underground cable. Mature power systems are likely to have thousands of such lines, all interconnected. The same basic maths applies to each and every line, but now the equations must be solved simultaneously. Structured procedures for such calculations are known as load flow. A basic load flow calculation provides information about the voltages and currents and complex power flows throughout a network, at a particular...

Wind Variability

Wind Variability Graphs

The wind speed at a given location is continuously varying. There are changes in the annual mean wind speed from year to year annualI changes with season seasonal , with passing weather systems synoptic , on a daily basis diurnal and from second to second turbulence . All these changes, on their different timescales, can cause problems in predicting the overall energy capture from a site annual and seasonal , and in ensuring that the variability of energy production does not adversely affect...

Solar Thermal Electric Systems

Solar thermal electricity generation systems most commonly use solar concentrators to produce high temperatures that can drive heat engines with acceptable conversion efficiency. Two main types of generator suitable for large scale generation have so far been demonstrated, both requiring direct or beam radiation. Climates with cloudy or overcast conditions, where most of the radiation is diffuse, are thus unsuited to this technology. The two technologies are Large collections or solar farms of...

Steady State Voltage Rise

The connection of a distributed generator usually has the effect of raising the voltage at the PCC and this can lead to overvoltages for nearby customers. The need to limit this voltage rise, rather than exceeding the thermal capacity of the line, often determines the limiting size of generator that may be connected to a particular location. An initial estimate of the voltage rise caused by connection of a generator can be obtained from analysis of the system as represented in a simplified form...

Large Wind Turbines

Recent progress in wind turbine technology has been breathtaking. At the time of writing 5MW wind turbines are commercially available. Ten years ago, the largest wind turbine on the market was typically an 800 kW machine with most manufacturers offering 600 kW units. At present, most wind turbines are fitted with rotors of 60-90 m compared to the 35-45 m of the mid-1990s. Due to economies of scale, larger machines generate electricity at a lower cost per kW h , particularly in offshore...

Equal Incremental Cost Dispatch

Input Output Curve Generating Unit

The merit order philosophy is adequate and convenient for rough scheduling but as a precise tool of economic dispatch it is inaccurate. The reason for this is that cost curves are not quite linear as assumed above they are better described by a quadratic function as in the example of Figure 7.5 . Such curves can be used to determine the overall efficiency of the plant at various output levels. As previously, it can be assumed that only two plants A and B are supplying a demand Pd. Following the...

The Asynchronous Generator

Torque Converter Negative Slip

Asynchronous or induction machines operating as motors are the most widely used electromechanical converters. In an induction machine the stator is identical to the one for synchronous machines shown in Figure 4.3 in which three-phase currents supplied to the stator produce a rotating magnetic field RMF . The rotor, however, is radically different and it has neither an external magnetizing source nor permanent magnets. Instead, alternating currents are injected in the rotor from the stator...