Future low carbon energy systems - Copenhagen Cleantech Cluster

More documents

Recommendations

Info

System aspects5Poul Sørensen, Jens Carsten Hansen, Nicolaos Antonio Cutululisand Peter Meibom, Risø DTU; Jacob Østergaard, DTUElectrical Engineering; Hannele Holttinen, VTT, FinlandAn energy system with large-scale integration of renewableenergy, particularly wind power, is expected to meet thesame requirements for security of supply and economic efficiencyas the energy systems of today, while delivering betterenvironmental performance, especially with regard to CO2emissions and dependence on fossil fuels.Wind power affects power systems at different scales of timeand geography (Figure 6), starting with local issues of gridconnection (power quality), and going all the way up to system-wideeffects (reliability and adequacy).Figure 6Effects of wind power on power systems at different scales of timeand geography [1]Areas relevant for impact studies Task 25System wide1000-5000 kmRegional100-1000 kmLocal10-50 kmTime scale relevantfor impact studiesGridstabilityPrimaryreserveVoltagemanagementPower qualitySecondaryreserveDistributionefficiencyReducedemissionsHydro/thermalefficiencyTransmissionefficiencyCongestionmanagementAdequacyof powerAdequacyof gridms…s s...min min…h 1…24 h yearsLarge proportions of wind power and other fluctuating renewablegeneration technologies introduce uncertainty intothe power system. In such cases the system’s flexibility ingeneration, demand management and intra-area transmissionmay therefore need to be increased. The layout andbasic structure of the grid, as well as operational practices,need to adapt to the presence of large amounts of fluctuatingsupply.There are four main areas of interest: renewable energy powerplant capabilities; grid planning and operation; energyand power management; and energy markets. Each of theseis important for the large-scale integration of wind powerat a system level. This chapter describes the system aspectsinvolved in using wind power at high levels of penetration.5.1 Renewable energy power plantcapabilities5.1.1 Power controlTo obtain the maximum benefit from a power system as awhole, large-scale renewable energy should replace energyfrom conventional thermal power plants; this way both consumptionof fossil fuels and the resulting emissions can bereduced.Some of today’s large wind farms already have some of themain characteristics of conventional power plants. One ofthese is the ability to control the amount and quality of thepower produced. Modern wind turbine technologies makeit possible to control both active and reactive power, thoughthe power a wind plant can produce at a given time is obviouslylimited by the strength of the wind.Since the wind itself costs nothing, reducing the power producedby a wind farm below the maximum power availablein the wind at that time reduces operating costs by only avery small amount. Still, such reduced production can berequired in critical system situations when other controlreserves are scarce, and it can be a low-cost option duringperiods where the market price of electricity is low or zero.In Denmark, low to zero electricity prices sometimes occurduring cold and windy periods. At such times, combined heatand power (CHP) plants need to increase production of heat forbuildings, leading to the generation of large amounts of CHPelectricity when the output from wind turbines is also high.5.1.2 Fault ride-throughThe behaviour under grid fault conditions (fault ridethroughcapability) of renewable energy generation is a keyissue in the large-scale use of renewables in a power system.This is reflected in the grid codes – the rules that govern thebehaviour of generating equipment, including grid-connectedwind turbines – now used by every country planning todevelop large-scale wind power.The purpose of fault ride-through is to ensure that the renewablegeneration is able to stay connected to the grid duringand after a grid fault. Today, most wind turbine manufacturersprovide wind turbines with fault ride-through capabilities.If the turbines are not able to stay connected during andafter the fault, the consequence is a sudden loss of generationwhich must be replaced by fast reserves from other generatorsto prevent loss of load. Fault ride-through is not uniqueRisø Energy Report 733
5System aspectsto renewable generators; similar capabilities are required ofconventional generators to ensure that the system will continueto operate if one generating unit fails.farm5.1.3 Black start and isolated operationAnother fault mode arises when part of the grid becomesisolated from the main synchronous system. If the isolatedarea is able to control its own frequency and voltage, a blackoutcan be avoided and the reliability of the power systemimproves. If the part of the system that is isolated is dominatedby renewable and decentralised generation, then thecontribution of these generators to the control of frequencyand voltage can be the key to avoiding substantial load sheddingor even a blackout.If a blackout cannot be avoided, it is important to re-start thesystem as soon as possible afterwards. This “black start” processcan be supported by renewable and distributed generation,provided that these generators support frequency andvoltage control. In cases like these, the control dynamics ofthe power system can be very important. Risø DTU has runa number of simulations of wind farm models connected tosimplified grid models, to test the ability of wind farm powercontrollers to provide the necessary grid support [2].5.1.4 ReliabilityThe reliability of wind power is an issue in normal operationas well as under fault conditions. Wind farm ownersmeasure reliability in terms of their ability to sell power. Inthis case, a simple measure of reliability is the ratio of actualproduction to the energy available according to wind speeddata and turbine power curves, taking into account failuresin wind turbines and the grid itself.From the point of view of the system operator, reliability is mainlyabout the risk that all or some of the predicted wind power willnot be produced. Factors affecting this measure of reliability are:forecasts; these generally cannot be avoided, but canprobably be reducedturbines, production of individual turbine drops suddenlyfrom rated power to zeroto the transmission systemAt the power system level, reliability is about the total performanceof all the wind farms in the system, not about failuresof individual turbines or wind farms.Another reliability issue is whether the power system canhandle peak loads. With large-scale renewable generation inthe system, many thermal power plants will have to operateat reduced load factors. This may reduce investment in newthermal power plants, which in turn might lead to problemswith system adequacy at peak loads when the amount of renewablegeneration is low.A major research challenge is to build reliability models thatcombine general reliability factors, such as grid failures, withfactors specific to wind power, such as wind forecast errorsand cut-outs at high wind speeds.5.2 Grid planning and developmentOne of the biggest challenges to the reliable integration oflarge amounts of wind energy in power systems is powertransmission. Areas with good wind potential are often locatedfar from load centres. To manage variable energy productionon a large geographic scale, the grid infrastructureand interconnections should be extended and reinforced.As the first phase of the European Wind Integration Study(EWIS) 1 concluded, without grid reinforcement Europe willnot be able to reach its targets for renewable energy [3].Large-scale integration of renewable energy requires a pan-European transmission network for effective cross-borderpower trading and mutual support for security and qualityof supply. There is a need for advanced simulation and analysistools, combined with dynamic calculations for the interconnectedEuropean power system. Planning tools shouldbe developed for the design of efficient grids.Risø DTU is taking part in several projects aiming to developsoftware tools and use them for grid integration studies. Oneof these is TradeWind [4], an EU-funded project which aimsto provide technical and economic justification for strategicdecision-making on the development of the EU’s grid andgeneration infrastructure [4].1 An initiative established by the TSO associations of the European transmission system operators (such as UCTE and ETSO) in collaboration withthe European Commission.34 Risø Energy Report 7
Page 6: Preface1This Risø Energy Report, t
Page 9 and 10: 2Summary and recommendationsFor the
Page 12 and 13: Danish and global climate andenergy
Page 14 and 15: Danish and global climate and energ
Page 16 and 17: Danish and global climate and energ
Page 18: Danish and global climate and energ
Page 21 and 22: 4Catalogue of energy technologiesUp
Page 23 and 24: 4Catalogue of energy technologiesTh
Page 25 and 26: 4Catalogue of energy technologiesci
Page 27 and 28: 4Catalogue of energy technologiesWa
Page 29 and 30: 4Catalogue of energy technologiesTh
Page 31 and 32: 4Catalogue of energy technologiesli
Page 33: 4Catalogue of energy technologiesTa
Page 40 and 41: Regional developments in energysyst
Page 43 and 44: 6Regional developments in energy sy
Page 54 and 55: Future energy systems to cope withc
Page 56 and 57: Future energy systems to cope with
Page 66 and 67: CO ² reduction strategies up to 20
Page 74: CO ² reduction strategies up to 20
Page 77 and 78: 9References~menuPK:64133163~pagePK:
Page 79 and 80: 9References9. The Danish Board of T
Page 81 and 82: 10IndexLMNLa Rance 23LDC 47, 60leas

Future low carbon energy systems - Copenhagen Cleantech Cluster

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?