comparison of integration solutions for wind power in the netherlands

8/13/2019 Comparison of Integration Solutions for Wind Power in the Netherlands

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Published in IET Renewable Power Generation

Received on 2nd September 2008

Revised on 21st April 2009

doi: 10.1049/iet-rpg.2008.0080

Special Issue selected papers from EWEC 2008

ISSN 1752-1416

Comparison of integration solutions for wind

power in the NetherlandsB.C. Ummels

1E. Pelgrum

2M. Gibescu

3W.L. Kling

4

1Technical Project Management, Offshore, Siemens Wind Power, Prinses Beatrixlaan 800, 2595 BN Den Haag,

The Netherlands2Market and Regulation Department, TenneT TSO, Utrechtseweg 310, 6812 AR Arnhem, The Netherlands3Power Systems Laboratory, TU Delft, Mekelweg 4, 2628 CD Delft, The Netherlands4

Power Systems Laboratory, TU Delft, Asset Management Department, TenneT TSO, Mekelweg 4, 2628 CD Delft,

The Netherlands

E-mail: [email protected]

Abstract: In this study, a commercially available unit commitment and economic despatch (UCED) tool is

extended for the simulation of wind power integration in an international environment. An existing generation

unit database for the Netherlands is extended to include conventional generation portfolios of neighbouring

areas to the Netherlands. Furthermore, wind power in Germany is modelled such that the spatial correlation

between wind speeds at different locations in the Netherlands and Germany is maintained. These additions

allow the assessment of the benefits of international exchange for wind power integration and a comparison

with other integration solutions. The UCED tool is applied for annual simulations of a power system with

generation portfolios foreseen for the year 2014. Four variants for international exchange possibilities are

investigated for different wind power penetrations. The opportunities of the following integration solutions

are assessed: use of conventional generation in isolated systems,use of international markets, flexible

combined heat and power (CHP), pumped hydro energy storage, compressed air energy storage and

interconnection to a hydro-based system. The solutions are placed in an order of potential with respect to

technical, economical and environmental aspects. The results show that the advantages of international

exchange for wind power integration are large and provide an alternative for the development of energy

storage facilities.

1 Introduction

Unit commitment and economic despatch (UC ED) are twooptimisation tasks requiring different optimisation proceduresand comprising different time frames. UC decisions aretypically assessed only once or twice a day, whereasgeneration despatch is carried out throughout the day. Withthe reasonable predictability of system load, intra-daycalculations for UC are in principle necessary only whenunexpected, significant changes occur in generation (e.g.outages) or demand. The emergence of internationalmarkets and the growth of wind power has complicated the

optimisation of UCED in the sense that more variablesand uncertainties (i.e. market prices, wind power forecasts)must be taken into account. Since there is only a conceptual

difference between markets and the traditional generationscheduling (i.e. market participant price bids instead ofoperating cost minimisation), solutions for the traditionalcentral optimisation of UC ED based on cost are stillhighly relevant[1].

A wide rangeof modelshas been developed for the simulationof UC ED or electricity market operation ranging from weeklyoperations planning to generating unit investment planning.

The Danish SIVAEL model[2]is a UCED tool capable ofminimising total system cost while supplying local heat andpower demand. This model has been applied in[3]for system

integration studies of large-scale wind power in Denmark.The Wilmar model [4] is used to simulate alternativesolutions for the integration of large-scale wind power into

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indeed lowers the short-term marginal cost curve of thesystem as a whole, depends on a number of factors. Themost important are the technical flexibility of the system

wind power is integrated into and the extent to which themarket allows an efficient exploitation of this flexibility.

The extent to which wind power may decrease market

prices in a structural way depends on the cost of additionalpower reserves and the decreased operational efficiencies ofconventional units, which increase total operating cost. Inthis paper, these aspects are taken into account by thesimulation model and are expressed in the total systemoperating cost. The operating cost [ME/year] will bemonitored for the Netherlands specifically. This also appliesfor the total electricity produced [TWh/y] per conventionalgeneration technology (nuclear, coal, Combined Cycle Gas

Turbine (CCGT), CHP, gas turbine etc.).

2.3 Environmental impactsThe environmental aspects of wind power are the mostimportant driving force behind the development of windpower. Electricity generated by wind power replaces fossil-fired conventional generation and thereby saves fuel andCO2 and other emissions. The simulation model integrallytakes into account emission cost during the optimisation ofthe UCED. For monitoring the environmental impacts of

wind power, emissions (CO2, but also NOxand SO2) willbe assessed at the system level for the Netherlands andpresented for each conventional generating technology.

3 Power system modelspecification

The power system model comprises a physical representationof different areas, each representing the generating systems ofthe Netherlands and its neighbouring areas: Belgium, France,Germany, Norway and Great Britain. Interconnectionsbetween these areas are modelled explicitly, transmissionconstraints within each area are not considered here.

3.1 The NetherlandsThe existing models database contained models for all larger(60 MW) conventional generation units in the Netherlands.

This database is updated to represent the Dutch powersystem for 2014, the year chosen for investigation. Up to2014, a large amount of new conventional generatingcapacity is planned or under development, comprisingespecially new coal- and gas-fired generation capacity. It isforeseen that some of the older installations will be shutdown by that time but market parties have not providedinformation on this. The Dutch generating portfolio for2014 is based on the existing portfolio with the addition of

new units specified in[11]. The interconnection capacity ofthe Netherlands is based on transmission capacity forecastsof TenneT TSO for 2014[11]and ETSO[12].

3.1.1 New conventional generation: New coal-firedunits (total 5.3 GW) are assumed to have a highermaximum operating efficiency of 44.5% and an efficiencycurve shape similar to coal-fired units already present in thedatabase. These new units do not have a must-run statusbut a minimum up-time and down-time of 16 h. This

allows for temporary shut-downs during periods of lowprices, for instance during weekends.

New natural gas-fired units (total 3.68 GW) are CCGTswith a maximum operating efficiency of 58% and anefficiency curve shape similiar to existing CCGTs. Of thenew CCGTs, two units (1.26 GW total) are modelled asindustrial CHPs with a must-run status, delivering steamto a separate industrial heat area. The heat load curves ofthese areas are modelled based on the existing curves in thedatabase. The heat areas are equipped with heat boilers

which are assumed only to be used during maintenance of

the CHP units, similar to existing CHP unit models.

3.1.2 New distributed generation excludingwind power: New distributed generation (DG) capacityin the Netherlands mostly involves installations, that is gasengines, in Dutch greenhouses. These CHP units produceelectricity, heat and CO2 for the greenhouses, with heatboilers as back-up and heat buffers for several days ofstorage. Due to the availability of a full heat back-up, thegeneration units are operated against spot market pricesand have a very high operational flexibility. A total capacityof 3000 MW of gas engines has been modelled, withmaximum electrical efficiency of 40%, no minimum up-time or down-time and a 10% unavailability. Ramp rates ofthese DG units are estimated to allow a ramp fromminimum to maximum output within 15 min.

Other, existing DG, is modelled as nondespatchablecapacity (3400 MW) and aggregated into a fixed schedule,simulated as must-take power on the basis of natural gas-fired generation. This capacity represents nondespatchableindustrial units, waste incineration and other small DGunits. The output of this DG is assumed to be 50% constantand 50% variable with system load and has an efficiencyof 19%.

3.1.3 Wind power: For the Netherlands, a 1-year dataseries of 15 min. wind power data for seven windpower penetration levels have been developed for 0 GW,2 GW (225 MW offshore), 4 GW (1 GW offshore),6 GW (2 GW offshore), 8 GW (4 GW offshore), 10 GW(6 GW offshore) and 12 GW (8 GW offshore), based onthe methodology described in[13]. It is assumed that windpower does not replace any conventional capacity, allowingan accurate comparison of the technical, economical andenvironmental impacts of wind power between differentpenetration levels. In practice, wind power has a certain

capacity credit [14, 15] and will lead to a change in thetotal installed generation capacity, but this is not consideredhere.



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3.2 Neighbouring areas

3.2.1 Areas and interconnectors: In this paper, theNetherlands (NL) is assumed to be a central area withinterconnections to Belgium (B), France (F), Germany (D),and Great Britain (GB), and Norway (NOR) to a very

limited extent. Each country is represented as a single areacomprising generation and load with interconnections toneighbouring areas based on [11, 12]. Only cross-bordertransmission capacities between countries are taken intoaccount. The power system with all areas and interconnectorsdeveloped and used in this paper is shown in Fig. 1,representing the Netherlands as part of the West-Europeaninterconnected system. The NODE-area (grey) is an emptyarea used to incorporate the transmission capacity limitsforeseen by TenneT TSO for 2014 for the Netherlands withBelgium and Germany together. Apart from the separateinterconnection capacities which may exist between theNetherlands and Belgium (2300 MW) and Germany(5400 MW), a net export/import transmission capacitymaximum of 5650 MW is applied between the Netherlandsand these countries.

The transmission capacities NL NOR (NorNed), NLGB (BritNed) and FGB (Cross-Channel) are high voltagedirect current (DC) sub-marine interconnectors, for whichan availability of 98% is assumed, other interconnectionshave an availability of 100%. Transmission losses areassumed to be 5% of the transmitted power for NorNed,and 4% for BritNed and Cross-Channel.

3.2.2 Area load: Load data for the areas outside theNetherlands for the year 2014 are developed using UCTEload data for the relevant countries for the year 2007 [16].

This assures that correlations among momentary loads inall countries are automatically taken into account. The loaddata are processed similarly as with the Dutch load data

using annual growth rates up until 2014 based on[17, 18].The growth rates for load in 2014 relative to 2007 are 1.08,1.08, 1.03 and 1.10 for Belgium, France, Germany andGreat Britain, respectively.

3.2.3 Fossil-fired generation: Models for conventional

generation units in the neighbouring areas of the Netherlandswere developed based on installed capacity estimates made in[17, 19]. Generating technology efficiencies and othertechnical factors were estimated based on and using theexisting models for the Dutch units in the database. Eachgeneration technology type outside the Netherlands ismodelled as an aggregation of units with identicalcharacteristics, with a total generating capacity equalling thecapacity foreseen to be installed in 2014. Nuclear generationunits in Germany and Great Britain are modelled as having atechnical full-load must-run operational status and no ramprate. French nuclear units have only a must-run status, which

allows part-load operation during moments of low load.

3.2.4 Hydro power and pumped hydro: Totalannually available hydro energy in Germany, France andGreat Britain are estimated based on yearly statistics from[20]. Norway is modelled only as a pumped hydro unit

without inflow. Since PowrSym3 optimises the UC EDon a weekly basis, an annual optimisation of hydro energyper week must be done first. It is assumed that reservoirhydro is operated such that the same amount of energy isavailable for each week. The UCED optimises the hourlydistribution of this weekly energy during the week itself.Hydro power has a very high operational flexibility: ramprates are assumed to be sufficient to allow a full rampbetween start and maximum output within 15 min.Pumped hydro units are modelled with a similar flexibilityas hydro power, but without a weekly energy inflow. TheUCED of pumped hydro in each area is optimised on a

weekly basis based on temporal differences in marginal costin that area. The generating and pumping efficiency areestimated at 90% each. The average unavailability ofpumped hydro is determined at 2%, due to the absence ofthermodynamic processes in these units.

3.2.5 Wind power: Wind power in neighbouring areas is

only taken into account for Germany. This is becauseGermany already has a large installed capacity of windpower, which is foreseen to increase significantly [17, 21].Furthermore, wind power outputs in the Netherlands andGermany are strongly correlated and a large interconnectioncapacity is available between these countries. In a North-

West European market, the presence of large-scale windpower in Germany could present additional barriers for

wind power in the Netherlands.

In order to correctly incorporate the correlation betweenwind power in the Netherlands and Germany, 15-min

average wind power data for the German areas EON-Netz,RWE and Vattenfall were obtained from the respectiveTSOs for the same period as the Dutch meteorological

Figure 1 Areas and interconnections included in the

simulation model

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& The Institution of Engineering and Technology 2009 doi: 10.1049/iet-rpg.2008.0080

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data (1 June 2004 to 31 May 2005). Also, day-ahead forecastdata were obtained for this period. Wind power and windpower prediction data are scaled to represent the 32 GW ofinstalled capacity foreseen for 2014. It is found that thecorrelation between the 15 min aggregated average windpower data sets for the Netherlands and Germany is 0.73.

Thus, interconnection capacity to Germany may not be(fully) available for exports during moments of low-loadand high-wind power, resulting in wasted wind energy.

Wind power in Germany is modelled such that it isintegrated with a higher priority than Dutch wind power inorder to guarantee that wind power in the Netherlands isnot integrated into the system at the expense of German

wind power.

3.3 Power system overview

Installed generating capacities per technology are based onforecasts made for the relevant countries for 2014 in[11, 17,19]. The installed capacities are presented per technologyand per country in Table 1.

Norway is modelled as a pumped hydro unit with agenerating/pumping capacity equalling the interconnectioncapacity between the Netherlands and Norway. The hydropower system of Norway has a high operational flexibilityand is assumed to be available for imports from and exportsto the Netherlands at all times. The exchange is dependent

only on the differences between marginal cost in theNetherlands and the value of the energy contained in theNorwegian reservoir. This approach is sufficient for thisresearch, with its focus on the system integration of windpower rather than the economical benefits of interconnection capacity, and makes it unnecessary to

model the Scandinavian system explicitly.

4 System simulations

In the system simulations performed here, the UCED isoptimised on a central basis: it is assumed that electricitymarkets function well. The objective function is formulatedat the system level that is no other transmission constraintsare taken into account other than those specified betweendifferent areas. The UCED is calculated using the equalmarginal cost method, in which the objective function is thetotal cost for heat and power generation, including emissioncost. Decremental despatch and de-commitment cost arecalculated for all units included in the simulation. Thesimulation program calculates an optimal maintenanceschedule for the simulated year beforehand and determinesunscheduled outages using Monte Carlo for all generationunits, energy storage units and heat boilers. Thecommitment and despatch of energy storage and heat boilersis based on the minimisation of the overall operating cost ofthe system.

Table 1 Generation technologies per country in 2014

Technology The Netherlands (GW) Belgium (GW) France (GW) Germany (GW) GB (GW) Norway (GW)

nuclear 0.4 5.9 64.9 14.1 11.9 2

coal 9.5 2.6 6.0 32.0 30.4 2

lignite 2 2 2 18.9 2 2

CCGT CHP Ind. 4.0 2 2 2 2 2

BF Gas Ind. 0.9 2 2 2 2 2

CCGT CHP Res. 1.5 2 2 2 2 2

CCGT 7.1 5.0 4.0 15.1 24.4 2

gas turbine 0.6 1.5 1.1 4.0 7.0 2

oil 2 2 9.2 5.3 8.4 2

reservoir hydro 2 2 13.6 3.7 1.8 2

pumped hydro 2 1.3 4.2 5.5 3.0 0.7

RoR hydro 2 0.1 7.9 2 2 2

other 6.3 0.4 2 8.2 2 2

total 30.4 16.8 110.9 106.8 86.9 0.7

wind power 10.0 2 2 32.0 2 2

maximum load 21.0 15.2 87.1 80.5 65.5 2

demand (TWh/y) 126 97 518 550 367 2



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As an illustration of the system simulations performed inthis paper, Fig. 2 provides an overview of the UCED inthe Netherlands during 1 week for the scenario with 12-GW wind power. The graph shows generation levels forDG, thermal units, integrated wind power and the amountof wasted wind energy. Total generation by conventional

thermal generation units follows the system load, DG andwind power. In this particular week, wind power is rampeddown at moments of high wind power and low load (allnights, except Sunday when there is little wind poweravailable) to prevent minimum-load problems. A goodexample of the use of thermal generation for balancing thecombined variations of load and wind power can be seenon early Sunday morning (thermal generation ramps upand wind power is decreasing).

4.1 Base variants

The base simulation variants consider seven levels for windpower capacity installed in the Netherlands, four designs ofinternational markets and three wind power forecastmethods. The base variants will be used to quantify thetechnical, economical and environmental impacts of windpower. For all base-variants, it is assumed that wind poweris integrated into the system by taking into account windpower in the optimisation of the UCED of conventionalgeneration capacity. In case no international exchangemarket is available, only the Dutch conventional generationunits are used.

4.1.1 Wind power levels: All base simulations will becarried out for six wind power penetration levels, asmentioned earlier (2 12 GW), and for a 0-MW windpower variant to be used as a reference.

4.1.2 International exchange: International exchangeis modelled and simulated for four market designs:

1. No international exchange

2. International market gate closure time day ahead

3. International market gate closure time 3 h ahead

4. International market gate closure time 1 h ahead

The base-case for the simulations is the Netherlands seenas an isolated power system. International exchange withBelgium, France, Germany, Norway and Great Britain isassumed to be zero at all times. This variant serves as areference to consider the integration of wind power in theDutch power system using the technical capacities availablein the Netherlands only. The other market designs allcomprise international exchange possibilities between theNetherlands and its neighbours, but using different gateclosure times. This means that the imports and exports ofthe Netherlands are optimised using the wind powerforecast available at market gate closure. After market gate

closure, the international exchange schedules become fixedand are executed as scheduled exchanges during actualoperation. For the day-ahead market closure, wind powerforecast errors are significant [8]. This will result in a sub-optimal scheduling of imports and exports from a windpower integration point of view. Forecast errors will havedecreased by about 50% if market gate closure is delayed upto 3 h ahead of operation, and no forecast errors areassumed to be present for a market design with near real-time operation (1 h ahead), which allows an optimalscheduling of international exchange considering windpower.

4.2 Wind power integration solutions

Technical limits may exist for the system integration of windpower in the Dutch power system. After the determinationand quantification of these limits, different alternatives willbe explored for overcoming these integration limits. Thesolutions considered here include three energy storageoptions for the Netherlands (PAC, UPAC and CAES),more flexible industrial CHP units and an increased

Figure 2 Example of a UCED for 1 week in the Netherlands for 12 GW installed wind power capacity and no international

exchange



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moments during theyear in order to balance theaggregatedloadand wind power and load variations. This was to be expectedsince the total generation portfolio is rather large compared tothe maximum load. The integration of wind power in theDutch power system does however result in an increase ofheat production at CHP locations (especially residential),

wasting of wind energy (especially during low-load periods)and increased exports to neighbouring countries (idem). Thisindicates that minimum-load problems pose a technical limitfor the integration of wind power, which is in line with theobservations made in[8].

The simulation results for wasted wind energy andinternational exchanges vary considerably between thedifferent international market designs, since they are mutuallydependent, and to some extent between the different windpower forecast methods investigated here.

5.1.1 Wasted wind energy: In Fig. 3, wind energyintegrated into the Dutch power system is shown for different

wind power penetrations and different market designs.Wasted wind energy becomes significant in the range of68 GW installed wind power capacity for the Dutch powersystem, in the market design without international exchange.

The slight change in steepness of the available wind energycurve at 2 and 6 GW installed capacity is due to increasedcapacity factor of wind power (offshore against onshore). The

use of international exchange provides significant additionalspace for the integration of wind power.

Fig. 4focuses further on a comparison of the amount ofwasted wind energy for different market designs. Only windpower forecast errors in the Netherlands are considered here.In case no interconnection capacity is available, an estimatedamount of 6.2 TWh/y or 15% of available wind energy inthe Netherlands cannot be integrated into the system. Incase international exchanges can be used for exports at high

wind power levels, additional wind power can be integrated,with only 0.05 TWh or 0.1% of available wind energy beingwasted for the 1 h. ahead market gate closure.

Interestingly, a day-ahead or 3 h ahead international marketgate closure time results in largeramounts of wastedwind powerat smaller wind power capacities. This is the result of themethodology applied for the optimisation of internationalexchange at market gate closure, which is based on theassumption that all feasible international transactions arebeing made. In case a significant wind power forecast error ispresent at the moment that these transactions become fixed,scheduled imports may prevent the integration of unpredictedsurpluses of wind power, leading to larger amounts of wasted

wind energy. For large wind power penetrations, however, thebenefits of international exchange capacity outweigh thedisadvantage of forecast errors. Clearly, a more conservative

Figure 3 Integrated and wasted wind energy in the Netherlands

Figure 4 Wasted wind energy for different international market designs



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scheduling of international exchanges (imports) will result inless wasted wind energy. This result illustrates the benefits ofpostponed international market gate closure times forintegrating wind power.

In case interconnection capacity is available and the market

design allows an adjustment of international exchange upuntil the moment of operation (1 h ahead internationalmarket gate closure), the potential for additionallyintegrated wind energy is high. Still, even the most flexibleinternational market design cannot prevent a small amountof wasted wind energy, starting from 8 to 10 GW installedcapacity in the Netherlands (bottom of Fig. 4, not visiblein Fig. 3). The reason for this is that, even thoughinternational transmission capacity may be sufficient, thiscapacity is not always fully available for exports. Thisapplies to Germany in particular. Germany has a significantmust-run conventional generation capacity and a large

amount of wind power (32 GW in the year 2014) which ishighly correlated (0.73) to wind power in the Netherlands.Both factors reduce the possibilities for exports of windpower from the Netherlands, especially during criticalperiods.

5.2 Economical impacts

5.2.1 Operating cost:Fig. 5shows the annual savings inoperating cost due to increasing wind power in theNetherlands, for the Netherlands itself without internationalexchange, and in case international exchange is possible (1 hahead market gate closure time) for the North-West

European system as a whole and the Dutch part as a dottedline. As the figure shows, the operating cost savings by windpower increase with the amount of wind power installed.For the fuel and operating cost used here, the overall annualoperating cost savings by wind power are estimated to be inthe order of 2 billion E annually for 12 GW wind powercapacity. The higher cost savings for the Netherlands

without international exchange are due to the highermarginal cost in the isolated Dutch system. Older and lessefficient units will be the first to be taken out of operation inan international market. Thus, the base-case with 0-MW

wind power is already different with respect to marginal cost.

In case no international exchange is possible for exports ofexcess wind power, the relative cost savings gained from

wind power start to decrease from 8 GW installed capacityonwards. Limits in the operational flexibility of conventionalplants lead to sub-optimal despatch, reduced operatingefficiencies and, ultimately, increased wasting of available

wind resources. In case the Netherlands is part of aninternational North-West European market, the technicalintegration limits for wind power are smallerand operatingcost savings are higher than for an isolated Dutch system. Insuch an international environment, slightly over one half ofthe total economical benefit of wind power is realised in theNetherlands, the rest is realised in neighboring areas.

5.2.2 International exchange: In case internationalexchange is possible, the integration of wind power in theNetherlands influences in principle the exchanges betweenall countries. In Fig. 6, imports and exports are shown for

each country with each bar representing a wind powerpenetration scenario. Clearly, the Netherlands increases itsannual exports and decreases its imports in case more windpower is installed. This influences mainly imports andexports of Germany and Great Britain, and Belgium to alimited extent.

Large interconnection capacities are present betweenGermany and the Netherlands and Dutch wind powermainly decrease the full-load hours for base-load coal andlignite in Germany, but also some CCGT. Wind powerfurthermore reduces the exports of base-load coal power

from Belgium and to a lesser extent from France duringperiods of low load (nights and weekends). Germanyreduces its imports from France at times of high wind inthe Netherlands. Exchanges with Norway stay constant in

volume since it is modelled as such, although the momentsof exports and imports are increasingly determined by windpower as its installed capacity in the Netherlands increases.

5.2.3 Generation output mix: InFig. 7, the change inannual electricity output between different generationtechnologies is shown for the Netherlands (no internationalexchange) with increasing wind power capacity. Nuclear,

Figure 5 Annual operating cost savings by wind power



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being a full-load must-run technology, is not affected by windpower integration. Wind power decreases the full-load hourequivalents of especially coal-fired units, but also CCGT

CHP and CCGT are influenced (note the large change at2-GW wind power capacity for CCGT). This means that theprofits of these units decrease, especially for must-run base-load generating units during low-load periods. The technicalflexibility of coal, CCGT CHP and CCGT does not requireadditional operating hours of peak-load gas turbines for windpower integration. DG (greenhouse gas engines) decreases itsoperation hours only very slightly: the must-run part is fixed,and the flexible units produce heat and power during otherperiods, with the heat being stored.

5.3 Environmental impacts

5.3.1 CO2 emissions: The simulation results clearlyshow that wind power leads to a saving of significant

amounts of CO2 emissions. In Fig. 8, the annual emissionsavings are shown for the Netherlands withoutinternational exchange, and for the North-West European

system as a whole (international exchange is possible in thiscase), with the Dutch part of that as a dotted line.Emission savings are estimated to lie around 35 Mtonannually for 12 GW wind power, with higher savings forthe isolated Dutch system. In case international exchange ispossible, older, less efficient units have already been pushedout of the market at the 0 MW wind power, therefore,emission savings by wind power are lower. It can be notedthat emission savings also positively impact operating cost,since CO2 emission savings are part of the total operatingcost. The change in steepness of the curves at 2 and 6 GWinstalled wind power capacity is due to the higher capacity

factor of offshore wind power. For the isolated Dutchsystem, there is a change at 8 GW wind power due to theincreasing amounts of wasted wind energy. The results for

Figure 7 Absolute electricity production change and relative output per technology in the Netherlands for different wind

power penetration scenarios, no international exchange

Figure 6 International exchange in North-West Europe for 012 GW wind power installed capacity in the Netherlands



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power (currently installed capacity), increasing to E 80million annually (PAC) for 12-GW installed capacity. The

annual economical benefits of heat boilers in the Dutchsystem are estimated to be E 38 million annually for 12-GW wind power.

Comparing the energy storage options in the Netherlandsitself it can be observed that UPAC and PAC allow thehighest operating cost savings followed by CAES andmaking CHP units more flexible. This can be explained bythe fact that PAC has the highest maximum pumpingcapacity, increasing the opportunities for large-scale energystorage at the lowest cost, compared to UPAC. CAES hasa relatively small reservoir that reduces possible synergies

with large-scale wind power. At high wind powerpenetration levels, power generation by CAES isincreasingly pushed out of the market by wind powerbecause of its operating cost (CCGT). Heat boilers are notused until the first minimum-load problems occur at about6-GW installed wind power; from then on, the operationalcost savings of this solutions increase rapidly. Of all optionsconsidered here, the operational cost savings by increasingthe interconnection capacity to Norway are highest (20110 ME annually). It can be noted that this is withoutconsidering the possible additional benefits of connecting

the Dutch thermal-power system to the hydro-powersystem of Norway itself.

6.3 CO2 emissions

InFig. 8, it was shown that system CO2 emission levels arereduced with the integration of large-scale wind power.Fig. 11shows the emission levels of CO2 for energy storage andflexible CHP units compared to the base-case. Interestingly,the simulation results show that the application of energystorage in the Dutch system increase the systems total CO2emissions for wind power levels below 8 GW. Additionalemissions with energy storage are highest at low wind powerpenetrations for NN2 due to its intensive use (because of its

very large reservoir capacity) and lie around 1 Mton/y.

As discussed previously in [9], from a CO2 perspective,energy storage is an environmentally friendly option onlyfor very high wind power penetration levels, when energystorage prevents wasted wind. The same is the case for anextra interconnector to Norway operated as assumed here.Notably, the use of heat boilers not only saves operatingcost but also CO2 emissions. Since the use of heat boilersat CHP locations specifically tackles the minimum-loadproblem as a result of CHP unit operating constraints, heat

Figure 10 Operating cost savings by flexible CHP units, energy storage options and extra interconnection to Norway, no

international exchange

Figure 11 CO2 emission savings by flexible CHP units, energy storage options and extra interconnection to Norway, no

international exchange



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boilers reduce the amount of wasted wind. Since the CO2emissions of boilers and wind power are lower than CO2emissions of CHP units, boilers reduce the overall amountof CO2emitted by the system as well.

7 Summary and conclusionsA previously applied UC ED tool is extended to comprisethe North-West European interconnected system.Representative models have been developed of theNetherlands power system, the neighbouring areas and theinterconnections between these. Annual simulations havebeen performed for a range of wind power penetrations of0 12 GW in the Netherlands, market designs (isolatedsystem flexible use of interconnections). Technical limitsto the system integration of wind power in the Dutchsystem have been identified and the economical andenvironmental impacts of wind power on system operation

quantified. Furthermore, the opportunities of energystorage and heat boilers for the integration of wind powerin the Dutch system have been explored. Pumpedaccumulation energy storage (PAC), UPAC, CAES, theuse of heat boilers at selected CHP locations and increasedinterconnection capacity with Norway (NN2) may provideadditional technical space for wind power integration.

The simulation results indicate that for the Dutch thermalgeneration system, ramp rate problems due to the aggregated

variations of load and wind power are rare. This can beexplained by the existing commitment constraints imposed

on base-load coal units (must-run status) and CHP unitsdue to heat demand, resulting in high operating reservelevels. The high reserve levels provide sufficient rampingcapacity for balancing wind power variability in addition toexisting load variations. For the optimisation of systemoperation with large-scale wind power, it can be noted thataccurate, actualisations of wind power output and acontinuous re-calculation of UCED are essential.

Although the additional variations introduced by windpower can be integrated, limits for wind power integrationincreasingly occur during high wind and low load periods.Depending on the international market design, significant

wind power opportunity may have to be wasted to preventminimum-load problems. Wind power integration benefitsfrom postponed gate closure times of international markets,as international exchange may be optimised further whenimproved wind power predictions become available.

The simulation results show that wind power productionreduces total system operating cost, mainly by saving fuelcost. Wind power reduces the number of full-load hours ofbase-load coal-fired generation, and to a lesser extent thoseof CCGT (with and without CHP-function). This hasparticular impacts on the profits of owners of these

conventional generation units. By replacing fossil-firedgeneration, wind power significantly reduces the totalexhaust of emissions (CO2, SO2, NOx). In case

possibilities for international exchange exist, wind powersignificantly reduces imports and increases exports of thearea it is integrated into. In the case study performed here,it is shown that the presence of large-scale wind power inGermany limits the useof exports for wind powerintegration in the Netherlands during some periods. Still,

international exchange is shown to be key for wind powerintegration, especially at high penetration levels. As such,possibilities for international exchange should be regardedas a promising alternative for the development of energystorage in the Netherlands itself.

8 Acknowledgments

This work is part of the project PhD@Sea, which is fundedunder the BSIK programme of the Dutch Government andsupported by the consortium We@Sea, http://www.we-at-sea.org. The authors acknowledge the use of system data

from Dutch TSO TenneT. Mr. Uwe Zimmermann andMr. Friedhelm Witte of EON Energie, Dr. BernhardErnst of RWE and Mr. Stephan Schlunke of VattenfallEurope are acknowledged for providing the German windpower data for their respective control zones.

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