Omission of reserve

It was decided that reserve would not be included in the simulations carried out for this study. However PLEXOS® is capable of modelling all the reserve categories required by the SEM. This decision was necessary due to the dramatic increase in problem size associated with modelling reserves. From preliminary testing carried out it was found that the inclusion of the four types of reserve in the SEM increases model simulation time up to eightfold.

Due to limited computational power available, there was a decision to be made between the inclusion of stochastic unit commitment or reserve

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more relevant to the thesis’ research question as capturing the effects of forecasting error was considered a priority.

Chapter 10

Conclusion and recommendations

To meet the 2020 RES-E targets set out for All-island of Ireland (AI)¹there are large variations (ranging from 5064MW to 6890MW) in the amount of wind capacity required to be installed dependent on assumptions made. It has been shown that the two largest factors affecting the amount of wind capacity required are (1) wind curtailment occurring from system operational

constraints (SOCs) and (2) the amount of non-wind, synchronous, renewables such as biomass that could be constructed. It is shown that if the entire

projected capacity of 377MW non-wind renewable, synchronous, generation plant is constructed, then 5064MW of installed wind will meet the RES-E targets; however if none were constructed, then 5911MW of installed wind capacity would be required in the most optimistic scenario. The

onshore/offshore wind mix also has small effects on the required installed capacity. Taking account of issues causing wind curtailment on the 2020 AI system dramatically increases the amount of installed wind capacity required to meet the RES-E targets. To help AI to meet its RES-E targets with the least amount of installed wind capacity it is clear that the system non-synchronous penetration (SNSP) limits must be increased as high as technically possible and also for the proportion of wind capacity installed offshore to be increased in the future.

A detailed examination of the effects of the relaxation of SOCs and the improvement of wind forecasting was also carried out. These effects are quantified in terms of changes to total generation costs, wind curtailment and generator dispatches.

1All-island of Ireland (AI), consist of Northern Ireland (UK) and the Republic of Ireland

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improvements in wind forecasting. With the relaxation of the five most influential SOCs, there are potential savings in total generation costs of 7.8%.

There are also large savings to be made with SOCs being individually relaxed.

Most notably, if the Dub(2/3) SOC constraint requiring two large generators in the Dublin area are to be constantly on-line by day and three by night is relaxed to Dub(1/2), one by day and two by night, there is a saving of 3.1% of total system costs regardless of the SNSP limit imposed.

It has been highlighted that the relaxation of the SNSP limit is beneficial;

however this will only deliver significant cost savings in conjunction with relaxing other SOCs associated with local voltage control. It has been demonstrated that increasing the SNSP limit beyond 65-70% has a limited value without prior relaxation of the other SOCs and it is also shown that there is limited value in increasing the SNSP limit beyond 70-75% even if all other influential SOCs are relaxed.

The results show that with a reduction in wind forecast errors from 8% mean absolute error (MAE) to 4% MAE, there are available savings in terms of total system costs under both stochastic and deterministic scheduling of 0.50% and 1.64% respectively. This work also strongly highlights the benefit of creating the day-ahead unit commitment schedule from wind forecasts through stochastic scheduling rather than deterministic scheduling as is presently the case. This allows the uncertainty associated with wind forecasts to be

accounted for in the day ahead unit commitment process. At today’s wind forecast accuracy levels, switching from deterministic to stochastic scheduling allows savings of 2.46% of total system costs in 2020.

Increasing the efficient use of the installed wind capacity in the future through minimising wind curtailment and therefore maximising usage of wind generation availability is of major importance. It has been highlighted that the relaxation of SOCs and the improvement in wind forecasts will both reduce wind curtailment significantly.

Wind curtailment is suggested to drop from an average of 14% to 8%, as the SOC of the SNSP limit alone is relaxed from to 60% to 70%. There is also a potential to reduce wind curtailment further from 8% to 4% when the four most influential local SOCs are relaxed and the SNSP limit is relaxed to 75%.

By increasing the proportion of offshore wind, it is shown to aid in the reduction of wind curtailment by reducing the amount of wind curtailment

10. CONCLUSION AND RECOMMENDATIONS

10.1 Recommendations to Academia and the Transmission system operators

occurring by at least one percentage point. Maintaining low amounts of wind curtailment is viewed as crucial to achieve continued investment in the wind energy industry; otherwise the installed wind capacities required for the RES-E targets will not be met. This work has also highlighted that an issue may arise in the future between the two jurisdictions (ROI and NI) with regards where best to curtail wind energy for the benefit of the system as a whole.

Reductions in wind curtailment come from realistic improvements in wind forecasts. There is a general agreement between stochastic and deterministic scheduling in relation to wind curtailment, showing possible reduction from 8.0% to 7.25% wind curtailment or an average 0.2 percentage point reduction in wind curtailment for every percentage point increase in MAE accuracy.

It has been shown that there are operational advantages from relaxing the SOCs for the dispatch of conventional generators allowing for achieving a more efficient generation schedule. However there are also negative effects, such as increased usage of open cycle gas turbines (OCGTs) as SOCs are relaxed. There is also a substantial effect on the relative contribution to total generation from the two jurisdictions when the NI SOCs are relaxed, with NI requiring support from ROI and GB in this case.

Improved wind forecasts also are shown to have an effect on OCGT

scheduling with realistic possible decreases in OCGT generation of 23% using deterministic scheduling and 8% using stochastic scheduling.

10.1 Recommendations to Academia and the Transmission system operators

This work helps quantify the benefits and costs in terms of wind curtailment associated with of the relaxation of system operational constraints and improvements in wind forecast accuracy in an electricity system with high wind penetration. From this it is justified that further investigations should be carried out to mitigate problems associated with voltage stability and inertia requirements, and into improving wind forecasting techniques will be justified. These investigations should be carried out by both the Transmission system operator and academia alike.

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Wind energy developers and existing wind farm owners should be particularly concerned by the predictions of increases in annual wind

curtailment if changes are not made to how the electricity system is operated.

It would be very much in the interest of the wind industry to investigate further the issues driving wind curtailment raised in this thesis.

This work also highlights the benefits in the reduction of wind curtailment from increasing offshore wind due to spatial correlation and therefore should be further investigated by offshore wind energy developers as a potential benefit in favour of regaining the offshore wind energy subsidies.

10.3 Recommendations to the Governments

The rise in wind curtailment also should be of concern to the Governments of ROI and NI. The current policy of meeting the 2020 renewable targets will not be met if wind energy developers find it no longer financially viable to invest due to high wind curtailment occurring. It is clear from the work done here that the Government must actively support the work of EirGrid and SONI’s DS3 programme if the renewable targets are to be met.

10.4 Recommendations to the international community

The issues associated with large scale wind integration investigated in this thesis, while important for Ireland in the next five years, will also become important the GB synchronous system in the next 10 years as well as in the synchronous systems of Continental Europe in the next 30 years. This work illustrates the need for studies to be carried out on these larger systems to ensure adequate time to plan and invest in required changes.