On 1 March 2013 the Single Electricity Market Committee (SEMC), the regulator of the wholesale market for electricity, published a key decision affecting all wind energy generators on the island of Ireland. The decision (SEM 13-010) sets out the SEMC's approach to the treatment of curtailment in tie-break situations and will have a significant impact on existing and future wind energy generators, their financiers and consumers up to 2018 and beyond. The SEMC also published the transmission system operators' methodology for distinguishing between constraint and curtailment events (SEM Decision 13-011). This methodology will play a central role in the implementation of the SEMC's decision on curtailment.
Increasing levels of wind energy
EU Renewable Energy Directive 2009/28/EC lays down binding 2020 national targets for the overall share of energy from renewable sources in gross final energy consumption. In order to meet these targets, Ireland and Northern Ireland will have almost 40% of the electricity consumption from wind by 2020; and it is estimated that an additional 3,000 MW of wind energy will be added to the 2,100 MW currently connected to the grid. Increasing levels of wind penetration pose technical challenges for the system operators of the single electricity market, in particular to ensure system stability and that the supply of electricity matches demand.
Dealing with excess wind energy
Article 16 of the EU Renewable Energy Directive 2009/28/EC requires that renewable sources of energy are dispatched in priority to other non-renewable sources. In situations where the supply of energy exceeds demand and there is no other basis (such as price) for dispatching down generators, a tie-break situation arises.
Transmission system operators' methodology for distinguishing between constraint and curtailment events (SEM Decision 13-011) now provides that in tie-break situations where grid security issues can only be resolved by reducing the output of one or a small group of price taking generator units in a tie-break, then this will be deemed to be a constraint event. On the other hand, where grid security issues can only be resolved by reducing the output of any or all of the price taking generator units in a tie-break then such reduction will be deemed to be a curtailment event. While both constraint and curtailment result in a reduction of generator(s) output, whether a generator is subject to constraint or curtailment can have...