The target of a 40% share of electricity from renewable sources in Ireland by 2020 is very ambitious.
Nevertheless, the power system of Northern Ireland and Ireland will be able to accommodate this transition. This is the main conclusion from an extended technical analysis of the future power system, performed by Ecofys, Siemens PTI, Ecar Ltd and DIgSILENT in collaboration with Eirgrid and SONI engineers as well as using independent Irish wind energy experts Professor Mark O’Malley – UCD and Mr. Peter Harte SWS Energy.
The Republic of Ireland has set itself a binding target to achieve a 40% renewables contribution to the total electricity supply by 2020. Northern Ireland is considering a similar policy target. During the next decade, wind power capacity will further grow considerably and will provide the dominant share of the total renewable generation.
The 40% annual target implies very high shares of wind power in the instantaneous generation output. Potentially, instantaneous wind penetration levels of up to 100% might occur. The All Island Facilitation of Renewables Studies investigated which penetration level is technically feasible.
The All Island Facilitation of Renewables Studies have been commissioned by the Irish and Northern-Irish transmission system operators EirGrid and SONI. The studies investigated the technical issues specifically around the dynamic and frequency stability associated with an increasing share of wind power in the instantaneous power balance of the system. Additionally, the studies proposed potential operational metrics to maintain secure and reliable operation of the power system.
Wind turbine generators are connected to the grid using power electronics. Their electrical behaviour differs from that of synchronous generators applied in conventional power plants. As a consequence, wind turbine generators – by replacing synchronous generators – reduce the rotating mass (‘inertia’) in the system and affect system robustness during and immediately after contingencies. Such contingencies may be, for example, unexpected loss of a large generation unit or of a transmission line.
Ecofys and consortium members studied the system response to various contingencies for 63 combinations of load and generation dispatches, including power exchange with the UK. In that way the consortium identified and qualified the key issues for reliable operation of the power system.
Conclusions from the study:
Two key issues have been identified as the most important, limiting factors for instantaneous wind power penetration:
- frequency stability after loss of power generation (for instance unplanned disconnection of a large power plant) and
- stability after network faults.
For wind power penetrations up to 60 to 80% of the instantaneous electricity demand potential stability problems can be controlled by applying adequate technical mitigation measures. A crucial precondition for enabling this operational range is that the power system capability of generators meet pre defined standards in a reliable and consistent manner. In addition a review of the standard distribution connected generator loss of mains protection is required as well as the ability of generators to deal with large frequency deviations. The studies suggest that above the 60 to 80% instantaneous penetration level wind power has to be temporarily curtailed. Otherwise there is a risk that system stability and, hence, reliability of electricity supply are compromised.
Temporary curtailment of wind farms is associated with losses in energy yield. However, the study indicated that respective yield losses on an annual base are limited. The identified operational range in combination with the highlighted technical improvements will allow meeting the 40% renewable electricity target for the All Island Power System in Ireland.
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