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Irish power system can accommodate 40% renewable electricity

Tuesday, 27 July 2010 17:14

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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.

Source: Ecofys