Pushing Ireland to its windy limits -- High penetration study

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Up to 3300 MW of wind power can be fed into Ireland's transmission system -- economically and without significant network reinforcement -- provided system operators adopt a more flexible approach to connecting wind farms into the network. This is a key conclusion of a study of the impacts of increased levels of wind penetration in the Republic of Ireland and Northern Ireland. It recommends that instead of reinforcing the system to accommodate a large amount of wind capacity, wind generation should be able to be shut down in the event of "contingencies" that might overload the system.

Commissioned by the two energy regulators, Ireland's Commission for Energy Regulation (CER) and Ofreg in Northern Ireland, the report is by English consultants Garrad Hassan. It looks at the impact of increased amounts of wind generation for three target years -- 2005, 2007 and 2010. At present, 30 wind farms are operating in Northern Ireland and the Republic, totalling 173 MW. The overall production capacity for all types of generation stands at over 6500 MW.

changing the rules

The report finds that a higher than previously envisaged amount of wind capacity could be accepted on the 110 kV transmission systems without the need for significant upgrading of the network. But rules governing transmission system operators will have to be changed, it says. At present, all generation, including wind, has to be "firm" or capable of operating during system contingencies. In many locations, the system will have to be reinforced before new generation projects are considered "firm."

The report recommends, however, that wind power should be treated as "non-firm" so that in the event of a contingency it can be shut down automatically if necessary. This concept, known as a Remedial Action Scheme (RAS), has been used in the US for wind farm connections. The benefits of RAS are substantial, says the report, and the equipment needed for automatic disconnection is much cheaper than system reinforcement. It also allows new wind power plant to be connected without lengthy delays associated with reinforcing the network.


Under RAS, up to 3300 MW of wind could be connected into the system, which would be able to withstand common faults. The power would only have to be disconnected under the less frequent contingencies. Beyond 3300 MW, disconnection will also be needed for the more common contingencies.

Another factor limiting the amounts of wind penetration in Ireland is "curtailment." At times of minimum electricity demand, the system could accept up to 800-1000 MW wind generation. Beyond this amount, wind plant would occasionally be forced to shut down -- or be "curtailed" or reduce output (be "constrained") during low-demand periods so that conventional generation running at the time is not forced to operate below its minimum load limit. As more wind capacity is added, the greater the curtailment, until at around 4000 MW of wind generation, around 40% of production is being lost through curtailment.

The report recommends a move to a more flexible operation of the plant mix to encourage a higher wind penetration above 1000 MW. This would involve switching off fossil fuel generation or changing the conventional plant mix.

The economic benefits of increased wind energy would outweigh the costs, with the biggest saving in fossil fuel consumption. Wind capacity of 1000 MW will save some EUR 75 million, or 8% of the island's annual fuel bill. The saving could rise to EUR 244 million a year with 3000 MW of wind.

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