Spirit of Ireland
Spirit of Ireland is a proposal to build pumped-storage hydroelectricity reservoirs in valleys in Ireland's west coast combined with large-scale windfarms to reduce Ireland's dependence on imported energy and fossil fuels. It would initially involve identifying up to five coastal valleys from counties Donegal to Cork, building dams on their seaward side and flooding them with sea water. These would provide a hydro-power back-up for the wind farms.
Typically, wind farms only produce 25 to 35 per cent of their maximum possible electricity output when measured over a long period. The proposed hydro-generating stations would come into play when wind speeds were either too low or too high to be useful. Each of the reservoirs would be able store up to 100 gigawatt-hours of hydro energy. 
Under the Spirit of Ireland proposals, a very typical natural valley water reservoir would have a dammed lake area when full of 4 square Km – e.g. average 2 km x 2 km. Based on studied shapes, depths and height from the sea etc, two such reservoirs would deliver some 200 GWh of electrical energy. A third reservoir would increase this to 300 GWh. This is a considerable energy store and in fact there are many valleys studied which would give considerably larger storage.
The long term strategy is to develop higher capacity electrical interconnectors with continental Europe via the United Kingdom which would allow export of excess generating capacity whilst allowing for the import of electricity in the event of sustained no wind conditions. This scenario would be expected to be very infrequent and during such times the reservoirs would be filled using imported electricity at off peak times which would command much lower prices. Locations for the pumped storage reservoirs have not yet been decided but are expected to be located in areas that are otherwise economically deprived which would help to fulfil the Irish goal of balanced regional development.