Examining the Spirit of Ireland proposals

The plan would work like this: Water storage reservoirs would be constructed at elevated heights along the coast, with the sea itself acting as the lower reservoir. Wind energy would be used to pump the water from the sea to the upper reservoir. The water would then be dropped back to the sea through turbines to generate electricity when needed. This would help to solve the issue of how to make use of wind energy that goes to waste - such as that produced during the night when demand is low.

Details of the proposals, and associated technical details, can be found here .

However, Andy Wilson of the Westport-based Sustainability Institute has raised some interesting questions about the proposals. Discussing his calculations here, Wilson writes the following:

To produce an equivalent amount of electricity from wind as is currently used by Ireland would require an installed capacity of around 10,000MW (10,000MW x 8760 hours per year x 30 percent capacity factor). That is not to say an installed wind capacity of 10,000MW would actually meet Ireland's electricity requirements as even with adequate storage capability, there still be wastage and conversion losses during the storage process of anything up to 20 percent.

It must be pointed out that the Spirit of Ireland plan does not envisage an installed wind capacity of 10,000 MW, but only a fraction of this. In other words, even if all the surplus energy could be stored until needed, with no conversion losses, it would be nowhere near enough. There are also insurmountable difficulties on the storage side.

Wilson also writes:

In order to balance out seasonal variations in supply from wind farms, Ireland would need storage capacity of between 800GWh and 2000GWh (2TWh) to meet current national electricity demand solely from wind (the storage requirement would depend on the installed wind capacity)... or in other words 500-1250 pumped storage facilities similar in size and capacity to Turlough [Turlough Hill pumped storage station in Wicklow].  The reality is that nothing like this number of suitable sites exists in Ireland. Even if the sites could be found, the environmental, social and agricultural impact of flooding hundreds of inland valleys with seawater (the Spirit of Ireland proposal is to use seawater in its pumped storage facilities) would be on a par with some of the worst excesses of Soviet planners during the times of Stalin.

and

If one extrapolates down to the rather smaller Spirit of Ireland proposals, one finds that a 10 meter deep lake (or combination of lakes) of 32km² in area, with a head of 100 meters (the height difference between the lake and the turbines), could store no more than 75GWh of electricity: about enough energy to meet Ireland's electricity needs for one day.

The full article is here.

It would be interesting to hear what Spirit of Ireland has to say in response to these calculations. Obviously it's great to have a national debate on large-scale investment in renewable energy, but it's important we pay close attention to the maths behind the proposals first.