An Interesting Renewble Energy Storage Concept

Stuart Staniford links to one concept:

Artificial islands for storing renewable energy?  The idea is to have a hollow center to the island and pump water out when there's excessive wind power, and then have it flow back in (powering turbines on the way) when the energy is needed later.  The basic idea of pumping water uphill as a storage mechanism is an old one - the Dinorwig power station in Wales was built in 1974 for example - but the island twist is new to me.  I haven't really thought about how far this idea scales - but that seems like a good future post.  How big a lake would we need to get a fully renewable US through the winter if we didn't trade renewable energy globally?

I was contemplating some sort of water pumping scheme to capture excess renewable energy production.  The islands are an interesting idea.  I think that if wind energy is really generated more at night, as many critics say, such stoarge makes for a very good idea.  You can utilize solar energy during the day, while converting stored water potential energy during peak times and try to balance the grid like we do today.  I was having a conversation with a really smart engineer last summer, and he made the wind blows at night argument.  My former employer had told me that he worked at a nuclear plant where they were constructing an upland reservoir where they could pump water during low demand times at night and then run the water through turbines during peak daylight demand, since they had to run the nuclear reactor at a constant rate.  As I pointed out to this engineer, this would be a potential, albeit somewhat inefficient solution, but it took advantage of the energy that was available when it was available.