At the Brave New Climate blog, there is a thread running on energy storage right now. One of the comments in that thread pointed to the “Energiespeicher” blog by German professor Eduard Heindl. I just added a permanent link to that blog (it is in German language).
“Energiespeicher” means energy storage, and professor Heindl has an interesting idea he calls “Lageenergiespeicher”, which might be translated as “Sysiphus” into English, or “statusenergystorage” for a more direct translation. He wants to cut out a VERY BIG ROCK out of a mountain and float it on water.
That would seem to get much more storage power per square meter of area used. A rock 500 meters in diameter and 1000 meters in depth would yield 1.7 TWh in storage capacity, using less than 1% of area and costing less than 10% compared to pumped hydro.
That blog has some other interesting information as well. The latest post points out that there now is a simulator running at David McKay’s “withoutthehotair” website where everyone can try to build their own energy system for the United Kingdom.