Yeah, it can be very good, but there's a limit. There's a very interesting project in Finland to build a pumped storage facility that uses a 1400m deep abandon

Yeah, it can be very good, but there's a limit. There's a very interesting project in Finland to build a pumped storage facility that uses a 1400m deep abandoned gold mine as the storage location. The idea is to use a relatively small amount of water but at very high pressure provided by the depth of the mine -- the high potential difference makes generation more efficient and reduces capital costs. If this thing turns out to be profitable, this will probably be done to all sufficiently deep mine shafts and other deep enough holes. PDF: http://laguna.ethz.ch/indico/getFile.py/access?contribId=2&sessionId=7&resId=0&materialId=slides&confId=12 http://laguna.ethz.ch/indico/getFile.py/access?contribId=2&s...