Harness gravity

The gravity power website raised more questions in my mind than it answered

I followed Joe Iliffe's advice (PE Nov 2012) and consulted the Gravity Power website. 

It raised more questions in my mind than it answered. It showed a 10 m diameter 'piston' of 'up to 210,000 tonnes' mass in a 2 km long shaft. How, I wonder, would such a monster be got in there and how would it be sealed throughout the working length against a pressure differential of over 200 bar (3000 psi)? 

Presumably it would be loaded in sections - a thousand or so - each of which would be transported laboriously to the site and carefully lowered down the shaft a distance of up to 2 km. Truly a modern-day Stonehenge type operation! And that is just the mass, to say nothing of the challenges presented by the 2 km shaft and the proposed Francis turbine, operating at several times the normal head. 

By contrast, the Cruachan pumped storage plant described in the same issue has some 14 times the energy storage capacity with vastly less technical and logistical problems. 

I know which one my money would be on!

Ian Berry, Enfield

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