G3dfatboy

Saw this thread on here and was wondering if anyone had perused this line of energy storage. I saw the Finish guys on youtube and polarnightenergy.fi who are doing this in a big way. It looks like reasonably simple concept for a small scale project. So, I am currently designing a solar/wind charged IBC based sand battery system which can be daisy chained with multiple units. The hot air would be run through a converted commercial boiler coil exchanging the heat into the water. No pressure, open system, no risk of explosions.. If anyone has made something work, I would be interested to hear of any pitfalls.