PCM being used for domestic hot water now, see companies like http://sunamp.co.uk/products/sunamppv/ http://sunamp.co.uk/products/sunamppv/ . Much better than

PCM being used for domestic hot water now, see companies like http://sunamp.co.uk/products/sunamppv/ http://sunamp.co.uk/products/sunamppv/ . Much better than water - higher energy capacity means smaller units and higher performing insulation making losses much lower. Heat loss is a bit problem in stored water DHW scenarios and will get even more of a problem if we begin building houses properly (which surely has to happen at some point).