I'm looking up some numbers now and it *might* actually still save some money... average cost of a sun boiler for 2 is 2500 euros, you can get a government subsidy of 850. That leaves 1650 euros as the initial investment... Estimating the average kWh usage of my heat pump to be 1.5kWh a day for hot water now, and a kWh costing 50 cents.... Say hot water costs me around 275 euros a year *now*, and the sun boiler saving about 50 percent of that... it would take 12 years for it to earn itself back.