I`m sorry I dont agree, I find them far too expensive in most cases, and when you factor in the high cost of PV and the small return in electricity it gives and the amount of electricity the GSHP uses its not viable. 10-20k would be far better spent using super insulation such as external wall insulation in new or retro fit, this negates the need for a high amount of heating. Then hot water can be supplied by solar thermal with maybe a back up wood or pellet boiler. All that will cost alot less than GSHP. Buildings need to be reducing their need for heating and utilising passive means and by super insulating and building air tight we can do that.