http://www.byfy.lth.se/fileadmin/byf...-1018EKweb.pdf
" The use of ground-source heat pumps for heating buildings and domestic hot
water in dwellings is increasing rapidly in Sweden. The heat pump extracts
heat from the ground by a U-pipe in a vertical borehole. In order to reduce the
electricity demand in the system, the combination with solar collectors is introduced.
This system may be designed in many ways and the advantages differ a lot.
Solar heat can also be used for recharging of boreholes when
neighbouring boreholes are thermally influencing each other. "