An increasing number of heat pump producers have developed heat pumps that can be connected to solar panels. In this thesis we have examined the possibilities of connecting solar panels to existing ground source- and geothermal heat pumps that has not been adapted to solar panels. During the work process, a prototype plant has been built to compare our theory with the practical results and with our designed sizing tool. The work has rendered in knowledge that will be used to build a sun module that can be easily connect to the existing heat pump system. The existing heat pump, our test plant, has been supplemented by an advanced storage tank used to allow different operating modes.