A solar heating system with underground storage of warm water in hard rock to meet demand in the colder months is described. There are no heat pumps. The system is being developed in a residential area north of Stockholm and will serve 36 family houses, four rows of terraced cottages and a service/nursing home with a floor area of 9,000 square metres. The solar collectors are on the roof and heated water is fed to the underground store through a borehole system in the underlying granite. Details of the thermal properties of the granite are given together with costs of construction and running of the whole system. The project is planned to be up and running in late 2001