Where a sufficiently large body of water is within easy reach of the house,
collector piping can be secured to the bottom of the pond. Stored solar energy is again collected. The piping is buried 1 metre underground between the pond and the house. The water should be deep enough that it never freezes at the bottom where the piping is laid.

Because no drilling and limited groundworks is required this can be an
economic solution where access to a pond exists. Permissions may be
required.