Water

If you have access to running water (e.g. a small stream) this can be used to provide a mini hydro-electric power.

Water also provides a better energy to heat conversion factor for geothermal heating. So a large pond will provide better heating potential. A typical Co-efficient of Performance will improve to 3.5:1 to over 4:1. i.e. for every unit of energy input in the system you will get between 3.5 and 4 units back.

Large scale wave and tidal systems are in the pipeline at the present and these could provide huge amounts of energy for the UK, but there are reasonable concerns over conservation issues, but there are technologies available that would negate these potential problems.