Solar thermal is very practical, and in most cases does not use any electricity. The power to run the DC powered circulating pump is derived from usually a 10-20 Watt small solar panel, thus eliminating the use of the grid to move the water. There are also thermosiphon systems that use convection to move the water through the solar panels. In the hotter months here in Southern Ca. my customers actually turn the gas pilot lights or electric elements off during these months, typically May through September. This is a very effective way to cut cost's and help reduce carbon production.