I was wondering is solar water heating a more cost efficient use of solar power over using large arrays to power your house or large solar thermal plants that are being contemplated all over the world.
It depends on how you do it. Passive solar is the most efficient and reliable. The more pumps, storage tanks and controllers you use the less efficient and reliable the system will be. The egyptians were successfully using passive solar 3,000 years ago and it still works the same.




