Heating water is probably one of the biggest line items on your energy bill. The average American family of 4 in 2012 spent between $250 and $550 that year to heat hot water. A cleverly designed solar hot water system can eliminate 50% to 100% of that cost, depending on usage.
DIY Solar Hot Water Heater
This is the “gateway drug” for heating water with the sun. You can build it yourself, in an afternoon, with 20$ in supplies. After you prove to yourself that indeed this solar hot water thing isn’t snake oil, you can move on to more advanced solar hot water systems.