On average, about 18% of home energy consumption is for water heating, the second largest consumer behind space heating.  The primary technology used to do this is the tank-type water heater (both gas- and electric-powered), but solar water heating can be a cost-effective way to generate hot water. 

Solar hot water systems vary, and one system we’ve mentioned previously is a passive-pump system by Virginia-based Sunnovations.  This video explains it.

Sunnovations offers a system with less parts, less maintenance, and a one-day installation because it doesn’t have a pump, controller, wiring, or expansion tank.

Sunnovations uses a geyser pump, or bubble pump, that starts working as soon as fluid in the system warms.  The gravity-fed system naturally circulates water, so, as explained in the video, a homeowner may get warm water even if the power goes out.

[+] Learn more about solar hot water from Sunnovations.