www.ecowatch.com has published a Guide to Solar Water Heater Systems that is quite informative.
Solar hot water heaters are split into two broad categories: passive and active. Active systems require circulating pumps and passive systems rely on gravity to move water. So active systems require electricity and may use antifreeze to exchange the heat to the water. The simpler passive solar collectors heat water in tubes, then pipe it directly to a faucet when needed.
Active and passive systems have subcategories that are specialized for various climates, tasks, capacities and budgets. What is right for you will depend on various factors, such as:
- Available space
- Availability of sunshine
- Your capacity requirements
- Building codes and regulations in your area
- Your installation budget
If you want to find our more the original article is at www.ecowatch.com