Once you have a passive solar design in place in your home, the question will be: what’s the best way to use this energy? One of the most efficient and simple answers is to use it to heat water. There are two main categories of solar hot water systems: passive and active.
Passive systems work on the same principle as do passive solar designs: use your own environment to your advantage. This system is perfect for climates that do not dip below freezing point. In an integral collector storage type of passive system, the sun heats water that would usually be heated by a burner. This is accomplished by siphoning cold water into long pipes with direct access to sunlight. The benefit of this system is its simplicity; there need not be any moving parts or machinery. This means very minimal maintenance. These systems are so simple that they can usually be made by adapting already existing classic hot water systems. The downside of integral collector storage is that the piping is heavy and that the volume of hot water is lower than in other options.
Thermosiphon passive systems are ones that function from the principle that hot water rises. In this system, the hot water is constantly rising into the storage tank, leaving the cold water in the bottom section of pipes to be heated by the sun. This movement of water means that this system is more reliable than the integral collector storage type, which typically doesn’t yield much hot water outside of daylight hours. This system is also low-maintenance. However, thermosiphon necessitates a very heavy storage tank, which usually needs to be on the roof. This means installation is expensive.
Active solar hot water systems are more complicated. They use pumps that require more maintenance and expense, but generally yield more hot water, more reliably. Active systems are needed for cooler climates, as they move the cold water from an inside container tank to heat it, and then back down to a hot water outlet. A direct active system is best, however, in relatively moderate climates. This kind of active system is still susceptible to freezing temperatures, which could stop the water in its tracks before it can be warmed via solar power. It is possible for this system to work in very cold places, but it has to be adapted to include antifreeze, which makes it a very expensive system.
The best system for cold climates is an active indirect system. This system uses antifreeze to keep the water in the outside collector from freezing. Then, pumps move the warm water to an inner storage tank. A heat exchanger transfers the heat to your home’s pipes, delivering hot water straight to your taps. This system is the most complex of them all, and correspondingly the most expensive. However, it’s the most reliable system and can even be used outside of the home, for hot tubs or even swimming pools.