Solar hot water systems can be an inexpensive way to produce hot water in the home. They are widely accepted applications of solar power around the world. It was in Israel during the 1950s when Levi Yssar came up with the first prototype of solar hot water systems. It was in Israel where flat plate solar systems were first used and perfected.
In the direct system, the hot water is mobilized through its collectors. It offers superior heat transfer from the collector to the tank.
It is also cheaper than the indirect system. However in hard water areas, the collectors are known to accumulate scale. It also has no freeze protection and no protection from overheat.In indirect solar hot water systems, a heat exchanger separates the potable water from the “heat transfer fluid”. The fluid will then circulate through the collector and after being heated, the fluid will return to join the potable water. This is a little bit expensive than the direct system but it offers freeze protection and protection from overheat.
In passive solar hot water systems, heat pipes or heat-driven convection circulate the water or heating fluid in the system. This is less expensive than the active system and requires low or no maintenance. However, passive system is less efficient than active system. Problems with freezing and overheating can also occur.
In active solar hot water systems, water and/or heating fluid is circulated in the system using one or more pumps. It offers superior efficiency and increased control over the system. Currently available active solar hot water systems offer a wide range of functionality like remote access, temperature readings and safety functions.
There are three types of solar collections that can be used in solar hot water systems in homes: flat-plate collector, evacuated-tubes solar collectors and integral collector-storage systems.
In flat-plate collector, collectors can be of two kinds: glazed and unglazed. Glazed flat-plate collectors are weather-proofed and insulated boxes that have a dark absorber plate under one or more polymer or glass covers. Unglazed flat-plate collectors, on the other hand, have metal or polymer dark absorber plate without cover. They are generally used for solar pool heating.
In evacuated-tube solar collectors, transparent glass tubes are lined up in parallel rows. These types of collectors are most commonly used in US commercial applications. Each tube has a glass outer tube and a metal absorber tube which is attached to a fin. The coating of the fin absorbs solar energy and bars heat loss.
In integral collector-storage solar hot water systems, cold water is preheated in the solar collector then goes to the conventional backup water heater thereby providing reliable daily source of hot water. These type of collectors are used only in mild-freeze countries because the outdoor pipes can freeze during very cold weather. The tanks or tubes in this system are insulated and glazed.