Types of Solar Water Heaters
The concept of solar water heating is simple. A solar thermal system runs water, or any fluid, through the water system. The water that runs through the solar panels are heated and are ready for use.
There are different types and designs of solar water heaters for residential and commercial use. Two things are common among them – collectors and storage tank. Solar water heaters are classified according to their types of collectors and circulation system.
Solar Water Heater Collector Types
Batch Collectors
Batch collectors heat water through an insulated box, in which the heated water is stored in dark tanks. If the demand for heated water is low, the water can remain in the collector for a long time making the water very hot. A tempering valve maintains the right temperature of the water by mixing cold water before it reaches the tap.
Generally, batch collectors do not work well with closed-loop circulation systems. They are not also recommended for users located in places with cold climates.
Flat-Plate Collectors
A flat-plate collector is a more common type of collector consisting of copper tubes and large, flat absorber plates which maximize its exposure to the sun. The water runs through the tubes and collects heat from the absorber plates. A well-insulated box and tempered glass makes sure that the heated water is properly heated.
Evacuated Tube Collectors
This type of collector is considered as the most efficient collector available for use. Each evacuated tube works like a thermos in principle in such a way that the metal tube, that contains the water, is enclosed by a larger glass tube. The space between each evacuated tube is a vacuum that prevents heat loss.
Solar Water Heater Circulation System Types
Active Circulation System
Active circulation system, also known as forced-circulation system uses an electric pump to circulate water from the collectors to the storage tank. This type of hot water system reduces water heating costs much.
Direct Circulation System
Direct circulation system, also known as open loop active system, is the least expensive type of active system to install. Water is circulated through the solar collectors that absorb heat from the sun. After it is heated, the water is then stored in the tank to be used directly or sent to a tank-less water heater.
This type of circulation system is not advisable to areas that have frequent freezing temperatures. However, when needed, freeze protection should be obtained in cold climate areas by re-circulating the hot water from the storage tank or drain the water down.
Indirect Circulation System
Indirect circulation system, also known as closed-loop system uses a non-freezing liquid such as water-ethylene glycol solutions or water-propylene glycol solutions to transfer the heat from the sun to the water that is stored in the tank. The fluid in the solar collectors is heated by the sun’s energy. It then passes through the heat exchanger and transfer the heat into the water. The liquid cycles back to the collectors while the heated water is delivered to the tap. Indirect circulation system solar heaters are applicable to areas with freezing climates.
Passive Circulation System
In contrary to active systems, passive circulation systems do not require pumps to circulate water into the system. A passive system only uses natural convection to move water from the solar collectors to the storage tanks as it is heated. Although, this system type is not as efficient as active system, it is still reliable to use.
