Solar Water Heaters
The types of solar water heaters used to heat water by the power of the sun.
The power of the sun is used in solar water heaters to raise the temperature of water to around 50 °C (120 °F) so it is useful as a source of hot water in the home.
Many of these solar water heaters use panels where the water is trickled down over a back panel that faces the direction of the mid-day sun. Glass panels cover the solar panels to insulate the inside from the outside air and to keep the water clean.
A pump may be used to circulate the water or natural convection of the water may be used to circulate it. Where a pump is used, some energy is wasted powering the pump, but it allows for easier control of the water flow.
Temperature regulation is required where the flow is stopped if the outside temperature is freezing, if it is dark or the temperature of the tank of water has reached the maximum setting.
This kind of system is called the direct-gain type.
Another type of system that is popular in colder climates is the evacuated tube solar collector. This is more efficient than panels since there is low heat loss due to the vacuum between the glass and the heat collector.
Copper tubes conduct the heat and transfer it to a circulating loop of antifreeze that passes through a heat exchanger to heat the domestic hot water.
Other, more sophisticated methods use mirrors to concentrate the sun onto a heat absorbing surface that transfers the heat to a fluid such as brine that carries the heat to a heat exchanger. These mirrors may then track the sun by means of servo-motors controlled by a computer.