Solar water heating is a popular use of the sun’s power. The basics are very simple – you have solar collectors to capture the heat, and you have a storage system to contain it until it’s needed. These can take various forms.
The simplest solar collector is a flat plate, with tubing fixed to its surface through which water flows. This assembly is painted black and usually covered with one or more panes of glass. The dark color attracts the heat, and the glass covering also adds to the heat available. People have also used panel radiators as the collectors, and again adding glass helps with the amount of heat collected. If you live in an area where the water can freeze at night, there are ways to avoid this – the system can be designed as a drainback system, which allows the water to drain out of the collector when it’s not being heated, or there can be a arrangement of piping, tanks, and/or heat exchangers that allow you to run antifreeze in the collector without it getting into your hot water supply.
The storage system can also be installed in different ways, depending on your requirements. One way is to have extra connections on a conventional water heater tank, and just circulate water from the collector into and out of the tank. You need to have controls that prevent the system from taking heat out of the tank and dissipating it from the collector plate at night, but these can be relatively simple thermostat controls. If you have a system with antifreeze running through the collector, you can have a similar arrangement, but have the antifreeze running through a pipe coil in the tank so that it doesn’t mix with your domestic hot water.
Another way of using the solar energy is to have a two tank system. In this case, the solar heating just heats the first tank of water to whatever temperature it can make from the day’s conditions. The first tank is a pre-heater for the water which goes into your regular water heater, reducing the amount of heating that is necessary to get it to the temperature you prefer. This brings us to another important concept about solar water heating – generally you will always need a conventional method of heating the water, as you can’t rely on the solar providing enough heat for your needs all the time, either because it is a cloudy day, or because you happen to be doing a lot of washing! However, you can rely on a good solar water heating system to reduce your energy usage significantly, particularly in the summer.