Solar thermal technologies convert solar energy (or radiation or light) into thermal (heat) energy. They are typically Solar Hot Water (SHW) or Domestic Hot Water (DHW) systems.
A solar hot water (SHW) system looks similar to a solar photovoltaic (PV) system. However, a solar PV system uses sunlight to generate electricity, while a SHW system uses sunlight to heat water and space.
Most solar hot water systems consist of solar collectors mounted on the roof of a house; a pump for circulating the heat transfer fluid (typically water + glycol); a heat exchanger for transferring the heat to storage; and one or two storage tanks for storing solar-heated water.
Solar thermal collectors absorb the sun’s energy and convert it to heat into hot water system or hot air system. There are five collector types for different applications to heat water or air: unglazed air, glazed air, evacuated tube (liquid), unglazed liquid, and glazed liquid.
Modern solar hot water systems are well suited for the cold Canadian climate because they produce energy when the outside temperature is well below freezing. They also have mechanisms that protect them from freezing in the winter and from overheating on hot sunny days. They can easily be retrofitted to your existing water heater.
A typical solar hot water system will reduce annual energy costs by 40 to 50 percent. Assuming a freeze-protected system with 6 m2 of single glazed flat plate solar collectors and two 270 litre (60 gallon) hot water tanks, you can expect that a solar water heater will provide you with 1500 to 3000 kWh of energy per year, depending on your hot water usage and regional climate.
- Solar water heating systems; a buyer’s guide, Natural Resources Canada
- Survey of active solar thermal collectors, industry and markets in Canada (2017), ClearSky Advisors Inc.
- Solar thermal challenge, MAPC
- Residential guide to solar hot water, Massachusetts clean energy center