How Solar Water Heating Collectors Work

Solar water heating collectors produce heat energy, distinguishing them from photovoltaic (PV) modules which produce electricity. There are several types of collectors: flat plate, evacuated tube, Integral Collector Storage (ICS), thermosiphon, and concentrating. Flat plate collectors are the most common type of collector in MW.

copper pipes are affixed to an absorber plate contained in an insulated box that is covered with a tempered glass or polymer coverplate.

Evacuated tube collectors consist of rows of parallel, transparent glass tubes that have been “evacuated” of air, creating a highly efficient heat insulator for the fluid that runs inside the length of the tube. Evacuated tube systems are generally used when higher temperatures or higher volumes of water are needed, as well as for process heating and solar air conditioning systems.

Evacuated tube collectors feature thin, copper tubes filled with a fluid, such as water, housed inside larger vacuum-sealed clear glass or plastic tubes.

Evacuated tubes use the sun’s energy more efficiently and can produce higher temperatures than flat-plate collectors for a few reasons. First, the tube design increases the surface area available to the sun, efficiently absorbing direct sunlight from many different angles. Second, the tubes also have a partial vacuum within the clear glass enclosure, which significantly reduces heat loss to the outside environment.

How It Works

1. Sunlight: Sunlight hits a dark cylinder, efficiently heating it from any angle.
2. Heat reflection: A clear glass or plastic casing traps heat that would otherwise radiate out. This is similar to the way a greenhouse traps heat inside.
3. Convection: A copper tube running through each cylinder absorbs the cylinder’s stored heat, causing fluid inside the tube to heat up and rise to the top of the cylinder.
4. Circulation: Cold water circulates through the tops of the cylinders, absorbing heat.

Evacuated tube systems are typically more expensive than flat-plate collectors, but they are more efficient and can produce higher temperatures. Evacuated tubes can reliably produce very hot water for batch or on-demand water heating and for many industrial processes, and they can produce enough heat to handle almost any space heating or space cooling application.