Types of Solar Collectors

— Bob Ramlow with Benjamin Nusz

ICS COLLECTORS

ICS stands for Integral Collector Storage. In an ICS unit, the hot water storage tank is the solar absorber. The tank or tanks are mounted in an insulated box with glazing on one side and are painted black or are coated with a selective surface. The sun shines through the glazing and hits the black tank, warming the water inside the tank. Some models feature a single large tank (30-50 gallons) while others feature a number of metal tubes plumbed in series (30-50 gallon total capacity). The single tanks are typically made of steel, while the tubes are typically made of copper. These collectors weigh 275 to 450 pounds when full, so wherever they are mounted, the structure has to be strong enough to carry this significant weight.

FLAT PLATE COLLECTORS

Flat plate collectors are the most widely used kind of collector in the world for domestic solar water heating and solar space heating applications. These collectors have an operating range from well below 0ºF to around 180ºF, which is precisely the operating range required for these applications. They are durable and effective. Flat plate collectors have a distinct advantage over other types in that they shed snow very well when installed in climates that experience significant snowfall. They are the standard to which all other kinds of collectors are compared. I only use flat plate collectors in systems I design or install and I highly recommend them.

EVACUATED TUBE COLLECTORS

While flat plate collectors are all essentially made the same way and perform the same way from one brand to another, evacuated tube collectors vary widely in their construction and operation. Evacuated tube collectors are constructed of a number of glass tubes. Each tube is made of annealed glass and has an absorber plate within the tube. During the manufacturing process, a vacuum is created inside the glass tube. The absence of air in the tube creates excellent insulation, allowing higher temperatures to be achieved at the absorber plate. Their similarity, however, ends there.

CONCENTRATING COLLECTORS

A concentrating collector utilizes a reflective parabolic-shaped surface to reflect and concentrate the sun's energy to a focal point where the absorber is located. To work effectively, the reflectors must track the sun. These collectors can achieve very high temperatures because the diffuse solar resource is concentrated on a small area. In fact, the hottest temperatures ever measured on the earth's surface have been at the focal point of a massive concentrating solar collector. Concentrating collectors have been used to make steam that spins an electric generator in a solar power station. This is sort of like starting a fire with a magnifying glass on a sunny day.

POOL COLLECTORS

The single largest application of active solar heating systems is in heating swimming pools. Special collectors have been developed for heating seasonal swimming pools: they are unglazed and made of a special copolymer plastic. The collectors don't have to be glazed because they are only used when it is warm outside. These collectors cannot withstand freezing conditions.

AIR COLLECTORS

Up to this point, all the kinds of collectors we have talked about have used a liquid as the heat transfer mechanism. Air can also be used as the heat transfer mechanism in a solar collector. Air collectors are flat plate collectors in size and construction. Instead off an absorber plate made of copper piping and copper fins, the absorber plate in an air collector is typically made of a solid sheet of aluminum. The aluminum absorber plate is coated with a selective surface or black paint and is usually dimpled to increase efficiency. When the sun shines on the absorber plate, it gets hot. Air is drawn from the building and is blown across the back of the absorber plate and heated. The hot air is then delivered to the building through ductwork. A blower circulates the air through the system.