In addition to the regional and local solar resources available, the efficiency of the solar collector plays a role in the overall amount of energy a system can absorb. Plenty of designs are out there but they generally fall into five categories: simple unglazed collectors, flat-plate collectors, evacuated-tube collectors, integral-collector storage, and concentrating collectors.
Simple, unglazed collectors work on the same principle that heats your garden hose when it is in the sun during the summer. It is simply a long tube put out in the sun through which water is pumped. It is really easy to build and can be used for solar showers and the like, but it is not as efficient as other types.
Flat-plate collectors are large and look somewhat like photovoltaic solar panels used to generate electricity. They have a frame with a glass front. Inside the frame is a series of pipes connected to a large metal sheet, usually painted black. As solar energy comes in, it heats the metal sheet and pipes. Water is pumped through to be warmed. This system is complex but approachable by the home tinkerer.
Evacuated-tube collectors use a metal rod and fin inside a vacuum tube to absorb heat, which is transmitted down the rod. The rods are inserted into a cavity that holds water to be heated. Water is pumped through the cavity to be warmed. A person with basic building skills could not create this system at home.
Integral-collector storage units have a large water reservoir in a larger box. The box is heavily insulated on five sides and covered with glass on the side facing the sun. The large vat of water is heated and then used directly. This cannot be used in places where deep freezes are possible, but it can be built fairly easily.
Concentrating collectors use a parabolic dish or mirror system to focus solar energy on a single pipe or small reservoir to heat the water inside. The orientation of these collectors must be changed throughout the day to follow the sun in order to achieve high temperatures. These are able to be built at home, but the control mechanism is likely to be difficult to build from scratch.
Tomorrow we’ll look at the types of collectors we’ll be testing as part of this project.