Location Guide: Solar Basics Solar Heating Collectors

Solar Thermal Cornwall

Solar Heating Collectors come in three basic type: flat plate, evacuated tube and concentrating collectors.

Flat-Plate are the least efficient, they consist of a well insulated and weatherproof container which holds an absorber plate below transparent covers. Water flows through the pipes located below the absorber plate and as it does so it is heated. This type of solar thermal energy collector, although it is in many ways inferior to tube collectors, is still the most common type of collector in a large part of the world.

Evacuated Tube solar water heaters use parallel rows of glass tubes. These tubes are one of several types (sometimes referred to as Solar Tubes).

Glass-Glass (Type 1) tubes consist of two glass tubes located one inside the other, they are then fused at one end. A surface to absrob solar energy is coated across the inner tube, this accepts the heat and inhibits radiant heat loss. The air is evacuated (sucked out) from the space in between the glass tubes in order to form a vacuum. This cuts down heat loss as there is no medium for conductive heat loss. These tubes perform very well in overcast conditions as well as low temperatures. Because the tube is 100% glass, the problem with loss of vacuum due to a broken seal is greatly minimized. Glass-glass solar tubes may be used in a number of different ways, including direct flow, heat pipe, or U pipe configuration. Apricus uses a high efficiency heat pipe and heat transfer fin design to conduct the heat from within the evacuated tube up to the header. For more information about heat pipes, click here.

Type 2 (Glass-Metal) tubes consist of a single glass tube. Inside the tube is a flat or curved aluminium plate which is attached to a copper heat pipe or water flow pipe. The aluminium plate is generally coated with Tinox, or similar selective coating. These type of tubes are very efficient but can have problems relating to loss of vacuum. This is primarily due to the fact that their seal is glass to metal. The heat expansion rates of these two materials. Glass-glass tubes although not quite as efficient glass-metal tubes are generally more reliable and much cheaper.

Type 3 (Glass-glass - water flow path) tubes incorporate a water flow path into the tube itself. The problem with these tubes is that if a tube is ever damaged water will pour from the collector onto the roof and the collector must be "shut-down" until the tube is replaced.

Concentrating collectors for are usually parabolic troughs that use mirrored surfaces to concentrate the sun's energy on an absorber tube (called a receiver) containing a heat-transfer fluid, or the water itself. This type of solar collector is generally only used for commercial power production applications, because very high temperatures can be achieved. It does need direct sunlight and does not perform well in overcast conditions.

The Stove Shop are experienced installers of Apricus across Cornwall, Devon, Dorset and Somerset, for more information on have your solar panels installed, click here.