Active Solar Heat Technologies

A solar collector is a device that captures solar heat and transfers it to heat water most commonly for sanitary hot water production, or in cases where a building has a very low heat demand, then often for both space heating and hot water. Larger scale active solar thermal technologies can also be used for cooling and steam production. Steam produced in this way can be used to drive turbines for electricity production.

Active solar heat technology produces heat for heating either water or air. Air heating solar collectors can be used to directly assist with space heating through the ventilation system of the dwelling. Solar air systems are of greater benefit in airtight houses with low energy demands. Water heating solar collectors are the most commonly encountered of the two.

• Flat Plate Collectors: Building-mounted flat plate collectors can be positioned both "in-roof" and on-roof due to their structure (heavy, rigid, robust box-like structure). The efficiencies of flat plate collectors make them very suitable for domestic installations or for installations where very high temperatures aren't required. They are often considered to be more optically appealing due to their flat surfaces, but this is a matter of personal choice.
• Evacuated Tube Collectors: Building-mounted evacuated tube collectors can only be mounted on-roof due to their lightweight structure, which is most commonly individual tubes monted on a frame. On average, an evacuated tube collector will provide approximately 20% more yield per m2 of aperture area than flat plates, which means that less installed area is required for similar heat outputs. High efficiencies from low radiation and high temperatures (very useful where high temperatures are needed in process/industry)

There are other categories of solar collectors which you might encounter, and most of them fall within the flat plate or evacuated tube categories above. Efficiencies vary from collector to collector and the main effect that the efficiency will have is on the amount of installed area required, i.e. the more efficient the collector the less installed area required. For further technical information, go to Solar thermal FAQ's.