Absorber
At the heart of every good panel is the absorber. This is the black looking surface which reacts to light to generate heat energy. On every panel there is such a surface which when light strikes it there absorber’s surface molecules vibrate, which causes friction. Friction creates heat and thus the process of vibration turns the energy in light into heat, which is captured by the panels.
There are different types of absorber surface. Virtually every type provides the same energy in direct sunshine; there is a limited amount of energy in a given are of light so in optimum conditions all panels perform similarly. Different types of absorber coatings have different performance values in non optimum conditions.
Black paint
is the lowest grade of absorber. It works well in very hot countries where the energy levels to raise the heat of water are such that you do not need as much energy as you need as in temperate climates. A black painted coated absorber will produce little heat in winter in the United Kingdom and although it will produce good heat in summer, the recovery time, after the heat is extracted, will be relatively long.
==Anodised coatings== (called selective coatings) are the best type of coating for most domestic water heating applications. The absorber surface is anodised, sometimes with aluminium oxide and sometimes with copper, so that if you looked at it under a microscope you would see hills and valleys which create a larger surface area for light to strike than simple paint. These coatings have a quicker recovery time. They are fragile, in the sense that if you touched the absorber surface it would mark, but as these surfaces are protected by glass, you cannot damage them.
Selective coatings last for many years unless they are installed close to a body of salt water. Salt in the air will fill the valleys of the surface over a period of time and reduce the absorber efficiency.
is used as an absorber coating, mainly in the United States, because it provides more heat and a quicker recovery time. European manufacturers, where the technology is more advanced, do not use black chrome because of the health risks in the manufacturing process.
provides the hottest coating of all in low light conditions with the shortest recovery time. It pergorms marginally worse than aluminium in high insolation.It is an expensive coating and there is no health risk. The stagnation temperature of an aluminium selective coated panel is around 175°C but the titanium oxide coating reaches and stagnates at around 230°C.
This level of heat generated by titanium oxide is unsuitable for domestic installations except when you use the solar panels for air conditioning support. In winter they will perform excellently but in a home in summer they will generate more energy than you will ever need, and that will mean “dumping” the heat and risking the panels overheating and warping as a result. Generally selective coating using aluminium oxide, as is used in genersys panels, is hot enough and properly balanced for domestic installations.
For commercial applications the titanium oxide panel should be default, especially in places where your solar system will never catch up with all the heat requirements, such as a hospital which needs a constant supply of jot water. In these cases a solar system can make an excellent contribution to the heat energy demand.
Of course there is much more to a solar panel than the absorber; the integrity of the casing pipe work and construction is important too, otherwise you will be climbing on the roof to service or repair them frequently, something to be avoided.