Solar thermal collector#Flat plate collectors
As a flat-plate collector, a certain building type of solar panels is called. The main feature is the orientation of a flat planar absorber surface to the sun ( no curvature, no concentration ). Flat-plate collectors are used for heating of swimming pool water, mixtures of water and antifreeze and air used.
Dissemination
On the German market, by far the largest in Europe, dominate insulation material insulated flat plate collectors compared to vacuum tube collectors at a ratio of 9:1. Vacuum flat solar panels are a niche product. Technically, the 'normal' collectors of the evacuated distinguished by the insulation or the related details in cover, frame and rack.
Construction
Cover
The cover has the task of the solar radiation - as completely as possible to allow the interior of the collector, and to prevent the escape of heat in the form of flow and possible radiation - even with a flat angle of incidence.
The material most commonly used is solar glass, sometimes even anti-reflection treated. For DIY projects often inexpensive garden Blank glass is used.
Plastics are largely disappeared from the market due to their limited resistance to UV radiation, heat, frost and others. Only in the area of the swimming pool absorbers ( the shrunken on the central component flat plate collector type ), there are still applications with black dyed polypropylene and EPDM.
Absorber
Today's flat-plate collectors are most commonly implemented as a copper absorber. In the 1980s, aluminum absorbers were common, this could not prevail over the long term mainly electrochemical reasons: Due to mixed installations with copper pipe special heat transfer fluids were used. After about 10 years of operation, however, showed damage due to errors during commissioning or maintenance. Absorber future based on aluminum are in development.
The aluminum absorber mainly used in the Mediterranean area (some with aluminum, some with copper piping) are usually coated with so-called stovepipe or thermal coatings. Such coatings are heat resistant up to 400 ° C. The lower efficiency is largely compensated by the higher average sunshine duration and ambient temperature in these areas.
Surface coating
Decides the coating adjacent to the insulation and the properties of the glass on the solar performance of the collector. You should be highly selective, that is capable of capturing much more than 90 % of the incident short-wave radiation ( approximately 300-3500 nm wavelength) by absorption, but give less than 10% of the absorbed energy again in the form of long-wave radiation emission.
Historically, it has been electrodeposited coating by a black chromating, the so-called black chrome. This layer contains hexavalent chromium, which is considered to be carcinogenic. Therefore, this type of coating has already product liability reasons, only a very small market share. Newer coatings not only allow higher efficiencies, but are also under production and recycling aspects as environmentally friendly.
The most common one applied by cathode layer on titanium base with blue color distinctly lower emissions is achieved as black chrome today.
This - English sputtering called - process is a physical process in which atoms of a solid body ( target) by bombardment with energetic ions (mainly noble gas ions) are released and pass into the gas phase, in order to subsequently deposit on the body to be coated.
These first production coatings of this type have been developed in the form of titanium - nitride-oxide coatings in Germany and brought by the company TiNox on the market. Another new development is a coating of Alanod - Sunselect. It is a ceramic -metal structure (presumably also the titanium-based ), which is applied as the titanium -nitride-oxide - coating in a vacuum sputtering method and also black blue shimmering. Since 2005 is available from a new BlueTec and now used by leading manufacturers of copper coating on the market.
Assembly
To connect the absorber plate with the copper pipe register, there are several possibilities.
After application frequency, these methods are commonly used:
- Ultrasonic welding
- Solder
- Plasma and laser welding
Currently, laser welding is technologically pioneering. In most cases, a whole surface is connected to the entire register. Alternatively, an absorber strip ( so-called fin ) can also vary depending connect to a copper pipe. Full-surface absorber now dominate over fin absorbers approximately in the ratio 4:1.
Another production method is the roll- bonding.
Thermal insulation
The insulation will keep heat losses from the collector to the sun side facing away from ( = back) as low as possible.
In solar panels only temperature resistant insulating materials can be used due to the high temperatures at idle. Especially, for example, mineral wool or foam glass are suitable; also requires wood fiber insulation boards are used. Polyurethane foam and others are only usable in less wear area. Gas-filled insulations are - depending on the material thickness - slightly less insulating than a vacuum, so anything larger collector are required to achieve comparable performance levels, especially at very low ambient temperatures or at a high temperature difference between the outside air and the intended use temperature. Under economic view ( price / performance) are insulated with the insulation flat plate collectors but much more efficient.
Framework
The frame has the task of holding together (side and back) of the components, as well as the stabilization during transport and wind stress.
Also used wood - Besides aluminum and plastic profiles is - eg panels, which are used as roof replacement.
Frame
The frame provides the connection to the site. Especially in free-standing panels, but also at elevated collectors these constructions should be carried wind, storm and weather resistant.
In addition to aluminum and stainless steel and galvanized steel and titanium zinc is used (especially as a sheet metal ). In eingeblechter form can also be used as a static timber supporting material.