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Solar Collector Technologies
Solar panels are used to convert the incident solar radiation into thermal energy.
The solar panels are divided into flat solar collectors and vacuum collectors.
The flat collector of black or semi-selective dye is a simple type of collector for
converting solar energy into heat.
It consists of copper piping through which circulates the heat transfer medium
(water or a mixture of water-glycol) which are in contact with a black copper or aluminum sheet (absorber).
To reduce heat losses, the absorber is placed inside an insulated housing, which on one side has a transparent
glass pane to allow the entrance of solar radiation. Flat collectors are used for heating water as well as space heating.
Source: CRES, TRASOL, Training material in the field of solar thermal systems
The flat selective collector is a flat collector, using a selective surface absorber instead of a simple black.
The black dye has been replaced by a high absorption material (~ 95%) and low radiation (~ 5%).
By using a selective absorber, higher efficiencies and higher water temperatures are achieved.
Flat selective collectors are used for domestic heating water as well as for heating and air conditioning of a place.
Vacuum collectors consist of series of parallel glass tubes. Each individual pipe is discharged to reduce
thermal losses. Tubular geometry is statically necessary due to the pressure difference between atmospheric
pressure and the vacuum in the interior. Inside each pipe there is a flat or curved aluminum plate attached to
a metallic (usually bronze) or glass tube. The aluminum plate is coated with a selective material. The heat transfer fluid
is water and circulates in the piping.
Some vacuum tube collectors have external mirrors behind the vacuum tubes or in the glass pipes.
Exterior mirrors increase the radiation collected by the collector, since usually the radiation passing through the empty space between the tubes is led back to the absorber. The use of the vacuum reduces the heat losses of the collectors and aims to further increase the efficiency and water temperature.
Vacuum collectors are used for space heating and air conditioning and under special conditions for water heating.
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