A device used to collect, absorb, and transfer solar
energy to a working fluid, such as water or air. The solar heat can
be used for heating water, to back up heating systems, or for heating swimming
pools.The heart of a solar collector is the absorber,
which is usually composed of several narrow metal strips. The carrier fluid
for heat transfer flows through a heat-carrying pipe, which is connected
to the absorber strip. In flate-plate absorbers, two sheets are sandwiched
together allowing the medium to flow between the two sheets.
Types of solar collector include:
How much energy does a solar collector provide?
The efficiency of a solar collector is defined as the quotient of usable
thermal energy versus received solar energy. Besides thermal loss there
alwas is optical loss as well. The conversion factor or optical efficiency
h0 indicates the percentage of the solar rays penetrating the transparent
cover of the collector (transmission) and the percentage being absorbed.
Basically, it is the product of the rate of transmission of the cover and
the absorption rate of the absorber.
| Efficiency graph of solar collector
The heat loss is indicated by the thermal loss factor or k-value. This is
given in watt per m2 collector surface and the particular temperature
difference (in °C) between the absorber and its surroundings. The higher
the temperature difference, the more heat is lost. Above a specific temperature
difference, the amount of heat loss equals the energy yield of the collector,
so that no energy at all is delivered to the solar circulation system. A
good collector will have a high conversion factor and a low k-value.
|Type of collector
||Thermal loss factor (W/m2
||Temp. range (°C)
||0.82 - 0.97
||10 - 30
||up to 40
||0.66 - 0.83
||2.9 - 5.3
||20 - 80
||0.81 - 0.83
||2.6 - 4.3
||0.62 - 0.84
||0.7 - 2.0
||50 - 120
||20 - 70
||0.75 - 0.90
||8 - 30
||20 - 50
Which collector is suitable for which situation?
The desired temperature range of the material to be heated is the most important
factor in choosing the correct type of collector. An uncovered absorber
is certainly not suitable for producing process heat. The amount of radiation
on that spot, exposure to storms, and the amount of space must all be carefully
considered when planning a solar array.
| Graph of efficiency and temperature
ranges of various types of collectors
(radiation: 1000 W/m2)
The specific costs of collectors are also important. Evacuated-tube collectors
are substantially more expensive than flat-plate collectors or even plastic
absorbers. However, a good collector does not guarantee a good solar system.
Rather, all components should be of high quality and similar capacity and
ENERGY AND POWER