This type of technology bases its operation on the heating of a thermal fluid by means of solar collectors for its subsequent use.
Among the different applications of solar thermal energy, the following stand out:
Among the types of solar collectors available on the market are the following:
Flat collectors with protection, identical to the planes if protection but add a transparent protective glass on top. This glass causes a kind of greenhouse effect by not being opaque to the infrared radiation emitted by the black metal plate. They improve the performance of unprotected flat collectors and are suitable for low temperatures (up to 80 ºC). Vacuum tube panel, the capture surface is isolated from the outside by means of a double glass tube that creates a vacuum chamber. They have superior performance to flat collectors and are suitable for low temperatures (up to 80 ºC).
Parabolic collectors: they have the same operation as flat collectors with the difference that the section of the solar panel is shaped like a parabola concentrating all the solar radiation towards a tube through which the fluid to be heated circulates. They have a high performance and are suitable for high temperatures (from 125 ºC).
The performance of solar thermal collectors must be considered when designing an installation. Manufacturers provide coefficients corresponding to the performance curves of the collectors, these curves are of the form:
R=R0- K (Tm-Ta)/I
Where:
R is the performance of the collector.
R0 is the optical factor or maximum possible performance of the collector.
K is the loss factor
Tm is the average temperature of the fluid in the collector (ºC)
Ta is the ambient temperature (ºC)
I is the incident solar radiation in (W/m2)
Thus, the greater the difference between the average fluid temperature in the collector (Tm) and the ambient temperature (Ta), the lower the performance by increasing the losses by increasing the heat emission of the collector to the surrounding environment.
When making a correct design of a solar thermal installation, the average seasonal performance throughout the year must be calculated, which is a function of:
Geographical location.
Orientation of the collectors.
Inclination of the collectors.
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