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Solar thermal energy: types of solar collectors Factor

The use of solar thermal solar thermal or is a major source of renewable energy that own other pledgible energy from the sun.

These technologies base their operation in a thermal fluid heating using solar collectors for later use.

Among the various applications of solar thermal include:

• hot water production.
• Heating.
• Solar cooling.
• Conditioning swimming pool water.

Each application requires different working temperatures of the thermal fluid and on the other hand, there is limited space for installation of solar collectors. Hence the need to consider the most appropriate type of sensor in each case.

Types of solar collectors available on the market are the following:

• unprotected flat collectors, consisting of a box whose base is a metal plate in black. These plates are united in their post-serpertín face through which circulates the heat transfer fluid (usually water with antifreeze). Estos captadores presentan bajo rendimiento y son adecuados para bajas temperaturas (hasta 80 ºC).

• Captadores planos con protección, idénticos a los planos si protección pero añaden un vidrio protector transparente en su parte superior. Este vidrio provoca una especie de efecto invernadero al no ser opaco a la radiación infrarroja que emite la plancha metálica de color negro. Mejoran el rendimiento de los captadores planos sin protección y son adecuados para bajas temperaturas (hasta 80 ºC).
• Panel de tubos de vacío, la superficie captadora está aislada del exterior por medio de un doble tubo de vidrio which creates a vacuum chamber. Present or superior performance to the sensors are suitable for flat and low temperatures (up to 80 º C).

• parabolic collectors: they have the same performance levels that the sensors with the difference that the solar panel section has a parabolic shape by concentrating all the solar radiation onto a tube that circulates the fluid to be heated. They feature high performance and are suitable for high temperature (from 125 º C).

The performance of solar thermal collectors must be considered when designing an installation. Manufacturers provide coefficients for the yield curves of the sensors, these curves are of the form:

R = R 0 - K (T m-T to ) / I

Where:

R is the performance of the sensor.

0 R is the optical factor or maximum possible performance of the sensor.

K is the loss factor T

m is the average fluid temperature in the collector (° C)

to T is the temperature (° C)

I is the incident solar radiation (W/m2)

So the greater the temperature difference between mean fluid in the collector (T m ) and temperature (T to ) the lower the yield by increasing the losses by increasing the heat output of the sensor to the surrounding environment.

When making a correct design of a solar heating should calculate the average seasonal performance throughout the year, which is a function of

• geographical location.
• Orientation sensors.
• tilt the collectors.