Thermal Solar Collectors
A solar thermal collector is a component of a solar thermal installation. A solar collector is a type of solar panel responsible for capturing solar energy and transforming it into heat. It is also called the solar thermal collector.
From solar collectors there are many types. The solar collector used will depend on the use that is going to be given. For example, if we want to heat a pool to a temperature of 25-28ºC, in the spring, we need a simple sensor, since the ambient temperature will easily be of this order or even higher. On the other hand, if we want to heat a fluid to temperatures of 200ºC, we will need concentration solar collectors to concentrate the solar radiation and transfer it to a small volume of fluid.
Types of solar thermal collectors
Currently, in the solar market we can differentiate the following types of solar thermal collectors:
- Flat solar collectors or flat plate collectors. This type of solar panel captures the solar radiation received on a surface to heat a fluid. The greenhouse effect is often used to capture the heat.
- Solar thermal collectors of concentration of solar radiation. This type of collector captures the received radiation in a relatively large surface and concentrates it by means of mirrors in a smaller surface.
- Vacuum tube thermal solar collectors. This solar thermal collector consists of a set of cylindrical tubes, formed by a selective absorber, located on a reflector settlement and surrounded by a transparent glass cylinder.
In low-temperature solar applications, that is, at temperatures below 80 ° C, such as swimming pool heating, the production of domestic hot water or even heating, mostly flat-plate thermal solar collectors are used, with or without glazed cover, depending on the application.
Connection of solar thermal collectors
When defining and assembling a solar thermal installation, it is necessary to take into account that solar collectors should be distributed in groups.
These groups of solar thermal collectors should always be formed by units of the same model and with a distribution as uniform as possible.
There are two basic options or types for grouping two or more sensors: serial or parallel type. In addition, you can configure a capture field by combining the two groups, which is what we call groupings or mixed circuits.
Connection of solar collectors in series
In the series connection, the output of the first solar collector connects directly with the input of the next, and so on consecutively. The temperature of the inlet fluid to each collector is higher than that of the previous collector, so that at the output of a group of collectors we can obtain higher temperatures than if we worked with the thermal jump of a single collector.
This type of connection has the disadvantage that the performance of the collectors decreases proportionally with the increase of the working temperature; therefore, this type of connection is only used in very specific applications, and with a maximum of 6 to 10 m2 of thermal solar collectors connected in series, according to the climatic zone.
Regarding the hydraulic behavior of this configuration, the total flow of the group of collectors will be the equivalent of the flow of a single collector and, on the contrary, the loss of load caused by the group will be the equivalent of the sum of the loss of charge of all solar collectors.
Connection of solar collectors in parallel
In the connection of solar collectors in parallel, both the output and the input of the collectors are connected to points of entry and exit common to the rest of the collectors.
With this configuration, the temperature of the inlet fluid is the same in all the collectors and the same thing happens with the exit temperatures, so that at the exit of the battery or the group of collectors we obtain the temperature as if we were working with the thermal jump of a single sensor.
Therefore, all the collectors work in the same point of the yield curve. This connection is the most common in low-temperature solar thermal installations.
Hydraulically, this configuration presents us with a total flow of the group, which is the sum of the partial flows of each collector, while the group's loss of charge will be equivalent to that of a single solar thermal collector.
Mixed collector connection
On some occasions, the volume of the collectors and / or the need for higher temperatures results in installations that combine the arrangement in series and in parallel. We call this type of connection of solar panels mixed.
Balancing of the catchment field
Basically, there are two methodologies to balance the flow of heat transport fluid in a field of solar thermal collectors:
Last review: May 29, 2018