This renewable solar energy system uses a type of solar panel consisting of linear collectors housed in evacuated glass tubes.
The evacuated tube solar collector consists of a set of cylindrical tubes. The tubes are formed by a selective absorber, located on a reflector settlement and surrounded by a transparent glass cylinder.
The vacuum has been made between the transparent outer tube and the inner absorber. With this, the thermodynamic losses by conduction and by convection from the absorbent surface are avoided and this fact allows to reach temperatures of more than 100 ° C and take much more solar radiation.
Types of solar collectors of evacuated tubes
Currently, there are two types of solar collectors of evacuated tubes, with techniques quite different in terms of heat transmission from the evacuated tube to the primary circuit.
- Evacuated solar collectors with direct fluid.
- Evacuated solar collectors heat pipe.
Evacuated solar collectors with direct fluid
On the one hand, the evacuated solar collectors with direct fluid, have a primary sensor of the primary circuit in the upper part of the collector; Each tube is connected to this sensor by means of a round circuit and a return circuit. Through this circuit the fluid of the primary circuit is circulated and heated during the course.
The inner circuits of the tubes present two basic configurations: the concentric circuit or separate circuit.
Evacuated solar collectors heat pipe
The other heat transfer trend in evacuated tubes is called heat pipe.
In this system, as in the previous case, the solar thermal sensors have a primary sensor of the primary circuit in the upper part. In this case, the evacuated tube has a sealed central copper tube filled with an alcoholic mixture. This tube is connected to the absorber of the solar collector by means of a condensing pipette. The condensing pipe will act as a heat transfer element to the primary circuit.
The solar radiation heats the absorber and evaporates the alcoholic mixture inside, which rises to the condenser located in the collector. At this point, the heat in the primary circuit will be released and the alcoholic mixture condensed, which will return to the lower part of the collector by its own weight.
One of the specific characteristics of this type of collectors is the possibility, depending on the model, to individually tilt each tube. This feature is very useful in the locations that, due to building requirements, it is necessary to mount the disoriented sensors of the south.
Operation of the evacuated tube solar collector
The insulating effect is achieved in the evacuated tube collectors by means of a evacuated in a glass tube or in the space of two concentrically arranged glass tubes. This technique greatly reduces the thermodynamic transfer of heat to the ambient air through reduced convective losses.
Especially in winter, evacuated solar collectors, due to their good insulation, obtain a thermal performance significantly higher than flat plate solar collectors, but thaw slightly in snow or ice cover. The resistance to very low temperatures is given as an average of -30 degrees Celsius.
Individual manufacturers cite the limit of 70 mm tubes at -50 degrees Celsius. However, frost protection must be provided at temperatures below -10 degrees Celsius for the lines. To make this protection, there are several possibilities. The most common solutions are antifreeze additives to heat the medium. For systems that work with pure water, the solar controller will control the temperature limits. If the temperature in the return drops to approximately 4 degrees Celsius, the heat from the storage tank or the alternative heating system is pumped to the solar system line system.