How does the thermal efficiency of a Dualsun panel compare to that of a conventional solar thermal module?

In terms of thermal efficiency, Dualsun SPRING hybrid panels are different from conventional solar thermal panels.

 The main difference lies in the front face of the panels.

A solely thermal solar panel consists of a double-glazed front panel, which makes it possible to create a greenhouse effect, while the Dualsun panel is covered with photovoltaic cells, therefore with single glazing.

The performance of thermal and hybrid solar panels is described by the following coefficients:

• a0: The optical yield, which represents the percentage of incident solar radiation that will actually be absorbed by the solar collector. It characterizes the transparence and absorptive capacity of the collector. The close this value is to 1, the better the quality of the collector in this respect.

• a1 (measured in W/K⋅m²): The first-order coefficient, representing the constant-percentage losses, due to conduction and convection essentially. The smaller this number is, the lower these losses are and the better the collector is in this respect.

• a2 (measured in W/K²⋅m²): The second-order coefficient, which describes those losses which increase as a function of temperature, due to infrared radiation essentially. Again, the smaller this number is, the lower these losses are and the better the collector is in this respect.

 The following table provides a comparison of these coefficients in a conventional solar thermal panel and a Dualsun SPRING panel:

*Sample coefficients for a commercially available solar thermal panel

We find that hybrid solar panels do not have the same performance as solar thermal panels.

This is normal and in fact intentional: the Dualsun SPRING panel was designed not to rise to very high temperatures so as not to negatively impact photovoltaic production. At the same time, this eliminates the risk of thermal overheating.

This way the stagnation temperature of a Dualsun panel never exceeds 80°C, while a conventional solar thermal panel can reach temperatures well above 100°C and consequently bring the heat transfer fluid to a boil.

By its very design, a Dualsun SPRING panel is therefore unable to reach hot water temperatures as high as a conventional thermal panel.

The normal operating temperatures of Dualsun hybrid SPRING panels are approximately:

• Summer: 55-60°C

• Spring/Autumn: 40-45°C

• Winter: 30-35°C

Thus it is necessary to plan for a larger hybrid panel area to achieve a coverage of domestic hot water needs similar to that of a conventional solar thermal installation, around 1.5-2 times more area depending on the application.

However, a Dualsun installation, compared to side by side photovoltaic (PV) and thermal (TH) modules rated at the same power, will take up 30% less roof space.

For reasons of aesthetics, space, durability and performance, the Dualsun SPRING panel is favorable. 

Also see the following thermal performance study, conducted by Transénergie, which shows that Dualsun panels can meet the annual coverage rate of hot water.

To better understand how the thermal performance of solar panels is calculated click here.