Why does the non-insulated DualSun SPRING panel perform better at low temperatures?

• a0 = Panel optical efficiency
• a1 = Loss coefficient [W/K/m²]
• u = Wind speed [m/s]
• A = Panel area [m²]
• G = Solar irradiation [W/m²]
• ∆T (water-air) = Tm - Ta [°C]
• Tm = Average temperature of the fluid in the panel = (Tin + Tout) / 2 [°C]
• Ta = Ambient air temperature [°C]

Mathematical explanation

The coefficients a0 of the insulated and non-insulated SPRING panels are very close

Values obtained in standard test conditions (STC), for an ambient temperature of 25°C under 1000W/m2 of sunlight.

• The difference in thermal performance between insulated and non-insulated SPRING panels lies mainly in the term "- a1.A.∆T(water-air)".
• When the fluid temperature is lower than the ambient air temperature the term "∆T(water-air)" is negative.
• Thus the term "- a1.A.∆T(water-air)" becomes positive and is added with the term "a0.A.G" in the calculation formula.

Physical explanation

The non-insulated version of the SPRING panel recovers more energy from its environment (air) when the water flowing through the panel is cooler than the ambient air. 

When the fluid flowing through the panel is cooler than the ambient air, the photovoltaic cells are also better cooled, which limits energy losses through the front face of the panel.

What is the thermal performance of the DualSun Spring panel?

PV/T thermal performance explained