How to explain the evolution of thermal coefficients of SPRING panels?


The SPRING 425 is the result of a continuous improvement process that has allowed a steady increase in thermal and electrical performance.

Since we sold the SPRING model with its polypropylene exchanger, the product has been improved several times (SPRING 280, SPRING 300, SPRING 315, SPRING 375, SPRING 400 and now SPRING 425) always with the objective of improving performances.

The SPRING 425 as its name suggests is more powerful. Indeed, the photovoltaic part goes from 375 W to 425 W and the heat exchanger on the rear face goes from 1.4m² to 1.6 m². It is therefore more powerful both electrically and thermally

Thermal performance is determined by independent bodies (KIWA, TÜV) using standard conditions (Conditions STC) on which we base our claims.

In march 2023 the change of certifying body (from KIWA to TÜV) for the SPRING 425 saw a slight drop in our thermal performance. This is in no way a drop in our performance but is linked to the test conditions which are not 100% identical.from one laboratory to another. Indeed, if we compare the performance of the same panel between the laboratories, we find very different results. :

  • KIWA laboratory seems to overestimate the thermal coefficients. The SPRING 375 had an A0 coefficient of 63.3% with the KIWA while it is 44.38% with the TUV

  • SPRING 425 has an A0 coefficient similar to that of SPRING 375 tested at TUV. There is a slight decrease, linked in particular to the increase in the efficiency of the photovoltaic cell. But as the exchanger is larger, the power of the SPRING 425 per panel remains higher than that of the SPRING 375


SPRING 375 non insulated

SPRING 375 non insulated

SPRING 425 non insulated 

Certifying body




panel area (m²)




A0 (%) (h=1.3m/s)




A1 (W/(m²K)) (h=1.3m/s)




power panel (Wth)
G = 1000W/m²
(Teau-Tair) = 0 K
u=0 m/s





> To go further: What are the technical characteristics of the SPRING exchanger?