The thermal power output (Wth/m2) listed on the front page of the technical data sheet is a normative value calculated from the η0 coefficient (0.57) determined during the Solar Keymark certification (n°011-7S2783 P) and a reference insolation G = 1000 Wth/m2:
Thermal power output = 0.57 x 1000 = 570 Wth/m2
The a0 and a1 values on the backside of the datasheet are characteristics used in modelling software to simulate thermal performances of panels with a wind applied in order to best simulate real-life conditions:
a0 = η0 – c6 * windspeed
a1 = c1 + c3 * windspeed
In the Spring datasheet, a windspeed of 1m/s is applied to determine a0 and a1 values in order to be consistent with module power values given on the first page of the Solar Keymark annex.