1.1 Evaluation strategy

Any attempt to measure slight differences in efficiencies (in the percent range) on complete modules is likely to be successful only if a large number of modules are monitored over long period of times. This is because it is far from trivial to prepare modules with similar initial efficiency (current mismatch between the cells, serial connections) and because it is not easy to measure complete modules before and after lamination. Ab-initio simulations of the optical properties of complete systems are also highly difficult, since several unknown parameters would have to be taken into account (surface structure of the cells, internal reflection at the backside of the cells, internal reflection inside the glass). Therefore we adopted the following experimental strategy to be able to predict as accurately as possible the efficiency gain in STC conditions (which will give the nominal gain in Wp of the module) and the total yearly energy yield (which is the quantity of interest for the operator of a PV system):

Selection of 24 standard multi-crystalline silicon solar cells with SiN antireflection layer, front screen-printed Ag and back Al contacts. Prior to measuring, all cells are tabbed with tinned-copper strings (normally used for cells interconnection)

• Measurement of the efficiency and of the short-circuit current Isc under STC (AM1.5g, 25°C), measurement of the spectral response and of the angular response of the cells. On this base, two similar groups of 11 cells are prepared. 2 cells are kept for calibration purpose.

• Individual encapsulation of each solar cell in mini-modules, in a standard Glass/EVA/Cell/EVA/Tedlar structure. The EVA foils are 1 mm thick and a curing temperature of 157°C was applied for 11 minutes. 11 Cells are prepared with the AR glass, 11 without.

• Repetition of the measurements with the mini-modules

• Preparation and outdoor monitoring of 2 modules (18 W each) with and without AR layer to evaluate temperature effects given by the aR layer

• Simulation of the expected yearly energy yields using a specially developed software (Real Reporting Conditions Rating [10]) using a meteorological database and taking into accounts all the parameters measured on the mini-modules.