Losses in a PV power system

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Irradiance loss

“Losses” of a PV array takes as starting point the energy which would be produced if the system worked always at STC conditions (1000 W/m², 25°C). One of the advantages of some amorphous modules, is that this “loss” is lower. Unisolar has even published efficiencies which constant or increased efficiency towards 150 W/m² . This is which explains (along with the temperature coefficient) why amorphous systems show a better productivity [kWh/kWp] than crystalline ones in middle Europe climates.

Most of PV modules series didn’t match the manufacturer nominal specifications. The real behaviour of modules by respect to the specifications has one of the greater uncertainties in the PV system performance evaluation.

Module Quality Losses

Module series are sold with a given tolerance, final flash-test assertions, and actual powers usually may lie under the nominal specified power, but stay in the tolerance. The Module quality loss is a parameter that expresses your own confidence to the real module’s performance, by respect to the manufacturer’s specifications.

Array Mismatch losses

Losses due to “mismatch” are related to the fact that the real modules in the array do not rigorously present the same I/V characteristics. A graphical tool helps for visualising the realistic behaviour of such an array, with a random dispersion of the characteristics of short-circuit current for each module.

Array wiring losses

The wiring ohmic resistance induces losses ( R · I² ) between the power available from the modules and that at the terminals of the array. These losses can be characterised by just one parameter R defined for the global array

AC Wiring losses

The AC wiring losses may simply be defined by the distance between the inverter and the injection point.

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