Testing PV modules in real conditions

The main aim of the outdoor I-V curve measurements of PV modules performed in a wide range of irradiance levels and changeable weather conditions is assessing of potential maximum energy yield of the modules in real conditions. The major differences of the outdoor and indoor measurements are the instability and wide variation of the outdoor irradiance, module temperature which follows irradiance with significant inertia. Additionally changes also spectral composition and diffused/global irradiance ratio as well as angle of incidence of the irradiance onto module’s plane. Assessing of modules outdoor performance is based on repeated (cyclic) I-V curve scans and further analysis of the acquired data.

PV Test Solutions offer turn-key installation of outdoor multichannel systems provided for long-term testing of PV modules under real operating conditions in order to:

• verify module’s rated power;
• characterize module’s energy rating and performance ratio;
• estimate module’s thermal behavior (thermal coefficients, NMOT);
• estimate module’s degradation rate.

Multiplexing measurements be a cost effective and flexible way to acquire both the complete IV curves as well as cumulated energy output of the PV modules. Our solutions offer can be combined with multiplexers to switch between IV curve measurement mode to MPPT device or passive load. The PV modules are connected to IV curve tracer unit via multichannel system that allow to measure up to 32 modules (or more on request) with only one measurement unit.

To estimate the degradation rates of photovoltaic modules the measured I–V curves need to be corrected to Standard Test Conditions. The installation includes pyranometer (or calibrated reference solar cell) for the measurement of incoming global solar radiation, located in the plane of the module and fast silicon sensor for verifying the stability of sunlight intensity during IV curve scan. Another parameter influencing the performance of PV modules is temperature. Measurement of actual PV module temperature is performed with specially enclosed miniature PT1000 sensor attached to the back side of modules. We also supply meteorological station in order to acquire following parameters: wind speed and/or direction, ambient temperature, relative humidity and air pressure (other parameters, e.g. diffuse irradiance, on request).