Sebastian Dittmann

kWh/Wp measurements & predictions of 13 different PV modules

At the begin of 2009 the Swiss PV module Test Centre at SUPSI-ISAAC started a new measurement campaign investigating thirteen different modules commercially available on the market. Two modules of each type have been exposed outdoors for energy yield monitoring and a third module, stabilised in advance, has been stored indoors as a reference. The modules covered a large range of different technologies ranging from multi-crystalline silicon (mc-Si) of which two with back-contact cells, 3 single-crystalline silicon (sc-Si), 1 hybrid mono-crystalline technology with amorphous silicon layer (HIT), 1 double junction amorphous silicon (a-Si/a-Si), 1 micromorph (a-Si/μc-Si), 1 Cupper-Indium-Sulfide (CIS) and 1 Cupper-Indium-Gallium-Diselenide (CIGS). The aim of the measurement campaign was to assess the quality of current technologies and the understanding of observed differences between technologies. Outdoor and indoor performance of the modules were analyzed over 15 months performing measurements under real operating conditions. The modules were therefore installed on a ventilated rack where each single module was connected to a maximum power point tracker delivering Im, Vm values in minutes intervals. The indoor measurements consisted in regular measurements under standard test conditions (STC) and 200W/m2, to determine the stability of the devices over time, and some initial temperature coefficient measurements and measurements at different irradiance levels. The annual energy output in kWh/Wp was calculated and simulations were performed based on the indoor measurements. The scope of the simulations was to explain the differences in energy output, by quantifying the losses generated by the two primary mechanisms: the temperature effect given by the temperature coefficient and the efficiency loss at low irradiances. Requirements for future energy rating of PV modules are given together with a discussion about the involved measurement uncertainties.

Current-soaking and dark storage effects of polycrystalline thin film solar modules

Polycrystalline thin film modules as CIS and CdTe are known to exhibit metastabilities and performance changes with light exposure or dark storage. In this report the behavior of CIS and CdTe modules from different manufactures is investigated in terms of dark storage after a prolonged outdoor exposure and short preconditioning with current-soaking (CS), An approach which could be used to preserve the metastable state- a condition closer to real operating conditions - of the modules during a period of storage in the dark. We observed power losses up to -2% in the first hour and up to -11% after 10 days of dark storage. By using current-soaking changes in power could be recovered for most of the tested modules.

Spectral responsivity of WPVS reference cells under varied temperatures and its influence on performance measurements beyond STC

The authors present the results of a study which investigates the temperature dependence of the spectral responsivity of WPVS reference cells and its influence on measurement uncertainties for performance measurements beyond standard test conditions (STC). Five crystalline unfiltered reference cells from three different manufacturers were spectrally characterized at different temperatures. The authors calculated the temperature coefficient of the reference cells at different wavelengths and temperature ranges and showed significant deviations from the temperature coefficient of the calibration certificate. However, it is shown that the tested commercial reference cells have a non-linear behavior for a temperature range of 25 to 60°C and therefore they cannot be used for measurements at high temperatures e.g. outdoor applications or temperature coefficient measurements. The report demonstrates how this affects performance measurements above 25°C.

High-speed multi-channel system for solar simulator irradiance non-uniformity measurement

We present a new tool for the measurement of the non-uniformity of a large-area pulsed solar simulator according to IEC 60904-9. We realized a prototype portable unit that can be controlled via a single USB port of a notebook. The system is composed by several photovoltaic cells and a series of custom designed electronic boards, allowing a high-speed multi-channel sampling of a single pulse. We describe the main components and the design solution, which is using readily available standard electronic and software components, allowing a possible industrialization of the system. Finally we present preliminary results of the prototype unit testing.