Davide Strepparava

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.

Modeling the performance of amorphous and crystalline silicon photovoltaic modules for different types of building integration conditions

In this work we use and further elaborate a model which has previously been proposed to model the daily energy performance of amorphous (a-Si) and crystalline silicon (c-Si) photovoltaic solar modules under real operation conditions. In the present work we expand the simulations to model, besides a conventional ventilated free-rack mounted installations (south-facing, 45° tilt), the performance of the same technologies to include BIPV installations conditions. For simplicity, we consider two extreme cases: (a) a south-facing façade installation (90°) and (b) a perfectly horizontal one (0°). The angle-of-incidence AOI response of the modules is then used to model reflection losses. Further, fully integrated PV modules -compared to ventilated ones - exhibit average operating temperatures that can reach +20°C differences in days of clear sky conditions. These offset is used to model the operating temperatures - and performance losses - BIPV modules.

Modeling the performance of amorphous silicon photovoltaic modules for different geographical locations in North-America

In this work we use and further elaborate a previously proposed approach which models the energy performance of an amorphous silicon (a-Si) PV module, including the well-known Staebler-Wronsky effect (typical for this technology). The extensions of the model to cover geographical locations representative of different climatic zones in North America (Mexico City, New Orleans, Seattle, and Fort St. John BC), using as solar and meteorological input parameters time series provided by GeoModel, shows that the model can be used to describe, the energy performance of a-Si and its very peculiar seasonal pattern. In addition it further reinforces the idea that this technology is more suited to warmer climates (SWE) and to latitudes (in the northern hemisphere) between 0 and 45°, due to the considerable spectral losses (on sunny days during which the most energy is produced) for this technology in winter time at high latitudes. Further, we show that for each site we are able to decouple spectral and SW effects, which are very specific to this technology, and act on similar time phases. SWE effects become more significant for warmer climates (Mexico City, New Orleans), whereas the impact of spectral losses are considerable at high latitudes (Seattle, Fort St John) in winter time.