Measuring and modeling the effect of snow on photovoltaic system performance

Today's demanding project financing climate requires developers to hone annual photovoltaic (PV) energy estimates with unprecedented accuracy - and to back the estimates with meaningful long-term performance guarantees. With some snowy locales in the U.S. and southern Canada becoming increasingly popular for MW-scale PV systems, lenders are now requiring that snow losses be estimated as part of their energy simulations. The literature is exceptionally thin on this subject - we have been unable to find even a single side by side study that directly quantifies the difference between an always-clean array versus an identical one left to naturally accumulate and shed snow. This paper describes the design and reports results for a side by side PV test bed installed in California near Lake Tahoe in December 2009. It has been designed to gauge the energy loss due to snow for three common tilt angles. Results from the first winter are presented, with insights for future model development and ongoing measurements.