A Comparison of Predicted to Measured Photovoltaic Module Performance

Published

March 1, 2009

Author(s)

Arthur H. Fanney, Brian P. Dougherty, Mark W. Davis

Abstract

Computer simulation models to accurately predict the electrical performance of photovoltaic modules are essential. Without such models, potential purchasers of photovoltaic systems have insufficient information to judge the relative merits and cost effectiveness of photovoltaic systems. The purpose of this paper is to compare the predictions of a simulation model, developed by Sandia National Laboratories, to measurements from photovoltaic modules installed in a vertical wall fa ade in Gaithersburg, MD. The photovoltaic modules were fabricated using monocrystalline, polycrystalline, tandem-junction amorphous, and copper-indium diselenide cells. Polycrystalline modules were constructed using three different glazing materials 6-mm low-iron glass, 2-mm ethylene-tetrafluoroethylene copolymer (ETFE), and 2-mm polyvinylidene fluoride (PVDF). In order to only assess the simulation model s ability to predict photovoltaic module performance, measured solar radiation data in the plane of the modules is initially used. Additional comparisons are made using horizontal radiation measurements. The ability of the model to accurately predict the temperature of the photovoltaic cells is investigated by comparing predicted energy production using measured versus predicted photovoltaic cell temperatures. The model was able to predict the measured annual energy production of the photovoltaic modules, with the exception of the tandem-junction amorphous modules, to within 6% using vertical irradiance measurements. The model over predicted the annual energy production by approximately 14% for the tandem-junction amorphous panels. Using measured horizontal irradiance as input to the simulation model, the agreement between measured and predicted annual energy predictions varied between 1% and 8%, again with the exception of the tandem-junction amorphous silicon modules. The large difference between measured and predicted results for the tandem-junction modules is attributed to performance degradation. Power measurements of the tandem-junction amorphous modules at standard reporting conditions prior to and after exposure revealed a 12% decline. Supplying post-exposure module parameters to the model resulting in energy predictions within 5% of measured values.

Citation

Journal of Solar Energy Engineering-Transactions of the Asme

Report Number

7335

Volume

131

Issue

2

Pub Type

Journals

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Keywords

copper-indium, measured, module performance, monocrystalline, photovoltaic, polycrystalline, tandum-junction amorphous

Citation

Fanney, A. , Dougherty, B. and Davis, M. (2009), A Comparison of Predicted to Measured Photovoltaic Module Performance, Journal of Solar Energy Engineering-Transactions of the Asme, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=861022 (Accessed April 23, 2024)