Comparison of Predicted to Measured Module Performance.
Comparison of Predicted to Measured Module Performance.
(287 K)
Fanney, A. H.; Dougherty, B. P.; Davis, M. W.
ES2007-36028; Session: 11-2 Solar Power Testing;
Energy Sustainability (ES2007). Session: 11-2 Solar
Power Testing. Proceedings. June 27-30, 2007, Long
Beach, CA, 1-15 pp, 2007.
Keywords:
computer simulation; photovaltaic module;
specifications; parameters; irradiance; temperature;
radiation measurements
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 facade
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 overpredicted 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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899