Prediction of Building Integrated Photovoltaic Cell Temperatures.
Prediction of Building Integrated Photovoltaic Cell
Temperatures.
(261 K)
Davis, M. W.; Dougherty, B. P.; Fanney, A. H.
Solar Energy: The Power to Choose. Forum 2001. April
21-25, 2001, Washington, DC, 2001.
ASME Journal of Solar Energy Engineering, Special Issue:
Solar Thermochemical Processing, Vol. 123, No. 2,
200-210, August 2001.
Keywords:
building integrated photovoltaics; performance
prediction; temperature; temperature model
Abstract:
A barrier to the widespread application of building
integrated photovoltaics (BIPV) is the lack of validated
predictive performance tools. Architects and building
owners need these tools in order to determine if the
potential energy savings realized from building
integrated photovoltaics justifies the additional
capital expenditure. The National Institute of Standards
and Technology (NIST) seeks to provide high quality
experimental data that can be used to develop and
validate these predictive performance tools. The
temperature of a photovoltaic module affects its
electrical output characteristics and efficiency.
Traditionally, the temperature of solar cells has been
characterized using the nominal operating cell
temperature (NOCT), which can be used in conjunction
with a calculation procedure to predict the module's
temperature for various environmental conditions. The
NOCT procedure provides a representative prediction of
the cell temperature, specifically for the ubiquitous
rack-mounted installation. The procedure estimates the
cell temperature based on the ambient temperature and
the solar irradiance. It makes the approximation that
the overall heat loss coefficient is constant. In other
words, the temperature difference between the panel and
the environment is linearly related to the heat flux on
the panels (solar irradiance). The heat transfer
characteristics of a rack-mounted PV module and a BIPV
module can be quite different. The manner in which the
module is installed within the building envelope
influence the cell's operating temperature. Unlike
rack-mounted modules the two sides of the modules may be
subjected to significantly different environmental
conditions. This paper presents a new technique to
compute the operating temperature of cells within
building integrated photovoltaic modules using a
one-dimensional transient heat transfer model. The
resulting predictions are compared to measured BIPV cell
temperatures for two single crystalline BIPV panels (one
insulated panel and one uninsulated panel). Finally, the
results are compared to predictions using the NOCT
technique.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899