Measured Performance of Building Integrated Photovoltaic Panels. Round 2.
Measured Performance of Building Integrated Photovoltaic
Panels. Round 2.
(339 K)
Dougherty, B. P.; Fanney, A. H.; Davis, M. W.
Journal of Solar Energy Engineering (Transactions of the
ASME), Vol. 127, 314-323, August 2005.
Keywords:
amorphous silicon; building integrated; efficiency;
electrical performance; single-crystalline; silicon
film; photovoltaic cells; polycrystalline; predicted
performance
Abstract:
Architects, building designers, and building owners
presently lack sufficient resources for thoroughly
evaluating the economic impact of building integrated
photovoltaics (BIPV). The National Institute of
Standards and Technology (NIST) is addressing this
deficiency by evaluating computer models used to predict
the electrical performance of BIPV components. To
facilitate this evaluation, NIST is collecting long-term
BIPV performance data that can be compared against
predicted values. The long-term data, in addition,
provides insight into the relative merits of different
building integrated applications, helps to identify
performance differences between cell technologies, and
reveals seasonal variations. This paper adds to the
slowly growing database of long-term performance data on
BIPV components. Results from monitoring eight different
building-integrated panels over a 12-month period are
summarized. The panels are installed vertically, face
true south, and are an integral part of the building.s
shell. The eight panels comprise the second set of
panels evaluated at the NIST test facility. Cell
technologies evaluated as part of this second round of
testing include single-crystalline silicon,
polycrystalline silicon, and two thin film materials:
tandem-junction amorphous silicon q-a-Si and
copper-indium-diselenide (CIS). Two 2-a-Si panels and
two CIS panels were monitored. For each pair of BIPV
panels, one was insulated on its back side while the
back side of the second panel was open to the indoor
conditioned space. The panel with the back side thermal
insulation experienced higher midday operating
temperatures. The higher operating temperatures caused a
greater dip in maximum power voltage. The maximum power
current increased slightly for the 2-a-Si panel but
remained virtually unchanged for the CIS panel. Three of
the remaining four test specimens were custom-made
panels having the same polycrystalline solar cells but
different glazings. Two different polymer materials were
tested along with 6 mm-thick, low-iron float glass. The
two panels having the much thinner polymer front covers
consistently outperformed the panel having the glass
front. When compared on an annual basis, the energy
production of each polymer-front panel was 8.5% higher
than the glass-front panel. Comparison of panels of the
same cell technology and comparisons between panels of
different cell technologies are made on daily, monthly,
and annual bases. Efficiency based on coverage area,
which excludes the panel.s inactive border, is used for
most .between. panel comparisons. Annual coveragearea
conversion efficiencies for the vertically-installed
BIPV panels range from a low of 4.6% for the 2-a-Si
panels to a high of 12.2% for the two polycrystalline
panels having the polymer front covers. The insulated
single crystalline panel only slightly outperformed the
insulated CIS panel, 10.1% versus 9.7%.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899