Measured Performance of Building Integrated Photovoltaic Panels—Round 2

[+] Author and Article Information
Brian P. Dougherty

 National Institute of Standards and Technology 100 Bureau Drive, BR/B320, MS 8632 Gaithersburg, Maryland 20899-8632Brian.Dougherty@nist.gov

A. Hunter Fanney

 National Institute of Standards and Technology 100 Bureau Drive, BR/B320, MS 8632 Gaithersburg, Maryland 20899-8632Hunter.Fanney@nist.gov

Mark W. Davis

 National Institute of Standards and Technology 100 Bureau Drive, BR/B320, MS 8632 Gaithersburg, Maryland 20899-8632Mark.Davis@nist.gov

Ethylene vinyl acetate.

A laminated product having 3 polymer layers.

Certain trade names and company products are mentioned in the text or identified in an illustration in order to adequately specify the experimental procedure and equipment used. In no case does such an identification imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the products are necessarily the best available for the purpose.

The Fig. 2 plots do not account for part-year, early morning shading caused by an adjacent building on the NIST campus. Data collected during these early morning shading periods were excluded from the data analysis.

J. Sol. Energy Eng 127(3), 314-323 (Oct 28, 2004) (10 pages) doi:10.1115/1.1883237 History: Received June 14, 2004; Revised October 28, 2004

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 (2-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 coverage-area 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%.

Copyright © 2005 by American Society of Mechanical Engineers
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Figure 1

BIPV Panel configuration

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Figure 2

Daily data reduction intervals for six different selection criteria

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Figure 3

Annual conversion efficiencies for the sunrise-to-sunset interval

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Figure 4

Performance comparison: PVDF versus ETFE front covers (March 23, 2002)

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Figure 5

CIS panels: Power outputs and operating temperatures (May 5, 2002)

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Figure 6

CIS panels: Operating voltages (May 5, 2002)

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Figure 7

Daily energy production for the paired 2-a-Si panels: (1) Based on the midday data from November and (2) based on the sunrise-to-sunset data from June

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Figure 8

Characteristic I-V curves for the paired 2-a-Si panels (November 2, 2002)

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Figure 9

Seasonal variation in coverage-area conversion efficiency based on the sunrise-to-sunset data interval




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