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Research Papers

Development of a Thermal Model for Photovoltaic Modules and Analysis of NOCT Guidelines

[+] Author and Article Information
Ty W. Neises

 Thermal Systems Group, NREL 1617 Cole Boulevard, Golden, CO 80401-3905ty.neises@nrel.gov

Sanford A. Klein

 Solar Energy Laboratory, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, WI 53706-1687klein@engr.wisc.edu

Douglas T. Reindl

 Solar Energy Laboratory University of Wisconsin-Madison, 1500 Engineering Drive, Madison, WI 53706-1687dreindl@wisc.edu

J. Sol. Energy Eng 134(1), 011009 (Nov 29, 2011) (7 pages) doi:10.1115/1.4005340 History: Received May 19, 2011; Revised October 14, 2011; Published November 29, 2011; Online November 29, 2011

The temperature of a photovoltaic module is typically required as an input to models that predict the module’s performance. Some common models use the nominal operating cell temperature (NOCT), as by the manufacturer. This paper develops a thermal model and uses it to analyze NOCT testing standards. Specifically, the standard correction factor charts found in the ASTM E1036 and IEC 61215 standards are evaluated. Results show that the correction charts were likely created assuming laminar flow correlations, while validation efforts and the fact that wind is often characterized by turbulence even at low wind speeds suggest that turbulent flow models may be more appropriate. In addition, the results presented in this paper show that the standard NOCT charts do not account for the backside insulation of photovoltaic (PV) arrays. These results suggest that the standard correction charts are inaccurate for any mounting types that differ from the open rack configuration. The paper concludes with recommendations to improve the usefulness of the NOCT.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of steady state energy balance on module at NOCT testing conditions

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Figure 2

Frequency of NOCT values for the mono-Si modules approved by the CEC

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Figure 3

Frequency of NOCT values for the poly-Si modules approved by the CEC

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Figure 4

Correction factor chart in ASTM and IEC standards

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Figure 5

Predicted correction factor chart for insulated mono-Si module: Calculated using the NOCT model

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Figure 6

Correction factor chart for uninsulated mono-Si module: Calculated using the NOCT model

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Figure 7

Correction factor chart of uninsulated mono-Si module: Calculated using NOCT model with a laminar flow correlation

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Figure 8

Correction factor chart of insulated mono-Si module: Calculated using NOCT model with laminar flow correlation

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