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Research Papers

Effects of Operating Temperature on the Heat Transfer Characteristics of Photovoltaic Systems in the Upper Midwest

[+] Author and Article Information
Wongyu Choi

Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843-3123
e-mail: wongyuchoi@tamu.edu

Michael B. Pate

Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843-3123
e-mail: mpate@tamu.edu

Ryan D. Warren

Nexant, Inc.
10495 NE DeVotie Drive,
Mitchellville, IA 50169
e-mail: rdwarren@gmail.com

Ron M. Nelson

1214 Arizona Avenue,
Ames, IA 50014
e-mail: ronn@iastate.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received October 20, 2015; final manuscript received March 25, 2016; published online May 17, 2016. Assoc. Editor: Pedro Mago.

J. Thermal Sci. Eng. Appl 8(3), 031012 (May 17, 2016) (10 pages) Paper No: TSEA-15-1301; doi: 10.1115/1.4033349 History: Received October 20, 2015; Revised March 25, 2016

This paper presents the heat transfer characteristics of a stationary PV system and a dual-axis tracking PV system installed in the Upper Midwest, U.S. Because past solar research has focused on the warmer, sunnier Southwest, a need exists for solar research that focuses on this more-populated and colder Upper Midwest region. Meteorological and PV experimental data were collected and analyzed for the two systems over a one-year period. At solar irradiance levels larger than 120 W/m2, the array temperatures of the dual-axis tracking PV system were found to be lower than those of the stationary system by 1.8 °C, which is a strong evidence of the different heat transfer trends for both systems. The hourly averaged heat transfer coefficients for the experiment year were found to be 20.8 and 29.4 W/m2 °C for the stationary and tracking systems, respectively. The larger heat transfer coefficient of the dual-axis tracking system can be explained by the larger area per unit PV module exposed to the ambient compared to the stationary system. The experimental temperature coefficients for power at a solar irradiance level of 1000 W/m2 were −0.30% and −0.38%/ °C for the stationary and dual-axis tracking systems, respectively. These values are lower than the manufacturer's specified value −0.5/ °C. Simulations suggest that annual conversion efficiencies could potentially be increased by approximately 4.3% and 4.6%, respectively, if they were operated at lower temperatures.

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Figures

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Fig. 1

Photograph of stationary PV system

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Fig. 2

Photograph of tracking PV system

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Fig. 3

One-line diagram of data-acquisition system

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Fig. 4

Hourly average ambient air temperature

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Fig. 5

Hourly average array temperature for stationary and dual-axis tracking systems

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Fig. 6

Array temperature less ambient air temperature for daylight hours versus solar irradiance

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Fig. 7

Array operating temperature frequency distributions

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Fig. 8

Hourly overall heat transfer coefficient for stationary system

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Fig. 9

Hourly overall heat transfer coefficient for dual-axis tracking system

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Fig. 10

Frequency distribution of overall heat transfer coefficients for the stationary and dual-axis tracking systems

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Fig. 11

DC power output per module versus module temperature for stationary system for different levels of solar irradiance

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Fig. 12

DC power output per module versus module temperature for dual-axis tracking system for different levels of solar irradiance

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Fig. 13

Temperature coefficients of power for stationary and dual-axis tracking systems

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