Comparison of collection and land use efficiency for various solar concentrating field geometries

Kyle Stephens, J Roger P Angel

Research output: Chapter in Book/Report/Conference proceedingConference contribution

3 Citations (Scopus)

Abstract

In this paper we analyze the effects of neighbor shadowing of tracking solar photovoltaic arrays when they are set out in solar farms for large scale generation. Closer tracker spacing yields more power per unit area of land, but less power per tracking unit because of shadowing. A model has been developed to quantify and compare efficiencies for different tracker aspect ratios and field layouts, on an hourly, daily and annual basis. The model accounts for atmospheric absorption as well as neighbor shadowing at low solar altitude angles. We have focused on the case of CPV arrays which are oriented normal to the rays from the sun. The field layout is best characterized by the ratio of total array area to land area (the ground cover ratio or GCR). We explore as a function of GCR both the fraction of all the direct sunlight energy that is intercepted by the arrays (the irradiance collection efficiency) and the energy lost by each array because of shadowing. Examples are worked out for rectangular arrays on dual axis trackers at 33° latitude. We find that for a ground cover ratio of 30% the annual irradiance collection efficiency is 50%, almost independent of the layout pattern or the array aspect ratio. For a ground cover ratio of 40%, the irradiance collection efficiency rises to 65%. The corresponding shadowing losses do depend on aspect ratio, thus for 30% GCR the annual average of shadowing loss is 7.2% for 3:1 aspect ratio, rising to 7.8% for 2:1 aspect ratio. High GCR is not realizable for higher aspect ratios, which lead to large swing radius, but for 2:1 aspect ratio 40% GCR results in shadowing loss of 11.5%. One conclusion is that a solar farm with arrays of 2:1 aspect ratio set out with 40% GCR is good compromise when land is scarce: 64% of all the direct sunlight energy incident on the land is harvested by the arrays, with only 11.5% shadowing loss. We have compared these efficiencies with those for trough CSP systems, which also harvest direct sunlight but with reflectors turning about a single, horizontal N-S axis. For given GCR, the shadowing loss is slightly less (0.5%) than for the above dual-axis arrays, however the irradiance collection efficiency is worse in winter, leading to a lower annual average for a given GCR. For example, at 40% GCR, a single-axis system realizes a 56% irradiance collection efficiency compared to 64% for the dual axis systems.

Original languageEnglish (US)
Title of host publicationProceedings of SPIE - The International Society for Optical Engineering
Volume8468
DOIs
StatePublished - 2012
EventHigh and Low Concentrator Systems for Solar Electric Applications VII - San Diego, CA, United States
Duration: Aug 13 2012Aug 15 2012

Other

OtherHigh and Low Concentrator Systems for Solar Electric Applications VII
CountryUnited States
CitySan Diego, CA
Period8/13/128/15/12

Fingerprint

gas cooled reactors
land use
concentrating
Land Use
Shadowing
Land use
Aspect ratio
Aspect Ratio
aspect ratio
Geometry
Irradiance
geometry
irradiance
Annual
sunlight
layouts
Layout
Farms
Cover
Energy

Keywords

  • Concentrating
  • Neighbor-shadowing
  • Solar

ASJC Scopus subject areas

  • Applied Mathematics
  • Computer Science Applications
  • Electrical and Electronic Engineering
  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Cite this

Stephens, K., & Angel, J. R. P. (2012). Comparison of collection and land use efficiency for various solar concentrating field geometries. In Proceedings of SPIE - The International Society for Optical Engineering (Vol. 8468). [846804] https://doi.org/10.1117/12.930240

Comparison of collection and land use efficiency for various solar concentrating field geometries. / Stephens, Kyle; Angel, J Roger P.

Proceedings of SPIE - The International Society for Optical Engineering. Vol. 8468 2012. 846804.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Stephens, K & Angel, JRP 2012, Comparison of collection and land use efficiency for various solar concentrating field geometries. in Proceedings of SPIE - The International Society for Optical Engineering. vol. 8468, 846804, High and Low Concentrator Systems for Solar Electric Applications VII, San Diego, CA, United States, 8/13/12. https://doi.org/10.1117/12.930240
Stephens K, Angel JRP. Comparison of collection and land use efficiency for various solar concentrating field geometries. In Proceedings of SPIE - The International Society for Optical Engineering. Vol. 8468. 2012. 846804 https://doi.org/10.1117/12.930240
Stephens, Kyle ; Angel, J Roger P. / Comparison of collection and land use efficiency for various solar concentrating field geometries. Proceedings of SPIE - The International Society for Optical Engineering. Vol. 8468 2012.
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abstract = "In this paper we analyze the effects of neighbor shadowing of tracking solar photovoltaic arrays when they are set out in solar farms for large scale generation. Closer tracker spacing yields more power per unit area of land, but less power per tracking unit because of shadowing. A model has been developed to quantify and compare efficiencies for different tracker aspect ratios and field layouts, on an hourly, daily and annual basis. The model accounts for atmospheric absorption as well as neighbor shadowing at low solar altitude angles. We have focused on the case of CPV arrays which are oriented normal to the rays from the sun. The field layout is best characterized by the ratio of total array area to land area (the ground cover ratio or GCR). We explore as a function of GCR both the fraction of all the direct sunlight energy that is intercepted by the arrays (the irradiance collection efficiency) and the energy lost by each array because of shadowing. Examples are worked out for rectangular arrays on dual axis trackers at 33° latitude. We find that for a ground cover ratio of 30{\%} the annual irradiance collection efficiency is 50{\%}, almost independent of the layout pattern or the array aspect ratio. For a ground cover ratio of 40{\%}, the irradiance collection efficiency rises to 65{\%}. The corresponding shadowing losses do depend on aspect ratio, thus for 30{\%} GCR the annual average of shadowing loss is 7.2{\%} for 3:1 aspect ratio, rising to 7.8{\%} for 2:1 aspect ratio. High GCR is not realizable for higher aspect ratios, which lead to large swing radius, but for 2:1 aspect ratio 40{\%} GCR results in shadowing loss of 11.5{\%}. One conclusion is that a solar farm with arrays of 2:1 aspect ratio set out with 40{\%} GCR is good compromise when land is scarce: 64{\%} of all the direct sunlight energy incident on the land is harvested by the arrays, with only 11.5{\%} shadowing loss. We have compared these efficiencies with those for trough CSP systems, which also harvest direct sunlight but with reflectors turning about a single, horizontal N-S axis. For given GCR, the shadowing loss is slightly less (0.5{\%}) than for the above dual-axis arrays, however the irradiance collection efficiency is worse in winter, leading to a lower annual average for a given GCR. For example, at 40{\%} GCR, a single-axis system realizes a 56{\%} irradiance collection efficiency compared to 64{\%} for the dual axis systems.",
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