Design Innovation Paper

Model (At Least) Twice, Build Once: Experiences With the Design–Bid–Build Process for Solar Photovoltaic Arrays

[+] Author and Article Information
Brian Dougherty

National Institute of Standards and Technology,
100 Bureau Drive, Stop 8632,
Gaithersburg, MD 20899-8632
e-mail: brian.dougherty@nist.gov

Matthew Boyd

National Institute of Standards and Technology,
100 Bureau Drive, Stop 8632,
Gaithersburg, MD 20899-8632
e-mail: matthew.boyd@nist.gov

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received July 19, 2016; final manuscript received February 8, 2017; published online March 21, 2017. Assoc. Editor: Geoffrey T. Klise.This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Sol. Energy Eng 139(3), 035001 (Mar 21, 2017) (8 pages) Paper No: SOL-16-1333; doi: 10.1115/1.4036055 History: Received July 19, 2016; Revised February 08, 2017

Commercial-scale solar photovoltaic (PV) arrays were designed, constructed, and are now operational on the Gaithersburg, Maryland campus of the National Institute of Standards and Technology (NIST). A design–bid–build process was followed where the contractors used photovoltaic system modeling tools both during the initial design phase and during the postbid, prebuild phase. To help investigate the specific aspects of the contractors' evolving designs, the authors conducted their own independent photovoltaic system modeling. This independent modeling helped identify design elements that could be improved and so aided efforts to maximize the annual renewable energy generation. An estimated 2.5% gain in annual energy generation is being realized as a result of this independent modeling effort. To provide context for the modeling work and the lessons learned, key events impacting the design–bid–build process are described. The installed systems are summarized and also contrasted with the proposed designs. The power generation at three sites are compared over two different 12-month intervals.

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Fig. 1

Ground-mount PV array

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Fig. 2

Parking lot solar canopy

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Fig. 3

Larger rooftop array

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Fig. 4

Example of series-strings adversely affected—by the lighter shading—by near shading (fence, inter-row) at the ground mount array at 3:15 pm on the winter solstice. East–west strings are on the left and north-south strings are on the right (Generated using PVsyst).

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Fig. 5

The impact on array annual energy generation due to the ice guard's size and relative position to the edge of the lowest row of modules at the parking lot solar canopy

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Fig. 6

Ice guard for each parking lot solar canopy shed

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Fig. 7

Modeled results that pictorially and graphically show the impact of near shading for the worst case of the year, on the winter solstice, at the larger rooftop array for a module row spacing of 61 cm (Generated using PVsyst)

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Fig. 8

Average daily specific yield for each month of the two reported periods (August 2012 to July 2013 and August 2014 to July 2015) for the three larger PV sites



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