FINDINGS #5, December 2012
Researchers Perform Climate-Specific Assessment of Multiple PV Systems
Photovoltaic systems represent a promising source of renewable energy. Whether they are practical, however, depends on the specific PV technology in question, the application, the cost of energy, and the location of the installation, among other things. With these issues in mind, GSA’s Green Proving Ground (GPG) program recently assessed five different PV systems installed at the Bean Federal Center in Indianapolis, Indiana. The five systems fall into two categories, one containing a single commercial-scale, 2 megawatt (MW), high-efficiency crystalline PV system, the other containing four smaller “laboratory” systems, each roughly 3 kilowatts (kW) in size and utilizing a different photovoltaic material, construction, or design. The objective of the commercial-scale system study was to investigate the practicality of on-site, largescale renewable energy generation on a Federal property in a Midwestern climate. It focused on quantifying cost savings, reducing dependency on fossil fuels, and reducing greenhouse gas emissions. The purpose of the laboratory systems study was to determine which of the four technologies, if any, offered a clear performance advantage in a diffuse, four-season climate. Findings for the commercial-scale system include a 7.9% overall site load reduction, while laboratory findings argue that none of the systems evaluated has a clear advantage over others under cool, cloudy skies.
What We Did
PERFORMANCE DATA COLLECTED OVER THE FIRST YEAR OF OPERATION
As part of a modernization project at the Bean Federal Center, funded by the American Recovery and Reinvestment Act, five PV systems were installed. Because few studies have been conducted that investigate performance and economics of PV installations in the Midwest, GSA’s Green Proving Ground program worked with researchers at Sandia National Laboratories and New Mexico State University’s College of Engineering to evaluate the systems during their first year of service, a 12-month period beginning in May of 2011 and ending in April 2012. To provide high quality production and performance data, researchers built and installed a dedicated, laboratory-grade data acquisition system (DAS), which monitored research parameters such as PV module temperature and sunlight intensity. To supplement the DAS instruments, the local utility, Indiana Power and Light, installed revenue meters that recorded the systems’ total AC energy production.
What We Measured
EVALUATION OF LARGE AND SMALL SYSTEMS INCLUDED WIDE RANGE OF PARAMETERS
The commercial-scale high-efficiency crystalline PV assessment utilized both the DAS instruments and revenue meter data to achieve the following research objectives: record system energy production, calculate system efficiency per installed watt and per unit area, validate pre-installation performance projections, determine what portion of the overall energy load the on-site energy generation represents, calculate life cycle cost and system payback period (in years), calculate avoided greenhouse gas (GHG) emissions, and finally, investigate different operations and maintenance programs.
The research objectives associated with the laboratory PV systems included a side-by-side comparison of energy production for the four different PV technologies under evaluation, a comparison of clear-sky and cloudy-sky performance efficiencies among the four systems, and a calculation of overall efficiency of each system per installed watt and per unit area of roof covered.
What We Concluded
COMMERCIAL-SCALE HIGH-EFFICIENCY CRYSTALLINE PV DELIVERS PRACTICAL ENERGY SOLUTION
The commercial-scale high-efficiency crystalline PV system is a practical, on-site energy generation solution, even in a diffuse, four-season climate. It offset 7.9% of the Bean Federal Center’s energy load during the study period, helping the Center meet statutory goals for improving energy performance and reducing GHG emissions. A simple payback of 19 years is well within the technology’s demonstrated lifespan.
SYSTEM MODELING IS A HIGHLY ACCURATE PERFORMANCE GUIDE
The commercial-scale high-efficiency crystalline PV system performed almost exactly as the pre-installation models predicted. The 3kW laboratory systems also performed to nameplate expectation. System modeling tools available to energy engineers, building managers, and PV system professionals today are adequate to produce accurate simulation results for both sunny and cloudy climates.
THIN-FILM OUTPERFORMS CRYSTALLINE PV ONLY IN UNIQUE FORM FACTOR
While there has been debate as to whether thin-film PV would outperform crystalline PV in cool, cloudy climates, results from the laboratory study indicate that it does not. The one system that outperformed crystalline PV, the Thin Film Cylindrical system, did so as a result of its unique design and not its thin-film active material. When comparing crystalline and thin-film PV types of similar construction, the crystalline PV outperformed the thin-film systems.
These Findings are based on the report, “Photovoltaic System Performance, Major General Emmett J. Bean Federal Center” which is available from the GPG program website,
For more information, contact Kevin Powell Green Proving Ground Program Manager.
Reference above to any specific commercial product, process or service does not constitute or imply its endorsement, recommendation or favoring by the United States Government or any agency thereof.