A state-of-the-art solar-panel array demonstration site at NASA’s Dryden Flight Research Center provides a unique opportunity for studying the latest in high-efficiency solar photovoltaic cells. This five-kilowatt solar-array site (see Figure 1) is a technology-transfer and commercialization success for NASA. Among the solar cells at this site are cells of a type that was developed in Dryden Flight Research Center’s Environmental Research Aircraft and Sensor Technology (ERAST) program for use in NASA’s Helios solar-powered airplane. This cell type, now denoted as A-300, has since been transferred to SunPower Corporation of Sunnyvale, California, enabling mass production of the cells for the commercial market.
High efficiency separates these advanced cells from typical previously commercially available solar cells: Whereas typical previously commercially available cells are 12 to 15 percent efficient at converting sunlight to electricity, these advanced cells exhibit efficiencies approaching 23 percent. The increase in efficiency is due largely to the routing of electrical connections behind the cells (see Figure 2). This approach to increasing efficiency originated as a solution to the problem of maximizing the degree of utilization of the limited space available atop the wing of the Helios airplane. In retrospect, the solar cells in use at this site could be used on Helios, but the best cells otherwise commercially available could not be so used, because of their lower efficiencies.
Historically, solar cells have been fabricated by use of methods that are common in the semiconductor industry. One of these methods includes the use of photolithography to define the rear electrical- contact features — diffusions, contact openings, and fingers. SunPower uses these methods to produce the advanced cells. To reduce fabrication costs, SunPower continues to explore new methods to define the rear electrical-contact features.
The equipment at the demonstration site includes two fixed-angle solar arrays and one single-axis Sun-tracking array. One of the fixed arrays contains typical less-efficient commercial solar cells and is being used as a baseline for comparison of the other fixed array, which contains the advanced cells. The Sun-tracking array tilts to follow the Sun, using an advanced, real-time tracking device rather than customary pre-programmed mechanisms. Part of the purpose served by the demonstration is to enable determination of any potential advantage of a tracking array over a fixed array. The arrays are monitored remotely on a computer that displays pertinent information regarding the functioning of the arrays.
The process for production of the advanced cells is more complex than is the process for producing typical previously commercially available cells. When laminated under glass in rigid framed modules, the advanced cells are robust enough to last outdoors for more than 20 years. Once the cells have been installed in the modules, the protective glass is coated with a dirt-repellent material. The demonstration is providing the opportunity to verify the effectiveness of the repellent, and to determine the effect, if any, of dust and dirt on the arrays.
NASA Headquarters funded a site-feasibility study for the demonstration. The study was performed by the U. S. Department of Energy’s Idaho National Engineering and Environmental Laboratory in Idaho Falls, Idaho. The laboratory is also supporting Dryden Flight Research Center’s public-outreach planning for the demonstration. Among the planned activities is the establishment of a Web site that will enable the public to view real-time information on the functioning of the arrays at the site.
This project can be characterized as part of a full-circle process of development of technology, transfer of the technology to private industry, and return of the technology to NASA (“spin-in”) from industry to assist NASA programs. This project has been part of the Innovative Technology Transfer Partnerships effort under NASA’s Aerospace Technology Enterprise.
Other solar-array sites are planned for construction in Hawaii and Arizona. A larger solar farm that may be constructed at Dryden Flight Research Center in the future might supply as much as one third of the electric power consumed by the Center.
This work was done by Gray Creech of Dryden Flight Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Electronics/ Computers category. DRC-04-21
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NASA Solar Array Demonstrates Commercial Potential
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Overview
The document discusses a solar array demonstration project at NASA's Dryden Flight Research Center, aimed at showcasing the commercial potential of advanced solar technology. The site features two fixed-angle solar arrays and one single-axis sun-tracking array, collectively capable of producing up to five kilowatts of direct current power on sunny days, sufficient to power two to three average California homes. The sun-tracking array utilizes a real-time tracking device to follow the sun, enhancing its efficiency compared to traditional pre-programmed systems.
The solar cells used in the demonstration are manufactured by SunPower Corporation and are derived from technology developed for NASA's Helios and Pathfinder-Plus solar-powered aircraft. These A-300 silicon cells are noted for their high efficiency, with the newer models achieving up to 20 percent efficiency—significantly better than the typical 12 to 15 percent efficiency of standard commercial-grade solar cells. This improvement is attributed to innovative design changes, such as routing electrical connections behind the cells, which maximizes space utilization.
The project is not only focused on energy production but also on evaluating the performance of the solar arrays under various conditions. It aims to compare the effectiveness of the tracking array against fixed arrays, assess the impact of a dirt-repellant coating on the protective glass of the solar cells, and analyze how dust and dirt affect overall efficiency. The efficiency of the arrays is monitored remotely, providing valuable data for future applications.
Long-term plans for the site include the establishment of a solar "farm" that could supply up to one-third of the electrical power needs for the Dryden center. The project is funded through NASA's ERAST program, with a total cost of approximately $130,000, and was constructed by Renewable Energy Concepts Inc.
Additionally, there are plans to create a public-facing website that will provide real-time information about the solar demonstration site and other planned solar array projects in Hawaii and Arizona. The life expectancy of the solar array system is estimated to be at least 25 years, indicating its potential for long-term use in renewable energy applications. Overall, the demonstration serves as a significant step toward transferring advanced solar technology to the commercial market, promoting sustainable energy solutions.
