Sandia National Lab researchers have developed a new system that provides a way for utility companies to predict and prepare for fluctuations in power output due to changes in weather. By observing cloud shape, size and movement, the system can monitor how clouds affect large-scale photovoltaic power plants.
According to a Sandia news release, the effects of clouds on small PV arrays are well-documented, but there is little research on how large-scale arrays interact and function under cloud cover. A small system can be completely covered by a cloud, which drastically reduces its power output, but what’s less well understood is what happens when only part of a large system is covered by a moving cloud shadow, while the rest stays in sunlight.
Sandia researchers’ work is currently focused at the 1.2-megawatt La Ola Solar Farm on the Hawaiian island of Lana’i.
“As solar power continues to develop and take up a larger percentage of grids nationwide, being able to forecast power production is going to become more and more critical,” says Chris Lovvorn, director of alternative energy of Castle & Cooke Resorts, which owns 98 percent of the island. “Sandia’s involvement and insight has been invaluable in our efforts to meet 100 percent of the island’s energy needs with renewable resources.”
Sandia engineers connected 24 small, nonintrusive sensors to the plant’s PV panels and used a radio frequency network to transmit data. The sensors took readings at one-second intervals to provide researchers with unprecedented detail about cloud direction and coverage activity.
“These techniques will allow a developer to place a sensor network at a proposed site, make measurements for a period of time and use that to predict plant output variability,” says Sandia researcher Josh Stein.
La Ola was commissioned in December 2008 by Castle & Cooke and SunPower Corp., a manufacturer of high-efficiency solar cells. The project uses SunPower’s Tracker technology. Panels rotate on a single axis to follow the sun, which increases energy capture by up to 25 percent. Since February, Sandia Labs has held a cooperative research and development agreement with SunPower to conduct research on integrating large-scale PV systems into the grid. This CRADA is funded with about $1 million of combined U.S. Department of Energy and SunPower funding and is expected to achieve significant results, which will be disseminated through joint publications over the next two years.
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