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Could renewables and storage power grid 99.9% of the time?


December 11, 2012
By Anthony Capkun

December 10, 2012 – New research by the University of Delaware and Delaware Technical Community College suggests that, by 2030, renewable energy could fully power a large electric grid 99.9% of the time at costs comparable to today’s electricity expenses. A well-designed combination of wind power, solar power and storage in batteries and fuel cells would nearly always exceed electricity demands while keeping costs low, the scientists found.

“These results break the conventional wisdom that renewable energy is too unreliable and expensive,” said co-author Willett Kempton, professor in the School of Marine Science and Policy in UD’s College of Earth, Ocean and Environment. “The key is to get the right combination of electricity sources and storage—which we did by an exhaustive search—and to calculate costs correctly.”

The authors developed a computer model to consider 28 billion combinations of renewable energy sources and storage mechanisms—each tested over four years of historical hourly weather data and electricity demands. The model incorporated data from within a large regional grid called PJM Interconnection, which includes 13 states from New Jersey to Illinois and represents one-fifth of the United States’ total electric grid.

The model focused on minimizing costs instead of matching generation to electricity use. The researchers found that generating more electricity than needed during average hours—to meet needs on high-demand but low-wind power hours—would be cheaper than storing excess power for later high demand. Storage is relatively costly because the storage medium—batteries or hydrogen tanks—must be larger for each additional hour stored.

One of several new findings is that a very large electric system can be run almost entirely on renewable energy.

“For example, using hydrogen for storage, we can run an electric system that today would meet a need of 72 GW, 99.9% of the time, using 17 GW of solar, 68 GW of offshore wind, and 115 GW of inland wind,” said co-author Cory Budischak, instructor in the Energy Management Department at Delaware Technical Community College and former UD student.

The study sheds light on what an electric system might look like with heavy reliance on renewable energy sources. Wind speeds and sun exposure vary with weather and seasons, requiring ways to improve reliability. In this study, reliability was achieved by: expanding the geographic area of renewable generation; using diverse sources; employing storage systems; and, for the last few per cent of the time, burning fossil fuels as a backup.

When there was more renewable energy generated than needed, the model would first fill storage, use the remaining to replace natural gas for heating homes and businesses and, only after those, let the excess go to waste.