Combined Wind, Solar Power Could Produce Cost-Effective Energy
December 11, 2012

Combined Wind, Solar Power Could Produce Cost-Effective Energy

April Flowers for - Your Universe Online

According to a new study from the University of Delaware and Delaware Technical Community College (DTCC) by 2030 renewable energy could fully power a large electric grid 99.9 percent of the time at costs comparable to today's electricity expenses.

The research team found that a well-designed system of wind power, solar power, and storage in batteries and fuel cells would keep costs low while nearly exceeding electricity demands. The findings of this study were published recently in the Journal of Power Sources.

“These results break the conventional wisdom that renewable energy is too unreliable and expensive,” said 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 team sampled 28 billion combinations of renewable energy sources and storage mechanisms using a computer model developed especially for this search. Each source was tested over four years of historical hourly weather data and electricity demands. The data was collected from a large regional grid called PJM Interconnection. This grid incorporates 13 states from New Jersey to Illinois, representing one-fifth of the U.S.'s total electric grid.

The team's new model focuses on minimizing costs instead of the traditional approach of matching generation to electricity use. Generating more energy than needed during average hours would be cheaper than storing excess power for later high demand, in order to meet needs on high-demand but low-wind power hours.

One of the highest costs in renewable energy is storage because the storage medium — batteries or hydrogen tanks — must be larger for each additional hour stored.

One of the most important findings of the study 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 meeting a need of 72 GW, 99.9 percent of the time, using 17 GW of solar, 68 GW of offshore wind, and 115 GW of inland wind,” Cory Budischak, instructor in the Energy Management Department at Delaware Technical Community College, said in a statement.

Electric generation capacity is measured in gigawatts (GW), with one GW being the capacity of 200 large wind turbines or 25,000 rooftop solar systems. Wind and solar do not generate at maximum all the time, so renewable energy generators must have higher GW capacity than traditional ones.

The study suggested a possible set up for an electric system with heavy reliance on renewable energy sources. Because wind speeds and sun exposures vary with weather and seasons, such a system requires ways to improve reliability. The authors suggest expanding the geographic area of renewable generation, using diverse sources, employing storage systems and only a fraction of the time, burning fossil fuels as a backup.

The model drew from storage first during hours when there was not enough renewable electricity to meet power needs. In those rare hours when neither stored electricity nor renewable power was available, the model drew on fossil fuels. When more energy was generated than was needed, the model first filled storage, then used it to replace natural gas for heating homes and businesses. Only after those were achieved, the model allowed the excess to go to waste.

The cost estimates of the report relied on technology available in 2030 without government subsidies. The team compared these estimates to the cost of fossil fuel generation in wide use currently — the cost of such fuels includes both the fuel cost itself and the external costs such as human health effects caused by power plant air pollution. The renewable energy projected capital costs for 2030 are about half of today's wind and solar costs, with maintenance costs estimated to be about the same.

"Aiming for 90 percent or more renewable energy in 2030, in order to achieve climate change targets of 80 to 90 percent reduction of the greenhouse gas carbon dioxide from the power sector, leads to economic savings,” the authors observe.