A well-designed combination of wind power, solar power and storage in batteries and fuel cells would nearly always exceed electricity demands, while keep- ing costs comparable to today’s electricity expenses, scientists at the University of Delaware (UD) and Delaware Technical Community College have found.

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

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

The study sheds light on what an electric system with a heavy reliance on renewable energy sources might look like. Wind speeds and sun exposure vary in relation to the weather and the seasons, requiring ways to improve reliability. In this study, reliability has been achieved through the expansion of the geographic area of renewable generation, using diverse sources, employing storage systems and burning fossil fuels as a peaking power backup.

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

During the hours when there was not enough renewable electricity to meet power needs, the model drew from storage and when neither renewable electricity nor stored power was available, fossil fuel was used.

When more renewable energy was generated than was actually needed, the model would first fill storage, then replace natural gas for the heating of homes and businesses and only then would the excess generation go to waste.

However, storage is relatively costly because the storage medium – batteries or hydrogen tanks – must be increased in capacity for each additional hour stored. Renewable electricity generators must have higher gigawatt capacity than traditional generators, since wind and solar do not generate at maximum capacity all the time.

The study used estimates of technology costs in 2030, excluding government subsidies, comparing them to the costs of fossil fuel generation currently in use. The cost of fossil fuels includes the fuel cost and the documented ‘external costs’, such as the human health effects caused by power plant air pollution. The projected capital costs for wind and solar in 2030 are about half of the current wind and solar costs, whereas maintenance costs are projected to remain about the same.