Reliability and low cost? Isn't that what critics say renewable energy is missing? If wind and solar can supply 99.9% of the nation's energy needs, then geothermal, hydro, biofuels, and some others can make up the balance.
From Science Daily:
Renewable energy could fully power a large electric grid 99.9 percent of
the time by 2030 at costs comparable to today's electricity expenses,
according to new research by the University of Delaware and Delaware
Technical Community College.
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.
Unlike other studies, the model focused on minimizing costs instead
of the traditional approach of matching generation to electricity use.
The researchers found that generating more electricity than needed
during average hours -- in order 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 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," said co-author Cory Budischak, instructor in the Energy
Management Department at Delaware Technical Community College and former
UD student.
A GW ("gigawatt") is a measure of electricity generation capability.
One GW is the capacity of 200 large wind turbines or of 250,000 rooftop
solar systems. Renewable electricity generators must have higher GW
capacity than traditional generators, since wind and solar do not
generate at maximum all the time.
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 percent of the time,
burning fossil fuels as a backup.
During the hours when there was not enough renewable electricity to
meet power needs, the model drew from storage and, on the rare hours
with neither renewable electricity or stored power, then fossil fuel.
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.
The study used estimates of technology costs in 2030 without
government subsidies, comparing them to costs of fossil fuel generation
in wide use today. The cost of fossil fuels includes both the fuel cost
itself and the documented external costs such as human health effects
caused by power plant air pollution. The projected capital costs for
wind and solar in 2030 are about half of today's wind and solar costs,
whereas maintenance costs are projected to be approximately 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.
