Stanford researcher suggests storing solar energy underground for a cloudy day

http://www.eurekalert.org/pub_releases/2015-11/su-srs112415.php

Public Release: 24-Nov-2015
Stanford researcher suggests storing solar energy underground for a cloudy day
US electrical grid can't affordably store enough standby electricity to keep the system stable; Stanford researcher Mark Z. Jacobson proposes an underground solution to that problem
Stanford University

A new study shows that wind, water and solar generators can theoretically result in a reliable, affordable national grid when the generators are combined with inexpensive storage.

Over the last few years, Mark Jacobson, a Stanford professor of civil and environmental engineering, and his colleague, Mark Delucchi of the University of California, Berkeley, have produced a series of plans, based on huge amounts of data churned through computer models, showing how each state in America could shift from fossil fuel to entirely renewable energy.

In a new study published today in Proceedings of the National Academy of Sciences, they use the data from those single-state calculations of the number of wind, water and solar generators potentially needed in each state to show that these installations can theoretically result in a reliable, affordable national grid when the generators are combined with inexpensive storage and "demand response" - a program in which utilities give customers incentives to control times of peak demand.
The proposed system relies on the ability to store and retrieve heat, cold and electricity in order to meet demand at all times.

Summer heat gathered in rooftop solar collectors could be stored in soil or rocks and used for heating homes in winter. Excess or low-cost electricity could be used to make ice, which would be used for later cooling when the price of electricity is high.

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As a demonstration of some of these technologies, Jacobson points to the Drake Landing Solar Community in Canada, near Calgary. The 52 homes there are heated in winter with solar energy captured and stored underground during the summer. Water warmed to 175 degrees Fahrenheit by the sun is kept in insulated tubing buried under 120 feet of rocks, earth and insulation. The stored warmth is enough to heat the homes in the community through winter, Jacobson said.

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And underground storage of energy is cheaper than batteries, he added.

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Widespread use of underground energy storage and the other types of storage he proposes would cost much less than batteries, Jacobson says. Storing electricity in batteries currently costs $350/kilowatt hour, compared with a cost two orders of magnitude lower for storing heat in soil, he said. Similarly, storage in concentrated solar power, pumped hydroelectric power and existing hydroelectric reservoirs costs one-tenth of storage in batteries.

"You eliminate air pollution and global warming emissions, stabilize fuel costs, create over two million more jobs than are lost in the U.S., you reduce reliance on international trade of fuels, and you reduce the risk of power disruption, such as from terrorism or massive failure, because more energy is distributed over larger areas," Jacobson said. "Most energy would be local. You can eliminate a lot of fuel emissions, just because you won't have to transport oil in tankers across the ocean, you won't have to use trains of coal cars to ship the coal."

This methodology for keeping the grid stable, he said, should work in many places worldwide.