Researcher suggests storing solar energy underground for a cloudy day

November 24, 2015 by Dan Stober
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.

An underground effort

The proposed system relies on the ability to store and retrieve heat, cold and 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.

Excess electricity could also used to make more electricity, by supplementing the energy-producing mechanisms that drive concentrated and pumped hydroelectric facilities. Utilities would also provide incentives to reduce energy use during times of peak demand.

In Jacobson's plan, hydrogen would also be used as a storage medium; during low-demand hours, excess electricity would be used to create hydrogen, which could be stored in fuel cells and used to power some vehicles.

Jacobson's new model foresees, and is dependent upon, an all-electric country, with virtually everything running 100 percent on electricity: cars, trains, buses, industry, heating and cooling, and with the electricity originating from wind, water and sunlight.

There would be no need for coal, , biofuels, nuclear power or enormous battery farms for storing electricity. Such a world, which would be 100 percent clean by 2050, can result in a stable grid, he said.

Jacobson's previous studies have drawn wide attention, but critics have argued that a national electric grid without power plants powered by coal for background power and natural gas to fill in gaps of supply would not be reliable. The wind doesn't always blow and the sun doesn't always shine, and batteries for the grid are not yet affordable enough for storing and managing the nation's electricity.

"The utilities and others who are against renewables have always argued that the lights are going to go out, the grid is going to be unstable, and it will cost too much to keep a clean, grid stable and reliable," Jacobson said. "Skeptics have never studied a system of 100 percent clean, renewable energy for all purposes, and particularly one that combines low-cost storage with demand response and some hydrogen, as in this new paradigm."

Jacobson, who is also a senior fellow at the Stanford Woods Institute for the Environment and the Precourt Insitute for Energy, briefed a congressional panel on his research on Nov. 19.

Restructuring the grid

In his new study, Jacobson and his coauthors, including Bethany Frew, now at the National Renewable Energy Laboratory, and graduate student Mary Cameron, suggest that combining existing low-cost ways of storing green energy and using that stored energy to smooth out the uneven demand for electricity, heat and cold simultaneously over the course of a minute, day, week or year could solve that problem.

All raw energy for this system would come from wind, water and sunshine – no natural gas, biofuels, coal or nuclear power. The resulting drop in would save tens of thousands of lives each year, the researchers say. Sixty thousand to 65,000 people die prematurely in America annually as a result of air pollution.

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.

An all-electric nation could reap a number of benefits. While the cost of electricity per kilowatt hour in Jacobson's system might be about the same as electricity generated from fossil fuels, users would actually spend about 30 percent less due to the fact that fewer kilowatt hours are needed in the new system because the efficiencies of electric engines exceed those of combustion engines, Jacobson said.

And underground storage of energy is cheaper than batteries, he added. Some wind turbines now shut down when there is no immediate demand for their electricity, because the cost of storing it is too high. Using excess electricity to produce heat simultaneously with using solar collectors to produce heat increases the availability of stored energy.

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.

Explore further: Engineers develop state-by-state plan to convert US to 100% clean, renewable energy by 2050

More information: Mark Z. Jacobson et al. Low-cost solution to the grid reliability problem with 100% penetration of intermittent wind, water, and solar for all purposes, Proceedings of the National Academy of Sciences (2015). DOI: 10.1073/pnas.1510028112

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16 comments

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Eikka
5 / 5 (6) Nov 24, 2015
In an all-electric situation, heat pumps would actually provide you with a lot of bang for the buck because they can multiply the heat being stored for the electricity input. That compensates for the cost of wasting high-price renewable energy into heat.

But the main issue is in the efficiency of the storage solutions. Batteries are near 100% efficient, heat storage in soil, or chemical storage in hydrogen, is not efficient. You lose up to 80% of the energy particularily in case of hydrogen.

So if you're running a wind farm at 5 cents a kWh and storing it to hydrogen, whatever you do get out is going to cost you at least 25 cents a kWh and that's still unaffordable.

particularly one that combines low-cost storage with demand response and some hydrogen, as in this new paradigm."


It's actually not a new paradigm. Maybe just new in the US. The problem is usually that "low cost" is "low efficiency".
Eikka
4.3 / 5 (6) Nov 24, 2015
Take for example Braedstrup in Denmark

http://www.solarg...?id=1646

There's a 8000 sq-m solar heat collector that produces about 4 GWh per year and stores it in water tanks adjacent to a CHP facility that provides district heating for the local area. Makes for 10% of the heating energy used by 1400 residences out of a small field of about 100x100 meters.

So basically, a football pitch for every 140 homes is enough to keep the Danes warm. If you tried to do that with solar photovoltaics, it would require five times the area and also bankcrupt you.

The question then is, why do we keep subsidizing solar PV instead of this?
Eikka
5 / 5 (6) Nov 24, 2015
There's also about a thousand different ATES systems peppered around northern Europe:

http://trca.on.ca...6551.pdf

The basic idea is that whenever you cool your home in the summer, you pump the heat down to an underground aquifier, and in the winter you pull it out with a heat pump.

It's not that people haven't thought about storing heat and cold underground. They have, and they do use it - it's just not a magic bullet that automatically solves everything.
gkam
2 / 5 (8) Nov 26, 2015
"The basic idea is that whenever you cool your home in the summer, you pump the heat down to an underground aquifier, and in the winter you pull it out with a heat pump."
---------------------------------------

Yeah, like storing your Summer heat in your swimming pool, and not using the pool heater.
Roderick
3.7 / 5 (6) Nov 26, 2015
Eika,

Physical efficiency of batteries is not the issue. It is the cost. And scalability.
kochevnik
4.3 / 5 (3) Nov 26, 2015
Solar provides 100% of my electric needs and the equipment cost was only three months electric bill in San Jose during ENRON fiasco
MR166
3.7 / 5 (3) Nov 26, 2015
The average house here in the NE needs about 500 gallons of oil 69 million BTU of heat each season. If you raise the water by 50F you would need about 650 cubic meters of storage. That is not a small amount of water.
Eikka
4 / 5 (8) Nov 27, 2015
Yeah, like storing your Summer heat in your swimming pool, and not using the pool heater.


No. The difference is that a ground-surface pool will lose the heat in a matter of days, so none of it will be available for use later.

Physical efficiency of batteries is not the issue. It is the cost. And scalability.


It turns out to be the same thing in practice. If you lose 80% of your input energy, the cost of the output energy is 5x the input per kWh even when the storage system costs $0.

That's the biggest obstacle towards any energy storage system. All sorts of things from compressed air to pumped hydroelectricity are nice on paper, but the efficiency in practical terms is around 50-70% and presents a significant cost-hike on the output power, plus the cost of the system itself.

That means the input power has to be extremely cheap in order to sell the output at normal prices. Renewable power just doesn't cut it because it's already expensive.
Eikka
4.1 / 5 (9) Nov 27, 2015
Yeah, like storing your Summer heat in your swimming pool, and not using the pool heater.


Furthermore: there's no need to heat your pool in the summer as it's already warm. If you're running your pool heater in the summer, in California, you're and idiot.

The point of piping your A/C unit into the pool is that it's an effective heat exchanger - it keeps under the ambient temperature because it evaporates water and gets rid of heat more effectively than typical A/C radiators, so you save money by using less electricity at the expense of using more water. It's simply an application of the swamp cooler.

A swimming pool does NOT store heat for the winter in any meaningful amount.
gkam
1.9 / 5 (9) Nov 27, 2015
Eikka, have you ever been to California? I mean, other than through the internet? People heat their pools here. I know, they should have gotten your permission first, but there you have it.

And the house is cooled not by evaporation, but through the Specific Heat of water. Put an insulated cover over it, and you can then pump out meaningful amounts of that heat back into the house in Winter.
MR166
3 / 5 (6) Nov 28, 2015
Oh yea, This is California as portrayed by LA is model of the Green philosophy ! Wow this house is more than 10 years old and needs to be totally demolished. But that is OK I will pay 10s of K dollars to use some wood from some old barn for my floor and that will make my 10 Million home Green.

SuperThunder
3 / 5 (6) Nov 28, 2015
"Oh mah gawd, humans not goin' extinct costs mah muuunaaay!? It it fer'iner extinction or blessed holy white jesus extinction?! Fernniniener extinction! YO CAINT HAVE MAH MUNAAAAY FERNININEER!!"

What every howler sounds like.
Roderick
4.3 / 5 (6) Nov 29, 2015
Eikka,

You are being sloppy. Economic cost and physical efficiency are not the same thing. The former reflects market price. The latter reflects energy lost during conversion. A technology can be highly physical efficient, yet too expensive to be competitive in the market. Solar panels have physical efficiency rates around 15%. But their prices are falling for a variety of reasons.
thermodynamics
3.9 / 5 (7) Nov 29, 2015
Eikka said:
The point of piping your A/C unit into the pool is that it's an effective heat exchanger - it keeps under the ambient temperature because it evaporates water and gets rid of heat more effectively than typical A/C radiators, so you save money by using less electricity at the expense of using more water. It's simply an application of the swamp cooler.

A swimming pool does NOT store heat for the winter in any meaningful amount.


Where are you coming from on this? Have you never heard of water-source heat pumps?

In locations where the swimming pool does not freeze hard you can use in-pool heat exchangers coupled to a heat pump to use the mass of the water as a buffer for swings in temperatures. If you look at the efficiency of water-source heat pumps you will find that water does store a lot of energy.

http://www.trane....mps.html

gkam
2.1 / 5 (7) Nov 30, 2015
Eikka does not understand how much thermal storage is available in a poll, that the A/C has to run a long time before the temperature of the pool changes to make an evaporation difference.
TheGhostofOtto1923
3.4 / 5 (5) Nov 30, 2015
Thermodynamics thinks that by rewarding a psychopath with 5/5s he can encourage that psychopath to change his behavior,

"The psychopath does not think that they have any psychological or emotional problems, and they see no reason to change their behavior to conform to standards with which they do not agree. They are well-satisfied with themselves and their inner landscape. They see nothing wrong with they way they think or act, and they never look back with regret or forward with concern."

"Most therapy programs only provide them with new excuses for their behavior as well as new insights into the vulnerabilities of others."

"... social factors and parenting practices only shape the expression of the disorder, but have no effect on the individual's inability to feel empathy or to develop a conscience."

""The World has only one problem, Psychopaths... The essential feature of Psychopaths is a Pervasive, Obssesive- Compulsive desire to force their delusions on others."

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