Scientists challenge economics of storing renewable energy


September 11, 2013

New research examines the economics of storing energy from renewable sources (Photo: Shutterstock/luchschen)

New research examines the economics of storing energy from renewable sources (Photo: Shutterstock/luchschen)

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True or false: solar and wind power are freely available and clean, and thus should always be stored when they generate more energy than the grid can use? It's easy to assume that renewable energy should never be turned off, but scientists at Stanford have done the math to find the break-even point where storing energy is better than "wasting," or curtailing, that energy, and their findings aren't necessarily as you'd think.

Though curtailing energy production results in an immediate energy loss, avoiding that loss through energy storage also requires an investment of energy, either through manufacturing batteries or building infrastructure. However, not all storage is the same, nor are the energy demands of creating wind and solar farms equivalent. By expressing all the energy in equivalent terms, the team could compare the return of energy garnered from solar and wind with the energy stored in batteries, per unit of energy required to build either (expressed as EROI for return of energy, and ESOI for the storage of energy).

Because solar panels are more energetically expensive to produce than wind turbines, the EROI values differ by a factor of ten. When looking at various types of batteries, even more efficient flow batteries, all had much lower ESOI values than the geologic energy storage methods studied, which were compressed air energy storage and pumped hydroelectric storage.

Factoring in these differences, the study's results show it’s currently always a better option to store solar energy because of the high energetic cost to recoup. However, the only storage options that are always better than curtailment of wind are geologic methods, with battery storage becoming better than curtailment depending on the fraction of energy being used in the grid instead of being stored or curtailed. In the graph below, you can read the ϕ in the bottom axis as representing that fraction. At the far right, if 100 percent of the energy is being curtailed or stored (i.e., none is going to the grid), then storing it is just barely a better option with any battery type. But at other rates it depends on the battery type.

A representation of the break even point for curtailing or storing energy, with the x-axis representing the percentage of the energy production being curtailed or stored and the different colored lines representing different storage options

It seems counter-intuitive that wind energy should be so cheap yet benefit in most cases from curtailment. But Michael Dale, one of the co-authors of the study, compared it to storing valuables in a safe. "You wouldn't spend $100 on a safe to store a $10 watch," he writes. In some situations it may even be preferable, in terms of energy expenditure, to build a new wind turbine rather than build storage for existing turbines.

The authors also make it plain that they’re condensing the question down to comparing one variable: the energetic trade-offs involved. But relying on economics alone avoids these considerations, and can even turn so-called green energy into the opposite. The authors calculated how much the life cycle of batteries would need to improve before becoming a viable option for wind – by a factor of two to 20, depending on the type of battery. But more importantly they also encourage the development of technologies that can use the otherwise curtailed energy in applications that aren’t harmed by being intermittent, such as systems to pump or purify water.

Sources: Stanford University, Royal Society of Chemistry

About the Author
Heidi Hoopes Heidi measures her life with the motley things she's done in the name of scientific exploration. While formally educated in biology and chemistry, informally she learns from adventures and hobbies with her family. Her simple pleasures in life are finding turtles while jogging and obsessively winnowing through her genetic data. All articles by Heidi Hoopes

The electricity that come off windmills is lousy with spikes and dips because of the way turbulence effects the power generated by the blades. if the windmills were pumping water or compressing air these variances in energy capture would be of very little importance because the electrical generation would come from stored energy. Had the Wind Energy enthusiasts gone this way from the start they could have become a reliable peak load producer and the price the charged for the electricity would have been nicely profitable for the producer, and reasonable for the utilities at the same time because of the expense of other peak load generating systems. I like pneumatic because those towers would make a dandy air tank.


Unless and until we find a low cost, long life battery, I imagine that it would be less expensive, and more effective, to employ a smart-grid and smart-home/building approach that will throttle demand quickly, down or up, as a means of "storing" or "releasing" electricity. For example, if the wind were blowing especially hard for a short amount of time, the utility provider could signal (via 3G or FM radio subcarrier or the 'net or whatever) the customer's home or building controller to temporarily use more, or less, electricity. The air conditioner could come down or up 0.5 degrees F, the electric water heater could climb 5 degrees, etc. A network of large buildings with hydronic heating and cooling systems could engage thermal ice storage systems. It would be turned on when power was in excess and the ice would be consumed when power was in short supply. 300 gallons of water, converted to ice, stores about 90 KWH of electricity. Of course, the quintessential storage application would be thousands of parked electric cars, all tied to their chargers, waiting for cheap electricity to begin, and then getting an unexpected price break in the middle of the day whenever the utility has extra power on its hands. This is to say that electric cars enable the use of much more wind and solar power.


I agree with Slowburn - raising water for hydro power or some sort of compression system for air, with turbine use later would have been a better option. Windmills - and solar panels - were sold to the public as cheaper (and 'greener') than coal-fired power, but will always suffer from gaps in the wind or sunshine supply, making them intermittent at best without storage.

The Skud

The Gizmag article titled "Graphene-based supercapacitor a step closer to commercial reality" represents a solution for storage of excess power from wind power sources.

No doubt the scientists who conducted this research were not informed of this development as this newest technological breakthrough is too new for their consideration.


Of course energy storage doesn't have to involve batteries or their like, you can store energy in form of hydrogen for instance!

Sascha Humphrey

Assuming we add grid energy storage only for the purpose of storing energy this may be true.

But utilities and end consumers add batteries for various of reasons and storing energy is not even the main one.

Димитър Мирчев

@JoeT, I really like your idea. The electric water heater alone would probably make it worthwile. Heating the water of thousands of households when you have the energy would definately lead to a much reduced peak power demand.


Agree that using the tower of a wind mill for energy storage seems to be an obvious next step in their development. But pumped fluid storage seems like it would be inherently for efficient than compressed gas systems due to losses associated with heat created during compression. I could even imagine a system that worked by raising and lowering a weight inside the tower that might have an efficiency advantage due to the direct mechanical linkage made possible that way.

Siegfried Gust

@ Sascha Humphrey Did you read the article only 5% of the solar energy was converted to hydrogen. Using platinum as the catalyst it take 1.8 watt hours of electricity to produce 1 watt hours worth of hydrogen. Then you have to compress it for storage.


There is also a big environmental cost to not storing wind power that should be factored in. As more renewables enter the system, the need for storage and baseload increase. It makes sense to use wind to pump water directly, and generate hydropower on demand. Operating a short inclined railway for tankers would be a good match for kites, and there are locations where reservoir facilities are underused.

Bob Stuart

In all of this discussion there is no mention of efficieincy... the most important variable in engineering.

Hence the results are moot and so much for Stanford.

What is the efficiency of the solar panels used in this analysis? What is the growth curve for solar panel efficiency. Has it topped out?

What is the efficiency of the fans used in the computations?

The fact that there are so many different blade designs indicates that the search for efficiency has not topped out. What does Stanford say it is?

One should never forget that Bill Allison, a Michigan Engineer, achieved a value equaling the Betz limit in the early 80's.

Bill Dickens

Lewis Dickens

Yes, anyone in the power industry will tell you in hushed tones that renewables fall far short when compared to fossil fuels. The variable nature of sunlight and wind is as much the culprit as adequate storage and transmission. And also correct that many are looking at double layer carbon and lithium ion capacitors as an augmented solution to mitigate the storage problem, the variable nature of the respective power sources remain an obstacle that is difficult to overcome. Barring some major innovation, the future models simply suggest that renewables will help stabilize fossil fuel prices over the long term. The population increases in the BRIC and MINT countries tend to offset the environmental impact equation. This is why I am watching BloomEnergy very closely. If these cats do what they say they are going to do, the larger economic picture may seem brighter.

Dennis Zogbi

Convoluted, scewed, irrational, obfuscated, mumbo-jumbo thinking here! No mention of the "real' cost of current, U.S. electricity! No mention of the declining availability in America of 'easy coal", cost effective coal! not a word on the elephant in the room in America, the astounding cost of radioactive waste disposal from current nuclear, 'enriched uranium system' monopolies? no input from the costs of safer, cleaner, Chinese pebble bed gas reactors? Chinese Thorium LFTR technologies? No mention of the renew-ability, the perpetuity of the Prairie Wind Corridor, a "waste all you want to" situation without cost penalties? When the supply, no matter how big or small, irregular or steady, is infinite, "efficiency" factors have a '0' denominator? "Fuel" is 'free" and infinite? Germany has some answers for your tortured, misguided, victimized, logic (mostly by the great Corporate American Propaganda Whores). Germany diversifies, decentralized, shared down with the common folk, de-nuked, and is winning the battle by selling product at good market prices to the world that is created with cost free, fuel free, Solar, Wind, Wave, Hydro, Geothermal, Biological, domestic energy. While you try to see the logic, see the light, examine Denmark and their energy achievements, Quebec, Canada, and their remarkable Hydro Systems, and understand that outside the 'Inch, Pound, Foot" reality of the U.S.A., lies a greater, international Science point of view.

Bruce Miller

Wouldn't it make sense to program those electric cars so they could be used for storage during periods when they are not in use. All they would have to do is let the car know when the owner requires a full battery around their driving habits and the grid would provide it. Any use of the cars storage capability would be reimbursed by the power company.


Bill Gross has some ideas on storage. See which is a bit dated (instead of half the cost, I believe they have it closer to 1/3 the cost). Interesting that China bought 2 GW worth of production capacity from eSolar (if I'm reading/scanning this accurately).


From it's beginnings at $75/watt solar is now down to about $1/watt. Put the same development energy into storage and the premise of the scientists becomes moot. Let's remember that the advent of oil virtually stopped the development of other energy storage for almost a hundred years.

Max Kennedy

The California Water Project is the largest consumer of electricity in the state, to extract and distribute water up to 400 miles away, and over 2,000' mountains. I think the wind turbines could be put to use to lift and move water when electric power isn't needed.


OK Kids, here's the low down on energy storage. I worked for SoCalEdison for 15 years, so I do know a little bit about the subject. First off, you have to do an energy audit, that means determine the total cost of the storage medium, what ever all of the factors may be. Raw materials, transportation/processing of them, labor costs both skilled and unskilled and everything else from start to finish. THEN you can begin to talk intelligently about the trade off of how much it costs to store the energy as compared to just generating it. When the cost of storage of a KW of electrical energy is LESS THAN the cost of generation of that KW of juice, then it makes it worthwhile economically. Maybe. And let's face it boys and girls, profits are what drives EVERYTHING in this world. No profits, no sales. If someone can find a better way to harvest the many GW of energy that hits the Earth every day than we currently use, and do it cheaply enough, then there will be no need for storage


Expanded Viewpoint

Recent articles about small devices capable of charging from "radiant energy" have failed to "connect the dots". If we could develop devices capable of converting cosmic rays into electricity, we could build a starship whose range is limited only by the life support systems. Tesla's dream of "free energy" is hidden in plain sight right in front of us,

Robert Fallin

when the constant load is All met by renewables and the peaks are the only time we use oil or coal....the storage "problem will dissspear.

Walt Stawicki

@ Sascha Humphrey: Energy storage via hydrogen IS a viable alternative to pumped water storage, compressed air and electrochemical cells (batteries) as, unlike those three, hydrogen can be stored AND easily transported to the end user (or distributed electrics generation substations) through existing sub-surface pipelines for immediate use.

Gas storage tanks are also relatively cheap to manufacture and maintain in comparison to battery banks of comparable capacity.

@ Slowburn: The cost of the methods used to produce the hydrogen dictate their viability - correct? Cal Tech researchers devised a means to quickly generate large volumes of hydrogen, over 10 years ago, consuming very little electric energy and no precious metals. Platinum (currently $1469.00/oz on 09/12/13) costs a great deal more than ferrous-oxide (rust) and doesn't produce nearly the volume of H2.

H2 fuel cells powered by wind or solar energy (electrics) IS viable - but tidal power is more reliable.

Larry Pines

@ Larry Pines

High heat takes a lot of energy as well and I could find any claims of relative efficiency. I will admit that not using electricity is an advantage but how much electricity could be generated from the same heat energy.

You can generate hydrogen quickly by oxidizing sponge iron in water without free oxygen but that does not make the process commercially viable.

There are time when generating hydrogen from water can make sense. if you can extract the hydrogen from sea water and have a fresh water shortage you might find that you can make a profit by selling both products of the fuel cells.


Any stored energy has high capital cost and big efficiency hits with a double conversion to stored energy and back again. The simplest, albeit partial, solution is to turn off variable power demand in times of less or no power. Examples are hot water heaters that can store hot water for 1-2 days. A big portion of industrial energy demand, possibly EV charging as well, can be timed when power is generated, which is when the most is available at the lowest cost. With this done, the amount of energy needed for storage (which is then higher cost, and should be billed accordingly to such demanding users) is much less. Billing power according to the true cost AND time available will naturally drive consumers in an optimal way.


Rather than costly storage adjuncts to the electricity grid, we need to look beyond electricity to solve all of the Big Three problems of "running the world on renewables", as we must eventually do, sooner the better:

Gathering and transmission Annual-scale firming storage Distribution, integration, and end use to deliver energy services

Attractive alternatives for complete, optimized, renewable energy systems include gaseous hydrogen and liquid anhydrous ammonia (NH3) C-free fuels, via underground pipelines, with very low-cost storage (< $1.00 / kWh capital) in large salt caverns -- for hydrogen -- and large "atmospheric" surface tanks -- for liquid NH3. We distribute these fuels for stationary combined-heat-and-power (CHP) , for transportation, and for industrial and chemical uses. All electric energy at the solar and wind plants is converted to these fuels, without the costly connection to, and expansion of, the electricity grid.

See our co-authored work at:

This concept now needs competent, comprehensive, technical and economic modeling and study. Please join us.

Alaska Bill

There has been a lot of discussion about this new algae fuel cell being able to store backup electricity at a comparable cost to fossils but from the reports they are skipping the renewable backup and going straight to powering homes.

Ken H

@Ken H

Interesting that it also acts as a CO2 scrubber

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