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Stanford study quantifies energetic costs of grid-scale energy storage over time; current batteries the worst performers; the need to improve cycle life by 3-10x

A plot of ESOI for 7 potential grid-scale energy storage technologies. Credit: Barnhart and Benson, 2013. Click to enlarge.

A new study by Charles J. Barnhart and Sally M. Benson from Stanford University and Stanford’s Global Climate and Energy Project (GCEP) has quantified the energetic costs of 7 different grid-scale energy storage technologies over time. Using a new metric—“Energy Stored on Invested, ESOI”—they concluded that batteries were the worst performers, while compressed air energy storage (CAES) performed the best, followed by pumped hydro storage (PHS). Their results are published in the RSC journal Energy & Environmental Science.

As the percentage of electricity supply from wind and solar increases, grid operators will need to employ strategies and technologies, including energy storage, to balance supply with demand given the intermittency of the renewable supply. The Stanford study considered a future US grid where up to 80% of the electricity comes from renewables.

Only about 3% currently is generated from wind, solar, hydroelectric and other renewable sources, with most of the electricity produced in the United States currently coming from coal- and natural gas-fired power plants, followed by nuclear according to data from the US Energy Information Administration (EIA) .

They quantified energy and material resource requirements for currently available energy storage technologies: lithium ion (Li-ion), sodium sulfur (NaS) and lead-acid (PbA) batteries; vanadium redox (VRB) and zinc-bromine (ZnBr) flow batteries; and geologic pumped hydroelectric storage (PHS) and compressed air energy storage (CAES).

The current total energy storage capacity of the US grid is less than 1%, according to Barnhart. What little capacity there is comes from pumped hydroelectric storage, which works by pumping water to a reservoir behind a dam when electricity demand is low. When demand is high, the water is released through turbines that generate electricity.

By introducing new concepts, including energy stored on invested (ESOI), we map research avenues that could expedite the development and deployment of grid-scale energy storage. ESOI incorporates several storage attributes instead of isolated properties, like efficiency or energy density.

Calculations indicate that electrochemical storage technologies will impinge on global energy supplies for scale up—PHS and CAES are less energy intensive by 100 fold. Using ESOI we show that an increase in electrochemical storage cycle life by tenfold would greatly relax energetic constraints for grid-storage and improve cost competitiveness. We find that annual material resource production places tight limits on Li-ion, VRB and PHS development and loose limits on NaS and CAES.

This analysis indicates that energy storage could provide some grid flexibility but its build up will require decades. Reducing financial cost is not sufficient for creating a scalable energy storage infrastructure. Most importantly, for grid integrated storage, cycle life must be improved to improve the scalability of battery technologies. As a result of the constraints on energy storage described here, increasing grid flexibility as the penetration of renewable power generation increases will require employing several additional techniques including demand-side management, flexible generation from base-load facilities and natural gas firming.

—Barnhart and Benson

The first step in the study was to calculate the cradle-to-gate embodied energy—the total amount of energy required to build and deliver the technology—from the extraction of raw materials, such as lithium and lead, to the manufacture and installation of the finished device.

To determine the amount of energy required to build each of the five battery technologies, the authors used data collected by Argonne National Laboratory and other sources. The data revealed that all five battery technologies have high embodied-energy costs compared with pumped hydroelectric storage.

After determining the embodied energy required to build each storage technology, the next step was to calculate the energetic cost of maintaining the technology over a 30-year timescale. To quantify the long-term energetic costs, Barnhart and Benson came up with a new mathematical formula they dubbed ESOI, or energy stored on investment.

ESOI is the amount of energy that can be stored by a technology, divided by the amount of energy required to build that technology. The higher the ESOI value, the better the storage technology is energetically.

—Charles Barnhart

The results showed that CAES had the highest value: 240. In other words, CAES can store 240 times more energy over its lifetime than the amount of energy that was required to build it. (CAES works by pumping air at very high pressure into a massive cavern or aquifer, then releasing the compressed air through a turbine to generate electricity on demand.) PHS followed at 210.

The five battery technologies fared much worse. Lithium-ion batteries were the best performers, with an ESOI value of 10. Lead-acid batteries had an ESOI value of 2, the lowest in the study.

The best way to reduce a battery’s long-term energetic costs would be to improve its cycle life, the Barnhart said. Pumped hydro storage can achieve more than 25,000 cycles; none of the conventional battery technologies featured in the study has reached that level. Lithium-ion is the best at 6,000 cycles, while lead-acid technology is at the bottom, achieving a mere 700 cycles.

The most effective way a storage technology can become less energy-intensive over time is to increase its cycle life.Most battery research today focuses on improving the storage or power capacity. These qualities are very important for electric vehicles and portable electronics, but not for storing energy on the grid. Based on our ESOI calculations, grid-scale battery research should focus on extending cycle life by a factor of 3 to 10.

—Sally Benson

In addition to energetic costs, Barnhart and Benson also calculated the material costs of building these grid-scale storage technologies. In general, they found that the material constraints aren’t as limiting as the energetic constraints. However, PHS has a different type of challenge—the number of geologic locations conducive to pumped hydro is dwindling, and those that remain have environmental sensitivities, Barnhart noted.

A primary goal of the study was to encourage the development of practical technologies that lower greenhouse emissions and curb global warming, Barnhart said. Coal- and natural gas-fired power plants are responsible for at least a third of those emissions.

I would like our study to be a call to arms for increasing the cycle life of electrical energy storage. It’s really a basic conservative principal: The longer something lasts, the less energy you’re going to use.

—Charles Barnhart

The study was supported by GCEP and its sponsors: ExxonMobil, GE, Schlumberger and DuPont.


  • Charles J. Barnhart and Sally M. Benson (2013) On the importance of reducing the energetic and material demands of electrical energy storage. Energy Environ. Sci., doi: 10.1039/C3EE24040A



Electric power production mix varies a lot from different countries. China, USA, India (and a few other countries) use fossil fuels for a very high percentage of their e-power production and contribute to harmful emissions.

Burning compressed straw directly or indirectly is not much cleaner than burning NG/SG.

Many clean e-power sources are intermittent and need power storage units or systems.

One way around this problem is to use clean intermittent e-power sources, such as Wind and Solar etc., for base loads and a controllable power source, such as over equipped hydro plants with large water storage (reservoirs), for peak loads.

This way, you can use close to 100% of the energy available form Solar and Wind etc and use hydro on an as required basis only, thereby stretching the use of clean hydro e-power while allowing the use of more intermittent e-power sources.

Transportation lost can be greatly reduced with very high voltage (750+ kilo-volts) AC and/or DC power lines.

High quality winds and water falls are often co-located in the same general area. They make ideal companions.


Harvey, what you say is all true but I put straw forward as an idea for a reason. Because straw is a secondary waste material from grain production we are going to get a lot of it produced each whether we use it or not. In many areas straw is still burned in fields, producing significant air pollution, because they can't find a good use for all of it: Straw can be tilled back into the soil because while straw provides few nutrients to the soil it does add organic matter and helps aerate the soil - but there is also evidence that too much straw may not be good for soil. (Straw can also be used in straw-bale construction which produces very energy efficient housing, but this style's not for everybody.)

So, if the only thing that's left is burning it doesn't it make more sense to burn it in a power plant, which has pollution control devices, and off set burning something not renewable?


Is burning straw directly to generate heat and eventually e-energy more or less polluting than using it to produce cellulosic ethanol, other liquid fuels and/or essential chemicals?

Using straw bales to insulate houses is a bit too risky. Ultra dry straw is not very fire resistant and would required extensive treatments..

Roger Pham

One important point of this article is that as renewable energy will reach 80% or higher penetration, there will be times in which there will be a great excess of solar and wind energy, much more than grid's demand, and what is the most cost-effective way to store this energy?

Sure, Pumped Hydro and Compressed Air cost less energy to make over their lifetime of energy storage in and out, but they are severely limited in their energy storage capacity. They cannot hold enough energy from seasons of excess renewable energy to be used in winter when energy demand will be very high. Thus, they cannot hold enough energy for seasonal storage, but are still great for short-term energy storages for hours to a few days the most.

On the other hand, Hydrogen can be stored very cheaply on a pipeline system connected to underground caverns. Hydrogen produced in springs and falls will be used in winters, in combined heat and power generation at 90-95% efficiency. The waste biomass issue as discussed earlier can be resolved by adding these renewable H2 into the waste biomass while being gasified or pyrolyzed, thus can double or triple the energy output of a given amount of waste biomass. Via F-T synthesis to produce diesel fuel or jet fuel, H2 addition can double the yield of the waste biomass, while the synthesis of methane (NG) can triple the output of waste biomass.

Once everyone will realize the true danger of runaway global warmings, then the green light will be turned on for phasing out of fossil fuels and the synthesis of CO2-neutral fuels from waste biomass and renewable-energy H2. The oil and gas industry will fully participate in this instead of opposing it. They will do "energy farming" instead of "energy hunting" like oil and gas exploration and drilling. Human have evolved from highly-unstable hunter-gatherer lifestyle to highly-stable farming-agricultural lifestyle from which civilizations can truly flourished. We can now repeat the same for energy. We will farm for energy, instead of using more primitive methods of hunting for energy (exploration and drilling), and go to wars and shed massive amounts of lives and blood for energy...


First of all Harvey, you don't know what you're talking about when it comes to straw bale construction. Straw bale walls are naturally fire-retardant. Fire needs both air and fuel to burn and in a straw bale wall the straw is packed tight and covered in plaster. Even when placed in a fire it will protect you better than a stick frame wall. "What many homeowners don’t know is that the majority of the fire protection required by code in a conventional home is in the form of drywall. That’s it! 1/2″ of gypsum board is all that is required to protect you from fire. Once that drywall barrier has been compromised, there is nothing to stop the fire from attacking the structural wood and/or steel framing in your home. And what's behind the drywall in most walls? A tall, thin cavity flanked by 2x6s and loosely stuffed with fiberglass. A conventional stick framed home is nothing more than a series of chimneys behind a thin layer of fire protection.

Second, I'm not suggessing we burn straw for base load. I'm saying we could use it as stored energy. Wind & solar thermal with stored heat can handle most of our electrical energy needs;
But we might still need a reserve for peaking power. Straw fuel pellets can be stockpiled for years but produce quick power with a little warning. We could use pyrolysis to turn the pellets into a gaseous fuel which would not only make for more responsive, gas turbine generated, power but it would also burn cleaner and leave most of the carbon behind as biochar so it doesn't get back into the atmosphere.


Oh yeah, and like Roger says: Adding hydrogen makes it work even better.



ai_vin...sorry, no wood nor straw bales were used in our building. Concrete, bricks, steel and fiberglass are the predominant materials. The last time I saw packed straw used as insulation was in my grand father's house many many years ago. His 75+ years old wood + packed straw house burned in a few minutes. Nobody was in at the time.

I have no doubt that packed straw is a good insulation material but there are many other alternatives requiring less space.

Hydro is ideal for peak loads. It can be varied at will and water can be stored (at no cost) in the large reservoir when not required. Higher water level = higher pressure = more energy generation per volume. As more Wind power is added, hydro can handle higher peak loads, with added over equipment.


Wind farms generate more CO2 than they supposedly save when built in certain areas. Check it out:


Yes Mannstein, "when built in certain areas." Of course the same can be said of building ANYTHING on a peat bog.


Harvey, I hear what you're saying but I believe we're talking about two different ways of building. I'm refering to straw >>bale<< construction. A bale is compressed by a machine in the field and further compressed by stacking in the wall and then loading by the roof. By the time a straw bale wall is finished the straw has a density of at least 120kg/m3. That leaves very little room in the wall assembly for air to feed a fire. They are then plastered inside and out. If built to code they have a 1, 2, and even 4 hour fire rating depending on the type and thickness of plaster. (That's not my opinion, it's what the tests done by the poeple who write the codes and insurance policies say.)

It sounds like your grandfather's house was a wood framed cavity wall construction with loose straw fill. 75 years ago builders thought nothing of using exposed sawdust in the attic and if they insulated the walls at all they'd hand stuff them with whatever they had and "packed" it down with their foot. If you used straw you'd be lucky to get a density of 40kg/m3 which leaves a lot of room for air to feed a fire.


I have no doubt that packed straw is a good insulation material but there are many other alternatives requiring less space.

Very true but think about this: You can build a 18" straw bale wall that will deliver R-35, it takes 10" of fiberglass to get that much. But that's just from the fiberglass, once you put it into a wall with studs and headers that act as thermal bridges you'll need more.

Here's another thing: All building materials have what's call "embodied carbon" - the amount of CO2 that was released through its production. (Globally concrete production counts for 4% of man's emissions.) However, wood and related materials are made from carbon taken out of the atmosphere, they actually sequester more CO2 than gets released. 10" of fiberglass will have released 4kg of CO2 per m2 while a 18" plastered straw bale will have seqestered ~60kg/m2 - net.


Also Harvey, I totally agree with you about hydro - but I have to point out that people like you and I, who are fortunate enough to live in regions with abundant hydro resources, sometimes forget that not everybody has the hydro option.

I'm not arguing against hydro, I'm showing that we have options for everybody.


Most grid storage technologies were not developed for grid storage. For instance, this study mentions Li ion batteries and says the issue is the number of cycles (they quote 6000 cycles as the possible number). Well, 6000 cycles is 20 years of commuting in an electric car, the application for which the standard large format li ion was developed. Also it is not stated, but price is the real driver, not cycles, even though cycles may determine partially the cost, it is not the only consideration. Manufacturing also determines cost. Anyway the point I want to make is that the current Li ion technology was developed for automobiles, not grid storage, and to presume that the two applications would not require a seperate development to optimize the cells for auto and grid is an admission of ignorance. Solar and wind programs that do not include their own battery development work are seriously failing.

Kit P

“Most grid storage technologies were not developed for grid storage. ”

For all practical purposes there is not such thing as grid storage. The power industry only produces the amount of power that is needed to meet demand. The industry only builds enough power plants to do that with a reserve margin.

“Solar and wind programs that do not include their own battery development work are seriously failing.”

Solar and wind is seriously failing to make very much electricity. Maybe we should to wait to worry about storage until the there is something to store.

Of course if you are in the business of selling very expensive equipment that does not last very long, maybe there is a certain logic to broken storage system storing energy from broken wind and solar systems.

Will S

"For all practical purposes there is not such thing as grid storage. "

Cradled in Virginia's rugged Allegheny Mountains, the world's most powerful pumped storage generating station quietly balances the electricity needs of millions of homes and businesses across six states.

Installed capacity is 3,003 MW. During operation, the water level fluctuates by over 105 feet (30 m) in the 265-acre (110 ha) upper reservoir and 60 feet (20 m) feet in the 555-acre (220 ha) lower reservoir.

Virginia has two other hydro-storage facilities as well.

Kit P

"Virginia has two other hydro-storage facilities as well."

Yes, one is the closest to where I live. These pump storage systems were built to for low cost coal and nuke generation.

We got not wind!



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