Comparing The Carbon Footprint Of Energy Storage Technologies

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Update –> This reader comment seemed very much worthy of more eyes: One flaw in their analysis — batteries can be recycled. The majority of the cost of making a battery is acquiring the raw materials, but once they are acquired, they can be recycled almost indefinitely as many times almost all of the raw materials are economically viable to recover — and that will only improve as recycling efforts scale up.

Stanford scientists recently completed a very interesting and useful study on the carbon footprint of different types of energy storage. Basically, the study examined how much energy is used to create different energy storage technologies versus how much electricity they can store over the course of their lives. While reading through the findings below, just keep in mind that increased production of a technology correlates with increased efficiency, and production of some of the battery technologies discussed (and several others not discussed or studied) is projected to increase significantly in the coming years.

Rather than repost Stanford’s entire article, I’m simply reposting the portion that captures the meat and bones of the study findings (excluding the basic and somewhat misleading intro). Check the key findings below or read the full article on Stanford’s news site.

Pumped hydro

The total storage capacity of the U.S. grid is less than 1 percent, according to Barnhart. What little capacity there is comes from pumped hydroelectric storage, a clean, renewable technology. Here’s how it works: When demand is low, surplus electricity is used to pump water to a reservoir behind a dam. When demand is high, the water is released through turbines that generate electricity.

Charles Barnhart, a postdoctoral fellow at Stanford's Global Climate and Energy Project, has developed a novel way to calculate how much energy is required to build batteries and other large-scale storage technologies for the electrical grid. Image Credit: Mark Shwartz
Charles Barnhart, a postdoctoral fellow at Stanford’s Global Climate and Energy Project, has developed a novel way to calculate how much energy is required to build batteries and other large-scale storage technologies for the electrical grid. Image Credit: Mark Shwartz

For the Stanford study, Barnhart and Benson compared the amount of energy required to build a pumped hydro facility with the energetic cost of producing five promising battery technologies: lead-acid, lithium-ion, sodium-sulfur, vanadium-redox and zinc-bromine.

“Our first step was to calculate the cradle-to-gate embodied energy,” Barnhart said. “That’s 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, Barnhart relied on data collected by Argonne National Laboratory and other sources. The data revealed that all five batteries have high embodied-energy costs compared with pumped hydroelectric storage.

“This is somewhat intuitive, because battery technologies are made out of metals, sometimes rare metals, which take a lot of energy to acquire and purify,” Barnhart said. “Whereas a pumped hydro facility is made of air, water and dirt. It’s basically a hole in the ground with a reinforced concrete dam.”

After determining the embodied energy required to build each storage technology, Barnhart’s next step was to calculate the energetic cost of maintaining the technology over a 30-year timescale. “Ideally, an energy storage technology should last several decades,” he said. “Otherwise, you’ll have to acquire more materials, rebuild the technology and transport it. All of those things cost energy. So the longer it lasts, the less energy it will consume over time as a cost to society.”

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,” Barnhart said. “The higher the ESOI value, the better the storage technology is energetically.”

When Barnhart crunched the numbers, the results were clear. “We determined that a pumped hydro facility has an ESOI value of 210,” he said. “That means it can store 210 times more energy over its lifetime than the amount of energy that was required to build it.”

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. “That means a conventional lead-acid battery can only store twice as much energy as was needed to build it,” Barnhart said. “So using the kind of lead-acid batteries available today to provide storage for the worldwide power grid is impractical.”

Improved cycle life

The best way to reduce a battery’s long-term energetic costs, he said, would be to improve its cycle life – that is, increase the number of times the battery can charge and discharge energy over its lifetime. “Pumped hydro storage can achieve more than 25,000 cycles,” Barnhart said. “That means it can deliver clean energy on demand for 30 years or more. It would be fantastic if batteries could achieve the same cycle life.”

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,” Benson said. “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.”

In addition to energetic costs, Barnhart and Benson also calculated the material costs of building these grid-scale storage technologies.

“In general, we found that the material constraints aren’t as limiting as the energetic constraints,” Barnhart said. “It appears that there are plenty of materials in the Earth to build energy storage. There are exceptions, such as cobalt, which is used in some lithium-ion technologies, and vanadium, the key component of vanadium-redox flow batteries.”

Pumped hydro storage faces another set of challenges. “Pumped hydro is energetically quite cheap, but the number of geologic locations conducive to pumped hydro is dwindling, and those that remain have environmental sensitivities,” Barnhart said.

The study also assessed a promising technology called CAES, or compressed air energy storage. 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. The Stanford team discovered that CAES has the fewest material constraints of all the technologies studied, as well as the highest ESOI value: 240. Two CAES facilities are operating today in Alabama and Germany.

Global warming impact

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, and replacing them with emissions-free technologies could have a dramatic impact, he added.

“There are a lot of benefits of electrical energy storage on the power grid,” he said. “It allows consumers to use power when they want to use it. It increases the amount of energy that we can use from wind and solar, which are good low-carbon sources.”

In November 2012, the U.S. Department of Energy launched the $120 million Joint Center for Energy Storage Research, a nationwide effort to develop efficient and reliable storage systems for the grid. The center is led by Argonne National Laboratory in partnership with the SLAC National Accelerator Laboratory at Stanford and a dozen other institutions and corporations. Part of the center’s mission is to develop new battery architectures that improve performance and increase cycle life – a direction that Barnhart and Benson strongly support.

“I would like our study to be a call to arms for increasing the cycle life of electrical energy storage,” Barnhart said. “It’s really a basic conservative principal: The longer something lasts, the less energy you’re going to use. You can buy a really well-made pair of boots that will last five years, or a shoddy pair that will last only one.”

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

Mark Shwartz writes about energy technology at the Precourt Institute for Energy at Stanford University.

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Zach is tryin' to help society help itself one word at a time. He spends most of his time here on CleanTechnica as its director, chief editor, and CEO. Zach is recognized globally as an electric vehicle, solar energy, and energy storage expert. He has presented about cleantech at conferences in India, the UAE, Ukraine, Poland, Germany, the Netherlands, the USA, Canada, and Curaçao. Zach has long-term investments in Tesla [TSLA], NIO [NIO], Xpeng [XPEV], Ford [F], ChargePoint [CHPT], Amazon [AMZN], Piedmont Lithium [PLL], Lithium Americas [LAC], Albemarle Corporation [ALB], Nouveau Monde Graphite [NMGRF], Talon Metals [TLOFF], Arclight Clean Transition Corp [ACTC], and Starbucks [SBUX]. But he does not offer (explicitly or implicitly) investment advice of any sort.

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18 thoughts on “Comparing The Carbon Footprint Of Energy Storage Technologies

  • Interesting topic, there are other things to think about than ESOI. Round trip efficiency (RTE) is also important.

    Lets taken an example of a 1KWhr storage device used once per day for 25 years, cycling 9125 times.

    If you have a RTE of 90% and an ESOI of 10, then you lose 912 KWhr total over its life because of RTE losses and it would take 912 KWhr to produce the device, a total of 1824 KWhr lost to provide the time shifting services.

    If you use something like CAES with an ESOI of 240, but a RTE of say 70%, then it costs 38 KWhr to produce the device, BUT you lose 2738 KWhr RTE losses, the total energy cost to time shift is about 50% higher than in the former case.

    Now the energy in these two cases isn’t identical because we are talking surplus energy being lost by RTE vs perhaps baseload to produce the first device, however when you have the first storage device at your disposal the difference isn’t that significant.

    The calculations seem to show that once the ESOI is much over 10, there isn’t much point chasing higher values, its diminishing returns, and RTE is just as important, in fact more so when its much less than 90%.

    Similar to EROI, an EROI of 10 vs 1 million doesn’t make that much difference for a solar panel etc.10 is perfectly good enough.

  • So, is flywheel storage dead?

    • It’s apparently not a solution for long term storage. It may have a role in grid smoothing.


  • Going Upstream: Transforming to Renewable Industrial Processes

    This analysis of green edge technologies cars, refrigerators, etc. that are manufactured by the classic industrial method. The research group l was a part of in grad school at Georgia Tech under Prof. Jack Winnick focused on how to shift traditional industrial thermal processes (those which used fuel oil) to industrial electrochemical processes which could be run on renewable electricity sources. Symbol Materials is a lithium mining company and process funded by MDV which uses an electrochemical process to extract lithium materials from geothermal brines. This industrial processes, with a financed solar system, can be a renewable industrial process. Further, companies like Toxco can use electrochemical methods to recycle the materials.

    The renewable world starts at the edge where people’s voices are heard the loudest. Therefore we get electric cars. Then we start engineering the rest of the manufacturing process to also be renewable in process and business. We are in the bottom of the 2nd inning on the introduction of EV’s and we are seeing the emergence of economically viable energy storage solutions. We are far from done in shifting how we live and satisfy our needs, but we have a healthy plan to deploy an Internet of Energy requiring renewable sources and networked energy storage everywhere, and we will get there. Let’s focus on how to turn those industrial processes renewable and this article will provide a moot point.

    Dr. Ryan Wartena


    Note who can find the German solar panel manufacturing plant that is solar power energized?

  • “Pumped hydro storage faces another set of challenges. “Pumped hydro is energetically quite cheap, but the number of geologic locations conducive to pumped hydro is dwindling, and those that remain have environmental sensitivities,” Barnhart said.”

    That’s just not correct. We have hundreds of existing dams that can be converted into pump-up storage facilities. They were built for things like flood control and irrigation but they can be adapted.

    And there’s closed loop pump-up where both the upper and lower reservoir are constructed on dry land. After the initial filling all is needed is annual replacement for evaporation losses.

    And there are existing, abandoned mines which are being evaluated for storage use.

    There needs to be further analysis of pump-up storage which doesn’t require pouring a lot of cement. Using existing dams or using no dams at all would result in a much lower carbon footprint.

  • One flaw in their analysis – batteries can be recycled. The majority of the cost of making a battery is acquiring the raw materials, but once they are acquired, they can be recycled almost indefinitely as many times almost all of the raw materials are economically viable to recover – and that will only improve as recycling efforts scale up.

    But we definitely have some CES opportinities to look into while we continue battery R&D… While it’s not ideal for every situation, (and there’s been lots of advances since either the Alabama or Germany plants were founded) if it was paired with commercial heating/cooling to increase efficiency it really could be a significant chunk of our energy storage solution.

      • Sounds good – otherwise it was a very good read!

    • A company called Lightsail claims to have furthered CAES. During air compression they spray a fine mist of water into the cylinder which absorbs most of the heat. The water is then stored separately in a well insulated area which preserves the heat. During generation the stored heat is used to expand the compressed air as it going into the turbine.

      Much higher round trip efficiency. And they are putting their devices into shipping container packages.

      If they can make this work it should be a winner. And everything in their system should be recyclable which will give it a low CO2 footprint.

        • Check out the founder/CEO of Lightsail. A most interesting young woman.

          And another woman who is making news in cleantech is the founder/head of the geothermal company that demonstrated fracking using CO2 rather than fracking chemicals this last year.

          • Man Bob – you are just a wealth of information.

            Why don’t we see any posts from you? Just prefer the informal stuff?

          • I prefer the role of relief pitcher. ;o)

            Actually, I take pride in not having earned a single dollar by by own sweat in almost 25 years. I’d hate to mar my record by picking up a couple of bucks by penning a piece here. And I have put together a few pieces which Zach has put up but not under my name. I let him put the measly returns into the company donut fund.

            Good to have you around. You’ve been contributing a lot of information to the site.

        • Here’s another storage approach I’m following. The concept sounds workable and the company says they have built the critical feature, the heat pump. They’ve received funding for a large scale test and we should hear something soon (or not if they fail)….

          “Isentopic claims its gravel-based battery would be able to store equivalent amounts of energy but use less space and be cheaper to set up. Its system consists of two silos filled with a pulverised rock such as gravel. Electricity would be used to heat and pressurise argon gas that is then fed into one of the silos. By the time the gas leaves the chamber, it has cooled to ambient temperature but the gravel itself is heated to 500C.

          After leaving the silo, the argon is then fed into the second silo, where it expands back to normal atmospheric pressure. This process acts like a giant refrigerator, causing the gas (and rock) temperature inside the second chamber to drop to -160C. The electrical energy generated originally by the wind turbines originally is stored as a temperature difference between the two rock-filled silos. To release the energy, the cycle is reversed, and as the energy passes from hot to cold it powers a generator that makes electricity.

          Isentropic claims a round-trip energy efficiency of up to 80% and, because gravel is cheap, the cost of a system per kilowatt-hour of storage would be between $10 and $55.

          Howes says that the energy in the hot silo (which is insulated) can easily be stored for extended periods of time – by his calculations, a silo that stood 50m tall and was 50m in diameter would lose only half of its energy through its walls if left alone for three years.”

          The suggested cost is very attractive. And efficiency is not bad, when cost is considered.

          We’re a few years from needing serious storage. Some grids are getting up to 40% of their supply from renewables without adding storage. At the end of 2013 we may or may not be above 5% wind and solar for the US as a whole, so we have time. I think that between what is happening with battery technology and a few other approaches we’ll crack this nut.

          • Yeah… this is a good solution currently, but I think in the long run battery technology will win out. It’s simply too efficient already – all we really need for grid storage is cycle life – which theoretically could be infinite.

            Even if these other technologies approach their theoretical maximum they won’t compete with the future of batteries – but we should still pursue them in the short run. The understanding we gain from their development is worth more than the development costs for most things like this, and there’s a very real possible application for transition technologies!

  • If we asked different questions, would we get different (the right) answers?
    e.g. Should energy storage be on-grid? – No, I don’t think so.
    First define the nature of your renewable energy resource:-

    Hydropower, geothermal = dispatchable and therefore no storage requirement.

    PV = incurably intermittent electrical energy, widely dispersed. You only need to store it when you get a ‘wrong-time’ surplus. If that might happen, arrange to put it into BEVs. You don’t need a very smart grid to do that! An on-grid storage facility would give a poor (ESOI/RTE) ROI. Whatever you do, don’t use EV technology for grid-scale batteries – higher demand for costly resources would mean higher prices. (and a big carbon footprint to boot)

    CSP + TES = heat is stored, (before-generator) short term = dispatchable electricity. Therefore, no need for any grid storage.

    Wind, wave and tidal = kinetic energy that can be stored (before-generator), long term = dispatchable electricity, on a large scale, and widely dispersed. Therefore, no need for on-grid storage, which is more expensive to build and crucially, has much higher running costs. The RTE of before-generator energy storage is 100%, as there is no (electrical) ’round trip’. The additional investment could be next to nothing, if marine renewables were all redesigned to SHARE storage facilities. The orthodox technologies and industry/market structures are dysfunctional. (Wind competing with wave, competing with tidal. How dumb is that?) See my post on this Q&A:-

    A gravity/compressed air accumulator could have a design life measured in centuries, if the one component subject to wear can be easily refurbished. Design for the circular economy – that’s far more resource and energy-efficient.

    Eliminating the wrong-time generation of electricity, and storing the energy instead, would save billions.

    Penetration of wind power in the UK market is currently around 3%. Wind adds 3 Euros per MWh (and rising) to system operation costs in Germany. On-grid storage is estimated to increase that, not reduce it. Wrong technology? wrong place?

    Weather forecasting is good enough so you can easily cope with the variables:-
    Shave the peaks off your wind energy graph and store it away for a calm day.
    Shave the peaks off your wave energy graph and store it away for a calm day.
    Store a wrong-time tidal energy surplus and generate electricity to meet peak demand – highly profitable, when the tide is on the turn at the wrong time.

    NB: These storage facilities can also be topped up from the grid, if needs be.

  • given Zachary’s concern about the Barnhart not taking into account recycling, can anyone find a journal article that estimates the energy required to manufacture a recycled lead-acid battery?

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