From Stanford University
Stanford scientists calculate the carbon footprint of grid-scale battery technologies
Americans take electrical power for granted whenever they flip on a light switch. But the growing use of solar and wind power in the United States makes the on-demand delivery of electricity more challenging.
A key problem is that the U.S. electrical grid has virtually no storage capacity, so grid operators can’t stockpile surplus clean energy and deliver it at night, or when the wind isn’t blowing.
To provide more flexibility in managing the grid, researchers have begun developing new batteries and other large-scale storage devices. But the fossil fuel required to build these technologies could negate some of the environmental benefits of installing new solar and wind farms, according to Stanford University scientists.
“We calculated how much energy it will cost society to build storage on future power grids that are heavily supplied by renewable resources,” said Charles Barnhart, a postdoctoral fellow at Stanford’s Global Climate and Energy Project (GCEP) and lead author of the study. “It turns out that that grid storage is energetically expensive, and some technologies, like lead-acid batteries, will require more energy to build and maintain than others.”
The results are published in a recent online edition of the journal Energy & Environmental Science.
Most of the electricity produced in the United States comes from coal- and natural gas-fired power plants. Only about 3 percent is generated from wind, solar, hydroelectric and other renewable sources. The Stanford study considers a future U.S. grid where up to 80 percent of the electricity comes from renewables.
“Wind and solar power show great potential as low-carbon sources of electricity, but they depend on the weather,” said co-author Sally Benson, a research professor of energy resource engineering at Stanford and the director of GCEP.
“As the percentage of electricity from these sources increases, grid operators will need energy storage to help balance supply with demand. To our knowledge, this study is the first to actually quantify the energetic costs of grid-scale storage over time.”
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.
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.”
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Surely any cost benefit calculation for both financial costs and energy costs should be cradle to grave. The paper only looked at one half of the issue, I suspect that battery disposal / recycling costs both financial and energetic would be significant.
They also ignored other technologies, one commentator mentioned compressed air, another ignored technology would be conversion of excess energy into hydrogen.
That’s not the way you do, you use Sodium Sulfur batteries. Presidio Texas has a $25 million BOB, Big ol Battery, that stores four megawatts of power for up to eight hours. That works out to $0.78/Watt Hr. which seems a bit expensive, but then it’s real-world technology, not the usual greenie pie-in-the-sky stuff.
Hoser said:
H2 is also the smallest gas molecule which makes it most difficult to contain, and it also makes steel brittle.
Oh, and I almost forgot, it is also a “Severe fire hazard. Severe explosion hazard. Vapor/air mixtures are explosive. Pressurized containers may rupture or explode if exposed to sufficient heat. Electrostatic discharges may be generated by flow or agitation resulting in ignition or explosion”. http://www.nfpa.org/assets/files/PDF/CodesStandards/HCGHydrogenMSDS.pdf
Re: @Eric Worrall: 2:33 pm
Eric, you and I blundered.
1 GW/day might be equivalent to 10 kilotons, and if there is a failure it would indeed be a 10 kiloton near instantaneous release…….
But that was just the energy STORED!
Let us suppose our capacitor or battery bank is storing a GW-day and it shorts out
You release 10 kilotons of electrical energy PLUS you will vaporize a million tons of METAL by the flash and immediate COMBUSTION cascade. We might be in the Mega-ton range of a disaster.
If you have a GW-day oil storage tank, or coal mountain, the inferno will be spectacular. How much mass other than the oil or coal is being burned?
Now imagine a Lithium-ion battery. The same amount of electrical energy will have to be released. But how much of the mass of the battery will burn in the atmosphere if it get’s hot enough? I recon a good deal of it is combustable. Ever see aluminum burn?
A ClaytonPower 400Ah Lithium-ion battery will store 617 kJ/kg
= 617 KW-sec/kg
= 0.171 KWH / kg of battery.
or 7.1 KW-Day per TON of battery.
Use your 8.6 x 10^13 joules = 1 GW-day
We need 140,000,000 kg of 400Ah Lithium Batteries just to store 1 GW-day.
1 GW-day is about one 100-car coal unit train
Coal energy = 6.70 KWH / kg coal
coal with 40% energy conversion = 2.68 KWH / kg coal
coal unit train = one hundred 100-ton hopper cars = 10,000,000 kg coal.
coal unit train 100 cars = 1.12 GW-Day elec gen
So imagine a 1 GW-day battery bank the size and mass of TEN 100 car coal unit trains.
Then imagine it shorting out and catching fire.
http://www.iafss.org/publications/fss/8/375/ (2005)
The thermal runaway of a ton of coal or oil is a LOT higher than 75 deg C.
A couple more numbers:
A kg of coal burned for electricity at 40% efficiency yields 2.68 KWH / kg.
Or you need 0.373 kg coal for 1 KWH.
A ClaytonPower 400Ah Li-Battery gives 617 KW-sec / kg or 0.171 KWH / kg.
or you need 5.83 kg battery for 1 KWH.
Therefore, you need 15.6 kg of battery to store the energy from burning 1 kg of coal at 40% efficiency.
This is my first post here though I have been following this blog for over a year. I find it very educational and I am starting to understand some of the complexities of so called global warming. I have spent most of my working life in construction mostly as a carpenter but I tend to actively learn as much about other trades as possible. One of those trades was well drilling and another was process piping for clean rooms. One of the storage types mentioned in the article was compressed air. I thought about that for a bit and realized that building a storage system using cargo containers would need a lot of area and a lot of reinforcing and rebuilding of the containers. We already drill wells and line them with steel pipe for water and petroleum. Some wells have quite large diameters and go quite deep. Process piping involves welding a smooth bead that doesn’t impinge on the diameter of the pipe sometimes from the inside and sometimes from the outside. This process would enable the casing to be seamless and airtight and could be done with currently available technology. Once the well is in place it would have a movable plug installed that would be heavy enough to keep the air under pressure at whatever pressure the system required to operate. It would be filled by any mechanically or electrically driven compressor pumps which could be powered by wind, solar, hydro, geothermal, tidal, natural gas, electrical, or whatever. The advantages of a system like this are low impact, small footprint, and they can be put nearly anywhere with little environmental impact. They also don’t have to be vertical allowing them to be placed horizontally into the sides of mountains to take advantage of the wind power available along ridge lines. Since I came up with this over the last hour and it therefore is quite rough I look forward to your input.
After doing some more figuring I realized that the horizontal idea won’t work with the weighted plug idea so please disregard that idea. Thanks.
Article in WSJ, Mar. 11, 2013, Opinion: Bjorn Lomborg:
Green Cars Have a Dirty Little Secret
It is chocked full of statistics. Read and file it. Much of the dirty little secret comes from the electric car’s lineage from a lithium mine and smelter.
If an electric car is recharged by a fossil fuel power source, it emis 6 oz / mile of CO2. Gasoline car: 12 oz / mile. But considering the 30,000 pounds it started with, the electric vehicle will have to travel 160,000 miles before it’s carbon footprint is better than a gas car. (Gas as an 80,000 mile head start, and only looses 6 oz per mile to the electric).
Assuming you don’t have to replace the batteries. You will. So, it will never catch up.
If Electric car is recharged totally by solar, then if a Leaf is driven 90,000 miles, it will total 76% CO2 lifetime of a gas car — 8.7 tons of CO2. Carbon credits amount to $48.
143 comments in just four hours on a Sunday night.
@Walter Royal at 5:40 pm
Vertical storage of compressed gas is technically feasible, but it will boil down to cost.
The real problem, however, is that you might be limited to 18 5/8 in casing to a depth of 1000 m.
That is only 175 m^3 of volume. If you put CO2 in the casing at 50 atm, you might get 500 kg/m2 or a total of 88 tons in storage.
While the surrounding earth might serve as some protection in the high pressure state, the earth’s temperature and heat flow will never allow CO2 to liquefy. It would be ideal for a room temp gas to liquify under pressure, like propane or butane, in vertical storage. CO2’s critical point is 73 atm and 31 deg C which makes it an atmospheric gas and potential source for high pressure storage, but it is not going to liquefy under these circumstances.
Two other design problems. We must design for maximum pressure at the top, Say 50 atm = 750 psi in an 18 5/8 casing. But we must also design for atmospheric pressure at the bottom of the tank and guard against crushing the casing from outside lithostatic pressure, maybe 1500 psi.
What would it cost? $0.5 million? Maybe $0.20 million if assembly lined? Uncertainty a factor of 4 either way.
http://www1.eere.energy.gov/geothermal/pdfs/egs_chapter_6.pdf (pg. 10). And what is the carbon footprint of all that drilling, steel and cement per 175 m^3 storage tank?
An interesting question, all in all.
A cool PPT on well design and completion: (3 MB)
http://gekengineering.com/Downloads/Free_Downloads/A_Guide_to_Well_Construction.pdf
One energy storage mechanism that is rather old hat is the freezing of large tanks of water when energy is cheap and plentiful, and then using the ice to assist air conditioning systems during peak power use. It counts as a means of storing electrical energy in a form you will use later.
I am of course totally disinterested in their carbon counting adventure as I see no evidence that CO2 is harmful in any way; but I like that somebody finally recognizes that making batteries costs energy. Well done, academics!
Personally I have invented a method for estimation of energy use during production of a product. As energy has a price, even in politically price fixed markets, it is possible to estimate the energy used in the making of the product by looking at the comparative price/performance ratio.
As the price/performance ratio of electric cars is far inferior to any gas car, I have concluded that transportation using an electric car is a very wasteful activity; in terms of money, and via dividing the amount of money by the price of energy, also in terms of energy used.
Simple rule: When something is cheaper it costs less energy. Energy is the Master Resource and becomes primary determinant of the price the more we move forward in automation of production.
@Stephen Fisher Rasey on March 10, 2013 at 9:16 pm
Thank you for that feedback. The costs were something I had no idea about on the scale involved. I wonder if dead wells could be sealed at the bottom and used for storage of compressed air. Why did you use CO2 in your example? Is there something inherent in its properties that make it conducive to compression more than normal air? I hadn’t expected to compress the air to a liquid just to store it at high pressure to use it to run turbines to take up slack in electricity production for peak usage. Once again I thank you.
@Walter:
I was using CO2 initially to see if I could get it liquify at high pressure. Alas the critical temperature prevents it from being stored as a liquid or solid. At best, it will be a supercritical fluid.
And that might be good enough.
http://www.peacesoftware.de/einigewerte/calc_co2.php5
I found this CO2 properties website where you can plug in pressure and temp and get back density plus a dozen other parameters.
At 40 deg C With pressures of 60, 70, 80, 90, 100, 110, 120 bar
gives densities in kg/m^3 of: 149, 198, 278, 485, 629, 659, 689.
so there is a point around 90 atm where you can stuff CO2 down the pipe without a great increase in pressure. You can more than double the amount of gas down hole between 80 and 100 atm. This might make it a very good gas for energy storage. Most of the energy will come back out at 80+ atmospheres without much decay for the first 80% of the energy input. That sounds promising to me….. technically speaking. the economics are still dubious.
Compressed Air at 120 bar, 40 deg C gives 132 kg/m^3 and 60 bar is 67 km/m^3, so it is very linear in the feasible range, at lot less energy storage available than CO2. 200 bar is 214 kg/m3. 300 atm is 300 kg/m3. 400atm is 370 kg/m3.
You could use CO2 from a coal fired powerplant but use solar or wind to compress the gas downhole whenever you have too much solar or wind power to use…. (HA! What a concept!)
As for using depleted wells instead of drilling new ones…. hadn’t thought of that.
120 atm would be 1800 psi…. I’ve seen 18 5/8 casing listed at 198 bar for burst pressure. (Modern Well Design p137 in Google books) Air would be the only gas available at a soon to be abandoned well and Air looks much worse than CO2 economically. You can get higher pressures at smaller diameters, but then you are storing less gas.
I see your point about air not being as good and I guessed that it might have something to do with its density so I looked up another atmospheric gas, argon, which has a higher density than co2. The site you sent me to had a calc for co2 and for nitrogen (which fared little better than air but no calc for argon. So I hand this back to you because you have the knowledge of which I have a severe lack. Both argon and co2 are easily made or extracted so a small mobile plant could be set up on site to produce either using solar and/or wind to run it and put it in the hole then to power the recycling of the spent gas back into the hole.There are hundreds of thousands of oil wells in the US so it wouldn’t be hard to find one to test this on.
Walter, getting argon out of the air would be very expensive in energy use. I was using CO2 only as a semi-sequestration from a CO2 rich source, such as a coal plant. The only working fluid practical for existing wells that dot the country would be plain old air.
I meant “semi-sequestration” as in a temporary storage of CO2 under pressure from flue-gas and then release it to the atmosphere when power demand needed it. But it is just a exercise in physics. Economically it is a dead end. It is far better to crank up the coal plants to meet demand. Using the well doesn’t reduce the amount of CO2 released, only when it is released.
Ok, I see what you were thinking. I was looking at it more as a battery to store solar and wind power without having to actually build batteries. The wind power to load the tubes wouldn’t have to generate electricity as it could pump the air straight into the hole and a network of piping and automatic switching would connect a group of wells together creating a large battery bank. I’m less enthused with solar unless they were hot line collectors generating steam to run a mechanical pump. At any rate the inconsistent power production of wind and solar would be somewhat mitigated by combining both systems at a site and by the volume of high pressure air available to run the generators.