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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Besides the embodied issue with renewables you should also look at efficiencies. Coal plants are 60% efficient but solar cells are at best 35%.
“Atlernative”, not “alternate”? It matters to pedants like me & many.
Ouch, I mean “alternative” (slaps self with wet dishcloth)
..now figure out re-wiring the entire country
Energy storage question: (and I know there are environmental controversies but I’m just asking for info/ideas) …. in areas such as West Virginia where there is a lot of potential for massive surface mining, has anyone examined the economics of setting up pumped hydro locations as, say, an elevated area is surface mined…?? Since a lot of money is already spend removing coal and reclaiming the land, could it be economical to set up reservoir basins for pumped hydro??
Probably couldn’t make enough of a difference for any national scale of electricity but might be of use for local/regional projects.
I know the enviro issues for such surface mining (mountaintop removal) and also for use of coal remain, but I’m wondering about the economics of it if energy storage such as pumped hydro were a priority….
I seem to recall some of this discussion before. Many times. Years ago. By sceptics. We were right.
This is a very useful study. 700 cycles seems a bit pessimistic for lead acid batteries, but then a more typical figure of 900-1000 realized with 6 volt golf cart batteries seems the limit based on my experience isn’t that much more.
Many of the technical dreams of the innocent (many of whom are politicians) do not survive a thorough cost analysis that considers ALL of the costs which can be anticipated.
Energy storage as a crutch to prop up renewable power generation. No thanks.
“Only about 3 percent is generated from wind, solar, hydroelectric and other renewable sources. ”
Isn’t Stanford in California and don’t they know that ‘hydroelectric’ is not considered “renewable”.
“while lead-acid technology is at the bottom, achieving a mere 700 cycles.”
Does this mean I have to get a new car battery after 700 starts?
Hey Charley, what about th 2nd Law of Thermo. How much of the power you put into each system can you get back out. Did not see any of that in your ESOI.
I wonder if they considered the cost of the AC to DC and DC to AC convertors needed for a battery storage system. Those things don’t come cheap.
My favourite energy storage technology is supercapacitors (or ultracapacitors) – e.g. http://www.greenbiz.com/blog/2012/06/10/ultracapacitors-next-big-thing-energy-storage
But lets do a little math.
Say you wanted to provide energy storage backup for a 1Gw alternative energy generator for 1 day – so 1Gw provided for 1 day when the wind doesn’t blow.
To do this, your ultracapacitor storage facility would have to store
1Gw x 1 day
= 1 billion joules / seconds x 86400 seconds / day
= 8.6 x 10^13 joules / day of energy
By an interesting coincidence, this is similar to the energy released by Little Boy, the nuclear bomb which destroy Hiroshima (6.3 x 10^13 joules – http://en.wikipedia.org/wiki/Little_Boy ).
So if your ultracapacitor storage facility ever suffered sudden catastrophic dielectric failure, as highly stressed capacitors sometimes do, the resulting abrupt release of energy would be indistinguishable from a 10 kiloton nuclear explosion.
http://silentadmin.gsans.com/my-toolbox/electronics/why-do-electrolytic-capacitors-fail/ ,
A Brisbane company has already developed zinc/bromine batteries that can charge and discharge 100% versus the lead acid much lower capacity. Here is the link. NZ has some taking the place of extra wiring needed to upgrade the capacity of end of line places that are remote. In Qld the batteries are located at small towns to off-set peak load and recharge in low use times.
http://redflow.com/redflow_Home
‘Renewable energy’ only makes any sense in remote locations, or if someone can invent a sensible means of storing electricity in a way hugely more cost efficient and effective than a giant battery.
In effect, this is the elusive Holy Grail of ‘renewable energy’ and is not going to be found anytime soon.
I don’t think they will have much luck with the battery push. Increasing the cycles would be great… except the fact that for most battery usage, cycles are meaningless because for most they get thrown away long before the charge cycles are used up.
Sorry link is http://redflow.com/
The irrational fear of carbon dioxide brings out the crazy, even in some smart people.
Alternative energy is very similar to alternative health.
It’s all a bit of harmless fun until you trully need either. No reiki master, acupuncturist or homeopath is going to cure you of cancer or replace your hip. When push comes to shove only fossil fuel or medicine is good enough for humanity. Everything else are just talking points.
David. coal plants being 60% efficient is bull biscuits; that’s beyond.the carnot cycle ideal.
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Here’s a story about a Scottish islander who brews whiskey. A storm brought down the electric so he used his Nissan Leaf to supply a week of elektrickery for his home until the supply came back on.
Once again sensible people realize that there is no such thing as a free lunch!
Lets not forget, When the adverts start, everyone jumps into the kitchen and puts the kettle on. The power stations have to ramp up the power for this hours before. It costs them, (and you) money.
The act of LOAD BALANCING is going to be a big money spinner. Britain has it’s “Electric Mountain”, its scale is truly amazing. It’s nothing to do with being “green”; just perfect common sense.
I’d say we’ll dealing with some ignorance here about grids, pumped storage and so on.
For example, the “turnaround loss” for most pumped storage facilities is 20% or more, if
it includes transmission losses. Whether these storage penalties were factored in is unknown from the description. A possible penalty of close to 30% might occur, depending upon how far away the facility is located. And pumped storage ain’t cheap – the figure I saw for one of California’s several planned facilities showed that a facility that has the output capacity of an equivalent nuclear power plant was not a whole lot cheaper than building a nuclear plant. Pumped storage facilities can only hold about 10 to 15 hours’ worth of maximum output. They therefore mostly can shift unreliable solar or wind power pretty much for a different portion of the same day. The same can be said for batteries or any storage medium – if the wind or sun disappears for more than a day or so, conventional backup is required. In other words, I don’t see how you can shutter any conventional plants, and these conventional backup facilities cost money to operate even if they produce no power whatsoever. Also, tell these “experts” that “renewable” does NOT mean unreliable. Geothermal is reliable and so is hydro (in the near and medium term). They also avoid the issue of solar panel carbon costs, ditto for wind. I’ve seen some very high carbon figures for producing solar. panels.
The pumped storage that was built in the past had a far different purpose : to allow cheap power from nuclear or coal plants to be produced above the current demand level, and send that to storage for later in the day when demand exceeded the base load plant capacities and therefore help avoid what was then very expensive gas peak load generation. They actually saved money, which California’s facilities will not do – they simply add to to cost of their solar and wind.
All rather theoretical since renewables (wind/solar) are never ever going to supply 80% of US energy consumption, surely (?). Cover the entire area with properly separated wind mills and one gets what – those brighter than me have probably computed this, but i have a notion I read it wasn’t enough.
“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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It is not necessarily the boot, but what the wearer subjects it to.
I mean, this is about a work boot, right ?
Or a modeled boot?
Speaking of Carbon footprints; you irrational CAGW science deniers criticize Al Gore unfairly.
Who knows or cares if he owns a private jet or just rides in them occasionally? Who cares how much he flies first class? What does it matter if his mansions consume more power than an African village?
Listen carefully to the man. He has carbon offsets and carbon credits. He helped invent the system and one of his companies is a “carbon credit” bank. That means it is clearly OK for him to leave a huge carbon footprint. His carbon credits pay for them! His companies are carbon credit zillionaires.
Al Gore could light an oil well head and use the 300 foot candle of flames to spit roast whole Brahman bulls 24/7 for the rest of his life without harming the environment in any way.
Just ask him.
In the matter of cycle life of a lead-acid cell; its definition must be carefully considered to account for devolution of the technology. Traditional lead-acid cells were disassembled and restored. There used to be cells in submarine service after many lifetimes.
About lithium cells, consumer grade cells are still rated 300 – 500 cycles and 3 – 5 years corrosion limits IIRC. http://batteryuniversity.com/