From Stanford University
Stanford scientists calculate the energy required to store wind and solar power on the grid
Renewable energy holds the promise of reducing carbon dioxide emissions. But there are times when solar and wind farms generate more electricity than is needed by consumers. Storing that surplus energy in batteries for later use seems like an obvious solution, but a new study from Stanford University suggests that might not always be the case.
“We looked at batteries and other promising technologies for storing solar and wind energy on the electrical grid,” said Charles Barnhart, the lead author of the study and a postdoctoral scholar at Stanford’s Global Climate and Energy Project (GCEP).
“Our primary goal was to calculate their overall energetic cost – that is, the total amount of fuel and electricity required to build and operate these storage technologies. We found that when you factor in the energetic costs, grid-scale batteries make sense for storing surplus solar energy, but not for wind.”
The study, which is supported by GCEP, is published in the online edition of the journal Energy and Environmental Science.
Climate change and renewable energy
Most electricity in the United States is generated at power plants that run on coal and natural gas – fossil fuels that contribute significantly to global warming by emitting large amounts of carbon dioxide. Solar and wind power are emissions-free and renewable, but depend on sunlight or wind to operate.
“For the grid to function efficiently, power supply needs to match power demand at all times, but with renewables, that’s not always the case,” Barnhart said. “For example, wind farms sometimes produce too much electricity at night when demand is low. That excess energy has to be stored or used elsewhere. Otherwise it will be lost. However, the U.S. grid has very limited storage capacity.”
A wide variety of technologies are being developed to address the lack of grid-scale storage. The Stanford team looked at several emerging technologies, including five battery types – lead-acid, lithium-ion, sodium-sulfur, vanadium-redox and zinc-bromine.
In a previous study, Barnhart calculated the energetic cost of building and maintaining each of the five battery systems for grid-scale storage. Lead-acid batteries had the highest energetic cost, lithium-ion the lowest, he found.
“We calculated how much energy is used over the full lifecycle of the battery – from the mining of raw materials to the installation of the finished device,” Barnhart said. “Batteries with high energetic cost consume more fossil fuels and therefore release more carbon dioxide over their lifetime. If a battery’s energetic cost is too high, its overall contribution to global warming could negate the environmental benefits of the wind or solar farm it was supposed to support.”
For this study, he and his colleagues calculated the energetic cost of grid-scale photovoltaic solar cells and wind turbines.
“Both wind turbines and photovoltaics deliver more energy than it takes to build and maintain them,” said GCEP postdoctoral scholar Michael Dale, a co-author of the study. “However, our calculations showed that the overall energetic cost of wind turbines is much lower than conventional solar panels, which require lots of energy, primarily from fossil fuels, for processing silicon and fabricating other components.”
To store or curtail?
Next the scientists looked at the energetic cost of curtailment – the practice of shutting down solar panels and wind turbines to reduce the production of surplus electricity on the grid.
“Curtailment of renewable resources seems wasteful,” Barnhart said. “But grid operators routinely curtail wind turbines to avoid a sudden, unexpected surge of excess electricity that could overload transmission lines and cause blackouts. Curtailment rates in the U.S. will likely increase as renewable energy becomes more prevalent.”
Shutting down a clean source of electricity seems counterproductive, but is storing surplus energy in batteries a practical alternative?
To find out, the researchers compared the energetic cost of curtailing solar and wind power, versus the energetic cost of grid-scale storage. Their calculations were based on a formula known as “energy return on investment” – the amount of energy produced by a technology, divided by the amount of energy it takes to build and maintain it.
Using that formula, the researchers found that the amount of energy required to create a solar farm is comparable to the energy used to build each of the five battery technologies. “Using batteries to store solar power during periods of low demand would, therefore, be energetically favorable,” Dale said.
The results were quite different for wind farms. The scientists found that curtailing wind power reduces the energy return on investment by 10 percent. But storing surplus wind-generated electricity in batteries results in even greater reductions – from about 20 percent for lithium-ion batteries to more than 50 percent for lead-acid.
“Ideally, the energetic cost of curtailing a resource should at least equal the amount of energy it cost to store it,” Dale said. “That’s the case for photovoltaics, but for wind farms, the energetic cost of curtailment is much lower than it is for batteries. Therefore, it would actually be more energetically efficient to shut down a wind turbine than to store the surplus electricity it generates.”
He compared it to buying a safe. “You wouldn’t spend a $100 on a safe to store a $10 watch,” he said. “Likewise, it’s not sensible to build energetically expensive batteries for an energetically cheap resource like wind, but it does make sense for photovoltaic systems, which require lots of energy to produce.”
Increasing the cycle life of a battery would be the most effective way to improve its energetic performance, Barnhart added. Conventional lithium-ion batteries last about four years, or 6,000 charge-discharge cycles. Lead-acid batteries only last about 700 cycles. To efficiently store energy on the grid, batteries must endure 10,000 to 18,000 cycles, he said.
“Storing energy consumes energy, and curtailing energy wastes it,” Barnhart said. “In either case, the result is a reduction in the overall energy return on investment.”
Other options
In addition to batteries, the researchers considered other technologies for storing renewable energy, such as pumped hydroelectric storage, which uses surplus electricity to pump water to a reservoir behind a dam. Later, when demand for energy is high, the stored water is released through turbines in the dam to generate electricity.
“Pumped hydro is used in 99 percent of grid storage today, ” Barnhart said. “It works fantastically from an energetic perspective for both wind and solar. Its energy return on investment is 10 times better than conventional batteries. But there are geologic and environmental constraints on where pumped hydro can be deployed.”
Storage is not the only way to improve grid reliability. “Energy that would otherwise be lost during times of excess could be used to pump water for irrigation or to charge a fleet of electric vehicles, for example,” Dale said.
It’s important for society to be energy-smart about implementing new technologies, Barnhart added. “Policymakers and investors need to consider the energetic cost as well as the financial cost of new technologies,” he said. “If economics is the sole focus, then less expensive technologies that require significant amounts of energy for their manufacture, maintenance and replacement might win out – even if they ultimately increase greenhouse gas emissions and negate the long-term benefits of implementing wind and solar power.”
“Our goal is to understand what’s needed to build a scalable low-carbon energy system,” said co-author Sally Benson, the director of GCEP and a professor of energy resources engineering. “Energy return on investment is one of those metrics that sheds light on potential roadblocks. Hopefully this study will provide a performance target to guide future research on grid-scale energy storage.”
Adam Brandt, an assistant professor of energy resources engineering in Stanford’s School of Earth Sciences, also co-authored the study.
This article was written by Mark Shwartz of the Precourt Institute for Energy at Stanford University.
Most countries don’t have enough water in some locations, but have ample water elsewhere. Despite Greenie objections we will build national and even continental scale water distribution systems. Such systems could also function as pumped hydro storage systems.
Use intermittent solar and wind to pump water up over hills/mountains then harvest the energy used on the other side when electricity is needed. The big advantage of such an approach is that transporting water isn’t time critical, as reservoirs along the way buffer supply to demand for periods of days to months.
Batteries, storage. Oh, yes, this is the problem with renewables such as solar and wind. Fact of the matter is that no one has come close to solving this problem in a cost effective way. That is why there has to be another form of base electricity production, something many renewable promoters too easily forget.
The best storage for wind energy is by leaving the material used to build those windmills in the ground and using the money to build much more efficient forms of energy production on much less space instead.
Liquefied air as storage.
http://www.newscientist.com/article/mg20928014.800-power-of-cool-liquid-air-to-store-clean-energy.html#.Ui4msX9r0pU
CellCube is vanadium redox as far as I can tell. If were really that good (ditto other great technologies) lots of outfits would sell them. Hype and reality often differ.
Compressed air and flywheels have a major drawback: catastrophic failure. OK if nothing goes wrong, best not to be nearby if something does.
Compressed air has another gotcha: Boyle’s Law. Air gets hot when you compress it. Either need good insulation, or give up a bunch of energy.
Then there is the shredded tweet problem …
@richardscourtney: Sure they consider economics in these pipe dreams. I’m sure, if you asked, you would receive superior economic benefits from controlling the climate and preventing the earth’s fevor to burn it to a cinder when compared to today’s costs. It’s easy, what number do you want?
Some observations/questions: 1. Peak electricty demands in the PJM area (east coat VA/MD/PA/NJ and west to MI) in winter are roughly 5-7AM and 5-7PM, when there is little sun and little wind. Summer is 10AM-10PM. Wind and solar aren’t very practical for over half the year because you need other capacity at peak. BTW: go live in western MI and see how many days of sun you get for the 6 cold months.I had a passive solar on a house in Kalamazoo. Worked great all three days in the winter we had sunshine. 🙂
2. How many tons of battery per gigawatt does it take to store all this “zero cost” renewable? What’s the price of raw materials when we start sucking these materials out of the market?
3. Don’t you need two lakes for hydro? If not, where does the water come from? If it would be darn near impossible to build one dam and artificial lake, how about 2 in tandem?
4. If batteries don’t work well in the winter in the UK, you ought to try them in the northern half of the US, Canada and AK.
Engineering details that could be overcome if there were no reasonable, less expensive alternative supplies.
Under any rational examination economics kills these ideas. I wonder when we will be rational.
I can see where wind would not be worth storing … it doesn’t make sense to try and charge a battery bank with a source that is not capable of charging the battery bank. You’d just waste a bunch of money building the battery bank.
“Likewise, it’s not sensible to build energetically expensive batteries for an energetically cheap resource like wind, but it does make sense for photovoltaic systems, which require lots of energy to produce.”
Ehhhhh? Only in a grant-driven world. Sorry, it’s totally the other way round. With expensively-generated energy, you’d better try to sell it directly. With cheap energy, you can afford to lose a bit in the accumulation cycle.
Jim Cripwell
So it is not “a simple matter of turning down the back up fossil or nuclear plant that are always required.”
Having personally operated power generating steam turbines I assure you that it is. These machines can rapidly respond to changes. Especially the gas-turbine and nuclear plants. However, the nuclear plants are somewhat limited by regulations. Every time a load is started, an adjustment is made automatically. You just don’t notice it.
There are limits of course, but the small gradual transients that solar and wind are likely to provide are better accomadated than the large transients of say, losing a large baseload plant.
It seems like they could build a natural gas plant next to a wind farm and use excess wind energy to preheat water for the boilers so they could use less gas. This probably would not make wind really useful but might nudge it closer.
But since ‘green’ energy is really about passing money to politicians cronies and throttling our economy any thing that might make it more practical will never happen and if it did happen the ‘environmentalists’ would suddenly find all the eagle and other bird deaths that they currently ignore to be a problem and would lobby against wind power.
dave ward
That article says that buyers are incentivised to consume all the wind and solar power that is created. When it was too much they did exactly what I suggested. Shut down or turned down the conventional sources. No mention of the use of batteries.
Also, nuclear is only slow to respond because of procedural limitiations brought on by government regulations. Many of the ones in the US were originally desinged to be peaking plants, but are now used as base load. Trust me, when the “All-Ahead Flank” speed was rung up on the Los Angeles class submarine I drove, it changed power very rapidly. From an engineering standpoint, the only thing faster than nuclear is the gas-turbine
I applaud any study of “energy storage” costs associated with solar and wind because it highlights the question that never seems to get asked: “What is the true cost of solar and wind power?” As things currently stand, declining costs of photovoltaic cells are daily trumpeted as evidence of solar’s eventual “cost competitiveness”. What is never included in those costs is the current capital expense of all that “spinning reserve” generation capacity that must stand by to pick up the slack “when the wind don’t blow and the sun don’t shine”.
When a battery storage system comes along that is more cost-efficient than a simple, natural gas combustion turbine and associated fuel bill, then you’ll have a “breakthrough”. Until that time, the cost of that stand-by turbine and its fuel bill should be included in the true cost of wind and solar.
What about storing the solar energy as low, less than 100c, temperature heat. Use my thermodynamic cycle, gravity, rankine, and my latent heat extracting sealed turbine. Efficiency beyond 80%, sealed environmentally friendly.
A single acre, 100 feet deep, can store 5 megawatts of heat with only a 40c temperature rise.
Jerome Lurtz, patents, on the web.
So it is now triple the cost. Brilliant. Fails the CFS test.
Build wind & solar because it is a good greenie thing to do. Then build a full capacity hydrocarbon powered system to use as base load and because people actually expect their lights to go on when they flick the switch.
Now they want to spend even more money to build a storage system because wind power produces electricity most often when it is not required and we don’t want to waste it.
Only professors with a panoramic view from an Ivory Tower and with a regular taxpayer supplied paycheck would think that is a good idea. The rest of the us can stop laughing now.
Because you can be smart enough to work in a university to avoid the reality everyone else lives in.
Common.
Frikin
Sense.
CFS.
CHRIS Y. at 11.27 am – We don’t know the battery duty cycle/cycle life on which the study based its conclusions, but as the dominant cost component of large batteries is the cost of the active materials, a system that extends battery life by limiting the depth of discharge to 30% of capacity would almost certainly be prohibitively expensive. IMHO battery storage of any type is a non starter for this application.
1) Shift thermal usage (water heaters, boilers, and air conditioners)
2)Build better pricing signals for high energy industries (smelting, desalination)
3)Integrate some backup (2 days maximum, some combination of pumped hydro, gravity trains, compressed air, liquefied air. and thermal storage, max 1 hour battery backup)
4) Use the 5% of US electricity supply that is conventional hydro to flatten supply
5)Expand interties between regional grids easing transport of renewables from one grid to another
6)Expand hydro using in place dams that do not have generators in place
These together will go a long way to building a reliable network that can provide more than 20% of electricity need. The system would give a long lead time (minimum 1 week) to prep slower cycle thermal plants to turn on and off in case of a protracted downturn. This way if the storage starts to drop you turn on slower systems to stabilize the grid and rebuild the backup.
As for FLYWHEELS, the best way to store energy in them on this scale is to build them from timber and burn them!
Wow, yeah! Let’s use crappy inefficient part-time sources of electricity and then store the electricity in crappy inefficient short-lived batteries before we get to use it. That’ll really improve things!
/sarc <–Do I need this?
ddPalmer says
“Solar panels absorb energy that would have been absorbed by the earth and buildings which would have then been re-radiated back to the sky. But if absorbed and converted to electricity it isn’t re-radiated, or at least isn’t immediately re-radiated. Wouldn’t a large number of solar farms cause an imbalance in the downwelling and upwelling solar radiation? Aren’t greenhouse gasses supposed to be bad because they cause just such an imbalance? What might be the effect on global temperatures if there are lots of solar farms in operation?”
Good point, I agree and have raised this same question before and never got a satisfactory answer since the consumption of all energy ends up as heat.
What you indicate is exactly correct, especially if someone installed solar collectors above our clouds, etc., since energy would be brought into earth that would never arrive in the first place.
Of course if we take energy stored as carbon and/or hydrogen and burn it or transform Uranium to electricity we are also generating heat that needs to be radiated to the universe in order to the earth in heat balance.
I tend to agree with Roy Spenser in his book “global warming blunder” which proposes that the earth tends to regulate it’s temperature naturally since the system is much more complicated that the simple minded CO2 theory.
Re: Old’un says:
September 9, 2013 at 2:00 pm
“As for FLYWHEELS, the best way to store energy in them on this scale is to build them from timber and burn them!”
Here, here! Best idea of the day!
“Energy Return on Investment”?
I will advice all not to make any of their real-world investments on this kind of analysis. A joule wasted is as joule wasted in my book, be it solar, wind or coal. Not that i ever heard of someone calculating the “Energy return on Investment” for battery storage of coal Power, much less installing it. Except for Hydro Power this is the achillevs heel of renewables and i hope Barnhart will redo his analysis with a more useful parameter like (monetary) “Return on Investment”.
@Clayton E. Cramer
… expand where you transmit the power. I guarantee that it is peak energy demand SOMEWHERE on this planet, no matter what the demand is where you are. Of course, it may not be economically feasible to build a worldwide power grid…
It’s quite economical to build a grid all around the world. In fact, it would cost very little (as giant world-wide projects go). Because it’s actually been done. Each country (speaking generally) has a grid.
Unfortunately, like fine wines, electricity doesn’t travel very well. Inductive resistance (I2R losses) mean that you start losing a lot of electricity. It is UK practice not to pass electricity over 100Km through standard lines. You can build special high voltage DC lines which lose less energy – they go about 2000km. But it would be very expensive to build a network of those unless there was a guaranteed continuous electric flow, and your proposal does not seem to cover that…
No one has mentioned the reason why 4 of the 5 chemical battery systems in the study cannot be used for baseload storage.
There isn’t enough lithium, lead, zinc, bromine and vanadium in the world for that level of usage.
For example current world lithium production, if used exclusively for lithium based electric car batteries would allow about 2 million cars to be built. The US alone purchases something like 8-13 million new cars per year. Even with a massive and highly efficient recycling program there would never be enough.
Energy storage for an economy wide transformation to base load solar would be much larger.
As soon as anyone tried to actually deploy some of these battery systems widely the inevitable would happen: the prices would go up explosively. In 2010 as wind energy really started to boom the price of neodymium went up by a factor of 10 within a year, as it went into shortage. And wind turbines only use a tonne or so of Nd each.
The only possible system which makes any sense at all is sodium-sulfur, because these two elements are abundant and aren’t likely to be very price sensitive in the long term. But even they can swing massively in price over the shorter term as the market swings between surplus and deficit. It takes a long time, and lots of capital, for production plants to be built.
There is plenty of sodium and sulfur in seawater…but for the sulfur, which is present as sulfate ions, to be useful it has to be chemically reduced to a low oxidation state first. And the only practical way to do that is to use…coal.
@J Martin Hydrogen is dangerous stuff, including burning with an invisible flame
Pale blue, nearly invisible.
If you can see the color of the flame, consider yourself luck — you avoided the explosion.
Hydrogen is dangerous stuff. It explodes under a huge range of air mixtures, unlike methane.
Here is a question for others. With Methane, or specifically household natural gas, we include tert-butyl mercaptan as a safety smell. For household applications for hydrogen, leaving it oderless would seem to be irresponsible, judging by natural gas standard handling.
The generation of hydrogen in household generators, would then need to add in a safety chemical, a problem of practicality. But I have to ask, Does a safety chemical added to hydrogen poison fuel cells? More specifally, can we find a safe safety chemical that won’t poison fuel cells that is affordable and can pass EPA global warming / ozone requirements?
I have an acquaintance who is a VP for operations at a company that installs power storage systems in China. Lithium batteries are prone to fires, and they have since switched entirely over to lead acid batteries, despite hazmat issues and relatively short life cycles. It’s still an awful solution and he admits it – but the Chinese are willing to pay.