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.
“…there are times when solar and wind farms generate more electricity than is needed by consumers…”
Anthony, here is your quote of the week. This is the most ridiculous, dishonest statement I’ve seen on wind and solar power. Wind especially. Its best is about 15% of rated capacity. This is putting a positive spin on the statement that they generate power only when the wind blows plus it often blows when you don’t need the power – the “times” for all practical and economic purposes when it is not needed is 100% of the time..
Too many IFs!
If the assumption was right that release of carbon-dioxide “contributes significantly”! to global warming…….(with no global warming in sight!)
If batteries weren’t too expensive for grid-scale storage! (They didn’t even touch the point how much 1KWh of the surplus energy would cost, if stored in batteries with, let’s say, 6 hours capacity!)
If,if,if……. if my aunt had eggs, she would be my uncle!
Did no one even mention the CellCube? Already solves the energy storage dilemma.
“Dave says:
September 9, 2013 at 11:19 am
Has anyone considered using excess electricity for electrolysis of water? This might come in handy once, or perhaps if hydrogen fuel cells become commonplace.”
Good Idea but fails on several fronts Dave:
Storage of Hydrogen, difficult and expensive/requires large volume and high pressures and special materials.
Fuel cells are two orders of magnitude the cost of traditional power plants.
Fuel cell stacks are costly to maintain and have fairly short life spans.
Chris.
Too many post-doctorate fellows working on this project and not enough engineers and cost accountants.
The BESET strategy is when used with hydro-electric dams. When there is excess wind electricity, you let dam water levels move higher (and use the wind power), and vice versa. No loss in efficiency. Obviously, it also means that wind power can only be a complementary source of power (not reliable, and can`t be greater -meaning more of – than hydro power). This is the strategy Hydro Quebec uses. With the majority of energy produced by hydro-electric dams, integrating wind is easy. Drawback is that wind is A LOT more expensive than hydro, and is added to the mix to make a specific group happy.
The notion that that any chemical battery in use today is the answer for large-scale environmentally friendly storage is absurd. Pumping water to a height or even using the excess to split water, Iceland-style, has to be better.
Tom Stone nails it.
Money IS energy.
The write up says Li batteries last 6K cycles. I will dispute this because there are at least a dozen differing chemistries of this type of cell all with different lives and densities.
They also last far longer if the duty cycle is less than 100%. Kept at a constant room temperature. We’re talking about 25,000+ cycles for LiFePo4’s here!
Also Sun comes around the highest demand times and wind is used as a load balancer anyway.
The best man in the game are high level pumped reservoirs. AKA “Electric Mountain”, North Wales.
Electric cars can be used as home load balancers if the day/night costing rates have a large enough difference.
Did they factor in the high costs of the toxic heavy-metal cleanup associated with lead, zinc, etc.???
Did they factor in the number of deaths associated with the mining, manufacturing and disposal of those same heavy-metal items?
@Greg Goodman at 10:51 am
Cruachan Dam: capable of generating 440 MW of electricity. It can go from standby to full production in two minutes,
Read on from the Wiki:
So, it can really only operate for 10 hrs as pumped storage. 12 hrs are “break glass in case of emergency.”
10 hrs at 440 MW is 0.2 of a GW-day. A fifth of a coal unit train; 20 cars.
That’s the problem with pumped storage. Good energy efficiency and response, but the electrical energy capacity you store is frustratingly low for the land it consumes.
“The Stanford team looked at several emerging technologies, including five battery types – lead-acid, lithium-ion, sodium-sulfur, vanadium-redox and zinc-bromine.”
Since when are lead-acid batteries an emerging technology?
“Batteries with high energetic cost consume more fossil fuels and therefore release more carbon dioxide over their lifetime.”
These people really do live in a world all their own. God forbid they should ever be put in charge of our planet.
Here is a zinc-air that produces two times the energy of a lithium-ion battery at a third of the cost,
http://cleantechnica.com/2013/09/09/zinc-air-battery-company-claims-novel-electrolyte-will-do-the-trick-ct-exclusive/
“If we build an electric vehicle with a 500-mile battery, with 500 recharges, that’s 250,000 road miles, so we’re looking at it that way. Five hundred cycles is a reasonable customer expectation,”
Another company, Eos has deployed a grid sized prototype that claims to have a 10,000 true (full discharge) cycles battery, or about 30 years, with a cost of 1000/kW and $160/kW-hr.
Eos also has a Zinc-air battery the size of a washing machine that will hold 1 MW and can handle up to 5,000 charge cycles and last 25 years.
http://www.elp.com/articles/2013/07/eos-energy-storage-develops-1-mw-battery-storage-device.html.
Look at it this way, couple a good zinc-air battery with a matched PV array and you can lock in your energy costs for 25 years – better than investing in Government bonds.
There is a very efficient pumped storage strategy that could use surplus grid energy:
Ice Storage Air Conditioning. (Wikipedia)
You run refrigerators to freeze a volume of water when rates are cheap or surplus. You use the ice to chill the air in your air conditioning units during the day.
One metric ton of water (one cubic meter) can store
334 million joules (MJ) = 317,000 BTUs = 93kWh
If we consider the energy I would get by lifting it to a higher altitude instead of freezing it, how high must I lift that ton of water to store the same energy?
Enthalpy of Fusion (ice) = 334000 J/kg
Enthalpy of Fusion (ice) = 334000 m^2/sec^2
If PotEnergy = mass * g * height
and g = 9.8 m/sec^2
height = PE / (m * g) = 34082 m
Freezing a ton of water stores the same energy as lifting it 34 KILOMETERS in the sky. Best of all, the water doesn’t go anywhere. It can be in the basement of a city’s office buildings. It can be close to where you need it. You don’t need to flood valleys miles away.
The only drawback is that it doesn’t store electricity per se. It stores the ice made with surplus electricity. It time-shifts refrigeration from times of excess power to times where you need to cool things off. But Air Conditioning is such a huge use of electricity, the time-shift of electrical supply to demand is cost effective and energy efficient.
(Discussed Jun 30, 2013 12:04 in WUWT …The Energy Store
A simple solution: Place a pulley around the wind turbine hub with a long wire to the ground. Attach an electric car to said wire. Fill car with as many climate scientists as possible for added weight. When the wind blows, car is raised to the top of the turbine tower thus slowing it and reducing output. When the wind stops the weight of the car plus scientists keeps the blades turning as it falls, Result…constant output for the turbine and an actual purpose for the otherwise completely useless climate scientists and electric cars. Now if we could only find a use for the hot air emanating from the scientists and the excreta as they s-hit themselves on the way down…
Many really excellent comments posted here. The common sense of WUWT readers easily trumps this “PhD” article. For example:
Richard111 says:
“I see this report as nothing more than another propaganda sermon against the demon CO2. Where is the proof that CO2 causes the climate to warm?”
That’s it in a nutshell. There is no proof. There is not even any credible evidence that CO2 causes global warming. There is no scientific evidence that the small portion of human-emitted CO2 makes any discernible difference in global temperatures.
The whole “carbon” scare is a scam on the taxpaying public.
I’ve always been enamored of the possibility of flywheels—not the clunky, iron ones but vacuum sealed carbon fiber flywheels. Unfortunately, they haven’t yet been good enough, but some recent news is promising:
http://www.scientificamerican.com/article.cfm?id=new-flywheel-design
“DGP says:
September 9, 2013 at 10:33 am
I don’t accept the initial premise of this paper that ‘there are times when solar and wind farms generate more electricity than is needed by consumers.” Also, I see no mention of the power lost in the conversion from AC to DC and back again (inverters).
Furthermore, if in fact solar and wind actually produced more than was needed, it would just be a simple matter of turning down the back up fossil or nuclear plant that are always required.”
Already happening in Germany, and causing lots of problems:
http://notrickszone.com/2013/09/05/handlesblatt-calls-germanys-feed-in-act-energy-madness-large-consumers-are-paid-to-waste/
Additionally I would remind you that it is NOT “just a simple matter of turning down the back up fossil or nuclear plant that are always required”. Nuclear is very slow to respond and normally runs at maximum output. Large Coal plants are also difficult to vary rapidly. CCGT can be wound down reasonably quickly, but this reduces the efficiency. OCGT’s are about the only suitable source of fast responding fossil fuelled power, but have poor efficiency. And in any case the service life and reliability of large boilers and turbines quickly drops with frequent thermal cycling. In conventional grids this can largely be avoided as the demand, and timing, is very predictable. Once you start adding wildly variable sources of supply (and give them priority access) the situation changes completely.
Coal energy comes from the coulomb bonds between electrons and the nucleus in atoms. Nuclear energy comes from the nuclear forces between particles in the nucleus which are MUCH MUCH stronger and, like stronger springs, can release a great deal more energy. We ought to be working full steam ahead on all forms of nuclear, since when the Holocene ends, we are probably going to need it.
It is a finite resource, but then, so is the human life form. Humanity will end or evolve eventually.
For the present, the sensible, technologically sound and solved solution to carbon alarm is, of course, contraception. But you never never hear the envirozealots talk about that.
The other Phil:
Your post at September 9, 2013 at 12:17 pm says in total
I’ve always been frightened that some idiot may try to build flywheels for storing electricity supply.
The UK generates electricity to the energy equivalent of ~30 Hiroshima atom bombs per day.
Storing a third of that in flywheels would be a major disaster waiting to happen.
Richard
Hmmmm…. started thinking about the battery farm they would have to create (every seen an inline UPS?) With that size, and it was Li-ion, one lightning strike is going to be a really big show.
Hydro pumped storage here:
http://en.wikipedia.org/wiki/Seneca_Pumped_Storage_Generating_Station
Get a satellite view and note the size of the reservoir behind the dam versus the circular storage area. Pronunciation is Kin-zoo; not Kin-zoo-a.
~~~
Dave says:
September 9, 2013 at 11:19 am
Any thoughts?” – about Hydrogen
Hydrogen is not friendly. Search on the topic using the word embrittlement. Having hundreds of thousands of Hydrogen generators connected to an equal number of (or multiple) storage devices would likely cause a reduction in the total population.
Dave, In reply to “any thoughts”; I would have thought that householders generating their own hydrogen and filling their own vehicles with it would bring with it the need for society to expand a number of services. Double the size of the nations fire brigade, treble the number of specialised burns units in hospitals, and increase mortuaries, cemeteries etc by perhaps 10%.
Hydrogen is dangerous stuff, including burning with an invisible flame, I read somewhere.
A massive problem with these energy storage schemes is the length of time they would have to be able to yield full power output during prolonged periods of calm or cloudy weather over a large area.
Blocking high pressure systems can last for weeks Anthony’s piece on the Russian heat wave of 2010 – http://wattsupwiththat.com/2010/08/19/noaa-on-the-russian-heat-wave-blocking-high/ – has information on the frequency and duration of blocking highs. Two weeks electrical storage for the whole of Western Russia – suggestions anybody?