13 Jul 2009: Report

The Challenge for Green Energy:
How to Store Excess Electricity

For years, the stumbling block for making renewable energy practical and dependable has been how to store electricity for days when the sun isn't shining and the wind isn't blowing. But new technologies suggest this goal may finally be within reach.

by jon r. luoma

“Why are we ignoring things we know? We know that the sun doesn’t always shine and that the wind doesn’t always blow.” So wrote former U.S. Energy Secretary James Schlesinger and Robert L. Hirsch last spring in the Washington Post, suggesting that because these key renewables produce power only intermittently, “solar and wind will probably only provide a modest percentage of future U.S. power.”

Never mind that Schlesinger failed to disclose that he sits on the board of directors of Peabody Energy, the world’s largest private-sector coal company — a business with much to lose if a solar- and wind-powered future arrives. But at least he and his co-author got it partly right. The benefits from wind and solar are mostly intermittent — so far. But the pair somehow missed the fact that a furious search for practical, affordable electricity storage to beat that intermittence problem is well underway.

For decades, “grid parity” has been the Holy Grail for alternative energy. The rap from critics was that technologies like wind and solar could not compete, dollar-for-dollar, with conventional electricity sources, such as coal and nuclear, without large government tax breaks or direct subsidies. But suddenly, with rapid technological advances and growing economies of manufacturing scale, wind power is now nearly at grid parity — meaning it costs roughly the same to generate electricity from wind as it does from coal. And the days when solar power attains grid parity may be only a half-decade away.

So with grid parity now looming, finding ways to store millions of watts of excess electricity for times when the wind doesn’t blow and the sun doesn’t shine is the new Holy Grail. And there are signs that this goal — the day when large-scale energy storage becomes practical and cost-effective — might be within reach, as well. Some technologies that can store sizeable amounts of intermittent power are already deployed. Others, including at least a few with great promise, lie somewhere over the technological horizon.

New storage approaches include improvements to existing lithium ion batteries and schemes to store energy as huge volumes of compressed air
Large-scale electricity storage promises to be a game-changer, unshackling alternative energy.
in vast geologic vaults. Another idea is to create a network of small, energy-dense batteries in tens of millions of homes. Under such a “distributed storage” scheme, utility computers could coordinate electricity flows over a “smart grid” that continually communicates with — and adjusts the flow of power to and from — local batteries. This would even include batteries in future plug-in hybrid or all-electric vehicles.

And one 2008 breakthrough could even fulfill chemists’ long-held dreams of producing a squeaky-clean and storable fuel by using excess electricity generated from renewable sources to cheaply produce hydrogen, which could then be used in fuel cells to power homes and cars.

In a world run mainly on fossil fuels, finding ways to store electricity was not a pressing concern: Power plants across a regional electrical grid could simply burn more fuel when demand was high. But large-scale electricity storage promises be an energy game-changer, unshackling alternative energy from the constraints of intermittence. It would mean that if a wind or solar farm were the cheapest and cleanest way to generate power, it wouldn’t matter when the sun shone or the wind blew.

One storage approach seems obvious: to improve battery technologies. Picture efficient, enormous batteries that can store tens of millions of

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watt-hours of juice. Today, the vast majority of new rooftop solar photovoltaic panels are connected to the grid, using it as a giant battery, pushing excess power onto the grid when solar panels provide excess power. The building then draws power from the grid when the sun doesn’t shine, with its meter spinning backward and forward with the ebb and flow of power. With relatively few solar roofs yet in play, utilities manage any ebb and flow by drawing down and ramping up generation at conventional power plants designed to balance fluctuating supply and demand.

A more robust world of solar and wind power might be better served by some sort of giant battery — or, more likely, many of them, widely distributed. The basic concept has been proven. Since 2003, the world’s largest battery backup has been storing energy for an entire city: Fairbanks, Alaska. Isolated as it is, and not part of any regional electricity grid, the metropolitan area of about 100,000 residents needs an electricity backstop more than most: In its sub-zero winters, pipes can freeze solid in as little as two hours. Six years ago, the city installed a huge nickel-cadmium battery, the same technology used for years in laptop computers and other portable devices.

Housed in a giant warehouse, the 1,300-metric ton battery is larger than a football field, and can crank out 40 million watts of power. Still, the Fairbanks battery provides only enough electricity for about 12,000 residents for seven minutes. That was enough to prevent 81 blackouts in the city in the battery’s first two years of operation.

Yet effective storage of electricity from solar or wind arrays that generate power equivalent to one large coal plant implies batteries on a breathtaking scale — hundreds of units the size of the Fairbanks array.

One possible answer? In Japan, so-called “flow” batteries have been used for years to store backup power at industrial plants. Conventional batteries store energy in chemical form. With flow batteries, charged chemicals
Cost will be key for determining which battery or other storage technologies prevail.
are pumped into storage tanks, allowing still more chemical to be charged and pumped away, then pumped back into the active portion of the battery and drawn down as needed. One big advantage: Battery “size” can be expanded by simply adding more chemicals and more storage tanks. In 2003, the local utility on small King Island, off the coast of Australia, installed a large flow battery to sop up and later release excess power from a wind farm.

As with the alternative generation technologies, cost will be key for determining which battery or other storage technologies might prevail. Aside from such typical economic concerns as raw material and maintenance costs and durability, storage technologies all face some losses in “round-trip efficiency.” Inevitably, some energy is lost as it goes into storage, and more is lost as it comes out.

Right now, hopes are riding high on lithium ion batteries, because they have impressive round-trip efficiencies, can pack in high densities of energy, and can charge and discharge thousands of times before becoming degraded. Because of those attributes, lithium-ion battery technology has become increasingly dominant in laptop computers and cell phones. On a far larger scale, a powerful lithium ion battery pack powers the pricey all-electric Tesla Roadster, and is slated to power the plug-in hybrid Chevy Volt next year.

On the grid, lithium ion experiments are already underway. One company, General Electric-backed A123 Systems, announced late in 2008 that it had been contracted to install a two-megawatt lithium ion storage unit at a California power plant owned by global utility giant AES.

Still, lithium ion remains a relatively expensive technology — 10 times more expensive than lead acid batteries with equivalent capacity. Technological improvements and manufacturing scale should bring lithium costs down over time, but by the time that happens, the world could be beating a path to the door of someone who’s found a way to build an even better battery.

Early this year, IBM revealed that it was launching a major research program into what looks like an even more promising technology — the lithium metal-air battery. Last month, a company called PolyPlus announced that it had already succeeded in developing one.

The PolyPlus battery and the IBM technology deliver an astonishing 10 times more energy density than even today’s best lithium ion technology. That means that, pound for pound, they offer about the energy density of gasoline. The key reason they can store so much energy is that they use oxygen, drawn from the air, in place of some of the chemical reactants used along with lithium in their lithium ion cousins.

There’s one big rub: Air isn’t just oxygen. Notably, it also contains
The stored power in electric cars, or anywhere on the grid, might not come from batteries
after all.
humidity, and the lithium has a bad habit of acting like ignited gasoline when exposed to moisture, creating a real risk of fire and explosion. Chandrasekhar Narayan, manager of science and technology at IBM’s Almaden Research Center near San Jose, Calif., has suggested that it will take five to 10 years to develop an effective membrane that will let oxygen into the battery while keeping moisture out.

Still in pie-in-sky mode, there’s “vehicle to grid” storage, or “carbitrage.” This enticing notion relies on idled storage in the batteries of the millions of plug-in hybrid or all-electric automobiles that will be in use in the future. There’s reason to believe this scheme could work. More than 90 percent of the time cars sit idled, and aside from days they’re used for long trips, most of their full energy storage capacity goes unused.

A single idle, electric-powered car could generate as much as 10 kilowatts of power, enough to meet the average demand of 10 houses, according to Willett Kempton, director of the Center for Carbon-free Power Integration at the University of Delaware. With vehicle-to-grid technology, controlled by an array of smart meters, car owners plugged in at home or work could allow the grid to draw off unused chunks of power at times when short-term demand is high. Conversely, cars could be recharged when demand is low.

The stored power in those electric cars, or anywhere on the grid, might not come from batteries after all. In March, Texas-based EEStor announced that it had received third-party verification of its “ultracapacitor” technology. The company claims the lightweight device, which was awarded a U.S. patent last December, can bottle up huge amounts of electricity far more quickly than any battery and can do so at lower cost.

Like batteries, capacitors store and mete out electricity. Small conventional capacitors have been ubiquitous in electronic devices as far back as the early days of radio. But capacitors, so far, haven’t been able to store electricity for long enough to come close to competing with batteries. They have found use as devices that level out fluctuations in voltage or that briefly store power for near-instant release.

EEStor claims that its device, which is one-quarter the weight of a similar
Donna Coveney/MIT
Work being done by Daniel Nocera at MIT could open up the possibly that electricity could be stored by splitting (and later recombining) abundant water molecules.
lithium ion battery, can hold a large charge for days. Its patent describes a 281-pound device that would hold almost the same charge as a half-ton lithium ion battery pack installed on the Tesla Roadster. The company’s ultracapacitors have yet to prove themselves in commercial products. But industrial giant Lockheed Martin has already signed up with EEStor to use future ultra capacitors in defense applications, and Toronto-based Zenn Motors, which has also taken an ownership stake in EEStor, says it will have electric cars on the road using the technology in 2010.

If advanced batteries or ultracapacitors aren’t the ultimate answer, maybe using excess electricity to make hydrogen that can be stored will do the trick. Hydrogen can be produced through simple electrolysis, but technical and cost hurdles have made electrolysis impractical. Today, industrial-scale hydrogen is produced using natural gas as a not-so-clean feedstock.

But that may have begun to change last summer when MIT announced that a team lead by chemist Daniel Nocera had made a “major discovery” that employs a new kind of catalyst using cobalt and phosphate — abundant and non-toxic materials — to kick-start electrolysis.

Outside observers say the process could be revolutionary: opening up the possibility that electricity made at any time by the sun or wind could be stored by simply splitting (and later recombining) abundant water molecules, perhaps even undrinkable sea water. The breakthrough has been hailed by scientist British scientist James Barber of Imperial College London as having “enormous implications for the future prosperity of humankind.” The website Xconomy reported in April that Nocera had quietly formed a startup company called Sun Catalytics. Efforts to reach Nocera for comment were unsuccessful.

And there is progress being made on an entirely different front — using excess electricity to pump compressed air into caverns, salt domes, and old natural gas wells, and then releasing the air to help state-of-the-art natural gas power plants spin turbines, lowering the amount of fuel consumed by as much as 70 percent. A consortium of utilities in Iowa, Minnesota, and the Dakotas is already working with the U.S.’s Sandia National Laboratories to develop a giant, 268-megawatt compressed air system. Called the Iowa Stored Energy Park, it would store excess energy from the region’s burgeoning wind industry.

POSTED ON 13 Jul 2009 IN Business & Innovation Climate Energy Policy & Politics Science & Technology Europe North America North America 


That was a nice roundup of storage technologies, but there are a couple more of note:
Solar thermal power plants can store the heat from the day to use over the nightime in tanks of melted salts, and excess wind power can be used to pump water into reservoirs for use in water turbine generators when the wind fails.

The most important technology for wind power reliability is probably simply having a more modern grid. In Germany researchers found that by having several wind farms hundreds of miles apart the chance of there being no wind at all at more than a small number of the sites was tiny, and the larger the grid the more reliable it became.
Posted by Michaelc on 13 Jul 2009

This post is so typical of greeners. It suggests that these methods to store wind energy are available in the quantities necessary immediately which a careful reading of the post shows and admits they are not and will not be ready for many years.

Wind towers and turbines are the 21st century's version of oil derricks. They are ugly beyond belief causing visual pollution and bird and bat deaths in the hundreds of thousands. When it takes a wind farm the size of Connecticut to power a city the size of New York...it is a ridiculous proposition.
Posted by Rand E Oertle on 14 Jul 2009

Most people I talk to find wind turbines to be visually quite attractive, even beautiful. "Ugly beyond belief" is, at best, highly subjective — and also beside the point. Proper siting can handle most bird/bat deaths; that's why the National Audbon Society supports properly sited wind development.

There's nothing in the article that says "immediately" and it's dishonest to imply that it does.
The electric system that will emerge over the next decade will be as profoundly different from the one we have now as the U.S. mail is from email--and will change things just as drastically. There will not be one big wind farm powering New York City. The key phrase is "distributed generation"; it means that all of the things mentioned in this article, and lots of others that are not mentioned, are on their way, in a wide variety of scales, locations, and applications. Rand, my friend, you are guilty of tilting at windmills! Would love to know if you think you've got a better idea than what is now unfolding, and still far from completely understood.
Posted by Jimzo on 15 Jul 2009

This is a weird suggestion but I have thought about it and see no reason why it could not be done. Energy can be "stored" in flywheels (remember the old John Deere tractor?). I see no reason why enormous flywheels could not be used. The advantage of a wheel of very large diameter is that the drive wheel can be placed at different distances from the axle using different amounts of power to develop the torque. Then the power of the flywheel can be downloaded at constant speed ( necessary for electrical generation) by again altering the position of the offtake wheel relative to the axle as the wheel slows down.

Am I nuts ? or is this feasible? Perhaps the main problem would be maintenance of the bearings.
Posted by richard sadleir on 16 Jul 2009

I'm intrigued by Luoma's reference to the micro-grid "a network of small, enengy-dense batteries in tens of millions of homes."

I want to know more about what's entailed in this kind of distributed storage scheme. Does it exist anywhere? Is it even close?
Posted by Nancy Anderson on 16 Jul 2009

No, Jimzo, Rand is absolutely right. I just got back from a trip to Hawaii, and at South Point on the big island, there is a wind farm. A few dozen very large windmills are there. Of that few dozen, only about a dozen are actually operational. The rest are rusted out eyesores, many with the blades missing. I can provide pictures, if you doubt it.

The author of this piece claims that wind is near grid parity. I call BS. Let's see real numbers that include land acquisition, installation, maintenance, power storage, transmission - all of the real costs associated with wind power - and compare them directly to a natural gas power plant. I expect that wind is nowhere near cost parity with real-world natural gas or oil power generation.

Wind and solar have their place in niche applications, but aren't appropriate for large-scale power generation. If you must have clean power, build a modern nuke plant, and stop wasting time and money on pie-in-the-sky so-called "green" power generation and storage schemes that have never been shown to work on a large scale.
Posted by Pete Nelson on 16 Jul 2009

It seems the author is among the large group of people who have never heard of concentrating solar thermal power (CSP). He thus uses Solar when he specifically means photovoltaics.
CSP, specifically solar central receiver technology stored sufficient thermal energy to generate 30 MWhrs of electricity, and they did that 20 years ago, using a warm and a hot tank of molten salt (NaKNO3-fertilizer). Solar energy is converted to heat in the receiver, the molten salt absorbes the heat and is placed directly into storage. The stored energy drove a 10 MWe turbine for 3 hours with no solar input, and with good sunlight it operated for over a week at the 3 MWe level. This was a first of a kind pilot plant and it proved all the objectives set for it. As the salt used is abundant and very cheap, multiple larger scale facilities can be built easily.

A similar technology can be used with trough plants, which are already in significant scale production, but the lower temperature of such lower concentration linear systems requires modifications, such as an input heat exchanger.

Incidently Pete, please include the exploration, drilling, pipelines, and CO2 mitigation environmental and dollar costs in your 'cheap' gas power plant.
Posted by Lorin Vant-Hull on 17 Jul 2009

Wind competes on utility economics with natural gas fired generation. It turns out that wind power is very effective at storing natural gas, which can then be used when wind is not available. There is a paper on the NREL web site that explains a Colorado Public Utilities
Commission decision that made a finding on a public record, after the issue of wind and gas
economics was extensively litigated. See: http://apps3.eere.energy.gov/greenpower/resou rces/pdfs/33177.pdf Both Xcel Energy and Mid American, a utility holding company owned by
Berkshire Hathaway, among others, own wind turbines. If the economics didn't work for them,
these utilities would not own them.

A large amount of wind can be integrated into existing utility systems at lower costs than storage. Large utility systems are designed and operated to meet variable loads and to flex to
meet changes in weather. This built in flexibility is also used to cost-effectively incorporate naturally variable renewable resources like wind and solar. Denmark, with about 20 percent of its electricity from wind is a good example of how this is done today. A number of peer-reviewed, published studies on the costs of integrating naturally variable wind on U.S. utility systems are found on the Utility Wind Integration Group's web site: www.uwig.org.

Ron Lehr
AWEA Western Representative
Posted by Ron Lehr on 17 Jul 2009

I am in agreement with Michaelc & Rand. A distributed electrical power generation system will have a balancing effect for the new 'smart grid'. A system of many solar & wind generators situated all across the country will always have some sort of power being generated. When one wind turbine is idle, there is a solar array producing power, etc.

Another point not generally mentioned is that power companies already distribute power across vast distances with the 'current' transmission grid(pun intended). As electricity demand increases in one city...Say any July day at 6:00 AM in Chicago, IL...There is little demand in Seattle, WA. (4:00 AM) or Portland, OR. which are supplied by hydroelectric power along the Coumbia River. Electrical power is simply transmitted east to Chicago until the demand is met with supply.

In the near future, we could have abundant wind & solar power from a decentralized power system throughout the midwest which could generate enough electricity to meet local demand. The wind blows at any and all times of the day & night. The sun shines at the hottest part of the day when air conditioning units spike up electrical demand each summer. A 'smart grid' would be able to automatically adjust electricity flow to the areas of demand.
Posted by Will Deliver on 17 Jul 2009

One of the most obvious yet overlooked storage mediums is Ammonia (NH3). Synthesized ammonia is a fantastic energy storage medium. NH3 is relatively easily handled and is capable of being transported over long distances with virtually zero energy loss. This can be done using standard pipelines. These are pipelines and storage technology that already exists. Work is currently being done on new ammonia synthesis technology that could revolutionize how NH3 is produced. Green intermittent energy sources being used to produce storable/transportable NH3 in quanities battery technology could never match. We need to wakeup and smell ammonia literally.
Posted by Steve Gruhn on 17 Jul 2009

Parity is a relative term, and critics of wind and solar power are generally happy to criticize as unfair any subsidy to these new technologies without acknowledging the deep subsidies used to establish and maintain fossil fuel and nuclear power. The largest uncaptured costs for conventional power are for transportation infrastructure and pollution, for which there are still no viable solutions for either nuclear or fossil fuels. Incorporate these costs into the equation and wind not only meets, but also beats coal and the other more expensive conventional fuels in an economic argument. For solar and wind, fuel need not be delivered and pollution and environmental effects are orders of magnitude below those for fossil and nuclear fuels. There is certainly a place for conventional energy in the future, but diversifying our electrical infrastructure is a national security concern, as well as creative and more ethical way to move forward.

Another storage alternative is using solar and wind power to refill hydroelectric reservoirs by pumping water upstream.

Posted by Tony Abbott on 18 Jul 2009

A few points:

If you think wind farms are ugly go take a look at the devestation being done to the mountains in Appalachia. If you don't know, they are literally blowing the tops off the mountains. Now, THAT is ugly.

A new study by a Dutch researcher concludes that Dutch power stations can integrate large amounts of wind power with little more than up-to-date, improved wind forecasts.

The study, by a Ph.D. candidate at Delft University of Technology, also concluded that there is no need for storage facilities because new forecasting models make it easier to integrate variable wind conditions into the power system.

"The results show that in the Netherlands we can integrate between 4 gigawatts (GW) and 10 GW into the grid without needing any additional measures," said Lex Hartman, director of corporate development at TenneT, the Dutch grid administrator.

Bart Ummels, the Ph.D. candidate, looked at wind power penetrations up to 12 GW (8 GW offshore), which is enough to meet about one-third of the Netherlands' demand for electricity. The use of wind power in the Dutch electricity system could lead to a reduction in production costs of $1.9 billion annually and a reduction in carbon dioxide emissions of 19 million tons a year, according to Delft.

For more information about the study, contact bart.ummels@siemens.com .
Posted by Larry Siegel on 18 Jul 2009

Another storage alternative is using solar and wind power to refill hydroelectric reservoirs by pumping water upstream.

This is an obvious one for the Pacific NW, and finally someone mentioned it — certainly not the author from the East Coast, and heavily invested in "correct" greenspeak. The problem is, of course, that hydropower is not favored because of its impact on fish (another longstanding debate). In fact the NW still hears regular calls for some of the Columbia River dams to be removed.
Posted by Tim Gammell on 20 Jul 2009

I don't understand the immediate aversion to the suggestion that energy storage and renewables
could be used help improve the electricity grid, especially given the fact that the current US grid operates at about a 40 percent capacity factor because electricity production and demand must be matched instantaneously. Consider any other situation where 60 percent of what you buy sits as reserve: wouldn't you want to lower that percentage if possible?
Posted by Stephen Elliott on 21 Jul 2009

Hi Jon,

What about pumped storage and marine pumped storage ? (See "Spirit of Ireland" project, Okinawa project in Japan, La Muela in Spain etc.)

Best, Olivier
Posted by Olivier - ObjectifTerre on 21 Jul 2009

Pete, you're completely wrong about parity. A recent study (2008) conducted by NREL concluded that wind costs approximately $1800/kW to install, and coal about $1830/kW, with existing air pollution control technologies. As emission controls become tighter, as they will and should, that gap in price will only widen. There are numerous other studies that reach a similar conclusion.

And when it comes to nuclear, you're proposing replacing one polluting technology that relies on a finite resource with a second that is absolutely no different. Countries with uranium ore would become the new OPEC, doing nothing to solve economic and political problems revolving around energy. We all have access to sunlight and wind, we better figure out how to use it.
Posted by Dave on 21 Jul 2009

I read the article and was impressed by the author's ignorance of Pumped Hydroelectric Energy Storage. This is a proven technology for storing electrical energy at utility amounts. There are many of these facilities east of the Mississippi River with reliable operating records of thousands of gigawatt-hours. The technology is available and the cost moderate compared with electrochemical batteries.

I also recommend Generation 3 or 4 Nuclear reactors to generate base load power. These need to be part of a system with full fuel recovery and recycle. As fission rectors can breed more fissile material than they use, reactors operating on recycled fuel can be considered a perpetual energy source.

I do support the collection of wind and solar energy wherever the resources are available. I also realize they need sufficient energy storage to be economical. I think these sources can supplement a nuclear base. I also advocate shutting down the oil and coal base load plants because of the unavoidable air pollution and solid waste generation as well as the misuse of coal and oil for fuel instead of chemical feedstock and transportation fuel.

Posted by Gregory Warner on 23 Jul 2009

Very interesting documents about storage technologies are available on the "Electricity Storage Association" website (on the "Technologies" page).

- Pumped Hydro
- Compressed Air
- E.C. capacitators
- FlyWheels
- Batteries (Li-ion, NaS, NiCd, Metal Air, lead acid etc.)
Posted by Olivier - ObjectifTerre on 23 Jul 2009

I can't wait for the day when storing excess energy is our biggest problem -- not generating it.
Posted by Penny on 02 Aug 2009

As noted by other commenters above, it is literally baffling why the author did not include a discussion of thermal energy storage associated with solar thermal electric generators, a.k.a. CSP. Thermal energy storage is scalable and relative to electrical energy storage at this point in time, very inexpensive. Also missing from this discussion are flywheels and various permutations on hydroelectric storage, including pumped storage and the wind/hydro synergy.
Posted by Michael Hoexter on 03 Aug 2009

Interesting - better (cheaper, faster, more reliable, cleaner, etc.) electricity storage is worthwhile. However, the challenge for intermittent technologies is also that they simply produce *less* electricity per kilowatt of "nameplate" capacity than traditional fossil fueled plants with naturally higher capacities. For example, if you have a 1 megawatt solar plant that has a 18% capacity, it will produce only 1/5 of the electricity of 1 megawatt coal plant with a capacity of 90%. This means that you will need five times as much solar name plate to produce the same amount of power - even assuming 100% efficiency in storing and flowing power. This is the ongoing challenge to "grid parity" on a 24X7 basis.
Posted by Game Changer on 04 Aug 2009

In several places the author seems not to understand the difference between energy and power - eg the reference to a "two-megawatt lithium ion storage unit". Actually, an ordinary AA battery can store 2MW of "energy".

(But getting the battery to release the energy at the 2MW level might be difficult.)
Posted by Professor Eigenket on 05 Aug 2009

Both sides of the equation, generation and storage, have a long way to go when it comes to alternative energy, but great strides continue to be made on both fronts.

I've been encouraged by the technological advances in recent years and remain hopeful that government funds will continue to be used (prudently) to further the research.
Posted by Global Patriot on 11 Aug 2009

The demonstrated energy density of Lithium air batteries is indeed far better than commercially available lithium ion batteries, but still falls well short of gasoline energy density:

"""...IBM technology deliver an astonishing 10 times more energy density than even today’s best lithium ion technology. That means that, pound for pound, they offer about the energy density of gasoline."""

Gasoline contains 46.4 megajoules (12.9 kWh) per kilogram and the best widely available lithium ion batteries contain about 0.7 megajoules (0.2 kWh) per kilogram, or about 65:1. The IBM/PolyPlus lithium air concepts have a theoretical performance of 5 kWh, or about a 25 (not 10) fold improvement, but lithium-air still falls 2.5 times below the energy density of gasoline.

However, I also note that electric propulsion is typically shown to be 2.5 times more efficient than are internal combustion engines. Thus two otherwise equivalent electric and combustion (gasoline) vehicles would theoretically have the same range, given equal weights of battery in the former and fuel in the latter.

Posted by Falstaff on 02 Sep 2009

We live on the cool wet thin skin of a ball of molten iron that is thousands of miles in diameter. This phenomenally massive amount of dense energy has been stored within the planet since it was formed many billions of years ago. Surely by tapping into just the outer surface of this Earth heat we can power all we need, and maybe even cool the effects of global warming by radiating more lost Earth heat into space?
Posted by horatio on 25 Sep 2009

If we have "grid parity" with wind as compared to coal, nuclear and natural gas, then why does wind power cost about twice as much as the other sources. I don't need to look at "funny numbers" from some group or another, I need only look at my light bill and the plans offered by the different light companies.

Also note, that were I to purchase "wind", I would only be getting "wind power" about half the time - the rest of the time it would come from other sources.

The costs associated with the grid should also be considered. Not only do these windmills spread out over wide areas far from urban centers need to be connected, but the management of the grid must be significantly overhauled to reliably integrate these intermittent sources and management them with the rest of the energy mix to maintain reliability.

Posted by estetik on 26 Nov 2009

One additional little known storage technology developed recently with little fanfare, is thermal storage using a phase change material. Or for lack of a better word ice that changes to liquid at 78 farenheit. The energy stored at the liquid frozen state is tremendous. The prototype has used solar, wind, and off peak electrical to store energy in form of heat, and then used as needed. Studies have shown this type of storage to be economical without government subsidies and also helps the payback periods for solar and wind. For more information see www.elcalresearch.com

Posted by Greg R. on 28 Dec 2009

I don't think solar has to match coal, petroleum and nuclear pound for pound for one simple reason. You find a spot, and set up the solar, and it repeatedly creates energy. Yes, eventually it wears out, so what. That just means jobs refurbishing an existing solar or windmill plant.

The fuels we rely on now have to be constantly mined, excavated and replenished, and we get so used to expecting to get them from where ever it exists on the planet that the U.S. is forced to have a huge standing army in reserve.

If the U.S. military used 10 percent less fuel they could literally donate enough fuel to run our entire public transit system in the United States. But the conundrum is we need the military presence all over the world to make sure we get ours.

The other thing about wind energy and solar is they exist as visual reminders, people who visually see them will actually study them more and say, I can design something better than that, and that becomes the game-changer.

So lets get it started.

Posted by Alessandro Machi on 09 Mar 2010

Why can't we just use water as the storage? Hydro electric power ?

The water is pumped back up a dam or storage tank and when the power is needed just releases the water to run hydropower. Every towns water tank needs to pump their water into their towns tank for the citizens use. Every ones extra solar can be used to pump that water into the tank. That reduces that need for power. Water can also be repumped back up into dams with solar and then when the energy is needed it re released to go through the hydro electric power all over again!

Posted by Danie Clarke on 21 Apr 2010

This answer in your article is the best ever. They are already testing it and even google is in on it. YOUR MENTION OF V2G

Still there’s “vehicle to grid” storage, or “carbitrage.” This enticing notion relies on idled storage in the batteries of the millions of plug-in hybrid or all-electric automobiles that will be in use in the future. There’s reason to believe this scheme could work. More than 90 percent of the time cars sit idled, and aside from days they’re used for long trips, most of their full energy storage capacity goes unused.

A single idle, electric-powered car could generate as much as 10 kilowatts of power, enough to meet the average demand of 10 houses, according to Willett Kempton, director of the Center for Carbon-free Power Integration at the University of Delaware. With vehicle-to-grid technology, controlled by an array of smart meters, car owners plugged in at home or work could allow the grid to draw off unused chunks of power at times when short-term demand is high. Conversely, cars could be recharged when demand is low.

Posted by Jim stACk on 03 Jun 2010

Why can't we use a large wound spring system to store energy for a home based wind mill? It seems to me with the proper gearing a wound spring could release it's energy over time when the wind is no longer blowing. The spring would be wound when the wind mill is over producing by engaging and disengaging different gears.

Posted by travle man on 19 Jul 2010

All these pseudoscientific talks focus on the "how?", but we should ask the question "why?" instead. Why do we need that much of energy? Do we really need Grand Cherokees, do we really need that much cosmetics, do we really need Britney Spears on MTV? We demand a lot. And general assumption underlyling is that we need is what we demand. Go get a modest life! That's what you need.

Posted by Mahmut on 15 Nov 2010

With respect to maintenance of the bearings on flywheels as Posted by richard sadleir on 16 Jul 2009, I understand that would be bearingless inasmuch as they "float" using magnetic levitation and can be sealed in vacuum chambers therefore reducing as much as possible any losses due to bearing friction or drag against the air.

A perfectly ballanced flywheel of several kilos spinning at several 10s of thousands of RPM would store a tremendous amount of energy.

Posted by Dave G on 02 Jan 2011

I like this article except i don't like the idea of using large chemical batteries as much. I think we can do better. I am going back to school for Electrical Engineering right now and hope to work on these issues as a career i have been brainstorming but i still need to learn more before i can truly become a player in this world... although i did theorize about storing energy as potential energy using water pumps and a hill.... but its been done, to no surprise since it is a very simple idea, although i am unsure how efficient it is.

Anyways i saw one negative post and i think this man is missing the point, sometimes it takes over a decade to make a power plant the idea that it may take a a few years for a technology like this to be viable is nothing short of amazing. Also we know as a species it is not merely a matter of renewable energy being more or less expensive than fossil fuels its a matter of living in a way where our planet can support human life for a more than just a few more generations. yes the energy problem is that serious. and i personally believe its worse than people let on.

Posted by porto on 01 Feb 2011

The costs associated with the grid should also be considered. Not only do these windmills spread out over wide areas far from urban centers need to be connected, but the management of the grid must be significantly overhauled to reliably integrate these intermittent sources and management them with the rest of the energy mix to maintain reliability.

Posted by Şiir on 10 Mar 2011

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jon r. luomaABOUT THE AUTHOR
Jon R. Luoma, a contributing editor at Audubon, has written about environmental and science topics for The New York Times, and for such magazines as National Geographic and Discover. His third book, The Hidden Forest: Biography of an Ecosystem, has been released in a new edition by Oregon State University Press. In previous articles for Yale Environment 360, he wrote about new technologies to harness the power of the ocean and how jatropha has failed to emerge as the miracle biofuel that many had predicted it would become.



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