Clean Power LightSail compressed air energy storage

Published on November 10th, 2012 | by Tina Casey


Entire Cities Could Run on Compressed Air

November 10th, 2012 by  

LightSail compressed air energy storageThe company LightSail Energy started out a few years ago with a student’s modest idea for a compressed air scooter, and now it has just raised $37.3 million in private funding to bring utility scale, compressed air energy storage to the market. That’s a big leap not only for the company but for compressed air technology itself, which has long been eyed for its clean energy potential. The problem has been to make the process efficient enough to deliver power at a commercial scale, so let’s take a look and see how LightSail solved the problem.

The Compressed Air Conundrum

As aptly described by writer Rachel Metz over at the MIT Technology Review, half of the compressed-air equation is simple enough from a clean energy perspective. You can use any form of alternative energy such as solar or wind to generate electricity, which in turn powers a motor that compresses air in a tank.

The  hard part kicks in when you try to store large quantities of compressed air. Compression adds energy in the form of heat (almost 1,000 degrees centigrade, according to Metz) and that leads to enormous complications.

The Indian car manufacturer Tata Motors has apparently found at least a partial solution for small scale compressed air, but LightSail is going down an entirely different road.

LightSail’s Compressed Air Solution

Danielle Fong, Chief Scientist and co-founder of LightSail, is the former student who dreamed of a compressed-air scooter. She solved part of the problem by designing two related features into the system. One involves using mist to cool the air, and the other involves recapturing energy from the spent mist, in the form of heat.

According to Metz, Fong and her partners also identified a compound that could be used to manufacture tanks strong enough to store bulk quantities of compressed air above ground, in relatively inexpensive facilities, leading to the conclusion that “there are no technical barriers to building units large enough to power entire cities.”

As for whether it works or not, the new round of funding indicates a pretty high degree of confidence. It was spearheaded by legendary investor Peter Thiel of PayPal fame, and it included early investor Khosla Ventures as well as Bill Gates and Innovacorp among others.

Compressed Air Meets Wind Power

As a side note, compressed air technology is also expanding its role in the alternative energy field through the avenue of wind power.

One example is a compressed-air wind turbine that is designed like a funnel, with no exposed blades, in order to cut down risks for birds.

Along similar lines, an Air Force veteran has come up with a low cost wind turbine  that uses a steady stream of compressed air from silos. The design is aimed at enabling small farmers on a budget to leverage their existing infrastructure, including silos and grid connections.

Alternative Energy and Democracy

Environmental and financial issues usually dominate the conversation about clean energy, but in announcing the new round of funding, LightSail CEO and co-founder Steve Crane teased out the truly transformative potential of alternative energy from a social and political perspective:

“We want to democratize energy – to enable renewable sources to supply energy on demand locally and at a lower cost than centralized fossil-fuel based generation.”

That’s the piece missing from the fossil fuel puzzle, the ability of a democratically organized community to make decisions about its primary sources of energy, just as it makes decisions about roads, zoning, schools, public safety and a host of other issues that are fundamental to the quality of life.

Image: Some rights reserved by ewan traveler

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About the Author

specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.

  • shellback

    No matter how brilliant the researchers are, the funders speak volumes. My first thought is that these cheap facilities will be put in well populated areas and the enemy of the week will cause the worst false flag of the year, thus catapulting the worst president ever into office,(I know, you thought this one was the worst, Heck he is not even a citizen). I am not saying that the technology is not viable.I am saying that it will be used for evil by “the man”, just like the mini compression poison darts still used today.

    • Bob_Wallace


      Crawl under your bed and stay there!!!

      (But be sure to look under first. Might be something evil hiding there….)

      • shellback

        If you need evidence, just ask your mechanic what he thinks about corn in your tank. This is going to be a green fad.

  • This is HORSE-PLOP

    Just another GREEN WIDGET SCAM

    Nothing new here whatsoever just a recycled old idea.

    No working widget will ever be produced, the Khosla Ventures money will stay safely in the bank.

    They are acting as a SHILL for the main con-trick.

    Now watch all the other suckers lose their money.

    “Yes, as through this world I’ve wandered
    I’ve seen lots of funny men;
    Some will rob you with a six-gun,
    And some with a fountain pen.”

    How true!

  • Thanks for Posting.

  • Techno

    Please do not forget Mr Pacheco had worked on his compressed air system to powwer his car, so please include this part also, we need to stop burning oil for transportation, etc.
    Do not forget Mr Nicola Tesla’s electric car, NYC would not be going tru all this stuff if his ideas/techniques would be in place today.

  • WilmotMcCutchen

    For a more complete explanation, see this US patent (2012)

  • Bob_Wallace

    There’s a more detailed article about Lightsail’s technology on Greentech Media –

    ““By holding on to the heat,” Crane said, “you can take the system from 60 percent thermal efficiency to 90 percent thermal efficiency.” That can make CAES more economically efficient than older generations of the technology, which can lose a huge amount of energy — perhaps as much as 80 percent — in heat.

    The LightSail team is working on the system’s round-trip efficiency, he said, but they have “consistently achieved over 90 percent thermodynamic efficiency.” This means, he explained, that 90 percent of the power used to drive the compressor’s piston now ends up stored.”

    They’re shooting for 70% to 75% overall efficiency. There are system losses in addition to the initial 10% thermal loss. There will be some heat loss during storage (which probably limits the upper time limit of storage) and some power lost supping the generator to turn air back into electricity.

    “An April 2011 Sandia Labs cost estimate, according to Crane, put the “present-worth cost of ten-year operation in year one” of a CAES system with 4 hours to 8 hours of storage capacity at $1,470 per kilowatt. The study also found that batteries are $2,000 per kilowatt and up at that scale. “They all conclude that compressed air energy storage is the cheapest type of large-scale storage,” Crane said, “with the possible exception of pumped hydro.””

    If they can get cost and efficiency to about where pump-up storage is then they may have a winner. But I suspect batteries are going to beat them out.

    Aquion (sodium-ion) and Eos (zinc-air) are both projecting under $200/kWh and at least 10,000 cycles. Aquion’s battery has undergone 5,000 charge-discharge cycles and has an efficiency of over 85 percent (third party testing). Eos has reported 2,700 cycles with no loss so far.

    Getting to 10k cycles and $200/kWh means storage at 2 cents per kWh which would be make renewables very affordable 24/365 power.

    Both companies state that they will be shipping in 2013.

    Then there’s Ambri’s liquid metal battery which, if it continues to work out, would provide even cheaper storage. An extreme game changer.

    • Bob_Wallace

      I just rechecked Eos’s web site. They are now reporting ” >5000 battery cycles demonstrated to date with no physical degradation”.

      And they claim that they will be shipping 10k cycle batteries for $160/kWh in 2013. And a 75% efficiency rating.

      At $160/kWh and 10k cycles that’s less than 2 cents per kWh storage. Five cent wind stored for two cents and a 25% loss would mean about nine cent out the back end. Very competitive.

      • Ronald Brak

        Zinc-air batteries certainly have promise, but the number of times people have promised low cost whatever and failed to deliver is huge, so while I really hope they can live up to their claims, I won’t be surprised if turns out their egos are writing checks reality can’t cash. But even if we don’t get low cost zinc-air batteries next year, maybe we’ll get them in 2014 or 15. We’ll just have to wait and see. Or make them ourselves. Either one.

        • Bob_Wallace

          Yeah, I don’t believe any of these products are real until they are on the market and tested. But we do have three different battery technologies that are testing out in prototype form and two of them are supposedly going to be manufacturing in this coming year.

          Aquion is setting up a factory in Pittsburg (?), they’ve been hiring for all sorts of factory/admin jobs. And Eos has contracted with a fairly large Chinese manufacturer to build for them. Feels like we’ll get some more concrete information on those two fairly soon.

        • mds

          I too am from Missouri (the show me state) when it comes to super solar and energy storage claims. Who can forget EEStor? What a fizzle they were.
          Still Bob this sounds like a serious contender and Bob has mentioned three more. Seems very possible one of them, or another dark horse, will succeed.

          • Bob_Wallace

            eeStore never produced a prototype. Both Aquion and Eos have prototypes that have been tested by third party labs. (IIRC)

            Ambri is reporting prototypes that are functioning as well or better than predicted but I think all testing reported so far has been in-house.

            Something interesting seems to have happened when Ambri went public, Aquion had been talking about grid storage and it seems they changed their pitch to storage for “remote grids”. They’re talking about their initial market being places like remote health clinics.

            I might be reading too much into that, but it seemed to me that Aquion might have taken a look at the Ambri liquid metal battery and decided it was going to win the grid storage war. (Huge speculation on my part.)

            But, I agree. It’s way too early to be counting those chicks. All we can do right now is count eggs and check them for cracks….

          • mds

            Good point. They still have to prove low cost production at scale, but I agree all four of these companies appear more promising than EEStor …so far. Four good contenders, with probably others still in stealth mode, is very promising news for solar and wind.

          • James

            Nobody with a brain ever took eestor seriously

          • Nobody with a brain should take LiteSail seriously either.
            Your wallets will get LITE.
            Directors will SAIL their yachts!

      • I’d be as excited, as an environmentalist, as anyone, to see that work out. Our business would be fine too (we have alternative applications…) But reach those numbers and energy storage + renewables start beating fossil fuels in more and more locations.

        However, it is somewhat curious that they say they managed to have no degradation with zinc-air. Almost all batteries degrade, and traditionally air batteries, specifically zinc-air, have been among the worst. The efficiency issue is considerable as well.

        If they can it through these stiff challenges, I would be heartened and encouraged.

        • Bob_Wallace

          All I’ve got to go with is what companies claim in their public releases.

          “Most cycles ever realized by metal-air battery >5000 battery cycles demonstrated to date with no physical degradation”

          “Proprietary innovations overcome historical limitations to electric rechargeability
          of zinc-air batteries ”

          I can’t find anything on their site about third party testing.

          • Seems pretty reasonable, but it’s important to take a grain of salt with press releases. Ours too of course. Most importantly, we’ve yet to demonstrate low cost. Our materials costs are very, very low, but these are not the only costs!

          • if i remember correctly, from a ~30min or so video by the head of Eos (that I think Bob shared), the company has built its battery in a completely diff way from all previous variations of the most popular zinc-air template (in other words, from the ground up, it’s a completely diff beast). i really don’t know enough about it all to have an opinion (just waiting until this or another option get to commercialization) but that was the essence of the grand claims of better performance. we’ll see..

        • mds

          Yes, no degradation at all is very hard to believe. That needs a further explanation or I have to wonder (almost assume) it is just a sales fiction. I believe the sadoway battery makes a similar claim, but they also have a good explanation how this is accomplished. It’s a liquid battery, not solid.

          Cycle-life is one of the most important factors in calculating cost/kWh of storage over the expected life of the system. It is irritating that cycle-life information is not given more often in battery product announcements. This should be one of the advantages of the Lightsail compressed air system. What is the expected cycle-life? What is the resulting cost/kWh for 4 hours storage? …for each additional 4 hours?

    • mds

      I don’t like what Crane has to say. “4 to 8 hours” Which is it? That’s a range with a two fold difference between the top and the bottom, very lame. Also, what does “present-worth cost of ten-year operation in year one”. How about something simple and clear like cost/kWh for capacity and (cost/kWh)/cycle-life for electrical storage cost per kWh added to initial electrical cost as you are calculating. I find it difficult to believe anything can be cheaper than pumped hydro since the structures can be used for 100’s of years once they are built. Pumped hydro is limited by geographical availability.
      What else is Mr. Crane being squirrely about?

      • Bob_Wallace

        I had problems trying to figure that out as well.

        I think the ‘first four hours’ are more expensive. You have to cover the compressor, etc. After that adding more hours of storage is cheaper, like flow batteries.

        Figured I’d worry about that if they get a prototype running…. ;o)

        • You have to pay for the compressor/tanks separately. The tanks are much less expensive.

          • Bob_Wallace

            Hi Danielle, nice to see you out on the web talking to people.

            Could you put this is another form – “present-worth cost of ten-year operation in year one”? I don’t understand.

            And, you’re pulling off the water which is bringing the heat with it and storing? Do I understand that correctly? How long can you efficiently store hot water? Are you looking at using natural/bio-gas for long term storage assist?

            I’d like to hear anything that you’re free to share at the moment. I do understand that you need to keep some information in house,.

          • Cost of ten years of operation:

            Providing power on demand, at a specific capacity factor, including operations and maintenance, energy cost, inefficiency, capital cost, and financing cost, for ten years.

            Present-worth cost:

            The cost to the present day. This includes the fact that there is depreciation over time, O&M and energy costs may change over time, etc. See

          • UKGary

            Depending where you are, you might not need to store hot water for very long. True, if you are placing the heat back into the air to recover the maximum amount of electricity, then you need to store the heat for as long as the compressed air,

            If you have alternate uses for the heat of compression – such as district heating, or the cooling effect of releasing compression – such as air conditioning or refrigeration. With such a tri-generation system,you could achieve very high energy utilisation possibly around 80% to 90% whilst accepting a certain reduction in electrical cycle efficiency.

            You might also be able to harness low grade heat sources such as exhaust steam from food factories, or solar water heating to upgrade the pressure of the compressed air.

      • You’re missing an important point. You can aim at a higher or lower amount of energy storage by adding or removing tanks.

        4 – 8 hours is just a typical range for the ratio of tanks you’d want for an installation. You could have just 1 hour, or 100 hours, if you install a different number.

        cost/kWh/cycle-life doesn’t account for efficiency or the time value of money.

        • mds

          Thanks for the explanation below. I think you might be missing an important point as well. If Lightsail tech really is better and you want a wider audience to appreciate this as a fact, then you need to simplify. I’d suggest defining some of the terms like capacity factor up front and provide a simpler definition of cost. Cost for the first four hours per kW and added cost for each four hours additional after that. A single cost for 4 hours or 8 hours is clearly blarney, imho.
          Again, thank you for the explanation and the very best of luck to Lightsail.

        • CRAP!

  • That would be the Vinod Khosla of bankrupt Range Fuels? Clearly a visionary self-promoter slopping at the public money trough when it comes to the Alternative Energy field.

    By the way, “degree centigrade” is not a unit of heat. Heat is a form of energy and is measured in energy units such as joules, btu, calories, etc. So “energy in the form of heat (almost 1000 degrees centigrade)” is nonsense.

    • Bob_Wallace

      How is Khosla “slopping at the public money trough”?

      Looks to me as if he’s putting up his own money and getting nothing back unless the company succeeds.

      It does seem that he takes chances on startups more frequently than others. Perhaps that’s just because people print his easy to identify name more often or because he’s more open to taking long shots. It could be that he really wants quick progress and is willing to accept a higher fail rate than those who are in it for the money.

      • Read up on Range Fuels, his previous alt eng venture.

        • Bob_Wallace

          Give me some guidance on what to read. Here’s what Wiki has to say…
          “*Range Fuels* tried to develop a technology that converted biomass
          into ethanol without the use of enzymes . The company broke ground on its first commercial-scale cellulosic ethanol
          facility in November 2007. Range Fuels won the 2008 *North American Fuels Technology Innovation Green Excellence of the Year Award*.[1]
          According to the *Washington Examiner*, Range Fuels’ Soperton, GA plant closed down in January 2011 after receiving a $76 million grant from the US Department of Energy , $6 million from the State of Georgia, and an $80 million loan guaranteed by the U.S. Biorefinery Assistance Program.[2] In 2008 Range Fuel also received $158 million in venture capital from Khosla Ventures, Calpers, and Blue Mountain, and other companies. [3]

          All I see there is that Khosia lost some money. I don’t see any government money flowing to him.

          • I don’t contend that he enriched himself, as far as I’m aware, he did not. I only claim that he misrepresented the potential of Range Fuels to a credulous series of Federal and State agencies resulting in huge taxpayer losses.

            I suggest looking at: and at: and the links from those articles.

          • Bob_Wallace

            I read the main link. I can see how one could claim that Khosla oversold Range Fuel’s potential. But I’m not sure that we wouldn’t find that to be true of most startups looking for financing.

            I certainly can’t see how he profited from government funds as your first post suggests. Looks to me as if he lost a lot more money than did taxpayers.

            I’ve got to say that I’m getting tired of the practice of searching around to find failed green energy companies and wailing about taxpayer money lost. Put things into in context of all the technologies that we now enjoy because we’ve taken risks.

            Perhaps it’s my background in science and in business. Lots of research doesn’t find anything interesting or useful. Lots of business startups fail. The people who don’t take the risk and accept the occasional failure do nothing to advance things.

            If startup successes were guaranteed then they could borrow money at current bank rates, about 1%.

            BTW, I hope you noticed that Range Fuels, like Solyndra, were “oversold” during the Bush economic bubble. During bubbles money flows too easily. Remember what it was like during the bubble? A half-page idea statement could get you a few million startup dollars.

      • i read a great long post on Khosla’s approach quite a while back. can’t find it now, but it’s pretty simple: the vast majority of his investments will fail, but since he focuses on truly breakthrough technologies, if one of them succeeds, he wins big. he has told other investors many times that they need to be more willing to fail, even eager to fail. who knows if that’s the best approach, but it certainly has its attraction.

        • HIS money is safe.
          It’s the late-comers who will lose out.
          Green Ponzi anyone?

  • freedomev

    Sill a really big energy loser, just not completely useless. Molten salt batteries are a much more eff, cost effective solution.
    Anyone who thinks using Compessed air for a vehice doesn’t understand basic physics.

    • dynamo.joe

      They claim 90% thermal effciency. So, no molten salt isnt MUCH more efficient.

      Also I’d like to see how exactly you are using these “molten salt Batteries” to store your excess wind and PV power.

      • Ronald Brak

        Oh it’s easy to use electricity for thermal storage, it’s just not that efficient. And if wind and/or solar capacity results in frequent free electricity it’s not such a big deal. The hard part is putting it in your car.

        Personally I don’t think compressed air storage will take off, but I hope that people working on it are able to come up with something cost effective. They do have some stiff competition, but good luck to them.

        • It’s an electrical energy storage system. The target is 70% roundtrip electrical AC to electrical AC. You *also* get access to 90% of the incoming power in kwhe as heat (kwht), until you expand, at which point you get extract, roughly, 80% kwht.

          You could, for example, charge up during the night, heating a building, and during the peak hours of the day, discharge and get air conditioning.

        • mds

          “The hard part is putting it in your car.”
          Actually, that is completely wrong. …well 97% wrong. That’s how often cars are parked in North America, based on an actual study some years back. Most of the time there is electrical distribution nearby, so charging while at home, at work, or at the store is not going to be a big tech leap.
          Most people seem to forget efficiency is only one factor in cost. It can be a very significant factor, but if you get the cost low enough then relatively inefficient systems can be economical to operate. Gasoline was once so cheap that we drove around in 15% efficient cars and nobody cared.
          If the Lightsail, or other energy storage, can get down to $0.02/kWh, then 70% efficiency means the real cost of storage will be $0.03. At $0.02/kWh 70% means $0.015/kWh. Even $0.03/kWh would be a huge advantage for solar in many areas of the USA and the world. There is already a huge market for solar in the USA sun-belt where 1/3 of peak demand is for AC, according to a recent study.

    • FYI: Molten salt batteries, sodium sulfur, went for nearly $3000/kW, $800/kWh, until a toxic gas emitting fire of unknown origin took them off the market.

      Why would using compressed air for vehicles portray one’s knowledge of physics as scant? After all, every internal combustion engine on the planet works by compressing and then expanding (heated) air.

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