Underwater Balloons Store Energy In Canadian Project

Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News!

The Canadian company Hydrostor has developed a way to store energy using pressurized air kept in underwater balloons and currently has a pilot project in Lake Ontario. The air is used at opportune times to turn turbines to generate electricity. CEO Curtis VanWalleghem generously answered some questions about the technology for CleanTechnica.

How did you come up with the idea to use underwater compressed air?

Cameron Lewis (Founder, Chief Technology Officer) was developing a wind site and analyzed adding a small pumped hydro facility that was deemed uneconomic after analysis. That got him thinking that instead of raising water in the air, why can’t I put the air under the water and accomplish the same thing.


How long can one of your underwater balloons last under normal operating conditions?

The supplier has offered a 10 year warranty, but is considering a 20 year warranty as there is very little wear-and-tear on the balloons since the air is stored at hydrostatic pressure (e.g. pressure same on outside and inside of balloon).

How many balloons are used in your current system?


Is the peak electricity output that can be created by the balloons 660 kW?

The peak output of the Toronto Island facility is currently 660kW due to the rating of the generator.

And what is the number of kilowatt-hours?

The underwater air cavity is designed for easy expansion and there are plans to expand the air cavity over the next couple years, so we are not publicly disclosing a storage capacity at this time.

How much space does the underwater balloon array occupy?

The entire structure has an areal footprint of approximately 10m by 40m.

What maintenance is required?

There are no moving parts underwater, so it is designed for little-to-no maintenance. We will be doing annual inspections of this facility to confirm this. The system is designed so it can be easily raised to the surface for inspection and replacement if required.

How much did it cost to build the balloon system and get it running?

We are not publicly disclosing project cost.

How does this cost compared to energy storage in the form of a lithium-battery system of comparable size?

Hydrostor’s Underwater-CAES system is less than half of the cost of the leading li-ion battery solutions with over twice the cycle life.

If the two-year pilot is successful, what will be the next steps?

Hydrostor is actively developing a number of projects around the world. We anticipate starting construction on another facility in late 2016/early 2017. Hydrostor is also in discussions with EPC firms regarding a strategic partnership for project construction.

How large a balloon system can you build, and where can the larger ones be located?

There is really no limit to the size of structure, as they represent a small fraction of the available space in oceans and lakes. The air cavity required drops roughly in half every time the water depth is doubled, so we initially will be targeting the deepest waters.

How much money can be saved by using your system by avoiding the cost of electricity when it is in demand?

This question is very site specific and related to the local electricity markets and rates.

How could your balloon system enhance fish habitat?

Yes, we include a significant amount of ballast that is designed to provide marine habitat.

Can underwater balloons be used in oceans, or are their currents and waves too volatile?

Yes, the system has been designed for oceans.

Image Credit: Hydrostor

Have a tip for CleanTechnica? Want to advertise? Want to suggest a guest for our CleanTech Talk podcast? Contact us here.

CleanTechnica Holiday Wish Book

Holiday Wish Book Cover

Click to download.

Our Latest EVObsession Video

I don't like paywalls. You don't like paywalls. Who likes paywalls? Here at CleanTechnica, we implemented a limited paywall for a while, but it always felt wrong — and it was always tough to decide what we should put behind there. In theory, your most exclusive and best content goes behind a paywall. But then fewer people read it!! So, we've decided to completely nix paywalls here at CleanTechnica. But...
Like other media companies, we need reader support! If you support us, please chip in a bit monthly to help our team write, edit, and publish 15 cleantech stories a day!
Thank you!

CleanTechnica uses affiliate links. See our policy here.

Jake Richardson

Hello, I have been writing online for some time, and enjoy the outdoors. If you like, you can follow me on Twitter: https://twitter.com/JakeRsol

Jake Richardson has 1008 posts and counting. See all posts by Jake Richardson

50 thoughts on “Underwater Balloons Store Energy In Canadian Project

  • That is brilliant. So simple as well. However there still has to be energy loss in pumping air against that resistant pressure. It would be the same loss, presumably, as pumping into a metal cylinder. Any engineers know what the loss is?
    They indicate the price as half of lithium and double the life cycle….so 75% less cost than a lithium battery, and presumably a flow battery as well. However, in pricing energy storage I have come to learn one thing: each energy storage advocate lies through their teeth about the other guys technology. Therefore everything they say needs independent verification.

    • “.. each energy storage advocate lies through their teeth about the other guys technology.” Memo to bloggers here: this is a principle of general application. False claims about your own work are actionable: in academic life, they destroy your reputation; in business, they lead to prosecutions by securities regulators and lawsuits from shareholders. But false claims about the other guys have no consequences, unless they are specifically defamatory (“Tesla cars catch fire”).

    • Air is pretty good gas, but as you pump it up, there is some heating,
      and there is some frictional drag. so assume you lose 33% just for a ROM guess…

      but it’s free energy. otherwise you lose the wind farm output entirely.

  • Hunh….what will they think of next? Put a bunch of these next to offshore wind turbines and you’ve got a pretty complete energy system right there.

    • Given predictable wind patterns, sea-based storage systems could make offshore wind a reliable 24/7 major power source. Why not pump all the water out of the monopile and then a micro turbine near the seafloor would generate power until it fills backs up. It probably wouldn’t pencil out.

      • Good idea if the pile is strong enough. You can do the patent, but the moustache has to go on the patent picture. Not sure what the pencils are for. Not a very long term storage, because volume is small, but even a small amount looks interesting.

  • I had a similar idea a few years ago, but couldn’t interest Desertec or the people who make towable rubber water containers.

    The ideal site is the coast of North Africa, which has next to no continental shelf; the sea depth drops to >2000m a few km offshore. You gets similar drops off volcanic islands like Hawaii and the Canaries. Underwater storage would complement Africa’s vast solar resource and make it despatchable.


  • Since they don’t talk about round trip efficiency I suspect there’s a problem.

    Half as cheap as lithium batteries and half as efficient probably means batteries win. Easier to site.

    • If it works the way I think it does they would just pump the air in with say 85-90% efficiency and then when they want to generate electricity they let it out to turn a generator with 85-90% efficiency. So all up it should have about the same efficiency as pumped hydro of say 76%. Of course, I could be overlooking something.

      All else equal higher efficiency is of course better, but if lower efficiency is cheaper to build it can be worth it if the cost of electricity regularly drops to or close to zero. It’s kind of windy outside at the moment and wholesale electricity prices are just about to hit zero. And if electricity costs nothing, lower eifficiency is not such a big deal.

      I expect rooftop solar will often push wholesale prices to zero during the day in Australia in the not too distant future. Of course, I could be wrong about this.

      Hasn’t hit zero yet. Might only get down to 0.7 US cents.

      • Heat loss during compression. That’s been the problem with CAES.

        One company claimed that they could extract the heat by flushing water through the cylinders and store the heat separately, then using it to reheat the air on the way to the turbine. But they seem to have had nothing to report for a while.

        • Oh yes, that’s going to mess things up, and if they try to reduce the loss make things much more complicated and expensive. Maybe they should just drop a lead weight off a pontoon.

          • Interesting that you suggest that. There’s an upcoming article about a storage idea using concrete weights raised and lowered from a barge. Their idea is to store a lot of energy by floating weights, then hooking them up as needed.

          • I’m psychic! And to prove it, I will tell you that I know you are going to respond with, “Ronald, you are so wonderful!”

          • Ronald, you’re full of crap. (But it’s humourous crap….)

          • You almost got it right! So close!

          • Didn’t someone also want to do that with train cars on a hill, and another doing weighs in a elevator shaft in a building. Lots of ways to skin a cat. The other item they don’t talk about here. Batteries have a much shorter time to go from charging to discharging for smoothing the grid. CAES and large pump hydro both have a longer lag. But since there are many time frames of storage there will likely be many solutions.

          • Yep. And a chair lift type approach with cars loaded with rocks.

            I can see some sort of gravity storage being useful for ‘deep storage’. Batteries and perhaps flywheels can take care of the short term stuff. But we need something for prolonged periods of low wind/solar that happen once or twice a year.

            We could store massive amounts of energy on a high bluff in the form of dense weights and play it out into the grid when needed. I suspect staying on dry land would be cheaper.

            Pump up hydro might be our best solution. Or biomass burned in converted coal plants.

            Just playing with my high bluff idea. Winches with two cable drums. Lowering a weight on one cable could wind in the other cable if they were wound backwards to each other. A simple gear system could keep the generator/motor spinning the correct direction. No dead time while a cable was being rewound.

            Slanted tracks at the top and bottom so that the next set of weights rolled into place (or discharged storage) via gravity. Any uphill movement of the weights would be stored energy.

            I’m guessing there are better solutions….

          • We all wanted to throw stuff down the deepest hole in the world when we were kids. Cool job, if you can find it!

        • If the rate of compression and decompression is slow enough relative to the rate of heat exchange with the surroundings, then the heat would be dissipated into the water on compression, and pulled back in decompression, resulting in an isothermal process.

          A perfectly isothermal process is in theory 100% efficient. In practice, if good heat exchangers are used to dump, and retrieve heat from the water, which is a stupendously good heat sink, it may be possible to obtain excellent efficiency.

          It all depends on if they have a good heat exchanger sitting in the water, and how good, and how efficient that heat exchanger is, what the water flow rate across the exchanger is, etc…

          70-80% round trip efficiency seems reasonable to me, with a bit of back-of-the-napkin calculations, especially since 660 kW isn’t really a lot of power in the grand scheme of things, to dump into a lake.

          Having the lake there is really key. Put a big chunk of aluminum in a lake, with lots of fins, and the thermal flux rate you can start tossing around before the water even notices is pretty large, especially if pump even a tiny amount of water of the last stage to even it right up.

          Like, for instance, if you can get within the film heating distance (not the right term, but I’m failing at recalling my thermodynamics and fluids course material) of just three cubic meters of water, which isn’t that hard to do, 660 kW would raise the temperature of that water by .05 degrees C per second. Get any kind of convection current across there at all, and you’ll be able to keep your temperature deltas to within a degree or two pretty trivially.

          OK. Nerd rant over.

          Cool idea! I’d love it to work!

          • I sort of follow you. But I wonder if keeping the rate of compression and decompression low enough to avoid the heat loss would render the system worthless in terms of storing a lot of energy and sending it back to the grid when needed.

          • Here’s a 500 kW heat exchanger, given 40 degree C temp differential.

            It’s worth $2k.

            So, that’s roughly the heat exchange rate we want, but lets say we want to do it with a 1 degree temperature difference, instead of a 40 degree.

            So, let’s look at the heat transfer formula convection:

            q = hc A dT

            We know q will be something like 500 kW ~ish to charge and discharge at around 660 kW. That’s a guess, but it an engineering guess, so it should be close enough. Probably conservative.
            dT is 1 degree,
            hc is the heat transfer coefficient. This can be anywhere from 1500 watts per sq. meter Degree Kelvin (W/(m2K)) to 3000 (W/(m2K)) for free convection in water, according to the literature.

            Let’s use 2000, for lols.

            Solve for the area of the heat exchanger, and you get about 250 square meters.

            That exchanger above is 62 sq ft or about 5.75 sq meters.

            We’d need about 50 heat exchangers that size, or about $100k of heat exchanger, assuming no gain from efficiencies of scale.

            If we’re allowed higher delta T’s the size of the heat exchanger shrinks quickly.

          • The reason water injection is being considered during compression is that the heat of vaporization is a handy and efficient way of storing heat energy and there is no heat exchanger. After compression, the heat must be removed and stored. This is a tricky set of moves with PV=nRT in the way. If you cool it, it wants to decompress. Any process that has multiple energy types is harder to optimize efficiency. More costly to deal with multiple types of energy conversion. The trick is to have P go up, but V go down the same amount simultaneously. Good luck with that, though. Hard to achieve.
            Makes me wonder if a lighter incompressible fluid might make a better working media.

        • If you scuba dive you know how much heat comes from compressing air. If not remember PV=nRT. P is pressure and T is temperature.

          • Good old Nernst equation. Good for you. Still remember Chemistry. And words like adiabatic.

        • well here it’s a lot lower…
          In CAES you are trying to run these up to 3000 PSI,here you are running the bags to closer to 150 PSI. and you using that to displace water.

          The efficiency won’t matter what will matter is cost.
          If it’s cheap it’s good.

          • Cost and efficiency both must be considered.

            If you have to put 2 kWh in to get 1 kWh but your competition needs only 1.25 kWh in for 1 kWh it may make sense to business with your competitor.

    • The link below gives more technical detail. It claims at least 60% round trip efficiency. There have been a lot of articles on this and I’m sure I saw somewhere else 60-80% mentioned. I’ll try to track it down. The system includes methods to utilize waste heat from compression cycle.

      Its also interesting how the project is a mash-up of off-the-shelf tech from different areas of marine salvage, horizontal drilling, power generation.


    • They have been working on these for a long time, IIRC we could find a article on this site for a company making these air bags several years ago. As for round trip, if smart, they would be using the work of other CASE projects and storing the heat during compression, to help with expansion, and then storing the cold from that. It help with efficiency, but I think that is still the soft spot of this approach. The under water air bags just help with the cost of storage tanks. Of course you need > 2000m high pressure line to get down to a depth of 2000m, pay Peter or pay Paul.

  • What is the round trip efficiency of the system? It is the number one show stopper if it doesn’t pay. Are they hard at work in improving the round trip efficiency that is why they have not published it? If I am the investor, that would be the first thing that I would ask and then calculate the feasibility of the idea’s implementation from there. I wish all reports include the honest assessment of the current state of the bottom line.

  • Round-trip efficiency is likely not fantastic. Compressing gas causes some of the energy to go to temperature rise, but the water will leach away that energy. Still, probably worth doing to provide ancillary service like voltage or frequency regulation and to offset some gas-fired peaker usage.

    • Waste heat recovery is incorporated in the system.

    • On the other hand, rapid gas expansion can be tapped for air conditioning or chilling.

  • Since they don’t talk about round trip efficiency I suspect there’s a problem.

    Half as cheap as lithium batteries and half as efficient probably means batteries win. Easier to site.

    • I agree.

    • Now you’re just repeating yourself. (-:

      • I had a very weird commuter event. I thought I had posted the comment but it showed not so I hit it again. And it showed up in a different part of the conversation.

        • Senior events. You will find they get more frequent. More frequent.

          • lol

    • “Half as cheap as lithium batteries and half as efficient probably means batteries win. ”

      Not necessarily. When a battery dies you have to recycle it and and buy a new one. With a compressed air system you can easily repair it.

      With regular maintenance a 60 years or more of use is possible. It is probably not possible to get that kind of lie out of a lithium ion battery. You might be able to achieve life that long in flow batteries or Ambrie”s molten metal battery. However these are new technologies that may or may not have a long life.

      Also increasing battery capacity is easy with this system. Just install air bags under water. The land cost are also lower with this system. The bottom of the ocean or a lake is generally free. A lithium ion battery facility is going to need land and that adds cost.

      • Without more numbers we’re just left wondering.

        I do think that in the short run efficiency will tip the scales away from cost for a grid that is trying to get rid of carbon as quickly as possible. Making up for that “half as efficient” loss means a lot more installation

  • The technology should scale well. The storage part is cheap, so the cost is in the compression/generation gear. So best when you need lots of mwh rather than mw.

  • better be no ships over when one ruptures.. sinks boats.

    • if the bags are made of cells wired together, but the bigger problem may be ships anchoring and tearing the bags…

      • No one has yet highlighted the crucial dangers of hungry sharks eating the balloons, or horny giant squid trying to mate with them.

        I bet the designers didn’t think of that, did they?

      • No anchor zones are clearly marked on navigational charts.

  • We have wind power in the Columbia River gorge areas and deep water behind some of the dams. Maybe this might work here?

    • …or you could just put in the pipes and pump the water back up to the next damn …or pump the water to a reservoir some distance above the river at the side.
      Pumped hydro is going to be more efficient and probably more cost effective.

      • The Columbia Gorge would seem to be a good place to install some PuHS. Plenty of water in the lower reservoir (Columbia River). Dig some reservoirs at the top and connect.

Comments are closed.