Guest essay by Eric Worrall
Hydrostor has created an interesting innovation in energy storage. The energy is stored as compressed air, in giant underwater balloons.
Hydrostor’s system works in several steps. Electricity is run through a compressor and converted into compressed air. This compressed air is then sent underwater.
“There, we have a whole series of what are effectively balloons, that fill… like lungs under a lake,” he added.
“They fill with air, and when they’re full you stop charging the system and it can sit there indefinitely. When you want power back, again, a valve opens … air comes rushing out, we run through a low pressure turbine called a turbo expander, and that reproduces power back to the grid.”
Energy storage is becoming increasingly important. In the United States, the Office of Electricity Delivery & Energy Reliability states that the development of technology to store electricity so it’s available on whenever it’s needed would be a “major breakthrough in electricity distribution.”
Read more: http://www.cnbc.com/2015/12/09/underwater-balloons-clean-energy-savior.html
This isn’t the first time I’ve heard of storing energy with compressed air. Hydrostor’s innovation is to reduce the cost, by using water pressure to maintain the storage compression, without the need to create high strength pressure containers.
Using water to supply the pressure to collapse the balloons might also improve the efficiency of energy retrieval. By storing the air underwater, and using the water pressure to collapse the balloon, the air would be retrieved at a near constant pressure, until the balloon was empty. Hydrostor claim an efficiency of 60 – 80%.
Hydrostor seem to be aiming at grid stabilisation rather than storing multiple days worth of grid supply, so it seems unlikely this proposal, as it stands, will fully solve the renewable intermittency issue.
Could compressed air storage be scaled up enough to solve intermittency? Even if you had enough renewable capacity to cover 100% of grid requirements, on average, if you wanted to go further than Hydrostor’s current plans, to completely eliminate the need for backup gas turbines for renewables, you would need to store enough energy to maintain full grid supply for at least a day, more likely several days.
My concern is energy stored as compressed air could, in principle at least, be released all at once, in the event of a storage system failure.
Imagine you wanted to store one day worth of energy to supply a major city, in case the wind didn’t blow that day – enough energy to maintain a 1 gigawatt supply to the grid.
To maintain a 1Gw supply of energy for one day, your storage solution would need to store;
1Gw x 1 day
= 1000,000,000 W x 86400 seconds
= 86,400,000,000,000 Joules of energy
= 86.4 TJ.
This amount of energy is the same magnitude as the energy released by Little Boy, the nuclear bomb which destroyed Hiroshima (63 TJ). An abrupt release of 84TJ of energy next to a populated area would cause serious damage.
How would such a release of energy manifest? During the Lake Nyos disaster, when 100,000 tons of volcanic CO2 at the bottom of Lake Nyos was abruptly released, the rising gas created a 25m Tsunami which did extensive damage to the thankfully mostly uninhabited shoreline.
In the case of Lake Nyos, the Tsunami damage was secondary compared to the lethal effect of normal air being displaced over a large geographic area, by an asphyxiating cloud of concentrated CO2. But a large Tsunami smashing into a densely populated coastal city, adjacent to the storage facility, could still cause serious loss of life, even if the gas bubble which created the Tsunami was breathable air.
Risk concerns aside, in my opinion Hydrostor’s solution is still a very interesting innovation. Storing energy underwater, utilising the natural pressure of the water, should substantially reduce the cost of creating storage “balloons”, compared to other schemes for using air pressure for energy storage, by dramatically reducing the required strength and potentially the cost of the materials used to construct the pressure containers.
There is at least one advantage of using rubber pressure storages at bottom of the sea compared to steel storages: rubber storages gives guite constant pressure till end of volume.
But you don’t utilize that sea bottom’s pressure without costs. You must do valuable work to pressurize the storages. When you compress air you are heating it. In some places (Finland, Alaska) you may utilize the excess heat in some others you can’t.
The eternal rubber is not yet invented?
If you made your storage at a hot place, such as a black smoker, there is a theoretical possibility it gives energy to your system.
I don’t want to start an argument.
But there is no reason to use rubber.
This system depends only on displacing the water, at high pressure relative to the compressor/turbine system. The use of rubber is a completely needless. Rubber used as a store of energy is actually quite rubbish anyway. It is a good way of throwing energy away. Hence its use as a shock absorber/damper in tyres and engine/machine mounts.
Of course, it’s a handy store of energy for model aeroplanes for children.
But that’s because children have boundless energy and they are oblivious to the fact that the elastic aeroplane drive system is quite lossy.
You can see this from rubber’s hysteresis curve on a force/displacement stress/strain graph. The area in the middle represents the W.D. energy that is lost each cycle as heat.
indefatigablefrog: “But there is no reason to use rubber.”
OK. I think you are right. A steel storage can be bell shaped and open at bottom. Then it can deliver near constant pressure to the turbine (whatever).
My mistake thing only about closed steel storages.
It’s a rare thing when a thread on the internet builds on understanding, rather than ending up stuck in antagonism
So what a rare treat!!
However, I looked into this topic briefly and found a company using (or intending to use) butyl rubber bags.
I expect that they are simply collapsing and filling the bags – rather than using the rubber’s elasticity.
But, it does look to me as though this idea may have potential.
Unlike most of the idiotic and implausible crap ideas that are flying around on a weekly basis.
“Designed and developed for Garvey’s project by Canadian firm Thin Red Line Aerospace, the bags use a butyl rubber bladder and a polyester-reinforced fabric for the outer surface.”
Read more: http://www.theengineer.co.uk/in-depth/the-big-story/compressed-air-energy-storage-has-bags-of-potential/1008374.article#ixzz3uEMkz22y
Claiming “60%-80% efficiency” is a huge red flag for me. A simple, inexpensive small-scale test or two would give a real efficiency number … either they haven’t done the tests or they aren’t reporting the numbers.
A red flag either way.
w.
Let’s visit Hydrostor for sake of reality check. Under Technology > How does it work? > Learn more you find
So the process is a bit more complicated than the one described at CNBC.
Steps 2 & 6 are significant. If compressed air is stored at a depth of 30 m (90 feet), and input is at 4°C (39°F), then its temperature is increased to 139°C (282°F) while compressed to storage pressure due to adiabatic heating. On release temperature of compressed air stored at 4°C (39°F) decreases to -87°C (-125°F). This is why heat needs to be stored separately and added back before use. With 100 m storage depth (300 feet) these figures are 277°C (530°F) and -133°C (-207°F) respectively.
Therefore thermal management is the key point. Design of heat exchangers and that of the well insulated heat storage facility are not described at the Hydrostor site, but if losses are to be kept low, they should be quite sophisticated and expensive.
To make up for (inevitable) losses, they say under 2, that “Additional heat can be added to further increase roundtrip efficiency.” That’s true, but energy for heating has to come from somewhere. If not from burning fossil fuels, which would immediately destroy carbon neutrality, then from another source, presumably nuclear. However, in that case it would be much cheaper to skip storage and produce electricity directly from that source.
Furthermore, to keep underwater balloons at the bottom, you need to anchor them to something. If it is concrete blocks, you need roughly the same volume of concrete as the volume of compressed air to be stored in balloons. That’s much, and cement manufacturing has a huge carbon footprint. Also, the balloons have to be made of something, presumably from plastic, which also adds to the footprint.
Therefore the process is complicated, expensive and fails to be carbon neutral. Otherwise it’s perfect.
Come to think of it, as air becomes so cold on decompression, heat exchangers close to the surface can be used to deliver additional heat before stored heat is added back. That way energy efficiency can be improved and no additional heat source is needed. That is, it would act as a kind of heat pump.
The cost is increased complexity of the system and the environmental damage done by industrial amounts of cold water output.
I do not know, for example, how to prevent heat exchangers getting clogged by ice. It can certainly be done, but at what price?
Neither do i know what the effect of a copious amount of cold water would be on marine or lake life, especially on plankton.
Also, releasing large volumes of air inevitably generates high levels of noise, not only in the frequency range of the human auditory system, but well below it in the form of infrasound. Against which there is no effective insulation.
These questions are not discussed at Hydrostore.
As I mentioned in a different post, one advantage of the system is that the air pressure in the reservoirs is almost constant from an empty reservoir to full reservoir. This means that the compressor and turbine can be designed for a specific pressure ratio, which should improve efficiency. The other aspect is that the temperatures on the outlet of the compressor will be almost constant, and should allow for use of a phase change material to store energy at a constant temperature. Using a series of phase change materials with decreasing phase change temperatures to cool the compressed air to near ambient should allow for a respectable fraction of the heat energy to be recuperated during energy recovery.
Looks like they’ve got the thermodynamics at least somewhat right, though I’m not convinced of the practicality.
Mechanical (electrical) energy storage is not easy.
And what about the rising of the seawater Level ? Balloons need space underwater !
The volume of the oceans is 320 million cu mi. There is no way that these vaporware balloons are going to change that by a millimeter.
It depends on how much energy we want to store. Is there an end to human craziness ?
The loss points: Converting wind/solar to grid quality electricity; Line loss to compressing station; compressor inefficiency; loss from piping to balloons; air storage leakage; return plumbing; low pressure turbine inefficiency; generator inefficiency.
Hmmm….Not including primary generation, that is 7 points of loss at the least.
Not to mention lifetime reliability of balloons and plumbing.
And remember: the air has to be pumped to *higher pressure* than the depth of the water, which ~16 psi per 33 feet of depth. And the balloons have to be tethered and anchored to resist the powerful buoyancy of each balloon.
Once again the carbon obsessed come up with an idea that is impractical, inefficient, unworkable, crazy expensive, non-robust. and claim it cures the non-problem they are so neurotically focused on.
Hydrostor’s innovation is to reduce the cost
Well, that’s the idea.
Not bad for a “Nature trick” — if it works.
One politician per module should supply quite a bit of compressed gas for a long while.
Before I read the article, I was thinking of pulling floats down, then releasing them to capture energy. But that is dependent upon density differences, so is not as scalable as pressure differences are.
I propose we build giant spring driven devices, a bit like old fashioned alarm clocks. During the day when the millions of acres of solar panels are generating excess electricity this is used to drive motors to wind up the springs…at night the process is reversed the energy stored in the springs is fed back to the motors which turn into generators and hey presto!
Buried concrete encased magnetic bearing flywheels are a much better and safer idea
There is nothing functionally bad about CAES. This underwater balloon idea is not the greatest. (understatement)
However, CAES allows you to capture the adiabatic heat of compression, and also use any thermal energy to increase the pressure of the stored gas — thereby allowing for more work to be done.
This is basically what a combined cycle NG/Coal plant does with some of the waste heat.
Residential and distributed CAES would allow the use of solar thermal to create a combined cycle solar PV/thermal system that would allow for round the clock energy production.
Is it super efficient? Nope — but sunlight and solar infrared don’t cost a thing unlike coal and CH4.
What happens when the water is displaced by bags of air and air tries to do what it does best in water?
At the end of the day this useless proposal is just rent seeking for money from gullible climate suckers.
The idea of underwater CAES has been around since before 2011. Another inventor was Prof. Garvey. See an article and pictures here. Will not fly – too expensive.
Why do the “balloons” have to be flexible, as in Rubber?
Can the reservoirs not be made of Concrete, in a clam shell configuration.
One inside the other “floating” on the compressed air.
If used in a high tidal area the tide comes “IN” then the air would be compressed and drive the turbine.
Tide goes “out” the air gets sucked back in. Some control required of the air pressures.
I know to simple But I do Like a KISS.
Yeah, large concrete tanks have been proposed. But, in a diving bell configuration.
i.e. with no “bottom”.
The air has to be at much higher pressure than the surrounding water if the stored air is going to do any work.
“much higher pressure”
what for?
Perhaps one should look into the history of Naval mines and the difficult and expensive process of maintaining a mine field against the ravages of the ocean environment before they get to wrapped around the axle concerning any of the other mechanics of such a system. It is a labor intensive operation.
I’m not very concerned about safety with this storage system. Since the contents of the balloon is at the same pressure as surrounding water, even rupture of the balloon will only release a giant bubble, there will be no explosion or shock wave associated with it. So there will be little reason for other balloons to rip as well.
What I am concerned about is the longevity of the system. Moving things have very serious issues under sea water as living organisms have tendency to stick to anything, and make it unmoving and fragile. Maintenance costs needed to keep these balloons working may be a limiting factor and serious hit to the efficiency figure.
As that bubble raises the pressure decreases and thus the bubble expands so when it reaches the surface it would in fact cause quite a disturbance if there was significant volume released at once.
Boils law. http://science.howstuffworks.com/boyles-law-info.htm
Sure, this would be a relatively inefficient way of storing energy, but so are all the other ways currently used for storing “surplus” generated electricity.
The real problem, as I see it, is the massive size required to store practical amounts of electrical energy. It quickly becomes a very large and complex project. And then you have the teensy problem of regular maintenance and repair in a very hostile environment.
Poor sea horses. Hasn’t anyone considered the sea horses!
Baby seals! Protect our baby seals!
The limitations of this system have been well explored in this thread. However, it seems to me that the most basic metric for understanding the proposal is yet missing. Maybe some of you with more engineering chops that I can easily do the calcs.
Suppose we envision a test system: a 100 meter balloon, 100 M below the surface. What is the enemy capacity of a cubic meter of air in KWH under those conditions? With this info, e
ven us amateurs can play with scaling a system, changing depth, balloon size, etc.
Second question, after asking the first: Since the top of our balloon is at 50M and the bottom at 150M, the pressure is not going to be equal everywhere. Wouldn’t the top be bigger than the bottom?
OK, one more. In the heat exchanger system they envision, there are two operational phases: Cheap energy time and expensive time.
Cheap energy is used to compress the gas and waste heat is stored. However, during expensive time when the system is outputting, you need to add more “expensive” energy to make up for the heat exchanger losses. Unless you use more “cheap” energy to heat an additional storage system.
Also, unless I am missing something, the efficiency of a heat exchanger drops as the delta T decreases. Thus the storage medium would have to be massive and store the heat at a much lower temperature. Problems at both ends of the cycle?
Energy storage madness. All this to avoid the obvious solutions of atomic energy or fossil fuel.
I have a battery operated sump pump, to avoid another flooded basement. By my calculations, a big 12 volt marine deep cycle battery rated at 122 amp hours stores, max, about 1.4 kilowatt hours.
1 amp x 122 hours x 12 volts = 1465 watt-hours.
Is this true?
My system requires a battery charger and an inverter, with total capital costs in the hundreds of dollars. Neither the inverter, the charger,nor the battery will last forever, either. The sump pump might last for many years. My old sump pump lasted 40 years.
Around here, a kilowatt-hour goes for about 13 cents. So, it costs me hundreds of dollars to store 13 cents worth of energy. My pump doesn’t run much normally and only draws 420 watts when it does.
It would likely be almost as cheap to just buy a small generator, and, it would cover my pumping needs indefinitely, unlike the battery. But it would be a hassle to set up the generator every time the power went out in a rainstorm.
I like the big spring idea, though. Imagine when that baby snaps. It could take your house down and kill anything standing nearby. I can just imagine the case report in the American Journal of Forensic Medicine, “Death due to sudden energy release in large alarm clock-like apparatus. Case report and review of the literature.” That would ring anybody’s bell.
Like I say, all this madness is due to cheap money.
Unfortunately, that money isn’t cheap in the long run. Luckily, like CO2, much of the wasted money goes back into the economy somewhere, even if it all starts with bars and brothels in the DC area.
“the wasted money goes back into the economy somewhere”
It’s called a “stimulus”.
“even if it all starts with bars and brothels in the DC area”
Hostesses are “stimulating”.
The NEW DEAL didn’t work.
The New Deal DID work – in history books.
Remember, history is written by history teachers.
This idea is not going to fly!
Air motors ready to buy:
http://www.ingersollrandproducts.com/am-en/products/air-motors/selection-guide
Their motor: http://www.ingersollrandproducts.com/am-en/products/air-motors/specialty-governed-motors/series-551/modelspec/4613 gives 4kW/5hp at 4.53 m^3 per minute.
Even with the efficiencies bought about by scale, it doe snot look good.
These tethered bags on the sea bed, would each require a pipe to feed/extract the air, the pipe would need to enter the bag from the bottom, be self supporting and reach the top of the bag to ensure only air enters the pipe.
To prevent each bag from over filling with air and wasting this expensively generated air, and to prevent water from entering the feed pipe, a valve would be required shore side, and instrumentation measuring water height in each bag to operate each valve.
The figures of 4kW for 4.53m^3 per minute will allow people to scale this up.
I suspect such a huge array of air bags and supporting valves/pipe work/instrumentation would be needed to give relatively little power.
http://www.marineengineering.org.uk/page49.html discusses the issues relating to air compressors in marine environments.
It is a much better idea to bury arrays of pressure vessels in the ground (insulated and inside concrete) for residential energy storage.
You could use the adiabatic heat of compression to heat a working fluid
You could also use thermal solar to increase the pressure of the exhausted air to allow more work to be done.
Scuba tank level pressures (20 Mpa – 3000 PSI) are just fine — scuba tanks last for decades
Charge discharge cycle number is effectively limited to valve/fitting survival
Obviously your working pressures for driving pistons would be much lower than the storage PSI of 3000, so you would just exhaust the air into a plenum and then use that air at lower pressure to drive a piston assembly.
Like I posted above.
There is nothing functionally bad about CAES. This underwater balloon idea is not the greatest. (understatement)
However, CAES allows you to capture the adiabatic heat of compression, and also use any thermal energy to increase the pressure of the stored gas — thereby allowing for more work to be done.
This is basically what a combined cycle NG/Coal plant does with some of the waste heat.
Residential and distributed CAES would allow the use of solar thermal to create a combined cycle solar PV/thermal system that would allow for round the clock energy production.
Is it super efficient? Nope — but sunlight and solar infrared don’t cost a thing unlike coal and CH4.
Furthermore it is simply Air — nothing special — Scuba tanks are routinely filled with 3000 PSI air, and people walk around with them on their back
My eyes glazed over when I read ” Office of Electricity Delivery & Energy Reliability.” That’s an actual government job? Why not just pump money. But I felt a bit better when I found out this was in Canada. To quote Nelson on the Simpsons Ha Ha!
A better idea would be to have ‘x’ windmills in a wind farm pump air directly (mechanically) to store energy and deliver energy when the mills are quiet. Indeed, I’m impressed (if engineers were involved) why this wasn’t built into each project. They knew at the outset what the expected wind frequency and strength would be and consequently the quiet time percentage. Just send me a tenth of a cent per kWh for the idea.