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Ditch the Batteries: Off-Grid Compressed Air Energy Storage (2018)
- wyldfire 6y agoAnother cool energy storage technique is using subterranean flywheels. They'd probably require less maintenance than other similar energy storage mechanisms.
- Animats 6y agoFlywheel energy storage has been proposed many times, and built a few times. Flywheel-powered buses have been deployed. Not too successfully. EMALS uses a big flywheel to power aircraft carrier catapults. The flywheel energy storage seems to cause most of the problems. The next generation of that system may use ultracapacitors.[1] [1] https://www.ga.com/capacitors/military-mil-spec-capacitors https://www.ga.com/capacitors/military-mil-spec-capacitors
- aidenn0 6y agoUT Austin's cannon-caliber railgun had some impressive pulsed-power output from flywheels for demos (a 150g projectile launched at nearly 2km/s), but they were fired a single-digit numbers of times.
- aspenmayer 6y agoIt would seem that flywheels can store a lot of energy, but due to the form of the energy storage (kinetic) it’s difficult to discharge the current quickly, so to speak. Especially compared to something like a capacitor which is designed for rapidly discharging a literal current, as opposed to the analogous metaphorical motive current in a flywheel.
- jhayward 6y agoThe flywheels GP refers to were homopolar generators [1]. They created an impressive current pulse, and extracted almost all the kinetic energy in less than one revolution. [1] https://en.wikipedia.org/wiki/Homopolar_generator https://en.wikipedia.org/wiki/Homopolar_generator
- aspenmayer 6y agoLike running an electromagnet in reverse to salvage current from a free-spinning motor? I’m trying to understand how the fields and forces interact.
- jhayward 6y agoThere is a paper [1] published that documents one of the early 1980's designs they used. [1] https://repositories.lib.utexas.edu/bitstream/handle/2152/30831/PR_81.pdf https://repositories.lib.utexas.edu/bitstream/handle/2152/30...
- aidenn0 6y agoA different paper specifically mentioning the railgun shows a more traditional alternator design: https://web.archive.org/web/20151017100843/http://www.utexas.edu/research/cem/IEEE/PR%2043%20Werst%20Publications.pdf https://web.archive.org/web/20151017100843/http://www.utexas...
- jhayward 6y agoYah, that's a railgun, but it's not what everyone around CEM called the railgun. The difference being one between a .50 caliber machine gun and something that can sink a ship from 100km away. I worked across the street from CEM at the time. Firing the railgun was a big deal. The mechanical stresses on the electrical systems were pretty severe. The vast proportion of what UT CEM was doing in that era was with the big gun, for Navy and SDI type projects.
- aidenn0 6y ago
- aspenmayer 6y agoIt seems that the flywheel is a monolithic system, and the proposed next gen ultracapacitor is a modular system. You probably only have one giant flywheel, as the mass is where the energy storage gains make it worthwhile. Maybe you have many of them in parallel, but the size would make scaling an issue. Not to mention that there’s an associated drivetrain and linkages and so on. It’s a fully integrated contraption. It works, but many parts must work in tandem for it to be so. This is in contrast to an electronic system, which would benefit from miniaturization and isolated redundancy. Racks of capacitors could run as hot spares when energy is abundant next to racks that may be down for maintenance. I doubt that a flywheel can be meaningfully inspected, let alone repaired or upgraded while operating. That is the benefit of a modular approach to certain problems and not others. The two approaches are not always mutually exclusive either. Capacitors could be used as regenerative brakes for flywheels, for instance. https://en.wikipedia.org/wiki/Monolithic_system https://en.wikipedia.org/wiki/Monolithic_system https://en.wikipedia.org/wiki/Modular_design https://en.wikipedia.org/wiki/Modular_design
- shrubble 6y agoIt's not monolithic vs modular...it's controlling a large amount of angular momentum / kinetic energy instead of... not having to do that.
- tren 6y agoMy Dad, (85 years old), recently posted an idea about using flywheels to store electricity -- it would give him a real kick if he knew people from here were taking a look at it: http://aoi.com.au/devices/KPW/ http://aoi.com.au/devices/KPW/
- quickthrower2 6y agoHi from NSW. And loving the 90's (and it'll come back in the late 2020's) HTML styling <body bgcolor="#e2ff09">
- deleted 6y ago[deleted]
- notmadnomad 6y agoFor fixed-site applications of sufficient land area and scale, it's difficult to beat pumped-storage hydroelectricity (PSH). The round-trip efficiency is around or above 70%, the same or better than CAES. CAES is probably best used in applications similar to flywheel (FES), away from occupied areas.
- doitLP 6y agoDo you have any recommendations on how to learn more about this? My brother has a steep hill on his property and Ive been wondering about the feasibility of PSH. How high the tank should be, the equipment, the power output.
- timeinput 6y agoThis isn't quite what you're after, but it's a pleasent read. https://ludens.cl/paradise/turbine/turbine.html https://ludens.cl/paradise/turbine/turbine.html there have been some discussions on here about it too. It at least gets you all the right words to start googling for turbine options which helped me to do some back of the envelope math. It's a steeper hill than seemed feasible to me.
- ehnto 6y agoThid has reminded me of this gentleman who has been using gravity fed old washing machines as turbines for electricity generation on his property for 16 years https://youtu.be/Xb6TIWub6KU https://youtu.be/Xb6TIWub6KU He doesn't need the pumped storage part of the equation due to a natural water flow, but it is part of the solution at least.
- creato 6y agoYou could start by just calculating the potential energy of the volume of the tank you are considering, and the difference in elevation between the reservoirs (volume x 1 kg/L x gravity x elevation difference, plug in the units of your choice and let google figure it out). I suspect the amount of energy is far less than you are imagining... It takes a lot of water to generate a useful amount of energy. This video (https://www.youtube.com/watch?v=66YRCjkxIcg https://www.youtube.com/watch?v=66YRCjkxIcg) does an interesting demo and points out that a 5 gallon bucket on a ladder has the same potential energy as a watch battery.
- Animats 6y agoThe system they like, the near-isothermal compressor with a "liquid piston", is described here.[1] They wrote up a description of a small prototype, but don't seem to have built one. The University of Arizona lab from which that paper came does not seem to be doing anything with energy storage any more. [1] http://www.u.arizona.edu/~deymier/deymier_group/refs/CAES.pdf http://www.u.arizona.edu/~deymier/deymier_group/refs/CAES.pd...
- tomhoward 6y agoSome guys I know built a full-sized car, with the engine built with Lego and powered by compressed air. https://www.youtube.com/watch?v=_ObE4_nMCjE https://www.youtube.com/watch?v=_ObE4_nMCjE
- protomyth 6y agoThere was an actual car project in India to develop a compressed air powered car https://www.downtoearth.org.in/blog/air/compressed-air-vehicles-can-be-a-potential-mode-of-urban-transport-in-india-62987 https://www.downtoearth.org.in/blog/air/compressed-air-vehic...
- telchar 6y agoI'll admit this article describes a much less bad system than what I envision when someone mentions compressed air energy storage. On a side note, I wonder what the state of research is on reducing the embodied energy in li-ion battery production. The mentioned figure in the article is surprisingly high (2-10 times the total energy the battery will store - presumably they mean over its lifetime), which now that I think aboute it, squares with what I have seen elsewhere on the embodied energy of electric car manufacture.
- maxerickson 6y agoThe 1126 MJ / kwh given at https://www.mdpi.com/2313-0105/5/2/48 https://www.mdpi.com/2313-0105/5/2/48 puts it at about 312 charge cycles. Certainly not 10 times the total energy the kwh of battery capacity will store. Probably not more energy than the battery will store.
- tachyonbeam 6y agoI'm highly skeptical of those figures, and considering that there are trillions of dollars of corporate interest wanting grid storage and electric cars to fail, maybe you should be too.
- Andys 6y agoThat doesn't sound right to me.. the amount of energy a Tesla battery could store over its lifetime is up in the hundreds of megawatt hours range.
- myself248 6y agoThe factory producing batteries pays for power just like everyone else. Whatever energy is consumed in production ends up built into the price of the finished product. Simple economics puts the lie to outlandish claims intended to manipulate markets.
- dmos62 6y agoExcept price of energy currently doesn't fully account for the ecological damage the energy production causes. In consequence, "simple economics" can't work in the long-term.
- diego_moita 6y agoSlightly of-topic: compressed air is the preferred source of power for the tools of Amish people, since their religion doesn't allow them to use electricity or internal combustion engines. https://www.cottagecraftworks.com/home-goods/self-sufficient-living/off-grid-power-tools https://www.cottagecraftworks.com/home-goods/self-sufficient...
- ortusdux 6y agoI've been obsessed with technology that skirts religious laws for a while now. Whole house pneumatic systems to run $800 dollar non-electric blenders. Elevators that spend the sabbath atomically opening on each floor. Automatic timers to complete forbidden circuits. I would love to spend an hour or two with a rabbinical scholar. Does walking in front of a motion senor complete a circuit? Are you allowed to ask an AI to do something on the Shabbat?
- aspenmayer 6y agoCan you use your smart speaker to call your rabbi?
- myself248 6y agoI'd call myself more amused than obsessed, but yeah, the same stuff fascinates me. Can Alexa act as a shabbos goy? Does that assign personhood to the machine, or are you still doing work by invoking it?
- lozaning 6y agoOne of the things you can do with samsung's connected oven is turn on Shabbat mode from your phone. Normally the oven will shut off after 12 hours of you not doing anything, but set the desired temp and turn on Shabbat mode and it will hold there indefinitely until until you turn Shabbat mode back off. You can also do something similar with the fridge where it turns off the ice maker and the auto door light. I share in your fascination of these kinds of workarounds.
- therockspush 6y agoThis stuff cracks me up. Do they think Hashem is up there looking down, thinking "Good one guys. You got me there. I thought I had all my bases covered. I'll save you some extra latkes when you get here." Someone help me understand why some folks treat this stuff like a tax loophole.
- jacknews 6y agoThe last example, using multiple small pressure containers, seems to get a hugely better energy density than the other examples, and starts to seem realistic for domestic storage. Are the figures correct, I couldn't find much follow up to that study? I can imagine small-scale CAES being ideal where there is also a cooling load (eg humid tropics), since the expanding air will be cool and dry.
- behringer 6y agoThis article seems to assume we'd convert the compressed air to electricity, but I could think of a bunch of applications that could use mechanical air power instead. Blenders, washers, dryers, dish washers, garage door openers. Basically anything that uses a motor.
- BHSPitMonkey 6y agoYou might be interested in this comment further up in the thread: https://news.ycombinator.com/item?id=24784669 https://news.ycombinator.com/item?id=24784669
- _underfl0w_ 6y agoIs your blender powered by a hand crank?
- hakcermani 6y agoI just saw this on a India trip last month ... roadside vendors crushing Aloe for a refreshing summer drink using a hand crank blender ..! I was thinking I need one for myself too ..
- tedk-42 6y agoEnergy as electricity is like money. Pretty easy to convert to other forms of work and readily accepted as an input to many systems. I doubt there's much of an ecosystem/incentive to build a compressed air --> <something> conversion systems that are general enough for anything to use.
- myself248 6y agoFor things like garage door openers that only run for a moment and only once in a while, the payoff would likely never come. But for things like dryers where it's a simple continuous motion for hours on end, I could see it easily justifying an air motor conversion. Bonus: Compressed air is inherently dry. It'll come out of the motor cooler than ambient, but pass it through a heat exchanger and you'll get almost-room-temp super-dry air. (And maybe use the exchanger to condense some of the moisture out of the dryer's exhaust; you're halfway to a ventless condensing dryer already!) I wonder if refrigeration appliances would be designed differently if they assumed compressed air as the power source.
- darksaints 6y agoWhile I'm a pretty big fan of low tech solutions, I'd just like to point out that electrochemical hydrogen compressors can basically already do this, but better. 80% round trip compression efficiency, up to 700 bar compression, no moving parts, and massively long lifetimes (in the 30-50 year range). The fact that the compression medium (hydrogen) is also an energy storage medium is just a cherry on top. It's just a matter of price coming down for 700 bar pressure vessels.
- DoingIsLearning 6y agoThe advantage of a system as simple as compressed air, is that anyone with a minimal technical background and shop tools is able to maintain and minimally repair the compression system. An electro-chemical hydrogen conversion and compression vessel would have far more points of failure with far greater technical barriers to repair. The access to specialized spares in a remote location would also be a major issue. I am not saying it cannot become a player in energy storage to eliminate the need for coal and natural gas energy generation. But it seems unlikely that would be a good choice for remote 'off-grid' location.
- jacknews 6y agoIndeed, compressed air seems ideal for hot humid climates (cool/dry air being a byproduct of discharge), which are are often quite low-tech.
- deleted 6y ago[deleted]
- jacknews 6y agoThis is a very interesting technology, and can be used with other gases too: https://www.sciencedirect.com/science/article/abs/pii/S0140700719302051 https://www.sciencedirect.com/science/article/abs/pii/S01407...
- tedk-42 6y agoGenerally I don't like this as an idea given the likelihood of failure of metals after a certain number of stress cycles (why planes have a lifespan)
- lopmotr 6y agoThat's aluminium. Steel is magical because it has an infinite fatigue life for cyclic stress below the endurance limit and you can design things to operate in this region. Pressure vessels are also designed to leak before bursting, so a crack won't cause an explosion. Having said that, you still need to do maintenance just like you do on a wooden house or a wheeled cart or anything that might fail dangerously. Wood rots over time!
- VanillaCafe 6y ago360 Wh for 18 cubic meters? Is this a joke? That is indeed the volume of a small room. You need nearly 40 of them, the volume of a large house, to give the equivalent energy storage of one 13.5 kWh Tesla Powerwall.
- lopmotr 6y agoEnergy density is only one factor. Cost per kWh is more important for people with plenty of land.
- mycall 6y agoHave fun making something as big as a large house without leaking air, for each installation.
- hinkley 6y agoThat’s the thing about pressure. A pressure vessel doesn’t care if it’s holding back enough gas to equal five cubic yards at 1 atmosphere, or 5 million cubic yards. It only cares that it’s at 3 bars or five. You’re right, a vessel the size of a battery array is stupid. Because it’s all surface area and no volume, compared to a vessel the size of an aircraft, or a small stadium. You’d build one of these for an area of town, and the “size” that matters for stationary centralized equipment is not the displacement but the volume of material to make up the skin, the valves, the generator, and the piping to connect it all.
- jillesvangurp 6y agoYou stopped reading too soon: e.g. " By discharging the cylinders sequentially, the discharge time can be greatly increased, making the system comparable to lead-acid batteries in terms of energy density. Based on their experimental set-up, the researchers calculated the efficiencies for different starting pressures and numbers of cylinders. They found that 57 interconnected cylinders of 10 litre each, operating at 5 bar, could fulfill the job of four 24V batteries for 20 consecutive hours, all while having a surprisingly small footprint of just 0.6 m3. Interestingly, the storage capacity is 410 Wh, which is comparable to the 360 Wh rural system noted earlier, which requires an 18 m3 storage vessel – that’s thirty times larger than the modular storage system. " Also you missed the points of higher pressure vessels and using the residual heat/cold for things like hot water. Basically you trade off lower electricity efficiencies, space, and heat. Excess heat is not necessarily a bad thing in a domestic situation. My take aways from this article: - there are a few scenarios where stuff like this makes sense. - there's lots of room for innovation and component improvement (e.g. more efficient dynamos are hinted at). This is currently a niche market and people have not put much R&D into this so far (i.e. I'd expect some improvements are entirely feasible). - sequential vs. monolithic setups have different properties. It boils down to cost / kwh and whether the requirements make sense. In an industrial setup, having a cheap but enormous vessel might not be the end of the world. In an apartment, you'd want maybe a smaller but higher pressure one.
- newyankee 6y agoI was wondering if one can store energy like this to power pneumatic tools in a factory
- sarthakjshetty 6y agoThere was a company called LightSail Energy [1] that tried to (unsuccessfully) commercialize this technology. Does anyone know what happened to it? Some searches online show that they had some founder problems. IIRC, they had great investors, but unfortunately it didn't work out. [1] - https://en.wikipedia.org/wiki/LightSail_Energy https://en.wikipedia.org/wiki/LightSail_Energy
- SagelyGuru 6y agoIt would be more efficient to use a pressure tank half filled with water and use water pump and Pelton turbine for the energy cycling.
- nine_k 6y agoWater is practically incompressible. If you wanted to compress the air 10x the atmosphere pressure, when it takes 10% of the normal volume, you would have to fill the tank with water for more than 90%. Without water, you can compress air 10x and put 10x more of it into the same pressurized tank.
- jandrese 6y agoI'm not a fan of this personally. Compressed air is dangerous. A full tank is basically a bomb. While we have the technology to make this safe, it has to be regularly inspected. If your homeowner slacks on the inspections they could come home one day to discover their energy storage has turned itself into a crater and flattened all nearby structures. One thing to consider is that the heat generated by compressing the air could be vented into the home to warm it up in the winter, or simply allowed to escape outside in the summer. When discharging the cool air would either be released outside or inside of the home, depending on if you want to cool it off.
- atrus 6y agoI mean, doesn't any big energy storage device become essentially a bomb? Batteries have some pretty impressive failure modes. As do large tanks of fuel. Even piped in energy sources can be dangerous as well. How many houses have literally exploded over a leaking gas line? Or burnt down due to faulty wiring? Large amounts of energy stored in an area is inherently dangerous, no matter the form.
- jandrese 6y agoPeople talk about batteries "exploding", but really they're just burning fast. An air tank explosion however will decimate everything nearby. Even small SCUBA tanks can release a tremendous amount of energy when they go, which is why they are typically refilled inside of water baths.
- Doxin 6y agoScuba tanks operate at wildly higher pressures than your average air compressor. Scuba tanks are at anywhere from 160 bar to 240 bar. The usual sort of compressor you'd use for running your tools tops out at 8 bar. Make no mistake, 8 bar escaping from a compressor is no joke. It's the equivalent of two elephants worth of air suddenly entering the room. It'll rupture eardrums and shatter windows but the building will still be standing. I wouldn't be so sure about that when a scuba tank decides to explode though.
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- ggm 6y agoI would like somebody to explain his "replace batteries every 2-3 years" comment. I think this is true of small scale Lead-Acid based UPS, but Neoen scale Li-Ion stacks come with a battery management system which I believe offers better than 80% effective battery energy density over a longer life: 5+ years. Certainly the assumptive economics behind grid-scale battery models from Tesla is, a far longer working life than this. And, the evidence of full cycle life on Tesla car batteries and even Prius, is better than 2-3 years of useful life. This may be because they over-provision so "rated" energy is met by replacement from a 110% sold capacity-type model. I think the rest of the article is great. Fascinating. Grid scale compressed air storage is a thing, and may have low energy efficiency, but so does PHES. The thing is, they can be huge, and they can sustain power for long periods. The heat loss story, I am confused by because usually this gets better with scale: you can exploit a lot of lower grade energy in heat/cool cycles, either to retain it in system eg heat transfer to another form of heat energy storage, or, for adjunct purpose like building heating or cooling. Fan, not expert, experts can put me right!
- ncmncm 6y agoCompressed air storage really begins to make sense when the tank is deep underground, or deep underwater, so you don't need an overbuilt pressure vessel. The very good idea of floating solar panels on a reservoir (cool panels are more efficient, and keeping them clean is cheap!) raises the question of what to do with excess power generated in the daytime. One alternative would be to pump water up out of another reservoir downstream, but there might not be one. So, just put a big air bladder on the bottom of the reservoir and pump air in. Same applies for offshore wind power. About half the energy you put into a pressure vessel becomes heat that you would not get back, under water. (But rock is an excellent insulator.) With enough spare water, you can draw almost the same amount of heat back in on discharge. Or, you might have a use for cold air.
- infogulch 6y agoThe efficiency loss compressed air suffers is mostly at the hands of the ideal gas law. Storing energy by pressurizing the container heats up the gas which increases the pressure requiring even more energy to store additional gas. When retrieving energy it depressurizes the container which cools the gas down which reduces the pressure which gives you even less energy. What if they could cancel out? Say you have two separate pressure vessels where to charge the system you pump air out of one into the other. Well the depressurizing vessel will cool down, but the pressurizing vessel will heat up. If they came to thermal equilibrium with each other their net temperature change would cancel out somewhat. This is great because it would restore the pressure on both sides to have more favorable conditions for energy storage and extraction. So I wonder if you could design a pressure battery that would exhibit no change in temperature on the exterior throughout the charge/discharge cycle.