[HN Gopher] Gravity Energy Storage: Alternative to batteries for...
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Gravity Energy Storage: Alternative to batteries for grid storage
Author : headalgorithm
Score : 48 points
Date : 2021-01-05 20:26 UTC (2 hours ago)
(HTM) web link (spectrum.ieee.org)
(TXT) w3m dump (spectrum.ieee.org)
| dzhiurgis wrote:
| Then there's compressed air under water storage. There have been
| trials but roundtrip efficiency isn't great IIRC.
| jandrese wrote:
| Usually when you see compressed air storage solutions they're
| talking about plugging up an old mineshaft or cave and pumping
| air in.
|
| Doing it under water would seem to have some advantages, like a
| less catastrophic failure condition and having a ready place to
| sink all of the heat. Downside is that the water would cool the
| air much more effectively than solid rock so you lose
| efficiency.
| jayd16 wrote:
| Are there any combination solar, hydro, fracking/oil plants?
| I'm joking but not entirely. Not sure how much water would
| fit in an oil field but it seems like a natural reservoir one
| could use.
| jandrese wrote:
| The trick would probably be getting your energy back after
| you've pumped the old oilfield full of water. Most oil
| fields aren't gushers, especially after they've had most of
| the oil sucked out of them.
| ed25519FUUU wrote:
| A lot of these storage technologies have been around for a long
| time (I have a "Nature" magazine from the 60s that discusses
| storing excess energy as wind in salt mines and in lakes. This
| was the 60!).
|
| What people underestimate is just how much energy we need to
| store. Lakes won't do it and neither will salt mines. Gravity
| certainly won't do it. We need to think much BIGGER.
| huhnmonster wrote:
| There are a bunch of other technologies as well. Huge flywheels
| [1], which are supposed to be used for very responsive power
| needs (i.e. grid stabilisation), trains loaded with weights
| which get pulled up a mountain and released [2], redox-flow
| batteries and so on.
|
| [1]: https://www.energydigital.com/smart-energy/worlds-largest-
| fl... [2]: https://aresnorthamerica.com/
| timr wrote:
| Also molten salt:
|
| https://www.solarthermalworld.org/news/molten-salt-
| storage-3...
|
| People talk about making "personal" molten salt units for the
| home, which seems a little terrifying.
| jandrese wrote:
| I wonder what the local zoning commission has to say about
| the guy building a personal toxic metal death ray in his
| backyard?
| peteradio wrote:
| That is why I will never live in a HOA neighborhood.
| jandrese wrote:
| The zoning commission runs at the town/country level, so
| even if you don't have HOA busybodies you still need to
| get the permits. The law is usually worded such that if
| you're doing something abnormal you don't get a "there is
| no rule that says a dog can't play baseball" loophole,
| you instead have to bring it up before the county council
| and justify the project.
| taeric wrote:
| Seems the train idea is similar to the old counterbalance
| system for trollies in Seattle.
| imtringued wrote:
| Hydro pump storage works because you don't have to pay for
| the weights. Building a train is worse than batteries in
| terms of economics.
| nabla9 wrote:
| This solution competes against short term storage, (typically
| tens of minutes, up to hours). Flywheels are commonly used and
| efficient energy storage for short term.
|
| Pumped hydro mentioned in the article is good for long term
| storage > weeks, months, even seasonal.
| DeRock wrote:
| Something that doesn't often get brought up in these energy
| "storage" discussions is the potential for duty cycling existing
| generation to time shift the duck curve. Eg. California (large
| solar generation) shares a grid with Washington and British
| Columbia (large hydro generation). When the sun is shining, hydro
| reservoirs can be filling, as solar is meeting the demand. When
| the sun goes down, hydro facilities can duty cycle on and drain
| the overhead. This requires some flexibility in reservoir levels,
| as well as the ability to stop/re-spin turbines on a daily
| cadence. But you eliminate all of the efficiency losses with
| schemes such as pumped storage (though gain some transmission
| losses due to the increase length of geographic arbitrage).
|
| The same opportunity exists on the East-West axis. The sun is
| still shining in California after its set on the East coast.
| abfan1127 wrote:
| Its my understanding that some hydro facilities do this. One
| issue I can think of is the losses of transmitting that much
| electricity from 1 area to another (1000s of miles away). the
| losses of transport coupled with the losses of "storage" and
| "generation" make it more expensive. I don't know the actual
| costs, just ideas I think about.
| ebiester wrote:
| The losses of transport are relatively small, smaller than
| would be expected: see
| http://insideenergy.org/2015/11/06/lost-in-transmission-
| how-...
| sdepablos wrote:
| Not so much with ultra-high-voltage lines. China has been
| doing it for years because of the really long distances
| between electricity production and consumption.
|
| https://en.m.wikipedia.org/wiki/Ultra-high-
| voltage_electrici...
| jonas21 wrote:
| What you're describing sounds a lot like open-loop pumped
| storage [1]. You don't hear about it much because it's already
| very common and has been for decades. There's something like
| 22GW of capacity in the US alone.
|
| [1]
| https://www.energy.gov/sites/prod/files/2016/10/f33/Hydropow...
| (p. 183-195)
| arawde wrote:
| It was my understanding that this is more of a seasonal thing
| than on a day to day basis. That is, during the summer,
| southern California uses a large amount of electricity for
| climate control, and so power is transferred along the Pacific
| DC intertie in a north -> south direction.
|
| In the winter, electricity usage in the north is devoted to
| heating, whereas in the south temperatures are mild. The result
| is that power is moved back up the intertie from south ->
| north. In the spring, snowpack melt refills the reservoirs in
| the hydroelectric system, allowing it to be ready to provide
| power to the south again once temperatures start to climb.
| baybal2 wrote:
| Excuse me, but the company in the article was debunked as pretty
| much a scam.
|
| You cannot physically make that work economically.
| imtringued wrote:
| Yeah all of them are questionable. The only one that has even a
| tiny chance of succeeding is the piston idea. You don't have to
| pay for the weight and you only have to cut the circumference
| of the piston out.
| huhnmonster wrote:
| This article surprised me since funding came from Softbank and
| not the state government as most does IIRC.
|
| Where I see the problem with all these forms of energy storage is
| that there is no one efficient approach (yet!) and innovation
| will come mostly from government funding, so governments decide
| what they see as the best opportunity.
|
| This seems like its pretty much hit-or-miss and betting on the
| wrong thing will arguably speed up the development of it but at
| the same time, we might end up at a point we could have reached
| quicker and cheaper had we used a different technology.
| fullstackchris wrote:
| Quite a while ago, I thought up of what I though would be a
| simple system that has a net positive energy output (it already
| sounds ridiculous, I know, but I just can't see what concept I am
| missing) that follows this principle. I finally have a relevant
| article I can share it with here on Hacker News!
|
| The gist of the system is as follows:
|
| 1. let a hanging weight freefall under gravity to spin a
| generator. (via a pulley connected to a chain drive or gears etc)
|
| 2. The power generated by the generator is stored in a battery
|
| 3. The weight is pulled up very slowly back to its drop position
| using a DC motor that uses power from the battery (the DC motor
| could be actually the generator itself but likely a specially
| tuned one for slow lifting will be better)
|
| 4. Repeat. The system lifting / reset process requires less
| energy than the energy produced by the drop, so there will slowly
| be a net buildup of charge in the battery.
|
| Super simple numbers example:
|
| PE of a 100kg mass falling 2m:
|
| PE = (100kg) _(9.8m /s2)_(2m) = 1960 J
|
| The mass falls at a near g acceleration - I know it won't be
| exactly g because of the moments of inertia of the generator and
| generating drive apparatus - but it would be quite close to g. At
| this acceleration the mass falls for ~0.63s, so the theoretical
| max power we can hope to extract using the generator is:
|
| P = W / t = 1960 J / 0.63s = ~3000 W
|
| Even if we consider a horrible electric generator with only 50%
| efficiency (just to be even more conservative and fair, and to
| capture any losses we've forgotten), we should hope we can get at
| least 1500 W from the drop.
|
| The "trick" of mine is mentioned in that very slow "reset time"
| for the weight. That is, use a DC motor to pull the weight up,
| but give it a long time to do so. In this way, the power used to
| lift the weight back up to its dropping point is much less than
| what was produced by letting the weight fall and spin the
| generator.
|
| Using the same numbers from the example above, if we let the lift
| time be, say 20 minutes (=1200s) and since we know the W of the
| lift is the same as the drop PE, then the power needed to lift
| the weight back to its original drop point is:
|
| P = 1960 J / 1200s = 1.63 W
|
| That means we produced about 1500 W (even with our crappy 50%
| efficiency generator), and only need ~2 W to reset the system.
| Assuming you put a nice battery between the generator and the dc
| motor - you get a net positive storage of energy over time.
|
| Does anybody see any glaring issues with such a system and my
| analysis? I know when anything in physics appears to be a free
| lunch, something must be wrong. (Though if you consider these
| long 'cycle' times, it isn't really a free lunch)
|
| Perhaps I don't understand exactly how DC motors / generators
| really draw or produce power in the real world - Physics 101 was
| a long time ago for me :)
|
| The trick to my proposed system, which systems like those in that
| of the linked article don't do, is my slow reset time. Obviously
| not feasible for massive applications or load balancing, but a
| net power storer nonetheless.
| polemic wrote:
| You need 1.63 W _for 1200 seconds_ (i.e. 1960 J, assuming no
| losses) to reset the system. I.e. the same energy you already
| got out.
|
| If this worked, you could get free energy from any sort of
| gearing system - e.g. you could put a fly-wheel on your bicycle
| and power all your up-hill trips from the downhill legs of the
| same size by switching gears at the right time.
| Ekaros wrote:
| Let's use Watt-Seconds to simplify things.
|
| 3000W * 0.63s = 1890 Ws
|
| 1.63W * 1200s = 1956 Ws
|
| Near enough the same. Watt is unit of power, Watt-hour is unit
| of energy.
| peteradio wrote:
| You seem to be comparing power differences and not taking into
| account that your battery would run out of energy in just the
| second attempt at lifting your mass to full height (assuming no
| other power inputs to the battery besides the falling mass
| generator).
| orange_tee wrote:
| Step 4 contradicts basic physics. What you are doing wrong is
| that you are confusing power with energy. If you lift the
| weight slowly you need less power because for the same work (=
| energy) done you can do it in twice the time. But using less
| power over longer periods of time will result in the same
| energy consumption.
| orange_tee wrote:
| These ideas are cute but they lack interest from major players.
| In Europe it seems the big players are betting big on hydrogen.
| The EU is looking to convert all gas pipelines to be hydrogen
| proof and for new pipelines to also be hydrogen proof. I know
| Japan is also very bullish on hydrogen infrastructure. With
| regards to energy storage, it seems to me the solutions that are
| most likely to be widely adopted are: batteries, pumped hydro,
| and hydrogen and the many synthetic hydrocarbons that can be
| obtained from it. Besides that, improvements to the energy grid
| can be made to eliminate the need to store as much energy in the
| first place.
| blue_box wrote:
| Could you share your resources, please?
| orange_tee wrote:
| I got it through word of mouth from people involved in
| projects, but I did a Google search for you and came up with
| many public trusted sources:
|
| https://ec.europa.eu/info/sites/info/files/hydrogen_europe_-.
| .. https://hydrogeneurope.eu/hydrogen-storage
| https://www.euractiv.com/section/energy/news/gas-grid-
| operat...
|
| Were we stand in 2021 is that policy is already on the books
| and funds being distributed for these projects. So hydrogen
| ready pipelines are definitely getting built. Whether they
| will prove useful remains to be seen.
| Hypx wrote:
| This being explored in the US too:
| https://www.energy.gov/sites/prod/files/2019/03/f60/fcto-
| sat...
|
| I suspect that utility companies in the US are only a few
| steps behind European utility companies. This should be a
| global thing before long.
| blackrock wrote:
| I wondered if you can use hydrogen instead.
|
| Use solar/wind to crack water into hydrogen and oxygen. Compress
| it to liquefy it. Store this in some temporary storage tanks.
|
| Then when you want to make electricity, pipe the hydrogen and
| oxygen into a fuel cell. Then electricity and pure drinking water
| comes out.
|
| Then you can bottle the pure drinking water and sell it locally
| for an additional profit.
|
| I haven't analyzed the cost for all the technology and
| infrastructure. But this idea seems mechanically simpler than the
| gravity brick idea. Additionally, you can transport the LH and
| LOX, to other areas if necessary.
| imtringued wrote:
| Hydrogen works despite the inefficiency because there is an
| existing gas infrastructure ready to be converted. If we had to
| build everything from scratch we would be desperate for other
| solutions.
| OliverJones wrote:
| The grid-nerd term for rapid-response capacity delivery is
| "frequency control ancillary services." It's a real problem in
| times of heavy load. If a local grid's frequency drops below
| nominal (60Hz US, 50Hz elsewhere) the regional grid has to
| disconnect. So without rapid-release stored energy a power
| generating org has to fire up extra capacity and keep it running
| to cover transients.
|
| Old missile silos might be interesting. But most of them are far
| from population centers.
|
| Pumped storage is still great given the right geography.
| Northfield Mountain has been running flawlessly for almost half a
| century, storing about 9 GwH.
| https://en.wikipedia.org/wiki/Northfield_Mountain_(hydroelec...
| But it takes about ten minutes to spool up. And the fish and
| boaters in the nearby Connecticut River definitely notice it.
| Florin_Andrei wrote:
| When the frequency of the generator is not tied to a mechanical
| property of it (like the spin of a turbine) - e.g. when the
| source is solar panels and the AC is produced via an inverter
| circuit, what are the remaining frequency-related issues?
|
| I imagine with solar the generator can pretty much pick any
| frequency it wants, it should not be influenced by load, it
| could simply stay in sync with the grid no matter what, is that
| right?
| bob1029 wrote:
| The problem with inverters is that they have no inertia to
| impart on the grid. When you have a gigantic spinning
| turbine, the amount of power it takes to change its speed is
| immense. This has huge implications for grid stability when
| we are talking about renewables.
|
| The resolution for this is something called a synchronverter:
| https://en.wikipedia.org/wiki/Synchronverter
| robbrown451 wrote:
| Seems like they'd do it on the edge of a natural cliff to avoid
| having to build a tower, or maintain an abandoned mineshaft.
| There aren't big cliffs everywhere, obviously, but where there
| are, seems like an economical option.
| imtringued wrote:
| Drilling holes for energy storage isn't economical at all.
| Gravitricity is never going to work on a large scale.
| wedn3sday wrote:
| Cliffs tend to move a bit, falling slowly over time. There may
| be more stable cliffs to use, but the ones near where I grew up
| on the coast have a fairly steady fall rate (a new cm/year).
| amelius wrote:
| https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...
|
| > Pumped storage is by far the largest-capacity form of grid
| energy storage available, and, as of 2020, the United States
| Department of Energy Global Energy Storage Database reports that
| PSH accounts for around 95% of all active tracked storage
| installations worldwide, with a total installed throughput
| capacity of over 181 GW, of which about 29 GW are in the United
| States, and a total installed storage capacity of over 1.6 TWh,
| of which about 250 GWh are in the United States.
| WalterBright wrote:
| By far the most efficient grid "battery" to reconcile
| fluctuations in demand & supply is to have a realtime price for
| electricity. Water heaters, for example, can be equipped with an
| internet device (at last, a reason for an internet connected
| water heater!) to monitor the price of electricity and shut off
| the heater during price spikes.
|
| Some "batteries":
|
| 1. hot water heater
|
| 2. HVAC system
|
| 3. EV charging
|
| 4. Some lights (like yard lights) can be dimmed or shut off
| during rate spikes
|
| 5. Same for street lighting
|
| 6. Computers can switch to low power mode
|
| 7. Refrigerators
|
| 8. Dryers
|
| This is far better than the "rolling blackout" bureaucratic
| solution.
|
| Note that the pump price of gas varies daily. This is the market
| reconciling constantly shifting supply & demand, and it works
| great.
| choeger wrote:
| Heating water with electricity is the literally last thing we
| should do. That is, once clean electric energy is cheap, we can
| do it. But we are not there yet. Hence we should at least use
| heat pumps or similar technology.
| WalterBright wrote:
| Meanwhile, there are hot water heaters in use everywhere.
| That isn't going to change anytime soon. Besides, in many
| places during peak solar there isn't anyplace to dump the
| electricity. Electric hot water heaters can take care of that
| problem, as water will stay hot in one for a couple days (I
| know from experience).
| dharmab wrote:
| A heat pump can approach 500% efficiency and is powered by
| outdoor ambient air (using direct heating as a fallback).
|
| https://www.youtube.com/watch?v=-vU9x3dFMrU
| WalterBright wrote:
| It still uses electricity, and can be shut off during
| electric rate spikes, acting just like a "grid battery"
| without the expense.
| war1025 wrote:
| I was talking with someone recently and they recently bought
| a new electric water heater. I asked why they didn't go with
| a heat pump option, and they said the dealer told them that
| heat pump water heaters are basically a "robbing Peter to pay
| Paul" situation where you end up taking heat you would have
| added to your house and putting it in your water instead.
|
| I guess in warm climates / seasons that is probably a net
| benefit, but I've noticed our electric co-op also promotes
| highly-insulated electric water heaters instead of heat pump
| water heaters.
|
| Not sure what I think of it all. We have an electric water
| heater and at first I was grumpy about the relative cost to
| run relative to natural gas, but I've come to terms with it.
| It's about the simplest device possible, and that has some
| value I think.
| war1025 wrote:
| The way the parent comment is worded, he is actually
| advocating for _not_ doing activities like running hot water
| heaters during peak load times.
|
| I know many utilities in my area have a program you can sign
| up for where they will cycle through the registered AC units
| to balance out peak load in the summer. I'm not entirely sure
| how they manage that, I suppose they have to have some sort
| of sensor switch they install in your circuit.
| WalterBright wrote:
| > you can sign up for where they will cycle through the
| registered AC units to balance out peak load in the summer
|
| This is inefficiently attempting to solve the problem in
| the same way while trying to maintain that flat electric
| rate. We need to get past the idea that electric rates must
| be flat.
| war1025 wrote:
| > We need to get past the idea that electric rates must
| be flat.
|
| I'm not aware of anyone that does minute to minute
| electricity pricing, but I know for many utilities you
| can sign up for alternate price schedules that have
| different rates based on the time of day.
|
| I would guess as much as anything it's a metering issue.
| sliken wrote:
| Seems a bit limited and expensive. Pumping water uphill when
| there's a surplus seems like a no brainer, doubly so when you are
| already using hydro and hydro production is already tied into the
| grid. Seems like pretty much the only way to cost effectively
| bank substantial amounts of energy for 6 months.
| ogre_codes wrote:
| There are a lot of places water/ hydro isn't an option.
| Pfhreak wrote:
| It's good but not perfect. Dams require a reservoir, which
| takes land out of use and changes the flow dynamics of a river.
| It can interrupt wildlife patterns both up and downstream. It
| introduces some risks of dam failure, and decommissioning a dam
| requires careful management of built up sediment. Flooded
| organic matter anaerobically produces methane.
|
| It also requires significant space and particular
| configurations (must be on a river, must be in a hilly or
| mountainous area, etc.) It also isn't necessarily scalable --
| how many more dams can we build?
|
| You can build a crane and blocks or drill a big hole in lots
| and lots of places.
|
| So yes, pumped hydro is better than fossil fuels. But also it's
| not something we can consider to be the ultimate solution to
| the issue of storage. By all means, let's use it (and we do use
| it today), but not stop there.
| deepspace wrote:
| I am not sure that this form of storage is comparable to a
| traditional dam. The fact that blocks of matter need to be
| physically moved by a crane severely limits the total
| capacity of the system. The most dense metals are only about
| 20x as dense as water, so we are not talking about a huge
| volume of water. The equivalent mass of water can be stored
| in a tank - no dam required and moved through a pipe - no
| river required.
| VectorLock wrote:
| It seems like using hydro as a demand-smoother changes the
| aspect of how much damming you need to do. Instead of having
| to construct a massive reservoir to provide constant power if
| the hydro is only intended to provide peaking or off-demand
| power then it seems like the reservoir could be much smaller
| - and conversely less environmentally impactful.
| Baeocystin wrote:
| Once you've committed to a dam, much of the environmental
| damage is baked in, whether small or large. And dams have
| _huge_ environmental impacts across the entire river
| system.
|
| They still have their place. There is a pumped hydro system
| here in the Bay Area (San Luis Reservoir) that is coupled
| to a hydro station, and produces power when it drains back
| in to the aqueducts. It's primary purpose is water capture
| and distribution, not power storage, but it does both.
| sliken wrote:
| Dams are expensive and have significant side effects. However
| the duty cycle on a dam is pretty low (they rarely run the
| turbines at 100%). So there's substantial additional capacity
| that could be had by pumping water upstream whenever there is
| a surplus of power.
| Hypx wrote:
| The other way is to electrolyze water and store hydrogen in
| underground salt caverns.
| ogre_codes wrote:
| I so hate IEEEs broken web-site. Every time someone links to this
| site I'm irritated by the broken scrolling.
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