Storing electricity in potential gravitational energy? - Page 1
Forum section: electronics / general

author: enjoy.cowboy
author_rank: Contributor
timestamp: January 20, 2020, 07:41:09 pm
content: A friend of mine sent me this. Get a load of this lot, building a gravitational battery thats worse, less efficient and more maintenance heavy than an actual batteryThe system responds in less than one second, tho! how could it be any faster than one second? the electrons would go flying off the cable

author: Berni
author_rank: Super Contributor
timestamp: January 20, 2020, 08:51:17 pm
content: Well lets take it from an engineering point of view.Taking in account the biggest baddest configuration of a 3000 ton weight on a 1500m shaft. This would have the storage capacity of 12MW/h. That is a quite significant amount of energy that would require the equivalent of a 50 ton Li-Ion battery to hold. Okay that's not bad so far, its a lot of battery.So how difficult is it to build one of these? Well the 3000 ton weight would be quite the hefty bugger. It would take the biggest trucks in the world (The huge house sized mining haul trucks) ~7 trips to transport 3000 tons worth of material. They also weigh about the same so its the weight of 7 of these trucks. That is a BIG weight. But okay you can build some steel skeleton and fill it with concrete, nothing too bad. So how about the cables to lift it? Well going for CertexTMRopetex 6 cable that can carry 328kN in a 20mm strand weighing at 182 kg/100m. Lets assume you need to keep half of its max strength as safety margin (Giving it optimistic here) then you need 200 strands to hold 3000 tones. If you have a 1500m long shaft that works out to 550 tones of only cable! Consider the size of the pulleys and winches you would need to handle this amount of cable.So looking at the pricing trends of lithium batteries that 50 ton battery would cost about 2 to 5 million dollars.If we look at just the cost of that 550 ton cable needed to lift that weight it would cost about 1 milion dollars for the cable alone judging by chinese large volume prices on galvanized steel cable. And then you also need the weight itself, the hole to put it in, the winches, the massive motor/generator and associated gearbox/mechanics. Yeah this thing is not gonna be cheap at all. Bear in mind that you still need the massive power electronics to covert and synchronize the power to the grid just like the battery needs.(No way in hell are you getting the generator to spin synchronously with the grid in this application)For comparison here is a list of existing operational energy storage facilities:https://en.wikipedia.org/wiki/List_of_energy_storage_projectsSo we already have battery storage facilities with 10x the capacity of this and pumped hydro plants with 2000x the storage capacity. The said battery facilities however offering pretty much instant response time while pumped hydro can then take over after about half a minute to 5 minutes.

author: Gyro
author_rank: Super Contributor
timestamp: January 20, 2020, 09:32:55 pm
content: Quote from: enjoy.cowboy on January 20, 2020, 07:41:09 pmFor response speed, Pumped Hydro is probably a reasonable comparison. Take Dinorwig in North Wales... Zero to 1.8GW in 16 seconds and 9.1GWh storage capacity.Ok, a lot more expensive (difficult to cost (UK £425M in 1984) against present day alternatives in terms of $/MWh but still looks very competitive). In terms of moveable heavy weights, water is a lot more flexible!https://en.wikipedia.org/wiki/Dinorwig_Power_Station

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 20, 2020, 09:44:45 pm
content: Quote from: Berni on January 20, 2020, 08:51:17 pmVariable displacement hydraulics would allow a constant speed generator to work.

author: Berni
author_rank: Super Contributor
timestamp: January 21, 2020, 06:07:37 am
content: Quote from: NiHaoMike on January 20, 2020, 09:44:45 pmThat's a nice idea. The hydraulics to handle 10 to 100MW of power would be pretty massive but likely significantly cheaper than power electronics for that sort of power. Keep the generator spinning and synchronized 24/7 while having a pump variable all the way to zero.

author: Marco
author_rank: Super Contributor
timestamp: January 21, 2020, 03:55:54 pm
content: Just seems to require way too much work and materials to me, for a rather small height displacement.Railway/buckets up mountains, digging out a cylinder of rock and pumping water under it, dropping weight into deep sea with stainless steel cables ... all those although they are pretty far out there intuitively it feels the costs might be manageable. Here though, I kinda doubt it.

author: PlainName
author_rank: Super Contributor
timestamp: January 22, 2020, 07:29:36 pm
content: QuoteHis beef was that water was better, neglecting to consider that big lakes can't just pop up in the middle of nowhere. Another beef with the towers was wind and stacking. There was probably some other issue he made up and demolished tooThis one would seem to answer those: no wind, existing hole in the ground. What's not to like? Bonus brownie point: it's a power generator right where old tech got stiffed (and everyone made redundant) by renewables.Regarding weight, why use one cable? Or even one weight? The output is surely the sum of the parts, not the work of the biggest bit, so if 3kt is a bit big, why not 3 x 1kt or whatever?

author: Gregg
author_rank: Super Contributor
timestamp: January 23, 2020, 05:15:10 am
content: This system doesn’t sound as lame as most of the other energy storage schemes. However digging large deep holes straight into the ground is very costly and fraught with problems the purveyors of this system haven’t even considered. Things like the cost of pumping ground water out of the hole and keeping the lower parts for collapsing due to the tremendous pressures on all sides.Old clocks used this same system to keep a reasonably constant tension on the escape mechanism compared to springs; the idea of stored energy from weights and cables is far from new. The power return is certainly more linear than flywheels or batteries. Once the weight is lifted, it doesn’t take a lot of effort or energy to keep it at a ready state. Pumped hydro has evaporation of water and inefficiencies of pumping that need to be addressed when compared to lifting deadweight.It shouldn’t be too hard to find some abandoned mine shafts that are vertical for a few hundred meters and employ some coal miners that have lost their jobs because of carbon concerns to shore things up and get a test bed ready. Plan B for if the cable(s) break and the weight plummets to the bottom is probably a good idea.This idea is presently only reasonable if there is already a suitable mine shaft near existing power lines.The right marketing and it is a kickstarter ready to be exploited.

author: Berni
author_rank: Super Contributor
timestamp: January 23, 2020, 06:25:27 am
content: Yes i do agree this is so far the best implementation of the idea.As for using multiple smaller weights. It doesn't really help much since you still need the same amount of cable to hold it up. The 200 cables certainly wouldn't be one single bundle going onto one winch. You would probably have a compound pulley system to have one long cable go up and down a few times before winding up onto a winch. Likely having a few of these winch and pulley compounds due to the amount of cable. This also provides redundancy if one cable was to fail the weight would not come plummeting down. it could be lifted back up, the cable replaced and put back into service.Just that comparing the cost of it to Li-Ion batteries makes it seam like it could have a hard time competing.Also if we are talking about storing energy in holes in the ground there is also the technology of using old empty natural gas wells as a massive compressed air tank. It has the potential of storing massive amounts of energy due to the size of it, tho compressing air is not quite so efficient due to the thermal effects.

author: blacksheeplogic
author_rank: Frequent Contributor
timestamp: January 23, 2020, 07:07:32 am
content: Quote from: dunkemhigh on January 22, 2020, 07:29:36 pmThat's a little simplistic, a large part is ROI, given the right geography and location it's possible to make a return on the investment with hydro by pumping during low demand period and exploiting the reserve during peek demands. There's losses but as long as off-peek costs are low enough compared to what you can sell the energy during peek demands it's been show there is a potential positive ROI. It's also proven to be economically viable.It's not good enough to show that energy can be stored and used latter, you also need to show ROI and many of these 'potential' solutions while they can store energy don't have the ROI sufficient to offset the cost and therefore attack investment. Neglecting to consider that big lakes can't pop up in the middle of nowhere is forgivable compare to the bigger issue with a lot of these other ideas neglecting that investors with the finical capability and risk aversion don't pop up anywhere near as frequently as big lakes in the middle of nowhere.Now, I will grant that there's a lot of green tree huggers out there willing to throw a buck or two into the 'pot' but that just encourages the dreamers who make a living hawking their ideas. Do you really think someone is going to front up with capital and give this a go just cos it sound cool?

author: iMo
author_rank: Super Contributor
timestamp: January 23, 2020, 07:37:57 am
content: This does the samehttps://en.wikipedia.org/wiki/Pumped-storage_hydroelectricityPretty common at least in Europe.

author: PlainName
author_rank: Super Contributor
timestamp: January 23, 2020, 07:38:26 am
content: QuoteInteresting idea, but I suspect it wouldn't float because 'fracking'. Not saying it would cause local earthquakes, but injecting stuff into the ground has a real bad reputation now.

author: blacksheeplogic
author_rank: Frequent Contributor
timestamp: January 23, 2020, 07:48:14 am
content: Quote from: imo on January 23, 2020, 07:37:57 amIt's a couple of years ago this video was made but it's on one of the UK's pumped storage facility and it discussed both the cost and the economics of the project.

author: PlainName
author_rank: Super Contributor
timestamp: January 23, 2020, 07:49:22 am
content: QuotePresactly. You could say that about anything but it doesn't change the fact that a BFO lake on flatlands isn't going to be a good deal. And I don't see people moving to hills just so they can have their land requisitioned to provide the storage.I think part of the problem, not just with this but any and all schemes dissed here and elsewhere, is that they have to fix every problem in every conceivable way to pass muster. And, of course, nothing is going to do that. So where there are already lakes up in mountains they might be a great way to store power, and where it's flat but with existing mining holes, maybe this kind of scheme is more appropriate.If it had been anyone else but thunderfoot, there would have been accusations of 'whataboutery'.

author: Berni
author_rank: Super Contributor
timestamp: January 23, 2020, 08:12:35 am
content: Quote from: dunkemhigh on January 23, 2020, 07:38:26 amYeah good point, same barrier that prevents the construction of new modern nuclear plants that could save the world from many milions of tons of CO2 emissions.There are some already operating compressed air storage facilitates such as the Huntorf CAES in Germany (870 MW/h) or McIntosh CAES in the US (2800 MW/h). Both of those are used to store power from a nuclear plant at night so it can be used during the day.There is also an idea to blurry steel tanks in the ground and use those as pressure containers. Not sure how economical that is but sounds like it could store a lot of power. Tho what happens if the tank fails.

author: mark03
author_rank: Frequent Contributor
timestamp: January 23, 2020, 04:33:41 pm
content: OT, but please: MWh, not MW/h. Drives me nuts! That, and I can't help wondering how many MW it has achieved by now, and how soon it will destroy the universe.

author: SiliconWizard
author_rank: Super Contributor
timestamp: January 23, 2020, 06:26:42 pm
content: This method of storing energy has been discussed before, so I suggest also reading all that's been said about it in other threads.As many have pointed out, there are many aspects that make it impractical for general use. I do think it could have some use for very long-term storage (for applications where it could be needed), as long as the structure holds up, but not for short-term storage as an alternative to batteries. Not like this anyway. And it turns out that in terms of needs, the short-term storage problem is the real problem we have.

author: Marco
author_rank: Super Contributor
timestamp: January 23, 2020, 06:42:10 pm
content: Quote from: Berni on January 23, 2020, 06:25:27 amIf we're going to go for low round trip efficiency I'd rather just do electrolysis and store the hydrogen in there.The deep sea gravitational storage using concrete spheres can work without thermal effects by the way, because you pull them vacuum to remove the water instead of pushing out the water with air.