New rail-based gravitational energy storage project begins in California
utilitydive.com
utilitydive.com
For perspective: if the U.S. loaded up all 1.5 million of its rail freight cars to 30-ton capacity and sent them 4km up to the top of Mt. Rainier, that would store 494 GWh of energy.
That's just over an hour's worth of our average electricity usage.
Gravitational storage is hard.
We just need to store enough to make load-shifting environmentally (and commercially) available. The 30 Gigawatt Hour Bath County Station gets there (https://en.wikipedia.org/wiki/Bath_County_Pumped_Storage_Sta...), but even the "smaller" Tesla 50MWhr projects do too.
Compressed Air is hitting 300MW-hr designs (https://www.greentechmedia.com/articles/read/texas-calls-for...). That's enough for a metropolitan solar community to loadshift the 12:00 noon sun to the 5:00 dusk peak-energy period. (Average home: 30kwhr per day. 300MW-hr design would serve over 10,000 homes easily, and doesn't need to actually hold the electric usage for the whole day. It'd realistically only need to hold 1/10th the energy or so, to load-shift a few hours here and there).
ARES seems to be in the 12MW-hr to 100MW-hr design size. This is smaller than Pumped Hydro but still useful. Smaller, cheaper projects that partially solve the problem is still a good thing.
It seems like a perfectly good solution to the problem. Buying up cheap energy from night (or noon-power solar arrays), and selling it during the 3pm to 7pm peak-energy time. As long as there's at least a 20% differential in peak pricing somewhere in the day, "small" 1MW-hr to 300MW-hr plants will be profitable.
----------
In any case: Wind continues to work at night. Nuclear works throughout the day. Hydro works throughout the day. We don't need to store EVERYTHING, we just need to store the excess from Solar from noon, and then load-shift it to 5pm to 8pm, while the sun is setting and solar arrays generate less electricity.
Basically, I'm just wondering how hedging costs affect your numbers.
The spread is grossly positive. Pumped-Hydro provides a location for baseline power plants (nuclear, coal, and even Wind / Solar) to continue to pump energy into the grid without getting shut down. Coal, Wind, and Nuclear plants, in particular, are typically very difficult to start back up again.
So it is profitable for these plants to continue to generate power, even when the plants pay money for the privilege for someone to "waste" it somewhere.
Then of course, later in the day, the "batteries" (ARES, Pumped Hydro, CAES, and what-not) sell the energy back to the grid when peak-energy occurs (usually around 5:00, when businesses still have the factories running but people have also begun to return home and turned on their air conditioning again).
That said, curious where you got your calculations from.
1.5 million * 30000 * 9.8 * 4000 / 3600 = 490 GW-hr
An 8 degree gradient is super steep. Regular trains (not funiculars) start to have traction problems around 2-2.5%
https://en.wikipedia.org/wiki/Bernina_railway for instance
The problem with steep railway lines is generally BRAKING, not climbing. Norfolk Southern ran freight up and down the Saluda grade in NC for over 100 years, and that's at nearly 5%.
Have the turbines directly lift a weight. And then lower the weight as needed to generate electricity.
This system doesn't need to fit that mass into a small structure and has a much longer working height.
In one of the patents, they work out an example system that can handle 30 megawatts, which might be the output of 10 or 15 turbines. The system absorbing the 30 megawatts for 30 minutes has a working mass of 1200 tons (conveniently, they use a working height of ~600 meters).
So all you need is a system capable of lifting 100 tons a distance of 600 meters (to store 1/2 hour of output). Which is probably something we are capable of building (there are cranes that lift much more significant distances), but it probably isn't something that would be economical.
http://www.artemisip.com/wp-content/uploads/2016/03/1984-Sal... (SH Salter, M Rea, proceedings of European Wind Energy conference 1984)
[0] https://en.wikipedia.org/wiki/Hydraulic_accumulator
[1] http://www.heindl-energy.com/hydraulic-rock-storage/overview...
Suppose we raise a 30-ton weight (i.e. a big shipping container filled to capacity with rocks) all the way up that 80m turbine. We've stored 30,000 * 80 * 9.8 / 3600000 = 6.5 kWh of energy.
That's 16 seconds worth of energy from the turbine spinning at full speed.
[1] https://en.wikipedia.org/wiki/Wind_turbine#Design_and_constr...
Also makes me wonder how a spring (instead of or in addition to those 30 tons) would scale to turbine tower size. Just don't think of the destruction when something breaks!
Maybe gravitational doesn't make sense, but compressed air might. Big compressor directly driven by the turbine (so as not to waste energy converting to electricity to turn an electric compressor motor) being used to compress normal air into large tanks inside the wind turbine tower which can later be used to spin another turbine-based generator using the same air. Not a physics major, but this seems feasible. Not sure of the potential energy storage, but I feel like the direct conversion of rotational energy to spin the pump has to be much more efficient than converting it to electricity first, then using that [many miles away] to compress air or drive a train up a mountain.
(An actual shipping container would break before you hit this point; a standard 40' shipping container has a maximum gross weight of ~30 metric tons-- you're not likely to fill it to its volumetric capacity with rocks or lead.)
5.5 Mile track * tan (8 degree slope) * 5280 feet per mile == ~4000 feet height.
But yeah, gravity storage as part of the Turbine itself doesn't seem too useful.
There are 36 in Germany alone[1].
https://de.wikipedia.org/wiki/Liste_von_Pumpspeicherkraftwer... (the corresponding English article lists much less)
This list is missing the one I know about -
https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroel...
Given the first thought is how does this compare to pumped hydro, I worry this is vaporware.
I don't have hard data - but wouldn't engineering a rail system not be as hard, and need less civil engineering work?
As you say, however, it's very geo/topo specific - so in places like North Wales, pumped hydro is still clearly the way to go, but in the Mojave, this rail based system could work well.
It reminds me of the defunct system we had in a house I used to live in - 8" or so diameter shaft in the basement floor with a weight, a cable, a winding, and a dynamo - you'd have the servants crank it up during the day so you could have electric light at night. Quite popular in the late nineteenth century among early adopters of electricity.
In general there is no silver bullet for the electricity system, rather, a better metaphor is a stack. This tech might fit one space in the stack.
Its cheaper to keep running a Wind Turbine and PAY to put energy onto the grid, than to actually power-off a Wind Turbine. If those Turbines stop spinning, its very, very difficult to get them spinning again.
But someone needs to "take" the energy. This ARES project is going to be paid in both directions. They profit as Wind / Solar farms pay for the privilege for their excess energy to be stored somewhere, and then they profit later in the day as they sell the energy back to the grid.
If it is too small to get you any money, it's still large enough to build as a part of something else, or to build a lot of replicas.
But yes, with a capital requirement of “a little under $55 million”, there's either some misreporting around, or this thing is a big no go.
Use water as the working mass. Lift it by converting it to steam and sending it up the mountain through insulated pipes. Condense it at the top, recovering the heat as possible, and let it run down to a turbine.
You have to counter losses, of course, and if you could get the heat energy back down to the bottom to reuse it that would be great. Otherwise, just use Solar and waste energy to heat the water to steam.
I think you might be able to get more energy out by "mining" gravity this way than you had to put in to run the steam cycle. You're taking advantage of the fact that water falls while steam rises.
Like I said, I have no idea if this would actually be feasible.
2000 feet are 609.6 m, thus according to supahfly_remix max. 12000 kWh can be stored per train, 5.5 miles are going to take about 4 minutes to climb and another 4 minutes to descend, let's assume (from thin air) the usage is 3 times below its max, then a train will buy and sell (0.05 also taken mostly from thin air) 2.5/h * 12000 kWh * 0.05 USD/kWh = 1500 USD, which means that salary for the driver is going to be perhaps 2-4% (depending on whether fully driving, or just observing for safety).
One of the biggest wins of this model, really, is the low environmental impact, relative to hydro or batteries. Fewer regulatory hurdles, more potential locations. But in the end, cost effectiveness is what will win, and to some degree, that will be location-dependent. Is there geography we can exploit? Will it be in a populated area? What's the proximity to wind or solar farms?
Solving the storage problem in a cost-effective way is the key to transitioning from poison fuels to clean power. Once it's cheaper than coal/LNG/nuclear, the world will switch over quickly.
Also, this thing requires a straight line high inclination slope and plain areas both up and down. I don't know how that compares with high walled valleys, but it is not a very common formation in nature. All said, it may be useful because it uses a different kind of landscape from water storage, so it can increase the total capacity.
Anyway, I agree, costs alone will say how much of it is created.
This is only true if the motor is connected to the grid (ie powerered). You need a magnetic field to create the current. If the induction motor wasn't powered when you spun it, it would not create any current as an induction motor does not need permanent magnets to create the field.
Pumped Hydro simply shifts lakes from one location to another with a pipe. You don't build towers, you just use the natural features of the earth.
Imagine if they scaled it up where instead of a few rail cars you scaled up to something along the lines of NASA's https://en.wikipedia.org/wiki/Crawler-transporter but on rails instead of tracks.
Does have relatively high efficiency though.
PS: "Cost comparisons with pumped hydro are difficult, he said, because there are so few projects and not many data points." Is pure BS, here is someones coursework on the subject: http://large.stanford.edu/courses/2014/ph240/galvan-lopez2/
The problem with Almonds is they are trees, so letting them die is far more costly.
Basically, if the water table is dropping then people are pumping out water faster than its being replaced. If you look into when that water was put there you quickly get into geologic timeframes. Aquifer's often do flow meaning that specific drop may only be decades old, but replenishment rates in many places are vastly smaller than extraction rates.
EX: Some places in China have seen 10+ feet drops in the water table per year.
PS: “Fossil water” or paleowater is a related idea. Basically water that's been undisturbed for long periods. https://en.wikipedia.org/wiki/Fossil_water
> using prehistoric water to farm Alfalfa is crazy IMO
Agreed -- completely insane. And we wouldn't, if water cost what it should cost.
I think they have lots of hills and lots of land. Probably not much water in that desert.
> Rail storage also does not have life cycle limits that batteries do. “There is zero degradation,” he said.
They must be using rails, wheels, and bearings made of unobtainum. I know little about conventional rail maintenance, but a quick search suggested annual grinding of rails and 10-year replacement intervals.
I dunno, large areas of land, large earthmoving equipment, and the labor to turn it into a pumped-water storage system are all pretty expensive too.
As to land use these tracks take up space at both end plus the space for the tracks between them unlike a pipe which can cheaply be placed under ground. So, per kWh stored these are likely far worse in terms of land used.
"ARES wants to lay a nearly 5.5 mile track up an 8 degree slope, gaining about 2,000 feet top to bottom. ARES would then put up to seven 8,600-ton trains on the track"
If the units were in SI[1], 1000 * 5.5[km] * 8/100 = 55 * 8 = 440m (no calculator/conversion needed)
And for the energy stored, just do 440m * ~10m/s2 (g) * 8,600,000kg
[1]no conversion, just an example
How big are these things?
8600 tons of lead would be 680 cubic meters - so ten or so standard sized shipping containers.
Two locos, four cars... I still don't see how that fits.
Unless these are HUGE trains, or they're using exotic matter, I don't see how that's possible.
(And also that 8600t isn't anything special.)
Also, having a long train is surely undesirable for this application, unless you have a plateau at the top and bottom at least as long as the train.
[1] http://recursostic.educacion.es/gauss/web/materiales_didacti...
Edit: Also, they are claiming 93% mechanical and electrical efficiency. I'm not sure if that is each or total, but either way it sounds impressive for storage and retrieval in a wide demand range.
Edit2: Is this company publicly traded? Or is it owned by a publicly traded parent company?
Edit3: It is a startup (and they are looking for funding).