Gravity Energy Storage: Alternative to batteries for grid storage

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.

The same opportunity exists on the East-West axis. The sun is still shining in California after its set on the East coast.

> 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.

Look to lithium ion for short time high cycle/fast response, vanadium flow for long duration (expensive currently, large sites), hydrogen potentially and fascinating long duration start up out of Massachusetts (forget the name right now). More tech will come down the pipeline soon.

Compressed air possibly but hasn’t really progress much over its existence so far (geological restraints too). My two cents

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.

You cannot physically make that work economically.

This is a critique of these ideas. The main points are:

- Lifting speed needs to be 40 kph

- Minimal height of lowest stacked state limits storage

Does no one do fundamentals at school anymore, water is around the same density as concrete (~2.4 times smaller) except you can just use a simple pump.

The reason they use concrete in these designs is because if they used water people would say it's stupid. That's literally the reason. It's the same for mineshafts. These concepts are introduced to confuse you.

"But pumped hydro requires some very specific geography—two big reservoirs of water"

So does concrete. Expect you are building the geography and it'll be around the same size if it stores around the same energy.

It's an interesting idea compared to other gravity storage solutions because

- It's the volume of the buoy rather than the mass that's important

- It could be colocated with and hooked up to offshore wind farms to smooth their generation

- You don't need to build a super-tall crane or elevated reservoir (but you do have to assemble the thing at the bottom of the ocean which sounds hard)

I haven't heard anything about it in ages so it must have turned out not to be practical.

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.

All known technologies.

Apparently storing energy in concrete blocks has no advantage over water, but brings in a lot of drawbacks (mostly the whole structure being exposed to weather).

The future of renewable energy is obviously Solar PV, with Wind and other offsetting to some extent, but Solar is predictable, cheap to build and easy to maintain.

I really wish there was more thrust into carbon capture and conversion to fuel with Solar power.

Let's see: A weight of 8 x 10^9 kg raised 100 meters = a potential energy of 8 x 10^11 kg-m

PE x 2.724 x 10^-6 kWh / kg-m = 2.18 x 10^6 kWh (2 GWh)

Allowing a little loss that's enough to supply 2000 houses with 1000 kWh each in one month ... or 20,000 houses with 40kWh in 2.5 days.

https://m.youtube.com/watch?v=NIhCuzxNvv0

Edit: out by a large factor. Should be that many kg, not tons.

So lifting trains into the air is going to have its work cut out to match plain old battery technology.

Pumped hydro mentioned in the article is good for long term storage > weeks, months, even seasonal.

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.

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.