The power capacity of that setup was like that of an AA battery, if I remember correctly.
You need huge amounts of water and lots of height difference.
They do say it is about equivalent to a single AA alkaline. It is not exactly an optimized efficient setup, but still, it gets the point across. Pumped hydro is a grid scale option, in places that have the ability to store a lot of water.
Pumped storage scales well though, as the stored volume scales squarely to the required container material (e.g. storing 25,000L will only take 10x the material while storing 100x the energy).
Wolfram Alpha [0] says this is about 5 Watt-hours, and gives some other handy comparisons:
> ≈ 0.45 × metabolic energy of one gram of fat ( ≈ 38000 J )
> ≈ 0.63 × energy released by burning 1 gram of ethanol ( ≈ 27000 J )
> ≈ metabolic energy of one gram of sugar or protein ( ≈ 17000 J )
> ≈ (0.02 to 0.09) × typical kinetic energy of a car at highway speeds ( 200000 to 900000 J )
> ≈ 0.5 × typical battery energy content of an alkaline long-life C battery ( ≈ 9.6 W h )
> ≈ 0.55 × typical battery energy content of a nonrechargeable Lithium-Thionyl Chloride AA battery ( ≈ 8.6 W h )
> ≈ 0.92 × typical battery energy content of a carbon-zinc D battery ( ≈ 5.2 W h )
Gravitational potential energy is just really, really low energy density. Fortunately it's reasonable to have pumped-storage reservoirs that contain trillions of litres of water.
[0] https://www.wolframalpha.com/input?i=1750+kg+metres+in+watt-...
https://www.epa.gov/red-hill/what-red-hill-bulk-fuel-storage...
They were recently decommissioned due to leaks, but I've often wondered if they could be repurposed as gravity battery storage.
edit: if you want to check my math. I calculated the tanks at ~567 million liters, and am saying there is 120 meters of vertical distance.
They would be equivalent to a 0.1856 GW h (gigawatt hours) battery if repurposed in this way. https://www.wolframalpha.com/input?i=567810000*120+kg+metres...
Oahu uses about 225MW on average in residential electricity [0], so this could store an hour or so of excess capacity. That's not nothing, but you might want to 5x or 10x it to really smooth out demand and supply peaks for the island.
Note that you also need a set of tanks or a lake at the bottom of the hill. The tanks are 75m tall, so how are you accounting for that in your 120m of vertical distance?
[0] https://www.eia.gov/todayinenergy/detail.php?id=49036 gives 2,018 kWh per person in Hawaii
>Oahu uses about 225MW on average in residential electricity [0], so this could store an hour or so of excess capacity. That's not nothing, but you might want to 5x or 10x it to really smooth out demand and supply peaks for the island.
https://spectrumlocalnews.com/hi/hawaii/top-stories/2022/08/...
This solar plant & battery system was completed last month. The battery is able to store 144 MWh. This shows me that planners and people thinking about this are willing to invest & commit to power solutions at this scale. I don't know if you are aware or have read up on the red hill controversy. These tanks were used to store fuel by the Navy. They leaked earlier this year and poisoned the Red Hill aquifer and have caused quite a bit of local controversy.
I'm struggling with the idea of writing a letter to the editor outlining this concept, but also emphasizing how converting these tanks to a water storage/ energy storage facility would improve local resilience to drought, bring down water costs, improve environmental conditions etc.
However, home scale conventional hydro is a thing. If you live on a hill with a creek that runs down it you can install a generator that produces a usable amount of consistent power for the cost of a few hundred meters of PVC pipe, a barrel, some connectors, and a small electric turbine. Search for micro-hydro if you want to know more.
Like all hydro solutions it's heavily dependent on the geography and only suitable for well under .1% of the population, but where it is feasible it can be a huge step towards off-grid living. Add in some batteries, maybe supplement with some solar panels, and you've got all of the electricity you need year round at a somewhat affordable price.
I've probably seen everything YT has to offer on that. :-D
While I really enjoy those videos and the "let's just do it" vibe with old washing machines as generators, I'm also somewhat happy that Germany has rather strict regulations on how to use water from streams and rivers. Some installations are quite disturbing for local ecosystems. But being off-grid in remote areas these solutions seem like a probable compromise.
A water tower needs to be built first and only stores a limited amount of potential energy. The problem is not the efficiencies but the cost of building a big enough tower. A tower with the same capacity of a pumped hydro reservoir would be insanely expensive. Or alternatively building many thousands of smaller towers that add up to the same capacity would also not be cheap.
There are a few alternative gravity systems being tested out in the form of e.g. big cranes with weights that drive generators, mine shafts with similar systems, etc. Proving they work efficiently is not the issue. It's just scaling their deployment cost effectively.
There are projects testing this, but ocean water is highly corrosive and maintenance is a nightmare.
Whether it's a water tower, a big crane, or whatever that holds the mass that you then use to drive a generator. You have to build it or use nature to have some natural height difference. Building infrastructure like that is expensive. So nature is preferable and way cheaper.
I come from a relatively flat part of the world; so that's not really an option there. Gravity based batteries are nice where they can be done cheaply. But otherwise probably not ideal.
The problem is that it's monumentally expensive. You will need to have a pretty big water tower to handle enough energy to run a microwave for a hour.
P.E. = mg(h)
So say we have 2,000 liters of water that is 50 meters high.
2000kg * 9.81m/s^2 * 50 * 80% efficiency = 784,800.0 joules.
Say you have a 1100 watt microwave. A watt is 1 joule per second. That gives you enough energy to run that microwave for about 11 minutes.
A better example would be existing municipal water towers. A 500,000 gallon water tower that is 129 feet tall costs about 2 million dollars. This is based on a public notice I found for a city in the USA.
That is 1892700 liters and 39 meters. I am guessing that the average height the water actually falls is 25 meters.
The average American household uses about 30Kwh per day. Which is 108,000,000 joules.
1892700 * 9.81 * 25 * .80 / 108,000,000 = 3.4
So 2 million dollars for 3.5 households-days worth of energy.
I don't know if having 1 days worth of energy is too much or too little per household.
And beyond the cost of the tower itself you need the generators and lines and holding pond for the water. Or underground tank or whatever you want to use.
It's very expensive.
However it is probably the cheapest option right now as far as current technology goes.
It would probably be cost effective for a off-grid shack in the woods, though.
Hmm that is an interesting idea, but it would be even more expensive.
If you take that water tower, place it on top of a 80 m hill, then dig down for say another 40 m for the second tank you now have a total of around 160 m of height difference. That would bring it up to 22 households-days or if my conversions are correct, 660kWh, which is not insignificant.
Then again if google is correct the price for an equivalent lithium bank would be only like 100k so it's not even close.
The above link has some numbers (2019 had it bookmarked so maybe it has improved)
> MY NOTE: well whoop-dee-doo. China generates 16.2 trillion terawatt-hours (TWh) a day. That’s 64 billion times more than all of the open-cast mines can provide. Better start digging more holes!
16.2 trillion terawatt hours a day is ~4 million times the total global insolation or 35 billion times total global energy usage. This is more wrong than asserting that a single man on a bicycle generator could produce our entire primary energy worldwide.
It also often covers interesting topics, and many of the stories are actually about something important or useful.
Additionally many of the things it 'debunks' are actually terrible ideas, and some of the arguments it uses are valid.
For gravity storage the costs and inefficiencies are a bit prohibitive for the use case of an unsubsidized high capacity (more than 1 day) option, and it's not really competitive with batteries for less (and is highly power limited).