The physics is simple: height times weight times gravity equals energy.
The problem is size. Raising 1 ton of water 1 metre stores 9810J, so to store a kWh (3,600,000J) you need to raise 1 ton 367 metres, or 367 tons 1 metre, or 36.7 tons 10 metres, or whatever combination you like. If you think your batteries are big and heavy, wait until you see pumped storage.
A ton of water is 224 Imperial gallons, or about 263 US gallons. A metre is about 39 inches, or three foot three. :-)
Normally if you have the right lay of land to make pumped storage work, you also have the right lay of land to make a conventional hydro system work. Which is why there are so few of them in the world, and why the electricity generators still waste capacity in the wee small hours.
My AGMs cost UK13 (about $23) each, off eBay: but even if they'd been new, they'd still have cost a lot less than a 100,000 gallon water tower.
They also weigh about 40kg each, instead of the 40-odd tons that your water tower is going to weigh when it's full.
I suspect your water tower weighs and costs about a thousand times as much as my batteries.[ Parent ]
100,000 gallons raised an average of 75 ft is:
100,000 * 8.3 lbs * 32 ft/s^2 * 75 ft = 1,992,000,000 lb*ft^2/s^2 = 23.3 kWh
That's equivalent to about 17 220 Ah, 6 volt batteries, which, new, are anywhere from $75-$100 each. Assuming you only discharge them halfway, that makes 35 batteries, which is like $2600, not including shipping.
Your point is still valid but, at the same time, for some people it may really be easier or more beneficial to build a storage tank on top of a hill than to purchase batteries.[ Parent ]
