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Comment by jrockway | Hacker News Reader

> Solar is so much more useful close to where it's consumed

I'm not really worried about this. Humanity has already invented the greatest utility-scale battery. Pump water uphill when it's sunny. Let it flow back down, through a turbine, when it's dark out. No lithium needed!

People often talk about the space required for pumped hydro, but it's probably a lot less than all the shopping mall parking lots in America.

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This article [1] on pumped hydro tempered my expectations a lot - It calculates that a nation-scale pumped hydro battery for the USA would need to be about the size of Lake Superior and have a 300 m height drop

https://dothemath.ucsd.edu/2011/11/pump-up-the-storage/

I've read that before. The big thing he's wrong about is requiring 7 days of storage. For coal, oil, and gas you need 7 days of storage to account for supply disruptions. Like when a hurricane lashes the gulf coast.

Solar and wind while intermittent have so much redundancy they never have week long interruptions. You can look at CAISO's charts of solar output in California. You get a couple of days in the winter where production is off due to weather. But not a week.

Pretty sure the UK already ran into this problem when the North Sea had low wind for a prolonged period. This year wildfire smoke would have cut into the valuable days for many solar installations in the northern US/Canada, many hazy periods were close to a week. The intermittency problem is only going to get worse as the amount the grid relies on grows, it's easy to cover the occasional 5% loss grid wide, but a 25% loss is a big problem.

A little deeper comment is one should compare the costs associated with a supply reduction vs the cost of the storage needed to mitigate the disruption vs how often that happens.

The argument that you can't afford 7 days of renewable storage is just restating that the marginal cost of fossil fuel storage is lower than the cost of electric storage. While ignoring the ability to curtail demand.

On the coasts, I think that's viable.

It's not viable where water is a valuable resource.

I wonder how efficiently a similar solar powered lift system would work for a "dirt battery"?

The *dirt battery I have in mind would be a vertical pulley system with small dirt scoops spaced at regular intervals. The scoops would pull dirt from the bottom of the pulley system and bring the material to the top were it is dumped into a mechanically locked, very large container. Over time the container would fill up, and when that stored energy is needed the container could be unlocked, at which point it would power a clockwork of turbines on its way down.

Thoughts, critiques?

It’s less efficient than normal electric batteries and will take up far more space.

Gravitational storage only works in the very particular case of water, where moving it is downhill nearly perfectly efficient and free, and where you can also get free energy from things like rivers feeding in.

Yeah, now that you mention it I suspect that the mechanical stress upon a system that lifts dirt (as opposed to one that pumps water) would result in expensive routine maintenance, and possibly even catastrophe (i.e. the chain breaks).

https://aresnorthamerica.com/

ARES Nevada is developing a 50MW GravityLine merchant energy storage facility on approximately 20 acres at Gamebird Pit, a working gravel mine in Pahrump, Nevada. This project will employ a fleet of 210 mass cars, weighing a combined 75,000 tons, operating on a closed set of 10 multi-rail tracks.

It's viable anywhere there's sufficient relief, even in deserts.

It uses at least an order of magnitude less water than nuclear does, per unit of electrical energy flowing through the system.

Here's an example of a system going into Nevada. 8000 MWH of capacity. Notice how tiny it is on the scale of the state.

https://www.cityofelynv.gov/pdf/CityCouncil2021/cc1-28-21/Wh...

Water use is just 500 acre-feet/year, which is tiny (Nevada's consumptive water use is 6000x this.)

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