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Comment by andbberger | Hacker News Reader

I don't get how any of these gravitational energy storage startups get past the napkin phase. There is no competition with pumped hydro. Who cares if weights on winches are marginally more efficient when you have many orders of magnitude more mass to move.

This site claims a max weight of 4.5e6 kg. Lake Powell, for example, has a max capacity of 3e13 kg!

So, SEVEN orders of magnitude less mass to move. Sounds competitive.

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You are looking at the wrong metrics. Capacities and efficiencies are interesting from a technical point of view. But the only metric that really matters is $/kwh of storage. And depending on where you are pumped hydro can be stupendously expensive and disruptive to the local environment or require expensive infrastructure to be put in place. Even just having access to water is a non trivial thing in a lot of places (e.g. deserts).

In some places pumped hydro does make sense of course but you have to compare basically on $/kwh what is the best solution taking into account the local environment. There are no silver bullets here. Which is why a lot of places seem to be ending up with lithium ion batteries, because they are there and can be put in place without a lot of fuss or rearranging of the local environment.

Pumped hydro is great but unrealistic in many countries. You need hills or mountains with space for new lakes. All obvious places already have them, for the others the ecological impact often is quite significant.

All obvious places may have hydro plants already, but not all hydro plants are reversible.

The country point is interesting, so the market is countries lacking topography suited to hydro plants? How big is that market really?

And considering that pumped hydro is currently the only viable grid scale energy storage mechanism (inb4 but li-on), those countries currently either 1) share a grid with neighboring countries that do have pumped hydro, or 2) forego energy storage altogether and use peaker plants like everyone else. If you do 1 you better trust your neighbors to never go to war with you, otherwise you better have 2.

So the market is: countries lacking topography suited to hydro plants, who currently share energy storage with neighbors who they don't trust, and who for some reason aren't just building peaker plants (which are essentially just normal fossil fuel power plants) and are holding out for a non-extant technology to be developed.

I'm not much of a capitalist myself, but even I can tell that that's a bad investment.

Assuming that pretty much everyone is planning on eventually phasing out peaker plants for environmental reasons: I'd say that the market is pretty huge if you can develop viable technology to service it.

Power to gas is promising. Just generate hydrogen or methane and feed it into existing gas pipelines. Storage infrastructure for gas already exists and has several TWh of capacity.

How do you convert power to methane?

To answer my own question: https://en.m.wikipedia.org/wiki/Sabatier_reaction

> All obvious places may have hydro plants already, but not all hydro plants are reversible.

Hydro plants are built reversible whenever possible. The ones that aren't ("run of river") are that way because it was impractical to impound storage.

> All obvious places may have hydro plants already, but not all hydro plants are reversible.

If a hydro site is convertible to reversible, chances are it’s been already. Most sites are not really suitable because regular hydro plants don’t need a lower reservoir or water source and so can be built in locations which don’t have one.

Meanwhile pumped hydro can be built in locations where normal hydro makes no sense because there is no natural downflow or upper reservoir e.g. Taum Sauk.

I think the salient point is this:

> All obvious places already have them

That is, we’re already practically at max capacity for hydro.

A salient point for the wrong conversation? We're talking about energy storage, not energy production.

https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...

This an overly narrow view of the problem. The footprint of pumped hydro is enormous and you can't just put it anywhere where you actually need the power.

The footprint of anything that stores enormous amounts of energy is enormous. (If you think it isn't - batteries, say - it's because you've ignored the socking great mine needed to extract the materials, the factories needed to make them, etc.). And we don't need it to be that near - we have pylons.

This seems to be one of the key indicators of green pseudoengineering - an obsession with avoiding transporting power. Pylons work. Really. If you can get large amounts of RELIABLE renewable power/storage, with low labour and machine costs, from a large amount of cheap land, land far away from people or crops or even trees, you do not have to worry about the rest. Worry about how to get those labour and machine costs down.

Okay, let's just say the footprint of something that stores energy vertically is going to be enormously lower. For what it's worth, this "Graviticity" thing may be utter nonsense, that's besides the point.

Pylons may work, but you need to pay off everyone owning the land those lines go across. In many areas, they can't build pylons at all because of rampant NIMBYism.

I may be wrong, but there is a limited capability for doing pumped hydro - you may run out of elevated lakes in a region, and if you want to create new ones then you will affect the environment.

A hole in the ground can be dug up everywhere, e.g. next to each single PV plant.

With seven orders of magnitude of difference, you'd have to dig a whole lotta holes before hydro has to start worrying about competition on the capacity level.

Many of these projects also falsely assume that there are enough abandoned mineshafts or other types of holes to convert into a battery storage system. They have to do this because you would see through the scam immediately. Digging a wide and deep hole is expensive and not economic unless there is something valuable at the bottom of the hole.

There is also the fact that weights are expensive relative to the energy they can store so you have to take them directly from nature (usually via dams or pumping water uphill).

Right, the thing to worry about is power, not energy. Ideally the pumps would be sized to fill/drain lake Powell in 12 hours. Which is ludicrous. The turbines in the Glenn Canyon Dam have a max (output) capacity of 890m^3/s [0]. It would take just over a year to drain the reservoir through them.

[0] https://web.archive.org/web/2016*/http://www.gcrg.org/bqr/6-...

Which is fine, as many regions have a strong seasonal availability of renewables. Storing energy for some months will be required to go fully renewable. There are also short term storage requirements, over the course of a day or a week.

Compared to energy loss over distance, which you don't really have if you dig your hole right next to you, it's more like 6 orders of magnitude, maybe less.

But maybe capacity is only part of the story. What about locality? Distributed energy storage may not be as efficient, but it has a lot of other benefits.

The power density for gravity storage such as this is directly proportional to the density of the storage medium.

Water is 1 tonne per cubic meter. Steel is 7.9 tonnes per cubic meter. Lead is 11.34 tonnes per cubic meter - which means that in the same amount of space, you can store vastly more energy if you use these metals instead of water.

The initial cost of set up will also vary depending on the metal you use but lead is cheap.

Also, water evaporates etc.

Wow the density makes a lot of sense. But why stop at lead, depleted uranium is 19 tonnes per cubic meter (1.67 times as dense as lead)!

Cost / density. You quite literally want the cheapest dead weight.

Cost of lead/tonne : USD 1900 (approx) Cost of Uranium/tonne: At least USD 60000 (approx regular uranium) even if you are able to source it.. and then you still have to build containment for this, get permits etc..

For that price, you could get much higher efficiencies if you went for a cheaper metal - even something like Tungsten which is extremely dense will be much cheaper.

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