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Comment by kolinko | Hacker News Reader

As for the price per kWh, I guess this system scales sublinearly (as opposed to more or less linearly with LiIon). They can probably increase the number of tanks storing oxygen in the future for way less than $300kWh (assuming they keep the same system wattage).

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If you're keeping the same power input/output (50MW in this case) then you can add more tanks and scale out capacity with cost savings on storage, generation or transformation. "A bigger gas tank doesn't make the car go faster."

Scaling it out proportionally would only have economies of bulk purchase and site engineering.

I came to precisely the opposite conclusion. Batteries keep getting cheaper every year, while air pressurization technology does not (that is a very mature technology). So if this air pressurization is only the equal of batteries in year one, then it's already lost.

The point is not about future price evolution, but the marginal price of storing 1h more, if you just need another tank it will be cheaper than having the same energy in a battery, with the same system to store and destore the liquid air. Li-ion is not a good fit for long term storage.

This system is already 500 MWh (that's huge). How much better scaling do you think it's going to get beyond that?

The expensive part is the 50MW bits. They can build out storage capacity cheaply, because it is just tankage.

But if you’re only inputting and extracting at 50MW then having more than 600MWh of storage means it takes longer than 24h to fully charge and discharge. If anything 500MWh of storage is already well into diminishing returns as daily storage makes money every day but long term storage has less frequent returns.

If every (normal) day you discharge less than you charge, you can build up a reserve for unusual events. When you get close to your storage limit, you can sell power from out of that reserve during periods of peak usage/price, when your solar array is running at capacity.

So, more storage is better.

Depends on the market price.

Storing for say 1 month means you get 12 payouts per year, storing it for 12 hours means you get 365 payouts per year. If your on average getting say 1c/kWh from the distance in values prices every day then your monthly sale needs to be at 30c/kWh to be worth it. Prices simply don’t rise that high every month making long term storage less valuable than daily storage.

On top of this these things aren’t 100% efficient. Buying at 7c/kWh and selling at 8c/kWh is losing money if these are say 80% efficient. Which means you’re never going to profitably buy and sell throughout the day. Thus the 500MWh capacity will mean some long term storage.

If we are going to go full-renewable we will need storage that works over night, storage for cloudy days and for days without wind. A low wind situation can last a week for example.

So we do need long-term storage and we will have to finance it so that when we need it, we can count on it

First Hydro is already effectively long term storage. It’s fixed across a year, but releasing 5x as much as normal is fine as long as releases are scaled back to account for the discharge.

Next solar and wind don’t correlate and solar output never hits zero on cloudy days. So, excess capacity always directly reduces the need for storage. Working out the ideal amount of excess capacity isn’t trivial, but unless storage costs tank dramatically something like 85+% on worst case days is likely viable. Which could then easily be covered by hydro.

Sometimes hydro is inconveniently on the other side of two national borders, as here, where Paraguay is on the other side of Argentina. There are good reasons to stay on pleasant terms with Argentina and Paraguay, but avoiding blackouts is among the less-good reasons.

While it’s natural to optimize for a single connection, having redundancy also avoids this issue. Paraguay > Argentina > Chile and Paraguay > Bolivia > Chile are both viable options. Countries should have strong grid conditions to every country on their border as it provided both countries redundancy at very low cost. As a side effect all of a North and South America should end up being able to share power with each other, as should all of AfroEurasia.

A large issues is islands, but plenty of people setup off grid houses completely dependent on Solar. It’s simply generally more expensive.

If you knew anything about Bolivian history you would not suggest Paraguay > Bolivia > Chile as a viable option. In any case, both routes depend wholly on the agreeableness of Paraguay.

I am very glad you are not responsible for planning for the availability of power I depend on.

I am saying it’s viable not dependable. Chile shares borders with 3 countries, each of those countries shares borders with another country. So no 2 counties could block Chile.

Now, if your saying Chile can’t trust it’s maintaining good relationships with any of those 3 counties then sure.

The only expense for excess storage, above capital cost of the tankage, is refrigeration to compensate for heat leakage through the insulation.

All the tradeoffs, together, are an optimization problem that is not hard to solve for conditions found. Since the ultimate source of power, solar, is the cheapest ever devised, they start with a huge advantage. It would be foolish to bet against them.

Sure, but it’s an optimization problem up against simply building more solar. That’s the part of the equation most armchair experts are ignoring. Excess solar production is basically guaranteed due to how cheap it is. It’s likely that some long term storage is optional, but at scale it’s likely to be relatively small percentage.

More solar generates power only when the sun is shining.

This apparatus is for use mainly when the sun is not shining, or when it is not shining enough. Sometimes the sun barely penetrates the clouds, and then you need a boost all day. Maybe it would be cheaper to import power from a dam in Paraguay than to keep your tanks full and cold until you need it. But it might be cheaper to buy power only if they know you don't really need to.

Energy economics are more complicated than we can safely generalize about here. The safe bet is that somebody spending $150M has thought it through.

Sure but note they didn’t get more than 10 hours of storage from this system. It’s designed to have close to zero long term storage like every single grid backup system currently in production. Something like 20% reserve capacity is completely rational, but you get there by having redundant daily storage so having one or more of them going online doesn’t break the grid.

You can always add more reserve capacity if you find uses for it.

Batteries should see drastic declines as well. $300 is already considered a steep price even though it is the all-in price. We are talking about $50 at the cell level for LFP chemistry soon.

And the Tesla Dalhousie guy says the LFP batteries they tested basically have unlimited recharge cycles. Allegedly 200 wh/kg was supposed to be commercialized by CATL for LFP this year, but I haven't heard anything about it so I assume either COVID has delayed it or they were just being too optimistic.

The other grid storage I wonder about was that Army salt water battery that Jeff Dahn said fairly effusive things about a few years ago. I have heard nothing of it since, so I assume it had cycle problems or other fundamental issues.

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