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Comment by pfdietz | Hacker News Reader

Hydrogen is a battery with very particular uses cases.

In particular: hydrogen is bad for use cases with large numbers of charge/discharge cycles, because the "cost of inefficiency" is proportional to the number of such cycles.

However, for use cases with small numbers of charge cycles, like seasonal storage or backup against rare grid outages, hydrogen's big advantage -- the low cost of storing it, vs. typical short term storage technologies like batteries -- will dominate. Storing hydrogen underground in caverns has a per energy capacity capital cost of just $1/kWh, two orders of magnitude cheaper than Li-ion batteries.

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Let’s assume at scale you’re buying seasonal power for 0$ so efficiency doesn’t matter and selling it at 10c/kWh given 1$/kWh and a once a year discharge you might break even in 10 years which looks fine except...

1$/kWh is only storage for already existing hydrogen. For this application you also need equipment to both produce and burn it which adds to these costs. Hydrogen generation can’t depend on 0$ prices for very long each week in the off season so you either need a lot of excess equipment that’s rarely used or be willing to pay more for electricity. Further, nobody building a grid would be willing to depend on seasonal storage running out on the last day it’s needed. So you need a large guaranteed storage surplus alongside redundancy in your generating capacity.

Start running the numbers and the annual ROI doesn’t look to be even enough to pay for the interest on your setup costs let alone profit. It might have some ultra niche applications but the economics don’t seem to work out for large scale deployment.

Here in Europe peak electric prices have been far above $1/kWh, rising to around $7/kWh in the worst-hit regions.

Due to the build-out of wind power we have also had a few nights of negative electricity prices in recent months.

If we had a hydrogen energy storage facility, it could probably have recouped quite a portion of its capital costs this year, depending on its scale. Europe will not be building much base load power in the coming years, so the imbalance of the grid will only continue to rise, allowing for more business opportunities in the energy storage sector.

Europe is experiencing those prices due to a dependence on fuels it doesn’t produce and a lack of daily energy storage.

Extrapoatgng prices to stay the same when you swap energy sources and introduce two different kinds of large scale energy sources is clearly wrong.

Ultra low or ultra high prices will represent a small chunk wholesale prices after you construct long term storage. You can’t build equipment that’s utilized 0.01% of the time and expect significant profit.

Yes, but the producing and burning is not proportional to the amount of energy stored, but to the rate at which the hydrogen is produced or consumed.

In the 100% renewable grid, electricity actually will be in surplus a good part of the time, because so much excess capacity would be installed. This is not the case now, so you can't use the current frequency at which curtailment occurs as some sort of baseline.

Yes, you'd need excess storage so it doesn't run out. Fortunately hydrogen storage is cheap. This is another argument for hydrogen over batteries.

You can run the numbers and see that in a hypothetical system for providing steady power in Germany, including hydrogen storage can cut the total cost nearly in half (subject to assumptions, of course.) Doing it with just wind, solar, and batteries ends up being far more expensive.

The amount of energy stored or is still limited by the rate it can be generated.

The absolute best case for seasonal storage is 1kW * 9 months = 6,480 kWh per 1kW of equipment if you are willing to pay unlimited prices per kWh.

However if you are depending on 0$/kWh which hypothetically occurs 1% of the time you are down to 55kWh per 1kW of equipment. In a world with mass storage wholesale prices will spend less time at 0$ so what matters is the prices when you’re operating not historic prices before you build these facilities.

PS: Conversely, if you’re using that stored energy the grid isn’t going to have a deficit 24/7 the entire winter at your maximum production rate. If you average 8 hours a day for 2 months that’s 480 hours of operation per year. Gas turbines are cheap but not that cheap.

>hydrogen's big advantage -- the low cost of storing it

Hydrogen by its very nature, due to it being the smallest atom, embeds itself into the walls of its container. It will rot the metal walls you use to hold it long term.

Look up "hydrogen embrittlement"

It's stored underground in caverns, not in metal pressure vessels. This is a demonstrated technology. It's also the same way natural gas is stored. The cheapest option is solution mined cavities in salt formations. Europe (for example) has enough salt formations to store many petawatt hours of hydrogen.

What’s the pricing compared to stored energy like pumping water up a hill? I get that it’s not exactly a universal strategy but not like underground caverns don’t have the same issue

The main issue with pumped storage is you need a lot of water. Imagine a elevated water tank like that used on farms. 20,000 gallons (75,000 litres) of water elevated at 18 feet (5.4m) has 1.1kWh of potential energy.

Or a lot of difference in elevation. With 900m head you can get 8 MW from only 1.5 m^3/s in a pipe less than 2 feet in diameter.

900m is a huge elevation difference. The highest pumped power dam currently in Japan (by hydraulic height, after looking at almost all the Japanese hydro pages on English Wikipedia) is about 780 m; the median is just under 400 m. Presumably most of the other hydroelectric dams have already been investigated for pumped power, but lack a sufficiently large lower reservoir.

Seasonal storage is an interesting idea. Rare grid outages seems pretty easy with batteries if the South Australia example is anything to go by though, and for medium-term storage there's also pumped hydro -- not sure where that compares in cost?

Rare prolonged outages are bad for batteries, since the capital cost is too high. You want something that has very low capital cost, even if it burns a fuel. Simple cycle gas turbines power plants might cost $0.50/W.

Existing battery technology works best when you don’t charge to 100% or discharge to 0%. On top of this you want oversized batteries to deal with battery degradation over time. This means any large scale battery system includes a buffer beyond normal use which you would only use if wholesale prices spiked.

On top of this grid operators want generation redundancy in case an individual power plant goes offline for whatever reason. Combining both you get quite a lot of excess capacity compared to the current grid.

> Rare prolonged outages are bad for batteries, since the capital cost is too high.

You could subsidies that by using your batteries to energy to peak load times?

Batteries sufficient for short term leveling would run out too quickly. If you build enough batteries for prolonged outages most of them would be unused during the leveling of short term fluctuations.

How long can south Australia power their load from batteries? I thought they had the one 100MWH battery so basically could power 100k house for an hour? And that battery was over 100 million dollars.

South Australia’s incredible week: 104.1 per cent wind and solar over seven days

https://reneweconomy.com.au/south-australias-incredible-week...

   South Australia aims to reach 100 per cent “net renewables” within a few years – over a full year – but in the past week it has already done better than that.

It would appear they are aiming to export excess renewable power to Victoria (neighbouring state).

I thought we were taking about battery capacity preventing a blackout during a major grid outage and not installed renewable capacity meeting the demand.

.South Australia had (maybe still has) the "world's largest battery" (installed by Tesla | Musk) which is an integral part of the SA state power grid that carries it through night times with no wind . . .

If there's "a major grid outage" no large scale battery (or gas fired plant or coal fired plant, etc) will prevent blackout .. as there is "a major grid outage" preventing power from being delivered.

Individual homes would be left to do what individual Australian homes do during bush fires, floods, tree falls, etc and turn to gas lanterns, home generators, and any community hubs that feed local rooftop solar through a local small scale battery (not common as yet, but they're about and increasingly so).

Fuel cells might end up better than batteries if you consider the cost/lifetime of batteries. Energy density and safety are also valid considerations, the batteries are already at the limit of what you'd want to sit on top.

Hydrogen isn't really anything you'd be more keen to sit on top than other batteries, or is it?

Hydrogen by itself has the energy density of zero. Batteries are nearing the energy density of high explosives (and for some types, such as Li-S, exceed it), and, unlike hydrogen, have all the components required for energy yield within micrometers of each other.

> Hydrogen by itself has the energy density of zero.

Not sure how you measure that? Oxygen from the air is plentiful.

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