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Comment by skrtskrt | Hacker News Reader

Is it possible that we could have a permanent (small) presence of fossil fuel energy to smooth out capacity?

I think there's certainly a lot of potential for us to drastically reduce fossil fuel usage with renewables while supporting off hours with something like gas turbines in the interim. The ultimate goal is to remove those too, but we could probably cut overall fossil fuel use by 70% or more in the meantime pretty easily, I'd imagine.

Not if we want to stop global warming. What we can do instead is store renewable power as methane or hydrogen and burn that when batteries are insufficient to cover. But perhaps advances in grid scale batteries will make even that obsolete.

It’ll be interesting to see what role hydrogen plays. Prices for using it to store energy are currently a couple times battery energy storage systems, and the component parts are not getting cheaper very fast (turbines + storage + electrolyzers), whereas battery storage is rapidly falling in price. But as you point out: we know how to use hydrogen/synthetic methane/ammonia as a storage asset if we need it.

I think it will be difficult to satisfy global storage demands with lithium batteries. But most countries already have infrastructure to store a couple of weeks to a couple of months worth of methane. Perhaps it makes economic sense to just use that infrastructure and pay the 60% conversion loss. Maybe other battery chemistries will be better options.

I’ve seen analysis that says we have enough lithium globally, especially if we use existing working recycling techniques widely. And there are other battery chemistries with earth abundant materials (e.g. iron redox) that could ease the lithium supply concern. But I think you’re right that geopolitics will play a huge role. As we’ve seen with the war in Ukraine and Russian gas, resources are not uniformly distributed, and we can’t rely on frictionless international trade to work consistently.

There is some leeway in global warming as on net the earth sequesters more carbon the higher the atmospheric CO2 levels, it’s just nowhere near fast enough to keep up with current output.

Unfortunately we already emitted enough carbon to force pretty catastrophic warming, so we'll need to become net negative for at least a couple of decades before we can talk about low net positive emissions.

You are far more optimistic than I if you assume net negative is a possibility any time soon. A significant reduction in methane might be possible which would provide similar benefits.

I wonder if biomass + carbon capture and storage could play a role here. If the biomass was source in a controlled way (and that's a big if) you could have the characteristics of a thermal power station and be carbon negative.

I think yes, when combined with carbon capture and storage. The technology has worked for some time (both the capture and storage parts), some of the new direct air methods are hitting $100/MWh when paired with generation, bringing prices of gas + capture around the price of solar + storage. However, siting it is tricky since you need the right geology, and there have been some very expensive failures to deploy. Maybe it will have a niche role until we solve storage + transmission + demand management (as someone else pointed out).

Hydro can largely fill that gap, it’s currently ~15% of global electricity generation.

Most of our good hydro projects are already built out. Maybe a few more projects in deep remote Tibet, but the ice packs are quickly disappearing and not building up much over winter, so I don’t expect hydro’s share to rise, and it will probably shrink in the recent future.

My point way you don’t need additional hydro to back up renewables.

15% of 24/7 is 100% of ~7h, 3.5 days a week. We would need some batteries, but nowhere near the kind of excess people calculate for a pure wind/solar grid.

I haven't seen an estimate done for the US, but for Germany one estimate is that to rely on solar and wind would require about 6,000 pumped storage plants which is literally 183 times their current capacity.

https://www.econstor.eu/bitstream/10419/144985/1/cesifo1_wp5...

If making more grid storage was cheap and easy, we would have built it decades ago.

That’s exactly the kind of meaningless and inflated number I was talking about. Notice how they exclude hydroelectric dams.

Existing hydroelectric dams currently store vastly more energy than the average pumped hydro facility and they can easily be adapted to add additional turbines for relatively minimal costs. Collectively North American dams are storing at a minimum several days of total grid output and theoretically much more depending on how you do the calculation.

Adding turbines doesn’t increase annual production, but it does increase flexibility as it makes minimal difference to discharge 1x water for 24 hours or 5x water for 4 hours and the rest over the other 20. Several dams have already been retrofitted like that as peaking power plants are simply vastly more valuable per kWh. It’s even better for the environment as rivers naturally have significant variability which is normally smoothed out by dams.

PS: Rarely mentioned in those kind of analysis is how sensitive the required storage number is to the exact mix and oversupply of wind/solar. A grid with 1.001x average annual demand looks very different than one with say 1.1 or even 2x.

The nice thing about hydro is that most projects come with their own battery. Wind or nuclear can be used to fill reservoirs back up. If the ice packs are drawn down too much, this might be the main use for hydro in the future, though I’m not sure it would save something like lake mead (though a project is planned).

TLDR: yes

It helps during the transition, and even afterwards.

France, by far a leader when it comes to nuclear (used to produce 90% of its gridpower this way) always used fossil fuel energy to complement it reactor fleet (each year fossil fuel produces 7 to 12% of France's electricity), mainly because maintaining enough reactors in order to cope with peak consumption (thus letting many underused) would be way too expensive, and also because nuclear load-following capacity is insufficient (bar over-provisioning reactors) due to their limited flexibility (at this game a gas turbine is way, way better): for security and burden-of-maintenance -related reasons one just cannot freely pump up/down the power delivered by a nuclear reactor, modulation limits and pauses are to be strictly respected.

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