The issue is you need to design for 1-2 weeks of little to no wind and very little solar in winter, when demand is it its greatest. This is what is so tricky, unlike more southern climates where you have pretty reliable solar year round (even if its reduced, its not close to 0 which is the case in the UK). Instead of storing a day or so, you need to store weeks of energy.

Also you're forgetting residential electricity is maybe 1/3rd of total demand.

Where do you get "close to 0"? From what I read the output is still 15-30% of the summer peaks, which is very different from "close to 0".

On average. That doesn't mean there aren't sunny weeks where you get a lot more, and dark weeks where you get less. For instance if you get snow, output is pretty much 0 unless you clean them.

I believe there were 7-10 days in January 2025 where both solar and wind were in the single % digit for instance.

Of those 7-10 days, how many were consecutive? A couple days of single-digit efficiency each winter would be trivial to manage with batteries. I'm sure we can figure out a solution for the snow issue, especially since panels are usually angled.

Don't get me wrong, I get where you're coming from! But especially in the last 2-3 years, it seems like people always evaluate solar under the worst 0.01% chance scenario, which other power sources never have to survive. For example, not even half the days in January 2025 had single-digit outputs, yet they're still called "close to 0".

What I'd love to know is e.g.: in 99% of years, what's the worst Dunkelflaute we can expect? How much battery storage/solar overbuilding would we need to cover that, how much would it cost, and how much will it cost in a few years (based on current development rates)? I'd argue it'd be okay to reduce power-hungry industry for at worst few days, in case a once-in-a-century year happens.

The issue is though that you are saying 0.01% chance scenario, but gas/nuclear doesn't all go down at once at the same time every year. It's a somewhat fair counter that you might have serious gas disruptions, but LNG does massively diversify potential supply (and in the UKs case we have and will have a fair amount of domestic production for the next while).

Also keep in mind the overbuilding a massive problem anyway _outside_ of those 1-2 weeks worst case scenarios. We already have highly negative prices occurring more and more, and IMO this is the definition of policy failure, because the negative prices only arise because subsidies _encourage_ plants to keep producing even though the value is quite literally negative of the output.

Finally I don't think it's once in a century, probably most years have a significant Dunkelflaute event. And not all industry can be shut down like that (eg aluminium production) without causing catastrophic damage, and even if they can it makes them an unreliable supplier.

> The issue is though that you are saying 0.01% chance scenario, but gas/nuclear doesn't all go down at once at the same time every year.

Over this summer, a huge number of nuclear plants in Europe went down all at the same time, because they either would have killed the nearby river ecosystem by overheating it, or because they didn't have enough water to operate safely. This issue is only going to get worse as climate change progresses, and unlike most Dunkelflauten, the heat & drought really affect most of the continent at once.

> Also keep in mind the overbuilding a massive problem anyway _outside_ of those 1-2 weeks worst case scenarios.

It's only a problem because power generation tech like nuclear is so expensive, and it would become even more expensive if they couldn't run as much as possible. If we had a fully renewable+battery-driven grid, the issue would disappear.

> Finally I don't think it's once in a century, probably most years have a significant Dunkelflaute event.

I think you might unknowingly be ideologically motivated, because I specified that we should build enough to cover every Dunkelflaute in 99% of years. The amount of battery storage in this scenario by definition suffices for 99% of years, which makes the point about unreliability moot.

You said your modelling needed "something on the order of 4000GWh of battery storage"

That's not outlandish given the cost of distributed batteries.

Are you upping that model?

(If you build more generation -- for example have renewable peak generation of 80GW rather than 40GW, that reduces storage requirements drastically, as on a dull quiet winter week where you're only getting 10%, you'd be generating 8GWh in a given period of time, instead of 4GWh)