[hwillis]

Numbers: In poland the solar output in December is 1/5th of July output while demand is ~10% higher. Insolation drops off quickly at higher latitudes so it dominates much more strongly than heating demand even if heating were electrical.

At the global scale this would ideally balance out- more equatorial solar is cheaper in the winter since they don't need air conditioning, so you just send it up north. That's the only really feasible solution to seasonal variation in individual countries- it's totally unreasonable to store 3 months worth of power. Its also important to note that even with 2x or 3x oversupply, solar is cheaper than nuclear currently is.

[1]: https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP [2]: https://www.pse.pl/web/pse-eng/data/polish-power-system-oper...

[rich_sasha]

I find these discussions usually collapse into a sequence of shifting goals.

You quote, and I believe, 5x solar irradiation power difference between December, plus a second-order 10% power consumption difference. Doesn't this mean already a 5.5x difference - if X panels are sufficient in July, then 5.5X would be needed in December? And July itself probably already needs overprovisioning anyway - Polish summers are not guaranteed sunshine. If "July" is overprovisioned 1.5x and we add the 5x for December for a combined 7.5x overprovision, plus batteries, is it still cheaper than nuclear?

If nuclear gets dismissed as an expensive fantasy, well, at least it has been built and operated at massive scale. I am not aware of any large scale operating exports of solar energy from equatorial regions to Northern Europe, or similar distance.

[hwillis]

You're massively misrepresenting what I'm saying. I am not dismissing nuclear or suggesting overbuilding solar by 5x. I am responding to someone who is dismissing solar now for the fantastical idea that nuclear is cheaper now. Nuclear is good. Nuclear should replace coal. Shutting down reactors that are not unsafe is ridiculous. We should build breeder reactors. Personally I think even many countries that have reactors should build more, and retrofit existing reactors to have much higher ramp rates a la French nuclear. Countries with no nuclear or hydro or geo base like Poland should definitely build nuclear plants.

But many countries have large amounts of nuclear- many enough to supply most nighttime power. And in almost all countries, solar is by far the best and cheapest immediate option, and those countries should be building as much solar as possible until the marginal return of nuclear or storage or infrastructure for imports are cheaper than just building more and more solar.

> I am not aware of any large scale operating exports of solar energy from equatorial regions to Northern Europe, or similar distance.

No country is even close to a solar oversupply, much less a 2x or 5x. If there is no margin, why would those projects exist?

[bryanlarsen]

Overbuilding is significantly cheaper than either months worth of storage or intercontinental HVDC electrical links. It's probably worth building links with Romania, but probably not equatorial North Africa. Instead if you want to hit 100% carbon free, overbuild solar to almost your 5X, mix in a good amount of wind, a couple days of storage and links with Romania or nearby.

IMO 99% is a much better target than 100%: almost all of the benefits for a lot less cost. Idle natural gas plants don't emit carbon.

(And by 100% I mean 99.99%. The grid isn't reliable enough to make more than 99.99% worth the cost).

[lightbritefight]

An ideal side effect of over overbuilding solar 5x for winter is that you could then use that spare solar in the other 3 seasons to make green hydrogen, an energy intensive process, to power retrofitted gas plants. You could store and ship excess gas as well, creating an adhoc "green energy interconnect" with other nations.

[Qwertious]

IMO the best use for excess summer solar for winter use is directly storing heat in a heat energy storage system (HESS, a fancy word for a bunch of sand/rock wrapped in a meter or two of insulation). Dump in the heat through resistive heating, use the heat directly for heating in winter. Batteries are expensive, but thermal mass is literally dirt cheap and scales up expoentially well thanks to the cube-square law. Just store and use the heat directly!

[adrianN]

Most of Polands heating is probably not electric. But it’s not unreasonable to store months worth of power, many countries have gas reserves in that ballpark. You just have to replace natural gas with a synthetic fuel.

[hwillis]

That's just not true, unless you mean resource reserves. Taiwan has the largest NG strategic reserve I know of (11 days) and the US has the largest petroleum reserve in the world at 19 days: https://en.wikipedia.org/wiki/Strategic_Petroleum_Reserve_(U...

Resource reserves are unextracted and not replenished. They are not the same as storage.

[rich_sasha]

I don't think this is right. Here's the first link I can find: https://www.intellinews.com/how-many-days-of-gas-consumption...

This quotes Poland as having 89 days' worth of gas consumption with storage full, Hungary at 133 and Germany at 108. These are actual storage reserves, not untapped resources, at least for Poland.

[Qwertious]

>You just have to replace natural gas with a synthetic fuel.

The word "just" is doing a lot of heavy lifting there. For heating, by far the most sensible solution is to use summer PV to heat up a bunch of sand/rock wrapped in a ton of insulation, then use the stored heat in winter.

[adrianN]

I did not claim that it's the cheapest method, I just pointed out that storing months worth of energy is feasible.