The main killer of solar is variability. Northern countries have shorter solar days during winter and can have _weeks_ of overcast days, so these countries would need some kind of backup: either long-term storage, or nuclear.
You have to be realistic of course. There are a few months in the winter where they don't perform well and returns drop well below a single kwh of power. But then you might start getting some bright winter or early spring days and you go back to getting many kwh per day worth of free power as early as February or March.
It's better if you have a battery and if your local energy supplier has favorable contracts.
Long term storage seems to be a be a hobby horse that comes up in a lot of theads like this. The reality with batteries is that the overwhelmingly vast majority is for dealing with short term supply/demand fluctuation. The supply spikes are as important as the demand spikes here. Empty batteries can absorb those.
Anything beyond four hours drops off rapidly in terms of economics. And a few hours is all most energy companies need for planning to spin up or down gas (or coal in some cases) plants or decide to import/export power via cables.
As for nuclear, it's is a lot less flexible and very expensive. And in any case very little of it is coming online for the foreseeable future (next 1-2 decades). We'll get probably quite a few TW of battery, solar, and wind deployed over that time. Nuclear is going to be a rounding error on that even in the best case.
What’s your plan for powering an entire modern industrial economy (cars, houses, industry) for an entire week in the middle of winter with minimal wind and solar? Because that happens fairly frequently.
If you don’t have one, then the default is to keep burning gas as a backup, which is what is happening
Long term storage has the simple economic challenge that it's simply redundant most of the time and therefore very expensive for the few times it might actually be needed. As a result, alternatives to storage tend to be more economical and practical. Having gas as a backup is a given for the next few decades. There are so many gas plants around and more are being built. Mostly short term storage is actually marginalizing a lot of those in their role as peaker-plants.
The plan for the last few percent of the renewable transition, which is what long term storage would be about is a lot less interesting than just getting the first 90-95% out of the way. Which will work fine without anything complicated or new. Burning some gas for the remaining percentages is not pretty as a stop gap solution but it's a lot better than what we currently do. We have a 3-5 decades to figure out the rest.
Towards the end of that period, most remaining gas plants will be running less and less. There are a lot of other solutions than long term storage btw. Including using cables to move power around over long distances. Connect sunny areas to dark areas. Or windy areas to calm areas. There are some plans in various stages of progress to connect e.g. Singapore with Australia, Morocco with the UK, the east coast of Canada with Europe, etc. Each of those projects adds many GW of power import and export capability. Add things like flexible demand to the mix and we gain the ability to turn things on/off selectively depending on power availability.
It's not the question of being positive, but being able to cost-effectively replace fossils. I just don't see it happening with solar in countries like Germany or England, because of that storage issue (no way to do it).
Germany has currently around 1.5kW of solar installed per person - even in October this yields double-digit GWs at 9am. They can't put all that power to use in summer, but it sure puts a damper on prices off season.
Sure, storage is still being built as there's a market for it, but for now it's still cheaper to just build more solar capacity.
https://cleantechnica.com/2026/06/08/solar-records-getting-b...
https://www.energy-charts.info/charts/power/chart.htm?l=en&c...
It would need to be increased around 20x to be a viable replacement, and this is just not feasible.
And no, wind won't help either: https://energy-charts.info/charts/power/chart.htm?l=en&c=DE&... - look at the period from 15 to 22 Jan. That's a week of almost no renewable generation, paired with low temperatures.