Is an investment foolish if it has a positive ROI? I live in Belgium, and even without subsidies and before the current increases in electricity prices, solar panels had a payback period of ~ 10 years (while they generally last ~ 25 years). Why would it be foolish to invest in this?

You say that they would be 10x as efficient in Southwestern USA. But how would you transport the electricity from the USA to Germany? Isn't that exactly the problem that the previous commenter is pointing out? I.e. production is not the problem, transportation is.

It's an opportunity cost, particularly in Germany against other RET investments such as nuclear/wind: https://www.sciencedirect.com/science/article/pii/S030142152...

last time that i checked, I couldn't find any nuclear reactor to my home. I have however 8kwh solar panel on my roof and I'm quite happy with that.

That sounds cool. Hope you live in a sunny place.

The same thing which transfers electricity from a distant nuclear reactor to your home can also transfer it from a distant solar panel.

This means that two different houses each with PV can support each other when one is sunny and the other cloudy.

In principle that would scale to the world; in practice that's the domain of politics rather than technology, and politics may push for one of many other solutions.

Not really true. Power from distant nuclear reactor or any other big generator comes over high voltage lines with small loses. Power from your panels go straight in the low voltage network which has high loses and is used for very short distances. That means you cannot support other houses which have clouds over them.

Transformers are quite capable of working in either direction.

Your statement about transformers makes little sense within a context of power grids. You start by pushing power into 230 V system, which has a maximum tolerance of around 250V, after that you can damage electrical equipment connected to those line. That alone will limit how much power you can push out into the grid. An then through how many transformers and miles of wires will the electricity you produce go before it reaches high voltage lines, which are needed to transfer power over distances?

On the other hand the nuclear power station turbine generates power with a voltage of 20 KV feeding it to a high voltage transformer, which steps up the voltage to 200KV and is connected directly to the transmission lines.

If I have a, for example, 2kV-to-240V transformer, and I put 240V on the 240V side, how many volts do I get on the 2kV side?

Is there a point to your rhetorical question or do you have troubles understanding the difference between an ideal component vs a real component in a live system?

The sun is responsible for a lot more of our energy than just solar. Photosynthesis, wind, solar (of course), hydro, are all energy sources that directly capture energy from the sun, which we then use. Like the parent poster said, it's about transportation. Sometimes nature does that transportation for us.

Absolutely, Sun is also responsible for oil and natural gas if you stretch the horizon longer. Perhaps the only source of energy we have not capture from the Sun is nuclear, which may have been a result of supernova explosions. This pedantry aside, Germany needs better energy policy that is grounded in fundamental resource economics, not driven by ideology/potitical will, but with a stern look at their national energy security (or lack there of) and secure it by the means that's necessary.

Cost of energy has multitude of secondary effects on GDP and food security; the importance of which cannot be understated.