alt Hacker News> Are you saying it's cloudy for four months straight?
No. But it's cloudy most of the time for four month straight (in average there's only 200 hours of sun between November and February in Copenhagen. Yes, you read it right, that's not even 2 hours per day in average!).
> A detailed chart would be nice but a good starting point to imagine is 60-70 days that average 50% solar power and the rest of the year is full solar power minus a couple particularly bad days
That's an insane assumption! An average of 50% solar power during the day is the higher bound of what you can expect in the middle of the Nevada desert! (Because you know, the sun rises and falls during the day, it's never going to give the full power during daytime). And because there's night half of the time in average, even in Nevada you end up with load factors around 25%! (Go check the figures!)
In winter in Danemark, the situation is obviously far worse! A 2-5% load factor is to be expected depending on the weather. (Just check the live data: we're in April, it's 11am and solar panels are delivering just 10% of their power right now https://app.electricitymaps.com/map/zone/DK-DK1/live/fifteen... )
> the 90% number isn't crazy.
If this number doesn't sounds crazy to you, it's just because you're completely off in terms of orders of magnitude involved. 90% is likely achievable in southern US with great effort, lots of storage for night times and significant over-paneling, but it's pure science fiction in Denmark.
> That's an insane assumption! [...] load factor
No no no no, that line has nothing to do with load factor. I'm talking about half the kilowatts for the house coming from solar, and half coming from the grid.
> Just check the live data
There's no way those panels are optimally angled and out of shade if they're making that little. Are those panels installed in rows on the ground? Rows that are pretty close to each other? Panels on a roof, the steeper the better, will see a much higher load factor in winter.
I'm other words, a home rooftop install will do much better in winter than a standard commercial install. That's a mixture of chance and optimizing for different things.
A thought experiment: You have one big solar panel mounted very high, with a multi-axis aiming system that points it directly at the sun. Do you think the amount of power you can make is going to be that far off a linear relationship with the number of hours of daylight?