Mainly that I've yet to follow through on my 5+ year old plan on building a small greenhouse and using solar for water pumping. For most use cases it's a fairly bad "business case" compared to simply buying the power you need. If anything, you would probably be better off setting up a storage sollution to buy power when it's cheap, and then using it when power is expensive, compared to actually setting up power generation yourself.

If I had a good area for them which wasn't some form of rooftop I might have. Rooftop installations are very expensive in Denmark because they are too heavy to be installed without building a lot of support. Even my carport would basically need to be an entirely different structure with a custom foundation to support a roof of solar panels. Which you can absolutely do, but it would be decades before it was worth it.

Because you mostly end up generating when you don’t need the power, and need the power when you’re not generating.

If the way things are structured in your country let you draw the same amount of kWh that you’ve put into the network, that works. Where I live they recently changed to buying the solar at market prices. When the sun is up during sunny months that’s zero or close to that. So you pretty much need the battery installation too.

My neighbour got a solar + battery installation, and it works well enough!