(Author here) Yes, this is how it works in the UK. I sell my excess electricity back to the grid. The selling price is a bit smaller than the buying price.

I'm very ignorant on this subject, but couldn't you just sell excess to grid and get it back for a minimal markup?

Sure, but it depends on the incentives in your country. Afaik, excess energy could be sold, but you'll have to checkout your local incentives and energy suppliers for specifics. In most parts of Europe, the are scaling down the prices for excess energy. Therefore, battery systems are being forwarded in some cases as sort of solution for solar panels maintaining like ca. 80% +? integrity efficiency over 20 to 30 years.

For example, I read that in The Netherlands the solar panel market has crashed completely or is crashing. Note here that saturation of the market ( many existing solar panels) can also cause that.

You need to find out;

1. energy usage
2. insulation options and materials
3. costs /benefits
4. energy contracts and energy incentives.
5. check out current physical electricity wiring and fuses in the house
6. DIY or professional?
7. budget etc

TLDR: dont buy solarpanels if you want to be rich. And buy them according and after you've done everything possible to insulate your house, whether in the colder or warmer climates. The efficiency, added value, and comfort reached by insulation outweighs everything else. Then , after doing that, check your kwh usage, and buy solars according to that.

Hope this is helpful, but seems you need to go outthere and do some exploration on the topic.

(Ed: layout)