Fun fact: At least in Germany you often end up paying taxes on self-consumed solar. They calculate the tax based on what you would have payed your regular supplier (or 20c/kWh). But otoh you get to declare your "solar plant" a business, with some nice perks: If you buy the solar equipment for net 20k€ you'll pay 19% or 3.8k€ taxes. You get that money back. In addition, the 20k€ are a business expense and reduce your taxable income (there are two modes for this, either 5%/year for 20 years or a huge block [50%?] the first year and some smaller blocks the next two or three years - I believe). So if you pay 30% income tax, you'll save about 6k€. All other expenses related to the solar plant (service, repairs, insurance,...) also count as business expenses, with the same effect.

If you're not earning more than 17.5k€/a in addition to your regular income, you can opt to forfeit the whole stuff in favor of the "Kleinunternehmerregelung" (small business provisions), but then you don't get the above business perks. Though after a few years you can change from a full business to a small business, so you'll have to do the math.

Sounds complicated? Welcome to Germany! :D

(Disclaimer: This might be not 100% accurate, so talk to your tax consultant if you're doing solar in Germany)