The price you can sell energy at is guaranteed (government subsidies). Your investment (maybe 100,000 €) will pay itself off in about twenty years (including insurance and the occasional maintenance). Modern solar panels have a lifetime of more than twenty years.
Because of all this banks will be more than happy to give you credit and if you have the necessary space you would be stupid if you didn’t do it. It’s free money.
Instead the next grid operator has to take the electricity and has to pay a certain government specified price for it. The electricity companies will sell electricity to the consumer and these will pay for it. So the end consumer pays the price. The goal is to reduce the price for renewable energy such that it is at the level of other electricity (from coal, gas, nuclear, ...).
There is no tax money involved. The electricity consumers pay for it.
They've just introduced a similar scheme in the UK, with the price guaranteed for 25 years. It looks like around a 10 year payback period on the installation so a very attractive proposition if you've got the cash available and plan to stay in your current home for at least the next decade.