At least in the UK, the solar subsidies were set in stone for 20 years at the time of installation; so even though new solar would get little subsidy I'm still getting the rates from five years ago when I installed my system.
Of course this makes the value proposition for moving power into the grid much worse, but it changes precisely nothing for power that you use from your panels (you are still getting 20 cents worth of power from a panel that has already been paid for by you).
For this reason it is best to rely on the subsidy as little as possible and maximise the power you use directly from the panel, either by changing your habits or by storing the power for later (in a battery). Sadly using batteries adds additional costs to this picture and is not currently worth it at all, even without subsidies.
How does that work? A new government can change the law and decide otherwise, well at least that is what they do here.