Poland is going all on solar. People are enthusiastic about generating their own power, government had to step in and curb the enthusiasm.

I don't know anything about the polish electricity system but if supply or demand isn't very elastic then excess of either can lead to pretty huge price fluctuations and knock on effects thereafter.

Did they add a solar tax?

bro the sun hardly rises above the horizon for 4 months of the year when power is needed the most.