That depends on the rig, and the scale you can do it on. Paying less in itself is worthwhile, however there's money to be made. In the U.K., even a domestic setup with the newest panels pays for itself quite soon. Adds to the value of the house too.
When the sun doesn't shine you freeze to death and sit in the dark. Coal is toasty warm and runs big power plants to serve your home. Plus, it employes a lot of people from mining it, to selling equipment to mine it, transporting it, selling it and on and on.
just like johnnyreb said, renewables are not reliable (especially in Poland where winter can be harsh and usually there is very few sunny days during the time)
Did you think anyone was suggesting solely relying on one form of technology?
Gone are the days when it was just coal, gas or another dirty fuel.
I'd not bother with anything Jim or other pretend conservatives say. One minute they're complaining about alleged inefficiency of one system and the next they're praising the inefficiency of another.