What are the current energy prices for 1 average family in Poland today?

Hi!

As I would like to invest and become a landlord in the future in Poland, I would like to know, if there is a short answer to it of course. What would to energy cost be like for example a family living in a house near Olsztyn?

Also, if anyone knows if there is gonna be some major changes in the energyprices in the next 5 years perhaps?

It depends on the square footage of the house, but in general:

house 70-90 m2 - 3500-4000 kWh / year
house 120-150 m2 - 4000-4500 kWh / year
house 170-220 m2 - 4500-5000 kWh / year

Just calculate kWh price per your estimated footage to get the annual price.