A lot of places in Austria (esp. Vienna) are heated with burner Technology (gas/oil/pellets). The article states that this energy usage has been converted and is included in the total amount.

A quick search indicates that 1kg of pellets generates ~5kwh. So when burning 4to. of pellets in winter that adds about roughly 50kwh per day.

When using burner tech to heat, a good way to reduce the cost and profit from pv is to add a heating rod in the buffer tank of the heating system.