Norwegian power generation is sized for the domestic market, so tax income from selling excess is marginal at best. The power bills however have indeed crept quite a way up. This was especially noticeable in the first winter of the Russian invasion, when the Nordics had to subsidize the bill that suddenly dropped on short-sighted German energy policy.
Germany benefits a lot from the open market. If only countries introduced a rule to export only the excess of the energy then Germany would be cooked, because prices would sky rocket for them, not 2x, 3x, but way more. Luckily for them they can make strategical mistakes and go away with it making others to pay for that.
"Excess energy" is not a static value. It dynamically depends on price point. Which depends on demand and supply which both depend on price. That dynamic (and circular) interplay is at the core of why economics as a discipline exists in the first place.
