Can someone explain why you would ever pay someone to take surplus power? Is it because they don't want it To go to waste? Otherwise can't they just get rid of it somehow?
It works like this: Every energy producer bids a price for their power, the lower your price the higher you are on the order book.
Then energy consumers will meet the demand by buying from the producers in the order of their price.
Once they have filled their power demand they pay everyone the price of the last price they needed to fill their needs.
So by setting a negative price they ensure they are always on top of the order book - but they don't actually have to pay for their power since other power sources have positive prices, and that's the price that is actually paid.
That's a good question and they've mentioned one solution being transferring the energy to Sweden or Norway and they'll dial back the hydros and store more water in their dams. Of course I wonder if they could just selectively put a windmill in neutral to solve the same problem.