[snowwindwaves]

In Ontario, Alberta and British Columbia, Canada and Washington, USA at least, I am certain that company that builds a wind farm gets a contract where some entity guarantees they will buy all of the power the wind farm will produce at a pre-determined rate(s). Otherwise nobody would put up the money to build the wind farm.

You are correct that new renewable plants never have to pay to export excess power, but conventional generation such as old-hydro, gas, nuclear, coal, etc that don't have sweetheart contracts with the government do have to contend with negative prices, and the system does have to pay someone to take that power. Then the local rate payers through some non obvious lumped in "market operating charge" or other mechanism end up paying for that power they didn't use.

You could feather the blades, but at least in the markets I've worked in they never would.

edit: Actually, the ratepayers don't pay to get rid of the energy they didn't use, the generators that generated it at a negative price have to pay for not being able to shut down.