This is idiotic. The fact is your electricity transmission system operator has to pay a lot of money to keep the grid stable at 50 or 60Hz or your electronics would fry. With wind and especially with solar power, the variable output is always pushing the frequency one way or the other, and that creates a great need for costly balancing services. Negative pricing is an example of such a balancing service. Sounds good, but for how long do you think your electricity company can keep on paying you to consume power?