From the article it doesn't sound like there was any sort of dispute...my guess would be that the contract formalized payment as a function of capacity and dema

From the article it doesn't sound like there was any sort of dispute...my guess would be that the contract formalized payment as a function of capacity and demand, in such a way that payment could be negative. This might not even be a mistake or from a need to distribute the power, it could just be a low-cost (due to rarity) sweetener.