Capacity power is electricity the grid keeps on reserve to meet its maximum load requirements. It's tapped into when the grid exceeds its base load and needs more juice. Power companies bid to provide that power at a set price. When the grid needs it, PJM begins buying the lowest-priced power and keeps buying more expensive power from other bidders until it has enough. Then, all of the capacity power providers get that last and highest price for all of the capacity power they provided.
FERC says allowing nuclear plants supported by state subsidies to bid into these auctions at lower prices than other nuclear plants could support is not fair. So, it's ordered PJM to set a minimum price at which Davis-Besse, Perry and other subsidized plants can bid in."
-- Dan Shingler, Crain's Cleveland Business