Suppose your coal or nuclear steam plant suffers not just fuel cost, but an additional cost every time you ramp its output up or down. At times when instantane

Suppose your coal or nuclear steam plant suffers not just fuel cost, but an additional cost every time you ramp its output up or down. At times when instantaneous demand is less than you are producing, it could well be cheaper to pay someone else to take the excess energy off your hands than to adjust your plant. That's simply a negative price. Hard to get freaked out over that.