Merit-order dispatch, computed live
Every half-hour, every plant on the grid bids at its marginal cost. Cheapest first, up the stack, until demand is met. The most expensive plant needed sets the price for everyone running that tick — including you, whether you're the cheap baseload or the plant that just tipped the market. It's never a replay of history. It's computed, tick by tick, from what you and the rest of the stack decide to do.