There is some context missing there: the amount of power buyers need. So a simplified example: Buyers are willing to pay $5 to secure 100GW of power. Sellers a

There is some context missing there: the amount of power buyers need. So a simplified example: Buyers are willing to pay $5 to secure 100GW of power. Sellers are: 80GW Solar at $3 and 20GW Coal at $5. At 100GW the price is $5 because it's the price that will secure 100GW. If buyers only needed 80GW the price would be $3. There is only one market price and it's the price that gets the required quantity of power (as you say).