Settlement

What does it mean by bid is successful for large merchant generator? Is there any risk any energy generated is not being paid? Or should the large merchant generator will be paid same as the price taker?

A bid is successful when the price offered is competitive/optimal to meet the demand and GSO issues a Dispatch Instruction. Only if the generator meets the Dispatch Instruction, it will be paid accordingly. Unlike a Price Taker which does not have to bid, any energy generated up to its registered capacity will be paid.