S&B-76: The REC Contract specifies that excess RECs are the “exclusive property of Seller” and may be “utilized in Seller’s sole discretion”. Does this mean that a seller may monetize excess RECs by selling them to a third party (assuming that it is not a shortfall year)?

That is correct. Any RECs generated by the Project in excess of the Delivery Year Requirement in any delivery year during the delivery term are the exclusive property of Seller, to be utilized in Seller’s sole discretion.