  We consider a mechanism design problem for energy procurement, when there is
one buyer and one seller, and the buyer is the mechanism designer. The seller
can generate energy from conventional (deterministic) and renewable (random)
plants, and has multi-dimensional private information which determines her
production cost. The objective is to maximize the buyer's utility under the
constraint that the seller voluntarily participates in the energy procurement
process. We show that the optimal mechanism is a menu of contracts (nonlinear
pricing) that the buyer offers to the seller, and the seller chooses one based
on her private information.
