Zonal pricing electricity markets operate sequentially. First, the suppliers compete in a spot market. Second, to alleviate the congestion in the transmission line, in a redispatch market, the suppliers in the importing node are called into operation to increase their production, and the suppliers in the exporting node are compensated to reduce their production. I characterize the equilibrium in a zonal market when the competition is imperfect and the spot and redispatch markets operate sequentially.
I also work out the equilibrium when the transmission line is taken into account in the spot market, i.e., it is not necessary to introduce a redispatch market to alleviate the congestion in the transmission line. I find that the consumers' welfare and suppliers' profits depend crucially on the type of redispatch design implemented by the auctioneer, and that could introduce long term investment distortions.