Economists know how to calculate optimal prices for electricity transmission.  These are rarely applied in practice.  In PWP-058, Green develops a thirteen node model, based on the transmission system in England and Wales, incorporating losses and transmission constraints. The model solved with optimal prices, and with uniform prices for demand and for generation, but re-dispatching to take account of transmission constraints.  Counting consumer surplus and generators’ operating costs alone, moving from optimal prices to uniform prices reduces welfare by 0.6% of the generators’ revenue.  Inappropriate generation investments, or an inefficient re-dispatch, could raise these costs significantly.