An Optimal Approach to Solving Technical Constraints in the Spanish Electricity Market

In the Spanish market, the transmission constraints are solved through an auction process by redispatching previously committed energy in the daily market. The Spanish system operator requires specific bids for increasing and also decreasing in an attempt to define a safe schedule. The new commitment is allocated to the best bids sent for the purpose of solving grid constraints. In general, these bids are simple. Hourly energy bids divided in blocks with their own bid prices, which will determine a time-decoupled optimization problem that could be solved on an hourly basis. Nevertheless, the thermal units which have not been previously committed in the daily market may present "complex conditions" that couple the different hours during the day. These complex conditions pose a time-coupled non-linear mixed-integer optimization problem that must be solved using decomposition methods. In this study, Benders decomposition is used to solve the time-coupled optimization problem, whereas a non-linear mixed-integer solver (SBB) is used to work out the time-decoupled problem on an hourly basis. Results of both coupled-time and de coupled-time optimization problems will be discussed. These results illustrate that simplifying the problem by decoupling it on an hourly basis yields suboptimal solutions. The models have been applied to the IEEE 24-bus test system