Optimising the scheduling of spinning reserve considering the cost of interruptions

Spinning reserve (SR) is probably the most important resource used by power system operators to respond to sudden generation outages and to prevent load disconnections. Although its availability has a substantial value, because it mitigates the considerable social and economic costs of outages, the provision of SR is costly. Unit commitment programs customarily include a reserve constraint in their optimisation procedure to ensure that a fixed amount of SR is scheduled. This approach is sub-optimum, because it considers explicitly neither the cost of providing this amount of reserve, nor the value that consumers place on not being disconnected. In practice, this means that the amount of SR scheduled is likely to be excessive during some periods and insufficient during others. To overcome this problem, a new formulation of the unit commitment optimisation problem is proposed, where the value of the reserve is included in the objective function. To achieve this, a method is developed for quick estimation of the expected energy not served of each combination of generating units considered during the optimisation process.