Enhanced system reliability using flexible ramp constraint in CAISO market

Generation fleet flexibility has been identified in all renewable integration studies performed by CAISO as one of the major factors required to enable high levels of renewable integration. The quantity of flexible capacity will be negatively impacted as a result of retirement or repowering of flexible once-through-cooling resources. This paper addresses management of the available CAISO's fleet ramping flexibility and offers a mathematical formulation for the solution of this issue. Operational issues associated with shortage of system ramping capability, which impact both grid and market operations, are presented in this paper. CAISO's implementation of the flexible ramp constraint as one mechanism to drive towards improved system reliability is discussed. The mathematical formulation and methodology to incorporate flexible ramp constraint into the market optimization application is given. Market results are included to demonstrate the benefits of the flexible ramp constraint.