Ramp requirement design for reliable and efficient integration of renewable energy1

With increased renewable penetration, several ISOs are instituting a product on ramp capabilities to manage operational challenges of maintaining real-time power balance. Ramp capabilities have been required ten minutes ahead based on the Gaussian-sigma rule (2.5 sigma for 99% confidence level) without considering costs, e.g. as planned by MISO. However, different from traditional reserves, the ramp product is used to manage both net load variations (foreseeable changes) and uncertainties (unforeseeable changes) and is regularly deployed through economic dispatches every five minutes. The product design can thus be subtle. The ramp requirements may not truly satisfy the required confidence level since the capabilities secured for the next ten minutes can be deployed in the dispatch after five minutes. This paper is on the analysis and design of reliable and efficient ramp capability products. Our idea is to add ramp requirement constraints looking five minutes ahead on top of the existing requirements ten minutes ahead. To explore cost minimization, however, the total dispatch costs over a design horizon depend on the embedded optimization of real-time dispatches. Simulation-based optimization is thus used to mimic real-time dispatches. Numerical results show that the net load variations and uncertainties are effectively managed at the minimal costs.