An ISO scheduled its Real-Time Market using forecasts of demands and forecasts of the maximum dispatch limits of renewable resources that depended upon weather conditions. These forecasts were subject to uncertainty.

The ISO would set a binding dispatch for resources within their forecast limits in the upcoming real-time market dispatch interval to meet forecast demand in that interval. In dispatching the system for the current market interval, the ISO also considered the need to position the resources so that they could be dispatched within forecast limits to meet forecast demand in the subsequent dispatch interval.

This is a deterministic optimization problem that could be solved by existing market optimization software. However, demands and dispatch limits of renewable resources are subject to random changes when the subsequent dispatch interval arrives. If the conditions changed from forecast conditions after the first dispatch interval, the ISO often did not have sufficient unloaded rampable capacity for the market to respond to the changes in forecast conditions in the subsequent intervals. This led to transmission constraint violations and corresponding spikes in market prices until the ISO could adjust its dispatch to meet the new forecasts.

We reformulated the ISO’s Security Constrained Economic Dispatch (SCED) to reserve rampable capacity on resources in the current SCED run to maintain rampable capacity that would enable the ISO to adjust its dispatch in subsequent intervals after random changes from the current forecast occur.

The reformulated SCED considers the costs and benefits of holding rampable capacity to meet random changes in the forecasts in the subsequent intervals.

This essentially developed a new ancillary service product for rampable capacity that was reserved by SCED. We also formulated constraints to address the deliverability of the rampable capacity procured in SCED considering transmission constraints.

The Rampable Capability Product was implemented in the ISO’s Real-Time Market. Experience showed that it resulted in lower costs, improved reliability, and improved pricing.

Another ISO later worked on implementing a similar product in its market. We worked with a participant in that ISO to ensure that the lessons learned in the other ISO were taken into account in developing the product in the new ISO.