Ramp Requirement Design for Reliable and Efficient Integration of Renewable Energy

With increasing renewable penetration, several ISOs are instituting ramp capability products to manage the operational challenge of balancing power in real-time. For example, in MISO's plan, ramp capabilities would be secured 10 min ahead based on the Gaussian-sigma rule (2.5 standard deviations for 99% confidence level). These products are used to manage both net load variations (foreseeable changes) and uncertainties (unforeseeable changes) through economic dispatches every 5 min. Ramp capabilities secured at time t may not be available to meet the uncertain net load at after the dispatch at t + 5 min. As a result, the required confidence level may not be satisfied. Also, the Gaussian-sigma rule is for reliability only, and might not be cost efficient. The requirement design can thus be subtle. This paper is on the analysis and design of reliable and efficient ramp capability products. To truly satisfy the required confidence level, our idea is to keep enough of the ramp capabilities secured at t for t + 10 min by adding constraints on the dispatch at t + 5 min. Moreover, costs are minimized by selecting the proper number of standard deviations through simulation-based optimization. Numerical results show that net load variations and uncertainties are effectively managed with significant cost savings.