An Analysis of Storage Requirements and Benefits of Short-Term Forecasting for PV Ramp Rate Mitigation
Daniel Fregosi, Nicholas Pilot, Michael Bolen, William B. Hobbs
Abstract
As renewable energy penetration on the grid increases, requirements are being placed on PV owners and operators to limit power ramp rates. PV power ramping is an issue for grid stability because generation load balance must be continually met. When a large PV resource significantly increases or decreases, another resource must compensate. To aid in grid stability, ramp rate limitations have been imposed on PV plants. This article addresses how much fast-responding storage is needed to mitigate high ramp rates of PV plants, and how much benefit is there from short-term power forecasting in terms of reducing the storage requirement. The results provide a baseline estimate for system planners and designers. Furthermore, the storage controller design and optimization are given, along with the open-source code, such that others can tailor the simulation to their specific plant and weather profile. Results from studying a 100 MW PV plant power production profile show a reduction in ramp-rate violations from 10% of yearly intervals to below 1% with 12 min of storage. With forecasting, the same level of smoothing is achieved with a 5-min rated storage. A sensitivity analysis shows the impacts of varying constraints, such as storage power rating, PV system size for geographic smoothing, forecast window length, and the ramp-rate limit magnitude.