Solar Variability Model for PV Plant Design and Power Buffering

This work is now seeing major demand from solar developers who are scrambling to meet new ramp rate requirements. Any new utility-scale power plant operator needs to commit to limiting changes in output (‘ramps’) to 10% per minute - a tall order for PV where a single PV panel could fluctuate over 70% per second. The model - originally published in 2011 and since validated at Sempra Generation’s 48 MW PV plant in Nevada was recently enhanced by accounting for cloud speed. Model application is simple: input plant layout high resolution measurements from a single ground sensor and NOAA cloud speed. The wavelet variability model (WVM) then accurately simulates the ramps experienced by a power plant. Cloud speed can be obtained for the entire US and much of the Carribean from NOAA numerical weather prediction data. Applications: For example simulations for Hawaii show that a closely-packed quadratic 20MW plant would exceed the 10% per minute limit (corresponding to a 2MW change in power output per minute) on average 37 times per day. The maximum 1-min ramp rate over a year would be 8.6MW per minute.