Cloud speed impact on solar variability scaling – Application to the wavelet variability model

The Wavelet Variability Model (WVM) for simulating solar photovoltaic (PV) powerplant output given a single irradiance sensor as input has been developed and validated previously. Central to the WVM method is a correlation scaling coefficient (A) that calibrates the decay of correlation of wavelet modes as a function of distance and timescale, and which varies by day and geographic location. Previously, a local irradiance sensor network was required to derive A. In this work, we determine A from cloud speeds. Cloud simulator results indicated that the A   value is linearly proportional to the cloud speed (CS): A=12CS. Cloud speeds from a numerical weather model (NWM) were then used to create a database of daily A values for North America. For validation, the WVM was run to simulate a 48 MW PV plant with both NWM A values and with ground A values found from a sensor network. Both WVM methods closely matched the distribution of ramp rates (RRs) of measured power, and were a strong improvement over linearly scaling up a point sensor. The incremental error in using NWM A values over ground A values was small. The ability to use NWM-derived A values means that the WVM can be used to simulate a PV plant anywhere a single high-frequency irradiance sensor exists. This can greatly assist in module siting, plant sizing, and storage decisions for prospective PV plants.

► The scaling (A) of correlations between pairs of sites is examined in detail. ► A   is found to be linearly proportional to cloud speed, with the equation A=12CS. ► Cloud speeds are found from numerical weather models. ► WVM simulations of PV output closely match RR statistics of measured power.