Using PWS Solar Insolation to estimate apparent panel efficiency


I installed an Ambient Personal Weather Station WS-2000 about three weeks ago. The WS-2000 has a pyranometer which estimates the total solar insolation at its location. I have taken today’s (11/16/2018) measurements and used them to calculate an apparent efficiency for the array.
My system has two arrays consisting of 21 LG NEON Black 300 Watt panels tilted 20 degrees with 5 facing NE and 16 facing SW. I used the given dimensions for area 1.64 m^2 per panel. The standard efficiency of these panels is 18.3%. My results are shown in the attached graph. The calculation is simple and the factor can be determined by averaging the values of the Power_Out to the Insolation at each point of the plot. This average was found to be 6.85900. Using a second method of least squares fitting the factor was that shown on the graph or 6.81912. Using this latter determination the efficiency was estimated to be 19.8%.