September's solar generation stats

We have a 2kW 8 panel solar array (Panasonic HIT panels), mounted on a south-facing roof at approximately 35-40° angle from the horizontal, which were installed at the end of August 2013.

This is the results from the first month of year 2!

To calculate a revised forecast for 2014-15, I took the total actual generated amount for the year 2013-14 (1929kWh), reduced it by 1% (1909kWh) to account for the predicted degradation of generation from the panels (see previous blog entry) and then divided it up proportionally based on the actual monthly generation results from last year.  These values are shown in green as the forecast amount for this year in the chart below, with September's actual total included:

The forecast based on last year's generation is 158.61kWh for September, but we've actually pulled in 205.13kWh for September 2014, 29% higher than expected. The only explanation for this is that September this year was sunnier than September last year.

With 420 hours of daylight in September (sun up to sun down for all 30 days), the average kWh generated per hour of daylight this year was 0.49kW, compared with 0.37kW from last September.