Solar Electric Production on the Dark Side of the Year

Having a solar electric system is great during the sunny summertime, of course!  But what about during the dark rainy winter season?  Here’s a look at some of the data on our electric production so far, with a focus on the first half of the dark side of the year when the nights are longer than the days.

A Dark Quarter Data Sample

91-Day Data Sample (9/22 – 12/21): Equinox thru Winter Solstice

In brief, it looks like we’ll get 22% of our annual electric production during the darker half of the year. Between the Autumnal Equinox (September 22) and the Winter Solstice (December 21), our Enphase Energy reports show a total energy production of 477 kWh. That means a total dark-half production of 954 kWh — assuming the period between December 22 and the Vernal Equinox (March 21) is similar.  In a previous post, I estimated a total annual production of 5265 kWh (based on a 30-day sample around the Autumnal Equinox).  Logically, the sunnier half of the year should produce around 4311 kWh, or 78% of the annual production.

Enphase Energy Report 9/22-12/21

Electric production 9/22 – 12/21

Within the 3-month dark-half data sample there was a peak day production on Sept 27 of 15.1 kWh and low day on Dec 19 of 0.33 kWh.  The average daily electric production was 5.24 kWh — about enough to power a single 1970’s-era refridgerator (or 4 newer Energy Star models).  In contrast, the expected sunny-side average daily production will be almost 24 kWh.

In conclusion, don’t expect the electric meter to run backwards much during the off season.  But it’s still producing something usable — even during those dark rainy winter days.