First Solar Year!

It’s official!  It has been over one year since we installed a solar electric system on the house.  It has been quietly working away producing electricity every day, with virtually no technical problems.  So far, so good!

We were not quite net-zero on electricity this year.  Energy use in the house was higher than normal and the energy production was about 11% lower than expected.  Perhaps the lower production was due to the record-breaking rainy spring this year.  But even so, the Washington State solar incentive for the 4.034 kWh produced will reap a bonus of $605 in addition to the free electricity.

System Rating Average production if in Germany 3.680 kWh
Expected Target Average production for Seattle 4.536 kWh
Actual for First Year Production for year ending 8/31/2013 4.034 kWh

Daily energy production varied quite a bit all through the year, depending on weather and day length. The peak production day this year was 25.5 kWh on June 18, 2013.  The lowest day produced a mere 0.3 kWh on November 19, 2012.  The daily average through the year was 11 kWh. The chart below shows the overall energy production pattern, as well as the variability.

Graph of first year energy production

Solar electric production chart 9/1/2012 to 8/31/2013

Now we begin another year. Hopefully by the time we complete the next lap around the sun, we’ll have a better idea what it will take to be net-zero for electricity–or even a completely solar-powered home.

Solar Electric Production in Rain or Shine

What is the difference between a sunny day and a cloudy day?  Up to four times the amount of solar electric power!!

Here is a comparison of two days in August with very different weather.  On August 13, 2013 there were clear blue skies all day.  Two days later on August 15, there were dark clouds and rain all day.  Although the day length was almost identical, the solar production was dramatically different, as this graph below shows.

Solar power rain or shine

Side-by-side comparison of power production for sunny day and dark cloudy day

The clear-sky sunny day produced 21.4 kWh of power, with peak production of almost 2800 watts.  The rainy day with thick dark clouds 2 days later produced only 5.1 kWh — about one quarter of the power — with peak production of 1100 watts.  Not every rainy day is as dark as it was on the 15th and even then there was decent power production, but clearly clear skies makes a big difference.

Solar Electric Report for a Rainy Spring in Seattle

The Spring report is in… and it’s showing lower-than-expected solar electric production for the sunny side of the year.  Could this be caused by the almost record-breaking levels of rain during the month of April?

Solar electric production from March 22 through June 21 this year was 1,464.04 kWh (1.46 MWh).  This means an average of 15.91 kWh per day during this 92-day period — considerably less than the 24 kWh average daily production I had predicted in an earlier post.


The peak production day was 25.5 kWh on June 18.  The lowest day was April 27 with only 3.38 kWh of electricity produced.  Seattle got almost 6 inches of rain during the month of April — twice the recorded average for April, and just shy of breaking the recorded-history record of 6.53 inches.  Even the month of May had more rain than average.  The question is, what was June’s excuse?

Spring Solar Electric Production
A chart of solar electric production between March 22 and June 21, 2013.