Wednesday, December 28, 2011

Results of a full year of solar electric (photovoltaic) panels on our house

It's been sixteen months since we installed solar panels on our house. A number of people have asked what our experience has been and I'd like to report this in figures and pictures as an update from my blog in September 2010. Here are the key figures:
  • The system was estimated to produce 4.73 megawatt-hours; actual production was 6.56 megawatt-hours. I believe that much of this is due to the Enphase microinverter technology.
  • Our electric bill dropped from 2,244.25 to 465.57, a savings of 1,778.68. Note that the $465 number is a bit more than the PG&E bill I copy below: there is a $12.03 monthly access fee as well.
The bottom line is that this system will pay for itself in approximately 13 years.
I've attached a bit of backup information below for those of you that enjoy the detail or are considering taking the plunge yourself.

First is the summary bill from PG&E for a year of electricity. You move to an annual cycle with a true-up at the end of the year. Note that we were still overall consumers, but provided electricity back to the grid during peak times in the summer: those are the negative numbers in November through May.

The summer solstice is peak generation time. I have captured a graph of my energy production on that top day and show the panels at the peak production time of the day.

Below is a graph of the total energy production of the array. Note that the graph is sinusoidal, except for the days that clouds moved in to cut production.

The figures go on to say that we have saved 5.6 tons of carbon from entering the atmosphere. While that certainly does not put us at a zero carbon footprint, it is good to know that I'm helping to save the environment while saving money.


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