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 Exceeds Expectations!

As a brand-new owner of a solar electric system, of course I want to know how it is producing — whether it is on target for producing 90% of the expected electrical use of the house.  The good news is that it’s on track for 100%!  I say this with only 6 weeks of data to look at.  What makes this estimate seem reasonable is the fact that the Autumnal Equinox is within those 6 weeks.

One of the biggest factors which affects the electrical productivity of a solar PV system is the length of day.  The longer the time of daylight, the more energy that is produced. In Seattle day length varies from a maximum of 16 hours in the summer to the minimum of 8 hours in the winter.  Midway through the year at the start of Spring and Fall, the day and night is about equal, at 12 hours of each.

You can never really know exactly how much electricity a solar PV system will produce in a year until it has produced it.  And it may vary year by year because of other factors, like weather and dust and debris accumulation on the panels.  However, in an attempt to predict how our new system is doing, I have taken a sample to extrapolate.  I chose Sept 7 through Oct 6, a 30-day period with the Autumnal Equinox in the middle of the time period.  The graph below shows the length of day and night on the 21st day of each month and the sample range between the red lines.

Amount of daylight for "average" month

30-Day Period (Sept 7 thru Oct 6): Averaging approximately 12 hours of daylight each day

During this 30-day sample period, the system produced a total of 433 kWh.  The best day produced 19.2 kWh, the worst day only 3.9 kWh, the average was 14.4 kWh.  Assuming this period is an “average” month for daylight, by multiplying this value by 12.16 (to get the 365 days of the year), it would seem to indicate the annual electric production potential.  This would mean annual production of 5,265 kWh.  That’s 100%!!!

Looking at one year of utility bills, the annual electrical use was 5,242 kWh.  The solar PV system was originally designed for an annual target of producing 4,536 kWh, or 90% of electrical use. But the installers unexpectedly upgraded a few panels to higher efficiency panels.  And could it be that September being historically the driest/sunniest month of the year in Seattle it’s not an “average” month for weather?

Call me an opptimist, but it’s fun to think it may turn out that the house electricity is 100% solar!  Net Zero Energy, here we come!



Oh, the joy of seeing the electric meter run backwards!

There are 3 major benefits to having a grid-tied solar electric production system, rather than being totally “off the grid”:

  1. You don’t have to purchase and maintain a set of batteries (save money!).
  2. You don’t have to find a place in your house to put all those batteries.  (save space!)
  3. You get the joy of watching your electric meter run backwards (joy!).

“Net Metering” is an energy swapping deal with the electric utiltiy company.  They take your extra electricity when you don’t need it, and they give it back to you when you do need it.  When your solar PV system is producing more electricity than you are currently using, the extra energy goes onto the utility power grid.  The electric utility company then sells it to your neighbors.  Then when you are using more energy in your home than the solar PV system produces, the extra energy you need is pulled from the from the grid.  The electricity you buy from the electric utility company at that point is free — until you run out of your solar production credits.

You’ll tend to produce extra during the daytime, and draw on your credit at night.  Overall you’ll be accumulating credit during the summer, and drawing down your credit through the winter.  In Seattle the days are so long during the summer that it produces enough during those few months to power a house through the rest of the year — even if the rest of those months are dark and rainy.

I have personally found the joy of seeing the electric meter run backwards so satisfying, that I have noticeably changed my electric use habits almost overnight.  I am much more conscious of my energy use.  I am much more likely to turn the lights off when I don’t really need them — when I can see by the light coming through the windows.  Our system was designed to meet 90% of the expected annual electrical use of the house.  I’m finding myself semi-consciously motivated to have this 90% system cover 100%.  It’s a bit irrational, but even when I’m somewhere else I find myself turning lights off!

Experience the joy for yourself!  Watch how it looks when the electric meter runs backward.  Click below to see a 25-second video:

Net Metering – meter running backwards!

Net Metering

Click to see the video of the meter running backwards!