9 Years of Solar

I just recently got my annual true-up bill for the net metering for the year and I owe $237.80 for the entire year. I have had a set of solar panels on my house now for a full nine years.  For 6 1/2 years, I have been powering Teslas with the panels. The diagram to the right shows a summary of the annual electricity charge or credit.

Summary of Annual Energy Bills

Summary of Annual Energy Bills

Last year my bill was $80 less, but in 2014, I traveled across country in the Tesla for an extended period of time.

Panel Cleanliness Test

I have paid to have my solar panels cleaned in the past.  The roof is very high and quite a challenge to get to the panels.  I’m not particularly fond of the challenging maneuver from the ladder to the roof, so I’d rather pay a professional a modest fee when needed.  He uses a soft brush and de-ionized water.  But I can quickly monitor the cleanliness of the panels on line before making an appointment.

The amount of energy I generated in early October is the same as in 2014.  In the graph below I just do a quick comparison of the amount of energy generated during an interval on a sunny day during the same time of the year when there is little to no use of electricity.  The panels may be a little bit dirty due to the extreme drought, but some El Niño rains should soon wash away any  dirt.

Year to Year Interval Energy Production Comparison

Year to Year Interval Energy Production Comparison

Free Energy in 2017 Onwards

I have only two more years to recoup the initial investment.  This calculation is extremely difficult as the electricity rates are very complex and constantly changing.  I’m assuming unless things change drastically my energy will be free in late 2017.  The panels themselves have a 25 year warranty but the inverter is out of warranty.  I may incur a cost at some point due to equipment failure.


Just recently, PG&E has managed to increase our minimum charges from just under $5 to a little over $10.  This monthly charge is our cost to be hooked up to the grid.  The only alternative would be an off grid solution which would be really challenging here as the solar production is so much lower in the winter due to the sun angle.    And the electricity use is relatively flat because the climate is so pleasant and the house well built and insulated, the air conditioner is only on a few days per year.  I have no use for a Powerwall.

Only two more years to drive and live on sunshine for free, or $10 a month.


3 thoughts on “9 Years of Solar

  1. Very interesting. Now do you think cleaning had an effect and how much? I am in my first year of solar since last mid-May, and am surprised how much less electricity is generated in the winter months, but am pretty sure that I will catch up pretty well in March and April. Here is my monthly generation in kWh for 2015 in northern california:

    Jun 15 1810.747
    Jul 15 1804.655
    Aug 15 1655.614
    Sep 15 1254.414
    Oct 15 1026.196
    Nov 15 772.375
    Dec 15 520.202

    Since I drive a VW e-Golf with a 24kWh battery about 13,000 miles per year, we spend about 270kWh per month on average, but a significant amount of the remaining energy goes towards washer/dryer/dishwasher/kitchen electric range and especially in the summer, air conditioning.

    I find the PG&E power consumption web site very interesting too, which shows me that we overproduced pretty well in June, July and August but started eating away at that accumulated credit from September-today and currently still have credit for about two months at Decembers consumption rate. Assuming production starts going back up in March, we should be good and be able to cover the $10/month connection charge.

    If it wasn’t such a huge investment I would augment my gas furnace with an electric heat pump system to more effectively use electricity for heating in the winter, too…

    • If you look at my earlier reports from years past, it shows that cleaning did work wonders once, but that right now I don’t need it. You can monitor your usage year to year. Check out more details from earlier blog posts.

      Depending upon where you live though, cleaning may have a bigger benefit than mine. I live on the western slopes of the Bay area and don’t have a lot of pollution of any kind hitting my panels (air, car, or even leaves).

      The problem with a solar pump for the gas furnaces is that you want them really in the winter when the sun is weak. So that calculation is going to be hard to figure out!

      • I have my solar system grid-tied through net metering so to consume the excess electricity I fed in at summer time later through the heat-pump in the winter wouldn’t be an issue. The real issue is that the installation of one is still so expensive, basically replacing the air conditioning and gas furnace with a new one that includes the heat pump feature, like a reverse air conditioning in the winter bringing heat in and cold out. Probably the better bang for the buck for now is to get some window maintenance done and wait with replacing AC/heater until it actually needs to be replaced.

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