Monthly Solar Production – October 2012


It looks like October’s production pretty much matches February’s, my first good month. In February, my solar panels produced 14.45 kWh per day while in October, they produced 14.48 kWh per day. I also went over the $1,000 mark in electricity savings, which I’m very happy about with another month still to go to hit the one-year mark.

However, this figure is slightly misleading since I was still on NStar’s 100% Green program for the first 5 months with my panels. Which is why I saved $86.87 in February but only $67.32 in October. In fact, if you assume that I was not on the program for the entire year, my savings would only amount to $881 with one month to go. So it does not look like I will hit the $1,000 savings mark in future years.

Here’s the updated numbers:

Period Ending Production As % of Usage Savings
Dec 21, 2011 223 kWh 32.5% $45.05*
Jan 24, 2012 288 kWh 34.5% $59.26*
Feb 23, 2012 419 kWh 72.2% $86.81*
Mar 23, 2012 484 kWh 87.7% $106.48*
Apr 24, 2012 663 kWh 110.4% $145.86*
May 21, 2012 536 kWh 107.4% $81.62
Jun 22, 2012 707 kWh 113.5% $107.72
Jul 23, 2012 767 kWh 75.1% $116.86
Aug 22, 2012 660 kWh 67.9% $98.93
Sep 21, 2012 616 kWh 77.6% $92.34
Oct 23, 2012 449 kWh 69.7% $67.32
Overall 5,812 kWh 74.5% $1,008.35

*NStar 100% Green Energy rate

If there seems to be some inconsistency, it is due to monthly usage fluctuations, the number of days per billing period and NStar price changes.

Well so much for the good months. I expect the next three months’ production to be pretty dismal. But it was a nice run as I had 9 straight months producing over 2/3 of my electricity usage and it should leave me at over 70% after an entire year.

It is more than I expected when I started and I am very pleased.


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3 thoughts on “Monthly Solar Production – October 2012

  1. If this is an inappropriate question for this site please ignore. How do you tell what percentage you are generating? I’m in WMass and WMECO bill will tell me what I generated for them and what they supplied for me but then there is the energy I generated and used. I have electric bills going back 4 years so I can average what I used in that time compared to what I’m paying WMECO now, rough Idea, but not exact. Thanks

  2. I get my generation data from my Enphase micro-inverters. When you owe money on your electric bill, it’s simply what you generated divided by (what you generated plus what WMECO supplied).

    When you have a negative electric bill, take the dollar amount that they credited you and add to it their flat monthly fee (NStar’s is $6.43). Then take that and divide it by the electric rate to determine how much extra electricity you generated that you didn’t use. So if you subtract that from what you generated, you can figure out how much you used. Then just divide what you generated by what you used (it will be over 100%).

    I actually just realized that I had forgotten in my calculations to add in the monthly fee for when I had negative months. I’ll update that next month.

    So thanx for posting, Miles!


  3. The formula is quite simple.
    (KWHs produced) + (KWHs purchased from utility) – (KWHs sold to utility) = (KWHs used)
    I determine the production reported by my system for the billing period. I add to that the amount I had purchased in the same period. Then subtract the amount I sold to the utility. That is exactly what I used for that period. The key is knowing your sytems production for the period. If you only have I production meter with no history, then you could use the numbers from the monthly production reports you send to the Production Tracking System.

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