Monthly savings - help validate my thought process

Leprechaun Registered Users Posts: 6
System: 10KW using 39 Suniva 260W panels and Enphase M215 microinverters.

I now have 5 full months of production that I have been tracking. Each month, the goal is to determine what the electric bill would have been if I didnt have the Solar PV system.

The most recent month was 33 days from 6/12 through 7/14 and a billed amount of $179.72 for a net of 1,393 KWH. Based on the Enphase Enlighten monitoring site says my system produced 1,506 KWH for those 33 days. So I estimated actual energy consumption at 2,899 KWH whether I had the solar system or not. At 2,899 KWH the bill from Duke Energy would have been approx. $380. If this thought process is valid that is a savings of $200 for that period.

Is this a valid thought process? See the attached PDF documents for the details.



  • NorthGuy
    NorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Monthly savings - help validate my thought process

    You need to subtract amortization costs for panels, inverters, and installation plus maintenance costs. Then you get savings.
  • Photowhit
    Photowhit Solar Expert Posts: 6,001 ✭✭✭✭✭
    Re: Monthly savings - help validate my thought process

    Something is hinky with your math. If you had no fixed/billing cost, the flat charge before you buy any electric, you per Kw hour charges are a bit over 13 cents for 2899Kwh and a bit under for 1393Kwh. Perhaps they charge more for over 1000Kwh or some other anomaly, but other wise it should be less once you take out the fixed costs.

    I checked out the PDF and that is indeed the case, looks like the monthly is correct, just figuring your system costs as Northguy suggested.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • Leprechaun
    Leprechaun Registered Users Posts: 6
    Re: Monthly savings - help validate my thought process

    Yes Photowhit, Duke charges a lower rate for the first 1,000 KWH approx 10.4 cents per KWH before taxes.

    My calcs were intended to compute gross savings before the system costs. My goal was to save $1,800 to $2,000 per year. That would put my payback around 10-11 years.