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home > solar power
Installing a microinverter based
solar electric power system

See more details on my blog
Overview System
Financing Panel
Hardware Grounding Rail


I have 39 solar panels installed ranging from 175 W to 375 W per panel.  In 2021 I installed heat pumps in both buildings and only use propane as backup, the trade-off of having these energy intensive devices is I have a significant electric bill in January February and March that runs to many hundreds of dollars due to the low solar production here in Maine.  However, from May through December I only pay the utility for connection fee.  In the late summer and fall I accumulate kilowatt hour credits that are applied to my bill in the winter.

The statistics shown come from my Enphase energy monitoring system data that I put into a spreadsheet to create the charts below and also from my electric bill.

Click here to see live and historic energy production

The chart below shows the estimated power that my solar panels should generate based on calculations from the PVwatts calculator provided by the National Renewable Energy Labs.  The calculations factor in weather data from the nearest reporting weather station to account for seasonal overcast.  The actual energy produced is obtained from my monthly reports provided by the Enphase Enlighten web interface (the real-time performance data from my microinverters).  I update the graphs in the middle of each month after I get my utility bill.

In the chart below actual usage lags behind the estimated due to the discrepancy between monthly estimated data and the billing cycle that ends mid-month.

Enphase have released a study showing that their microinverters out perform PVWatts calculations by up to 8%.  They looked at regular string inverters and found that they underperformed PVWatts numbers by up to 8%.  So this validates my decision to invest in Enphase inverters.

My electrical power usage varies a lot due to variations in my business use of energy intensive tools, lighting and computers.  Energy consumption also peaks in the winter when I use the heat pumps - it stays below freezing for weeks here in Maine.  When I purchased my first Chevy Volt in May 2012 my monthly usage went up by around 3-400kWh/month.
date panels
September 2009 21 175   21 3675
August 2010 +2 175   23 4025
June 2011 +2 175   25 4375
July 2011 +1 180   26 4555
May 2012 Purchased Chevy 2012 Volt
(uses around 3-400kWh/month for charging)
June 2012 +3 230   39 5245
March 2013 +2 245   31 5735
October 2016 +1 245 32 5980
November 2017 Purchased 2017 Chevy Volt
April 2021 Installed Heat pump in house
November 2021 Installed Heat pump in workshop
November 2021 +5 375 37 7855
March 2022 +1 375   38 8230

solar power imort and esport chart history

The chart above shows power imported from utility in red, solar energy generated in yellow and net power in green Basically, the chart shows how much energy I saved by using solar power, which is clearly more in the summer months.  At my latitude in Maine USA (44 degrees) we get about 1/3 of the solar energy in the winter compared to the summer.  My 2017 Chevy Volt uses 3-400kWh/ month year round.  I added 2 heat pumps in 2021 which dramatically increased my consumption in the winter.

My utility info:

Banked generation for last 12 months


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