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home > solar power
Installing a grid intertied
solar electric power system

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Overview System
Financing Panel
Hardware Grounding Rail


On average I use from 15 - 30kWh/day.  This powers my home, charges my Chevy Volt (around 10kWh/day) and home based business and relevant equipment.  For reference, average US homes consume upwards of 25 kWh/day.  If we were to eliminate all the business usage I believe I would average below 13kWh/day.

The design goal of the system is to generate some surplus power in the summer months and much less in the middle of winter, averaging about 80-90% of my needs annually.  The 31 - panels produce 5.8kW of power in theory, but that ideal performance is derated due to orientation and efficiency issues so the actual peak power is 4.5kW in the summer.  As I observe the overall power over months, the seasonal variation of available sun hours becomes quite clear (see Lifetime Energy below).

Current local conditions Live web cam view

(if image is black - it's dark outside)

The chart below shows the estimated power that my solar panels should generate based on calculations (see bottom of page) 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 (above).  I update the graphs in the middle of each month after I get my utility bill.

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 small electric heaters to supplement the propane and wood stoves when outside temperatures stay below 20F for weeks.  When I purchased the 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 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

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 Chevy Volt uses 3-400kWh/ month year round, and the house about the same - but both have seasonal variations that increase in winter.

In the chart below, blue shows energy imported, yellow solar energy produced and green is the net amount I'm billed for.  As you can see it goes negative in the summer as I accumulate credit that gets used up in the Fall.


Here is the chart generated by the PV Watts calculator:
PV Watts results


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