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



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Overview System
sizing
Financing Panel
Siting
Hardware Grounding Rail
Installation
Inverter
Installation
Panel
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REAL TIME AND HISTORICAL STATS

On average we use from 15 - 30kWh/day.  This powers our home, charges our Chevy Volt (around 10kWh/day) and 2 home based businesses with all the computers 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 we 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 our needs annually.  Our 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)


ESTIMATED vs ACTUAL STATS
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 actual energy produced is obtained from 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.


Our electrical power usage varies a lot due to variations in our business use of energy intensive tools, lighting and computers.  Energy consumption also peaks in the winter when we use small electric heaters to supplement our propane and wood stoves when outside temperatures stay below 20F for weeks.  When we purchased the Chevy Volt in May 2012 our monthly usage went up by around 300kWh/month.
date panels
installed
Watts/
panel
  Total
panels
Total
Watts
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



Chart shows power imported from utility in blue, and the net power we used from the grid after factoring the solar power we exported back to the utility (for full retail credit under the Net Metering contract we have with the utility).  Basically, the chart shows how much energy we saved by using solar power, which is clearly more in the summer months.  We get about 1/3 of the solar energy in the winter compared to the summer.  About 10kWh on a sunny day in winter compared to a peak of around 30 kWh/day in the summer.



Electric rates have been dropping lately.  In 2010 we paid around $.15/kWh, in 2013 it is now around $.13/kWh

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