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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

To design a solar power system you first need to know how much power you use.  Actually before that you need to really work at reducing your usage so that your system costs will be lower.  My wife and I have already done all we can think of to reduce our energy footprint - read more about that on my Sustainable Living page.  By reviewing my past 12 months of electric bills I learned that we use an average of 550 KWh/month.  This is pretty good considering that we both have home businesses which use computers and equipment.  As a frame of reference the average US household used 880KWh/month in 2006.  Take a  look at your recent electric bill and see how your home stacks up - there may be room for improvement!

So using 550kWh as a design goal was the starting point.  For reasons that date back to off-grid solar houses that ran on DC and batteries, solar systems are rated in the total KWh capacity of the solar panels and not the AC power produced.  Since the inversion process is inefficient there is typically a derate factor used to calculate the AC KWh of a given solar array.  This is typically calculated at .77.  So a 1 KW solar array will yield about .77KW of usable AC power.  However the Enphase micro inverters I plan to use have better efficiency that is calculated at .819 - a significant improvement!

The US National Renewable Energy Laboratory has a web site tool called PV Watts that allows you to calculate the performance of a given solar array based on solar wattage, it's location, climate, tilt, orientation and capacity.  By trying a variety of panels of different wattages and quantities (see panel siting) I settled on an initial price performance trade-off of using 21 175 Watt BP 175B panels that produce a total of 3675 Watts at the panels.  That translates into an annual production of around 3923 KiloWatts of AC power depending on weather variables.  (I have added panels over the years since the original installation - see below)

Here is the result of the PV Watts calculations showing the estimated monthly AC energy production for the current array (29 inverters).
PVwatts table

Note: I have been adding panels as I can afford them:
added 2 175W panels: Aug. 22, 2010
added 2 175W panels June 29, 2011
added 1 180W panel July, 2011
added 3 230W panels June 2012
added 2 245W panels March 2013
added 1 245W panel on house October 2016

See the next page for more details of the system performance and costing.  Click here to see current  and historical performance charts since my system was installed.

September 2011.  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 by up to 8%.  So this validates my decision to invest in Enphase inverters.

Below is an updated system diagram as of June 2012, click on the image to download a full page printable pdf version.
Complete solar power system diagram
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