Planning a renewable energy system is a relatively strait forward procedure.

     First thing you do is determine your average power usage for the whole year. My utility bill has that information printed on it.

     For instance my last year's total usage was 30232 kwh (KiloWattHours). That was for a leap year.

         30232/366 days = 82.6 kwh per day.

 Divide that by 24 hrs/day and you get 3.44 kw/hour.

That's like having 34ea 100 watt bulbs plus a 40 watt bulb burning continuously.

     That's the average continuous usage for my house. If I were to generate 3.44 kw per hour continuously into a net metered system for the above year then my electric energy usage from the electric utility would be zero.

     Now suppose my location averaged only 275 days with 10 hours of available sunlight. How much energy would I have to generate to meet my house needs?

         30232 kwh /275 days = 109.93 kwh per day

     Divide by 10 hrs give you 10.993kw/h

Now you're looking at an eleven kwh average system if you wanted to be energy independent. That's 3.2 times larger generating capacity than the average use.

     I am currently paying $0.0902 per kwh to my utility company. That would be my savings for every kwh that a home system would give me.

     If I were to install a net metered solar pv system   ( 16 solar pv panels at $800/panel) that delivered 2.56 kw for 10 hrs for 275 days a year then my yearly savings would be:

2.56kw x 10hrs x 275days x $0.0902 = $ 635.01/year

     With the 30% Federal tax credit, it would take
   16 x $800 x 0.70/ $635 = 14.11 years to break even.

     Consider that the cost of public utility electricity is continuing to rise but the home system efficiency will drop about 20 % in 25 years. (That's less than 1% a year.) Your cost for electric service will likely rise at a higher rate than that.  As long as you are connected to the public utility electric grid you will always have a residual expense for the connection.

     You will have to make your own calculations to determine your probable annual savings. I live in the Blue Ridge Mountains of Virginia. Your weather and utility rates may be different from mine.

After Thought

     One axiom I learned in engineering school was "NEVER DESIGN A DWARF.  NEVER!" because the bean counters will take that dwarf and likely trim it to the point where it won't be efficient or effective. When you plan, I'd suggest you plan long range for your eventual  independence from the electric utility grid system.

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Karl Kinkel - President
Karl Kinkel, President & Founder
Longsgap Services LLC
5262 Elk Creek Pkwy
Independence, VA  24348
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