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.
