Is a solar system for me?
Some Rules of Thumb:
Grid-Tie:
If you have state incentive paying half the cost of
a PV system, the system does pay for itself in 15-25 years, depending
on your electric rates. Financing the system will help make it comparable
to an electric bill. Battery backup adds considerable cost to smaller
grid-tie systems, but is easily incorporated into larger ones. This
will change as more advanced small inverters become available.
One quick formula (sorry):
2.2kW grid-tie system - does it pay?
Assume 4 avg hours sun per day:
4 X 2.2kW = 8.8 kWHr/day
20yr X 365 days X 8.8 = 64,240 kWHr/lifetime
If the system costs $16,000:
$16,000 / 64,240 = 25 cents / kWHr
With a subsidy:
$8,000 / 64,240 = 12.5 cents / kWHr
12.5 cents per kWHr is comparable to grid electricity.
Of course there are "real life" factors which complicate
this, and subsidies have to come from somewhere.
Load analysis usually will show an even greater payback
from improved efficiency, such as compact fluorescent bulbs.
Off-Grid:
If you are one-half mile or more from a power line,
a PV system will be cost-effective. If you have a lot of electrical
loads, the break-even point may be one or two miles. We are almost
4 miles from the power line and in our case if we had 4-6 people
to split the cost, grid power would have been reasonable. We put
in an off-grid system for $15,000, vs. probably $80,000+ for grid
power. The only load we have a problem with is tractor block heaters
which drain the batteries because of the length of time they are
on. We use a generator for that, and a heated garage would solve
the problem.
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