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What Does PV Really Cost?
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QI have located several calculators to assist in sizing a potential solar energy system. However, the result- ing information varies greatly. Would you have a
suggestion of an online calculator that would give a general
idea for size and cost? — Jim Neville, Oklahoma City
AOnline solar calculators, like those at nrel.gov/ rredc/pvwatts and FindSolar.com, can accurately calculate the size of the array you need. But they
forecast widely varying costs and payback periods, because
they often lag by weeks or months in accounting for changes in local incentives and in market prices for photovoltaic
(PV) equipment. Moreover, they often use different interpretations of accounting rules for internal rate of return
(IRR), discount rate, opportunity cost and the like.
Denis Oudard, president of Bay Pointe Solar in Louisville, Ky., chairman of the Kentucky Solar Energy Society
and organizer of the Louisville Solar Tour (denis.oudard@
baypointe.biz), holds an MBA from the University of Chicago. Once you’ve figured out the system size, he suggests
checking with local installers for current equipment costs.
Then, he says, keep return-on-investment calculations simple. “You could take into account only the amortization of
JERRy W. LEWiS
58 April 2010 SOLAR TODA Y solartoday.org
With a body temperature
of 101°F ( 38°C), the dog can
be applied directly where
needed. For instance, it can
be comfortably located
directly on your feet, or
even under the covers.
the equipment each year,” he writes.
“Let’s say your investment is $30,000 after incentives,
with straight line depreciation over the 30-year life of the
equipment, or $1,000 per year. Then compare that to
the revenue stream. This would enable you to take into
account the opportunity cost. The other issue is the risk-
adjusted return. Investing in the production line to make
a car, for instance, has a huge potential for downside, and
it’s almost impossible to calculate the risk. So it’s hard to
get investors to look at the venture unless the IRR shows
marvelous returns. In the case of solar, the sun is going to
come up every day, so there is practically no downside.
It’s like buying a bond, but one that returns 12 percent.
It’s the safest, highest-return bond anyone will ever have
an opportunity to see.”
Qi’ve heard the expression “Three Dog Night” refers to staying warm through a winter night. What is the actual heat content of a mutt? —
Nanook du Nord, Nome, Alaska
AEvery mammal generates heat from metabolism. It appears that a 40-lb (18-kg) bag of kibble has roughlythe same British thermal unit (Btu)content
as 32 lb ( 14. 5 kg) of firewood.
Sameer Aidoor, an electrical engineer and exercise physiologist, notes that a 115-lb (52-kg) herding dog metabolizes 3,500 kilocalories over 24 hours, derived from roughly
This may not sound competitive with
the space heater, but remember that the
dog doesn’t have to heat the room air. With
a body temperature of 101°F ( 38°C), the
dog can be applied directly where needed.
For instance, it can be comfortably located
directly on your feet, or even under the covers, where the space heater would be impractical. Moreover, at 11 cents per kilowatt-hour, the space heater costs about $1.30 to
run for eight hours, whereas the kibble to
operate a dog for the same time costs only about 24 cents.
You could operate up to five large dogs overnight for the
cost of running a single space heater.
If you don’t have access to a Newfoundland, two 60-lb
labs or three 40-lb spaniels will do even better, because you
could sleep between them. Of course, like firewood, the
dogs must be dry to heat efficiently. —ApRiL FuEL