The economic feasibility of small wind generators is compared to that of solar cells, primary batteries, thermoelectric generators, and engine generators. It is shown that small wind generator plants offer an attractive alternative to primary battery systems and constantly running engines to generate power in remote areas. The limitation is an annual average wind velocity of at least 9 to 10 mph. Presently available units are most useful in the average load range of 10 to 1000 watts

Dodge, R.

English

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ECONOMIC CONSIDERATIONS OF UTILIZING SMALL WIND GENERATORS
Robert Dodge
!
Pennwatt Corporation
Houston, Texas
Free power from the wind? The wind may be free, but certainly not
the power, as anyone knows who has tried to capture a few of these "free"
kilowatts.
The usual motivation for considering a small wind generator is
economy. That is, the prevailing notion is that wind power can be easily
exploited and, therefore, must be a most economical form of power genera-
tion.
The purpose of this paper is to provide a practise! guide to the
system designer to enable him to make a decision as to whether a wind
generator is a practical solution. Only small generator plants up to
5 kilowatts are considered.
If the object of considering a wind generator is economy, then the
designer should have an appreciation of the alternate power systems that
are available, the costs, and the pros and cons of each.
In our industrialized society, most inhabited areas have commercial
power, therefore, we can eliminate these areas from consideration. Even
those uninhabited areas where commercial power can be brought in reason-
ably are not good candidates for small-scale wind power generation.
These limitations do not mean that wind generators are not practical.
On the contrary, there are numerous applications in remote, isolated sites
where wind-power generation certainly does provide a practical solution.
A good example is the powering of marine aids to navigation signals. In
most instances, these lights and sound signals are situated at remote,
inaccessible locations. Other obvious applications are remote communi-
cation relay stations, weather data gathering stations, including weather
buoys, cathodic protection, and water pumping.
These are five possible solutions available today to generate power
in inaccessible remote locations: solar cells, primary batteries, thermo-
electric generators, wind generators, and engine generators. Figure 1
shows the relative economics of these alternatives plotted as dollars per
kilowatt-hour versus the average electrical load.
Of these five options, the primary battery is probably the least
understood but the most widely used. The primary air cell has been around
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for some 40 years, ever since it was used to power our first radios in
rural America. The air cell consists of a container with a zinc anode
and an air breathing porous carbon cathode. The cell electrolyte is
usually sodium or potassium hydroxide. These cells are characterized
by a very low self-discharge and can be employed in series and parallel
to provide up to several years of power. The cost of the cells yields
energy at about $12 per kilowatt-hour. The weight is approximately 11
pounds per kilowatt-hour.
The primary air cell can be used to solve almost any remote power
problem and, therefore, can be used as a basis for evaluation of any
other system. For example, a 1-watt load would consume 8.76 kilowatt-
hours per year. The cost of primary cells would be $12 x 8.76 = $105 per
year. The weight transported to the remote site would be 96 pounds.
These figures, although high per kilowatt-hour, are so reasonable that no
serious consideration of a more complicated system should be entertained.
The only possible exception would be where the cost of transporting the
batteries to the remote site is so high as to change the economics dras-
tically. In some cases where environmental considerations prohibit on-
site disposal of spent batteries, the additional cost of disposal would
also affect the economics.
The following assumptions form the basis for determining the costs
per kilowatt-hour shown in figure 1.
Solar cells:
Primary battery:
Thermoelectric:
Wind generator:
Diesel generator:
Amortization
Amortization
Amortization
Fuel
Amortization
Amortization
Fuel
Cells, 5 years
Batteries, 5 years
Housings, 5 years
Batteries, 1 year
Housings, 5 years
Generator, 3 years
Batteries, 5 years
25C per gallon
Generator, 3 years
Batteries, 5 years
Housings, 5 years
Engines and Generators,
2 years
Housings, 5 years
25£ per gallon
An annual interest charge of 8 percent is assessed to all systems.
All the systems considered are continuous power systems. Each is capable
of handling intermittent loads equal to several times the average. All
use battery storage to provide continuous power except the diesel gener-
ator. The solar cell economics were generated assuming a 30° latitude
and 10 days storage in the secondary battery. The assumptions for the
thermoelectric system were propane fuel from tanks, with the tanks
171
transported to the site. The battery storage is ten hours. The wind
generator system assumes a 10 mph annual wind velocity. The battery
storage is 10 days. All secondary batteries are industrial type, low-
discharge, lead calcium. The diesel generator consists of two complete
plants, housing, and automatic controls for unattended operation and
The amortization periods are conservative and no doubt proponents
would argue that their machines would or could operate much longer. How-
ever, no attempt has been made to add the cost of transporting equipment,
fuel, and men to the remote site. Obviously these costs could greatly
influence the cost per kilowatt-hour of any system. Since they vary con-
siderably with the location, each installation requires separate evalua-
tion.
The chart (fig. 2) shows clearly that for loads up to 10 watts, the
primary air cell has the advantage. In cases where transported weight is
a problem, the solar cell or small wind generator should be considered.
From 10 to 100 watts, either the thermoelectric or the wind genera-
tor are good selections. The wind generator has the advantage when
transported weight is considered.
The 100 to 1000 watt range certainly favors the wind generator. In
this range, the load is too light for effective use of a diesel genera-
tor, although at about 500 watts the diesel engine begins to look favor-
able. In this range the weight of propane for the thermoelectric
becomes unreasonable. A 1000-watt average load requires 12600 gallons
or 53000 pounds of fuel per year.
From 1000 watts and up, the diesel generator has a definite advan-
tage. True, the systems are complex and, hence, prudence dictates
redundancy. However, the low cost per generated kilowatt-hour makes
their consideration mandatory.
All the systems except the engine suffer from being modular. That
is, they consist of a parallel arrangement of units or cells so that in-
creasing their size by increasing the number of the same size cells af-
fords little saving per kilowatt-hour. It is the battery that is
required with the wind generator that causes the cost to level out at
about $1.50 per kilowatt-hour.
If the storage battery can be eliminated from the wind generator
system for applications such as cathodic protection, water pumping, or
possibly the electrolysis of water, the cost per kilowatt-hour is much
less. This is particularly true for larger machines. For example, a
10-meter machine could easily generate 12000 kilowatt -hours per year.
The cost of the machine and tower would be about $12000. Therefore,
using the same 3-year amortization and interest, the cost is only U3C
per kilowatt-hour, a figure very comparable with small diesel plants.
In summary, small wind generator plants offer an attractive
172
alternative to primary battery systems and constantly running engines to
generate power in remote areas. They are particularly advantageous where
the costs of transporting fuel or batteries are high. The limitation is
an annual average wind velocity of at least 9 to 10 mph. The presently
available units are most useful in the average load range of 10 to 1000
watts.-
DISCUSSION
COMMENT: I object to your making these look so favorable in areas where
the cost of diesel fuel may run from SO cents to a dollar a gallon. I
don't think there is this large a difference in costs. I think Clews'
calculations did not agree with yours.
A: I used 25 cents. Actually, the cost of fuel is quite small compared
with the cost of the amortization of the machine.
* 30.00
*30-
».20-
AT UNATTENDED REMOTE SITES
AUTOMATIC POWER INC., HOUSTON, TEXAS JUNE 3,1973
(WEIGHT TRANSPORTED TO REMOTE 8ITE/KWHR
I WATT 10 wans 100 WATTS
AVERAGE LOAD
1000 WATTS 10 KW
Figure 1
173


Economic considerations of utilizing small wind generators

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