The Mehrkam Wind Power Turbine

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PHOTO1: A 40-KW, six-bladed MEDC wind turbine provides power for Terry Mehrkam's rural Pennsylvania homestead. PHOTO 2: The Ray Groff family of Bath, Pennsylvania began generating power with this 12-KW Mehrkam windplant in 1977. PHOTO 3: The control room for Terry's home-based wind generator. PHOTO 4: The Bronx Frontier, a New York City-based community group, utilizes wind power.

Four decades ago, windplants were a common sight on North
America’s farms and homesteads. At present,
however–mainly because of the efforts of the Rural
Electrification Administration–the great majority of
yesterday’s draft-driven pumps and generators have been
either disassembled or simply left to the mercy of the

Naturally, there was no real problem with the
wind-powered equipment . . . it’s just that the
then-inexpensive (and freshly installed) “grid juice”
seemed to present a very attractive alternative at the
time. These days the advantages of utility power
are becoming less obvious . . . and many folks, both rural
and urban (yes, breezes blow in the cities, too!), are
considering–or already have installed–their own
wind power turbine systems.

Not long ago, MOTHER EARTH NEWS sent one of her editors to
Hamburg, Pennsylvania to talk to Terry Mehrkam, founder of
the Mehrkam Energy Development Company. Terry’s firm is a
small but growing operation that not only designs and
markets truly “state of the art” wind power systems, but has
actually been so successful at doing so that the demand for
MEDC-designed equipment is outstripping the present

Terry — who is best described as the firm’s
designer, engineer, and part-time maintenance crew . . .
when he’s not busy managing the business, that is — has
some definite opinions as to how a wind generator should be
built. The article that follows details both the Mehrkam
system and the reasons for its success.

It should come as no surprise to anyone that countless
people are scrambling for ways around the high price of
energy . . . whether that power comes from oil, gasoline,
or public utility lines. But–in their search for a
“better way”–many folks are overlooking a
time-tested, practical alternative: the wind.

One possible reason for the lack of interest in windplants
is that in times past the use of “air power” was limited to
areas of near-constant high winds, such as the Great Plains
or North America’s coastal regions.

These days, however, it’s a different story. Even though
the weather hasn’t changed much, the available hardware
has, and wind systems are coming into their own for several
reasons: [1] Equipment reliability has improved
substantially since the early days of windpower use. [2]
Wind-driven generation plants are becoming quite
cost-effective, and will prove to be even more so as public
power costs increase with each year. [3] Thanks to the
above mentioned advances in technology, many modern
windplants can now be utilized even during minimal wind
periods and are thus more practical than some of their fore
runners. [4] “Down time” — for regular equipment
maintenance and overhaul — has been reduced to a bare-bones
minimum through sound engineering.

A New Twist to an Old Idea. . .

Since the “early” generators were, by and large, used only
in extremely windy areas, the manufacturers designed their
equipment to charge optimally at higher windspeeds (in the
neighborhood of 18 to 20 miles per hour or more) . . .
which meant that shaft RPM could range from 225 to over
900 — depending on the unit — and blade tip speeds
would often approach 180 MPH!

Now it doesn’t take a degree in engineering to figure out
that a piece of machinery running at such speeds will
undergo severe stress . . . and that eventually the hub or
blades — or some other moving parts — may very well

With this reliability problem in mind, Terry Mehrkam set
out eight years ago to develop a windplant that
did not incorporate a “built-in” failure potential.
Actually, the young designer had no intention of going into
the wind energy business at all. . . he was merely
searching for a way to reduce commercial power consumption
in his father’s manufacturing enterprise. “We made a lot of
components for nickel plating,” Terry explains,
“and — even back in 1972 — were using three to four
thousand dollars’ worth of electricity per year. So we were
curious about the potential of wind turbines. I
had for years been interested in aeronautical
theory, airplane flight dynamics, and what not . . . and I
was always a tinkerer by nature, so I designed and built my
own wind turbine: a 10-kilowatt, two-bladed

Mehrkam’s initial design attempt–though
successful–didn’t quite meet his requirements,
because the machine just wasn’t productive at low
wind speeds. So, soon thereafter, he built a larger
prototype, a 45-foot two-blader which would later serve as
a guinea pig for various blade designs.

Not wanting to waste his time “reinventing the wheel”, the
Keystone Stater researched countless technical studies in an attempt to hit upon the right type of airfoil and
blade twist for his windplant.
Unfortunately–primarily because his central
Pennsylvania location experienced only average winds most
of the time–none of Mehrkam’s early blade designs
performed as well as he had expected them to. “So I decided
to try a four-blade model, and immediately found that the
additional ‘arms’ resulted in smoother operation . . . it
was a very passive machine when compared to the two-blader.
The idea was to have at least one blade going through one
quadrant at all times so that we wouldn’t get into the
stress, flex, and dynamic frequency problems which occur in
units using fewer blades.”

Of course, what Mr. Mehrkam had done, in effect, was to
kill two birds with one stone: By incorporating two
additional blades into his design, he came up with a
smoother-running windplant and could shorten each blade
while still reaping the same amount of power as that
provided by the larger-span, two-bladed windplant .

…With Excellent Results

Spurred on by the obvious success of the four-blade design,
Terry took the next logical step: He added yet another pair
of airfoils to further reduce his machine’s shaft speed and
to make it even more productive at low wind speeds.

Again, his calculations proved correct . . . the new
six-blade model not only ran smoothly — with a minimum
of equipment stress and an easy-to-live-with 40 decibel
noise level output, as measured directly below the
blades — but, even more important, charged in an unbelievably
slight breeze. (After an initial 7MPH gust — which is what’s
required in order to get the machine rotating from a
standstill — the Mehrkam windplant will continue to spin in
air currents of as little as 2 MPH . . . with an effective
charge being delivered in a 5-MPH wind. An 8MPH zephyr will
produce as much as a kilowatt of power, and that figure is
increased to between three and four kilowatts as wind speeds
rise to 10-MPH.)

Obviously enough, in areas where average wind speeds are not
great, an air-powered generator that can perform useful
work ail year round has something to say for itself. Terry
Mehrkam has since calculated that, under light breeze
conditions, his six-blade model is about 15% more
productive than was his own “four-feather” design . . . and
a whole lot more efficient than conventional windplants
that might only begin to charge at 12 MPH or more!

The Economic Factor

Naturally, a breeze-powered backyard plant isn’t everyone‘s
cup of tea (because of space limitations, nearby neighbors,
and initial costs) . . . nonetheless, anyone considering an
alternative source of power for individual (or group)
residential — or small-scale
commercial — applications should consider using the

Besides the fact that MEDC’s equipment can produce usable
power from very little wind — independent of the public
utility grid if desired — the cost-per-kilowatt of such a
system, installed, currently averages about $650 . . . with
some installations ( those that are used exclusively to
provide resistance heating and thus don’t require
inverters, batteries, or other power-conditioning
equipment) running as low as $550 per kilowatt, all told.
When you compare such figures with the $1,000 (and greater)
cost per kilowatt of the average utility, wind-powered
electricity looks pretty good . . . not to mention the fact
that such a generating setup can earn federal tax credits,
increase the value of the property it’s on, be a worthwhile
investment in itself, and sometimes enable its owner to
sell excess power back to the local utility!

Designed With Dependability in Mind

Since Terry Mehrkam’s original windplants were used to
provide complete independence from the power company
(though, to date, the majority of MEDC’s customers are
hooked into the utility lines . . . for reasons of backup
convenience and/or economics), they were designed to be
low-maintenance, high-reliability pieces of

A typical MEDC turbine assembly alone, comprising blades,
hub, driveshafts, transmission, generator, and exterior
nacelle, weighs in at about 4,000 pounds . . . and is, to
say the least, built to heavy-duty specifications.

Besides employing an oversized, helical-geared, fully
sealed transmission — to absorb shocks better and guarantee
reliability — Mr. Mehrkam uses roller bearings
throughout each powerplant, and ties the hub to his
120-volt DC generator (or single or three-phase alternator,
depending on the buyer’s requirements) with oversize
shafts, which incorporate two electrically operated disk

The blades themselves are of an extremely high-strength,
low-flex extruded aluminum design, and are either coated
with polyurethane or anodized to guarantee weather-ability.
But better yet — from a standpoint of practicality — the
airfoils are mounted to the hub with special failsafe
locks, which also allow blade pitch adjustment to be made.
What this all boils down to is that each windplant can be
“custom tuned” to its own particular site . . . to provide
a high degree of efficiency throughout a wide range of
local wind velocities.

The company’s 7,000-pound tubular tower — which will measure
anywhere from 40 to 65 feet in length on the 40-KW
windplants that MEDC markets — is constructed of 3/8″
steel and has a diameter of 30 inches. Because the design
is relatively “clean” and narrow when compared with open
frame towers, the “wake effect” of air flowing around it is
reduced drastically . . . and this, of course, adds to the
overall effectiveness of the turbine, which is positioned
downwind of the tower.

High-wind flex protection is provided by internal stringers
which crisscross within the tube to a height of 20 feet
from the base . . . while the bottom of the tower is set
solidly into 20 cubic yards of buried concrete.

Since the needs of Terry Mehrkam’s customers vary widely,
his systems can differ with each installation. For example,
at MEDC’s Hamburg, Pennsylvania test site, a DC generator
provides power through a voltage regulator to a series of
ten 12-volt mining car batteries. These, in turn, feed a
rotary inverter which provides 120-volt AC power to the
Mehrkam household. In many applications, the use of a
solid-state synchronous inverter has been found to be more
practical (especially in installations with a utility
company buy-back arrangement) . . . or — as in the case of
most of MEDC’s clients — the generator can be replaced with
an alternator which naturally produces 120-volt AC service
and is controlled through a solid-state panel.

The fact that the Mehrkam wind turbine is essentially a
one-speed machine makes power control much easier, too.
Unlike many smaller, two-bladed windplants that work on a
proportional basis (that is, an increased speed results in
more power throughout the entire operational range), the
MEDC generator is either coming up to speed or losing speed
under normal wind conditions . . . and the optimum kilowatt
capacity of any one of the company’s windplants can be set
for airspeeds of 25 to 35 MPH by adjusting the blade pitch
and the shaft speed (which can be controlled via excitation
of the generator).

Once the generator is excited to the voltage output at a
given speed, it “locks onto” that RPM and shouldn’t vary
more than 10% overall. Of course, if a really severe blow
should happen along, the rotor will automatically shut down
at its “redline” of 60 RPM (the result of an approximately
40-MPH windspeed), though all the turbines are designed to
withstand gusts of up to 120 MPH. Hence, in Mehrkam’s
designs, greater output is obtained by increasing the
size rather than the speed of the blades.

There’s a Future in Wind

Even though wind power isn’t practical for all of us, it’s
surprising just how many people could take advantage of
this inexhaustible source of energy but don’t realize it.
Terry Mehrkam’s rule of thumb states that a potential buyer
who is consuming at least 20,000 kilowatt hours of power
per year (and lives in a locale with an average annual
wind speed of at least 9 MPH) might well consider a
wind-driven powerplant.

Terry’s experience also contradicts the idea that
windplants are suitable only for rural areas. The Mehrkam
Energy Development Company has sold a good number of
machines in the past several years, and they’re by no means
all set up in the boondocks. One 225-KW
installation — in fact — is located at an
Allentown, Pennsylvania amusement park, and a smaller
(40-KW) plant provides power for The Bronx Frontier . . . a
community development group located in New York City. To
date, Mehrkam has completed (or has contracted to build)
installations in other parts of New York and Pennsylvania
(where construction of a 2-megawatt unit is now in
progress), plus New Jersey, Colorado, California, and as
far away as Hawaii . . . where five plants are

In all, the prospects of Mehrkam Energy Development
Company–and windpower in general–look great …
and as the cost of conventional (and often
nuclear-generated) power continues to rise, their future
should become that much brighter.

EDITOR’S NOTE: In 1981 Terry Merhkam fell from a tower platform and was struck and killed by one of the blades of a wind turbine.