Apples to Apples….
Comparing wind turbines is much like comparing cars and trucks you may want to purchase. Understanding the various types of turbines on the market is the first step.
Every turbine built has an area or wind type situation where they operate efficiently and effectively. Paul Gipes book, “Wind Power” is the standard in the industry for understanding small wind turbines. We recommend potential buyers learn enough about turbines to not be mislead by a “used car salesman type” who may convince you that the decades of facts regarding various turbine types are irrelevant to your decision on a wind turbine purchase.
Upwind Turbines
An Upwind turbine almost
always has a tail fin, that acts as a rudder to turn the turbine
blades into the wind, or move it out of winds that are getting
too strong. The wind hits the nose cone and blades with the
generator and tail fin last. Most often the upwind turbines
have a low cut in speed, around 5mph, and may appear to be
spinning out of control in winds over 20 mph, before they start
to furl, or move out of the wind to protect themselves, at wind
speeds near 35mph. Noise can often be a problem, particularly
if you are in a more congested area. Upwind turbines work well
in Class 2 and Class 3 winds. The upwind turbines have problems
with heavier gusts of wind, particularly in areas that seem
notorious for gusty winds of 40mph and much higher.
Vertical Axis Turbines
VAMT’s as they are referred to are easily recognized. They resemble eggbeaters, or vertical panels on a circular frame that rotate around a central tower. The application preference for a Vertical Axis turbine is often urban or developed industrial areas. They can do well in low wind conditions. One major issue for a vertical axis turbine is high wind speeds for a combined amount of time. The propensity is that they suffer metal fatigue from the centrifugal force and gravity that can not be ignored in their design. They have recently begun to show up in the American market again after decades of abandonment due to the inherent flaws in the technology. Old design patents have been purchased by Chinese companies, where they are being built and imported. They are finding their way into the American marketplace. Used in a low wind urban setting, they may do well for the purchaser.
Downwind Turbines
Wind hits the generator
head or nacelle first and the back of the blades on a downwind
turbine. Some downwind turbines have a sensor that activates
the braking system when wind gusts or sustained high winds
occur. The Raum 3.5 has a braking system that starts at 35
mph. The Proven downwind turbine, has a rudder below the
nacelle that solves the precursing or tendency to slowly shift
out of the wind. However, Proven turbines also have a patented
hinge system on the blades, that allow the blades to cone
slightly when the wind speeds increase, controlling the rpms, so
the machine is not spinning out of control. This cuts down on
wear and tear and maintenance. The cut out speed on the Proven
turbines with this hinge system is 159mph. It has been known to
survive winds of 196mph in a typhoon off the coast of Japan.
The difference between other turbine types and the Proven
downwind turbines, is that they will not shut down, or have to
stop to protect themselves in high winds or gusts of wind, and
will continue to produce power at the optimum levels. The
patents on the hinge system and the tilt up monopole have been
held for decades. Some of the turbines installed in harsh
conditions and climates are still working after 30 years. This
has made them one of the very best turbines for areas of high
wind such as we have in the Northern Plains States. Harnessing
the wind with a Proven Turbine, means you harness all the wind,
not just average winds.
Towers
The higher the turbine the more wind it will catch. However,
the taller the tower the more expensive they become. A good
rule of thumb, is to place your turbine 300 to 500 feet from
obstructions. Another is to make sure your turbine is planted
on a tower at least twice the height of the nearest
obstruction. If your home is 24’ high, and you are planting the
turbine 300 ft. away, you will want to consider a tower that is
twice the height of the structure. In this example, a 48’ tall
tower should be used. You can of course go higher, but it is
not recommended that you go lower.
You have probably seen lattice towers, guyed towers and sleek monopole towers. It is cheaper to install a lattice tower since the footings are not extensive and the structure is climbable for making repairs or doing annual maintenance. It is more difficult to mow around them, and you won’t want livestock leaning or rubbing on the tower. The guyed towers, are less expensive as well, with the pole being less stout, it utilizes guy wires to anchor it in an upright position. Again your have the issue of mowing around the wires or fencing it off from livestock. The monopoles have a more extensive foundation. Generally the foundation base is sunk into a hole with rebar and concrete to hold the monopole in place. Some manufacturers have set depths and length/width and rebar specifications for the different soil types that can be found. From Gumbo to Sand, to crushed granite and loamy soil, engineers determine the specifications on everything including the appropriate mix of the concrete. There is one drawback to the sleek monopole, and that is it can not be planted in the Northern Plain States in winter. The concrete must be allowed to cure completely before the tower and turbine are put in place. The monopole are less obtrusive. You can mow around them, run livestock around them, and they are more visually attractive. They are more expensive than a lattice or guyed tower. The Engineer certified tilt up monopoles for the Proven turbines are galvanized steel and stainless steel. They are structured specifically to hold the weight of the various sized turbine heads or nacelles.
Generators
There are two prominent types of generators being used in most turbines today: Induction (Asynchronous) and Permanent magnet.
Induction generators require electricity to start them, regardless of the speed of the wind. They are less expensive, and are basically plug in and go, since additional equipment, inverters, controllers or rectifier are not required. Induction generators can not be used off the grid.
The permanent magnet generators are
started by the wind. They are gearless, brushless, with few
moving parts that will wear out or need repair. The permanent
magnet generators are quieter. However, they require an
inverter to operate compatibly with the electric grid. This
type of generator can be off the grid, for powering remote
cabins or telecommunication towers, or remote stock pumps.
Inverters
Basically, what the inverter does is convert DC (Direct Current)
into AC (Alternating current) to be compatible with the power
supply from the grid connection. Inverters are also equipped
with safety features that will shut down power going back to the
grid if the electric suppliers system goes down. This protects
anyone who may be sent out from the electric company to work on
the grid system, from being harmed by thousands of volts of
electricity. Safety is the largest concern on all systems.
On the "contact" page of our website, we have included links to
various websites that will provide additional sources of
information about wind turbines. Knowing your kilowatt usage
and whether you want to reduce or eliminate your current
electric utility costs is your first step. Learning about
turbines in general allows you to make smart choices on the
turbine that will work best to meet your kilowatt usage needs,
and the environment where it will be planted. Class 2 winds
will not provide Productive Power thus the expenditure for a
turbine may not be in your best interests. Class 3 and Class 4
winds are productive and readily found in the Northern Plains
States. Wind is a Free source of power, that is clean and
environmentally friendly. Once the initial investment for a
turbine is paid, your electricity is free. Each state has
incentives that offset the costs of a turbine investment. The
Federal Stimulus Plan allows an uncapped 30% tax credit on the
entire cost of the renewable energy system. The links for each
states tax incentives vary widely, and can be found on the last
page of our website.