Maintenance

About once per month, each turbine in a field requires a light inspection.  Workers must climb the ladder within the tower to access the components within the nacelle.  Because of the tower’s height, safety is very important: workers must wear hard hats, gloves, and a fall-arrest harnesses when working.  Workers visually inspect the generator, gearbox, electrical components, and computer for any obvious signs of wear or leaks.
 
Every six months or so, turbines undergo extensive maintenance.  Worn parts are cleaned and replaced, moving parts are oiled, and output is checked to ensure maximum efficiency.  Since it is generally understood that components will fail on the turbine (especially with such weather differences in the Midwest), spare parts are usually within reach.

A worker gears up to inspect a wind turbine

Photo from Suzlon Wind Energy

Spare Parts

Wind farm operators keep some supplies close at hand for basic repairs.  Turbines often require new cable, tape, fasteners, sorbent rolls, electrical cleaner, grease, and deicer to keep them running.  This is especially true in areas like the Midwest, where temperatures fluctuate between seasons causing even greater stress on expanding and contracting components. These items—and the safety supplies mentioned above—can typically be purchased from an industrial supply distributor.
 
Of course, not everything can be repaired on site.  Sometimes, stress and damage from wind, temperature changes, or vibration will cause a major failure of the sails, computers, or generators.  Although turbines are generally manufactured overseas, these international companies have warehouses in the United States that stock those spare parts.
 
When a turbine is de-commissioned for a major repair, the spare parts are brought to the turbine site (which is why the gravel access roads remain even after a turbine’s construction is complete).  The top panel of the nacelle is hinged to open so that a crane can remove the old parts.  New parts are installed and tested before the turbine can operate again.  

Sails and other spare turbine parts
in a large warehouse - just in case

Photo from Suzlon Wind Energy

A simplified illustration detailing the components within the nacelle

Illustration by Tom Haskell

A—One of the three sails, necessary to harness the wind. 
 
B—Hub that holds the sails together
 
C—The wind shaft of the turbine
 
D—Main drive gear, which turns the generator shaft
 
E—Generator gear, receives power from the main drive gear
 
F—Generator shaft, which turns the generator and has the brake wheel.
 
G—Brake wheel, from which the turbine’s speed is controlled
 
H—Brake that clamps to the brake wheel (similar to disc brakes on an automobile)
 
I—Generator from which electricity is produced from the shaft’s rotation
 
J—Transformer that supplies electricity to the power grid
 
K—Similar to a tail fan, the yaw sensor detects when winds shift
 
L—The yaw control turns the hub of the turbine into the eye of the wind
 
M—A controller computer to regulate all aspects of the turbine’s operation
 
N—The nacelle houses all of the turbine’s gears and equipment, similar to the cap of a custom windmill.
 
O—The tower of the turbine.

Generating Electricity

Fundamentally, the process of generating electricity with wind turbines is no different from grinding grain with custom windmills: turbines still require sails (A) to catch the wind; gearing (C, D, E, F, and G) to transfer the rotational power to mechanical energy; and methods to turn the sails into the eye of the wind (K, L, and M).
 
What separates turbines from custom windmills is time.  New building materials, wind studies, and modern physics have allowed turbines to be built with taller towers (O), be safer, and be more energy efficient than its predecessors. 
 
Assuming favorable winds, a computer (M) will automatically initiate turbine operation.  If equipped, the computer may first turn motors within the hub (B) to adjust the pitch of the sails (A).  In light winds, the sails turn upon their own axis to expose more surface area to the wind.  Conversely, when strong winds are detected, the sails turn to expose less area.  In dangerously high winds, the turbine will brake (G and H) to prevent operational failure.
 
Next, the yaw control (L) within the nacelle (N) will luff the sails into the eye of the wind.  On older models, a small tail fan turned the nacelle—exactly the same way a tail fan automatically turns the cap of a custom windmill.  On newer models, winds are determined by a set of sensors (K), and a computer turns a motor that luffs the nacelle. 
 
Once the sails begin to rotate, the wind shaft (C) begins turning the gears within the nacelle (D) that generate electricity.  On smaller wind turbines, the wind shaft may run directly into the turbine generator (especially since smaller systems tend to have greater rotational velocity); on utility turbines, the wind shaft turns a gearbox (E) so that the generator (I) turns faster on the generator shaft (F).  The rotation turns a series of magnets against metal coils that convert kinetic energy into electricity, just like a turbine in a hydroelectric dam. 

Supplying Electricity

People always ask: how do wind turbines supply electricity when the wind is not blowing? Contrary to popular belief, wind turbines are not capable of storing electricity.  Brush’s wind dynamo had this capability because it was a small-scale, low voltage turbine that recharged a set of batteries from which his home drew electricity.  But because utility-scale turbines produce high-voltage electricity, there is neither a method to reserve a turbine’s over-production, nor can the power grid draw from a reserve if no wind is blowing. 
 
If wind turbines produce more power than what the grid demands, that power is wasted. Turbines that are not running because of maintenance or weather mean electricity is drawn from existing power plants.  It is because of these drawbacks that wind turbines are only built where steady winds exist.  Years of research and planning go into every wind turbine location to ensure that there will not be extended periods of down-time from poor wind conditions.
 
It’s a wind turbines’ transformer (J) that plays a key role; it acts as a “buffer” between the raw power of the wind and the demand of the electric grid by providing a steady flow of electricity to the power grid at all times. These transformers are also monitored from a central location to ensure power demands are met.  Because the wind can be unreliable, they can never truly “replace” power plants as many politicians and activists claim.