Wind Turbines versus a Coal-Fired Power Plant

Posted by PITHOCRATES - August 26th, 2013

Economics 101

The Diameter of a 6 Megawatt 3-Blade Rotor is Greater than two 747-400s parked Wingtip to Wingtip

One of the largest coal-fired power plants in the world is in Macon, Georgia.  Plant Scherer.  Whose furnaces consume some 31,000 tons of coal a day.  Producing 3,500 megawatts of electric power.  Enough to power three good sized American cities.  A few million households.

One of the largest offshore wind turbines available on the market is 6 megawatt.  Which is huge.  One blade can be as long as 250 feet.  A typical 3-blade rotor can have a diameter of just over 500 feet.  To get a feel of this magnitude the wingspan of the world’s most common jumbo jet, the Boeing 747-400, is about 211 feet.  Which means one blade of a 6 megawatt wind turbine is longer than the wingspan of a Boeing 747-400.  And the diameter of a 3-blade rotor is greater than two 747-400s parked wingtip to wingtip.

A 6 megawatt wind turbine requires a tower of about 300 feet tall.  So the blades can spin without hitting the ground.  Which is about the same height of a 20 story building.  And if it’s an offshore turbine you can add another 2 stories or so for the tower below the surface of the water.  So these things are big.  And tall.  Some of the largest manmade machines built.  And some of the most costly.  It takes a huge investment to install a 6 megawatt wind turbine.  That can only produce 0.171% of the electric power that Plant Scherer can produce.

There is a Small Window of Wind Velocities that we can use to Generate Electric Power with Wind Turbines

So how many 6 megawatt turbines does it take to match the power output of Plant Scherer?  Well, to match the nameplate capacity you’ll need about 584 turbines.  If we install these offshore in a line that line would extend some 56 miles.  About an hour’s drive time at 55 mph.  Which is a very long line of very large and very costly wind turbines.

We said ‘nameplate capacity’ for a reason.  If 584 wind turbines were spinning in the right kind of wind they could match the output of Plant Scherer.  And what is the right kind of wind?  Not too slow.  And not too fast.  These turbines have gear boxes to speed up the rotational speed of the rotors.  And they vary the pitch of the blades on the rotors.  So the turbine can keep a constant rotational input to the electric generator.  If the wind is blowing slower than optimum the blades can catch more air to spin faster.  If the wind is blowing pretty strong the blades will turn to catch less air to spin slower.

In other words, there is a small window of wind velocities that we can use to generate electric power with wind turbines.  Too slow or no wind at all they produce no power.  If the wind is too great the blades turn parallel to the wind.  So the wind blows across the blades without turning them.  They also have brakes to lock down the rotors in very high winds to prevent any damage.  So if a storm blows through 584 offshore turbines they’ll produce no electric power.  Which means they can’t replace a Plant Scherer.  They can only operate with a Plant Scherer in backup.  To provide power then the winds just aren’t right.

The more Wind Turbines we install the more Costly our Electric Power Gets

Now back to that nameplate capacity.  This is the amount of power a power plant could produce.  It doesn’t mean what it will produce.  The capacity factor divides actual power produced over a period of time with the maximum amount of power that could have been produced.  A coal-fired power plant has a higher capacity factor than a wind turbine.  Because they can produce electricity pretty much whenever we want them to.  While a wind turbine can only produce electricity when the winds are blowing not too slow and not too fast.

So, if the winds aren’t blowing, or if they’re blowing too strongly, it is as if those wind turbines aren’t there.  Which means something else must be there.  Something more reliable.  Something that isn’t weather-dependent.  Such as a Plant Scherer.  In other words, even if we installed 584 turbines to match the output of Plant Scherer we could never get rid of Plant Scherer.  Because there will be times when those windmills will produce no power.  Requiring Plant Scherer to produce power as if we never had installed those wind turbines.  And because it takes time to bring a coal-fired power plant on line it has to keep burning coal even when the wind turbines are providing power.  So it can be ready to provide power when the windmills stop spinning.

Wind may be free but 584 wind turbines cost a fortune to install.  And this investment is in addition to the cost of building, maintaining and operating a coal-fired power plant like Plant Scherer.  All of which the consumer has to pay for.  Either in their electric bill (adding a surcharge for ‘clean energy investments’).  Or in higher taxes (property tax, income tax, etc.) that pays for renewable energy grants and subsidies.  Which means the more wind turbines we build the poorer we get.  Because we have duplicate power generation capacity when a single power plant could have sufficed.


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