Sunday, August 3, 2014

The Truth About Wind Energy - Part One

Subtitle:  Wind Energy for Long Term Power

Following the success of a 30-article series on The Truth About Nuclear Power  see link, this article begins a similar series on Truth About Wind Energy, TAWE.    Arguments rage about wind power, with detractors making wild claims about high electric power costs, grid instabilities, unfair subsidies from government, death to flying birds and mammals, unsightly turbines blighting views, and others.   Supporters show that wind has enormous potential to replace almost every other form of grid power, that grids operate stably and will be even better in the future, subsidies are found in other forms of power generation - especially nuclear power, there is an urgency to develop renewable power and global warming has nothing to do with it, and many other points that favor wind power. 

This series of articles, planned to be approximately one dozen, takes the many arguments and looks at each one factually, with sound engineering, economics, legal aspects, and policy objectives.

This first article is a work in-progress, and will likely be modified from time to time.   As with TANP articles, each article in the series will be linked at the bottom as it is published.

A first effort at topics for TAWE include:  Is wind economic? Costs to install wind turbines? Annual output, capacity factor? What about subsidies? Technology types for turbines? Onshore vs Offshore potential? Impact on existing grids? Backup power supplies required? Experience shows us what?    Emissions from backup plants?   Impact on birds, bats? Safety – is anyone injured? Brief history of wind power? Longterm outlook for energy supplies?  Time-shifting energy via storage and discharge?   A concluding chapter. 

Update: 8/4/2014 - Is wind economic?

The calculation for wind energy economics is very simple, in that the cost/benefit analysis is fairly easy to perform.  As with most cost/benefit analyses, we begin with the benefits.  It makes no sense to calculate the costs of a system if there are no benefits, so we must determine first if there are any benefits. 

Benefits are found from average output in kW multiplied by average hours per year of generation, multiplied by the average price per kWh for power sales.  

1)  $ = kW x hrs/y x $/kWh

Power from wind is given by the equation (2)

2)  kW = 1/2 / 1000 x Eff x density x Area x Velocity ^3

Where W = Watts power produced
Eff   =  percent of available wind energy extracted by the turbine
density = air density, a constant usually at 1.225 kg/cubic meter
Area = swept area of the wind turbine blades, square meters
Velocity = wind speed in meters per second

For a sample calculation, 
Eff = 0.4
Area = 5,026 sq meters (from a rotor 80 meters diameter)
Velocity = 16 meters per second (equivalent to 36 miles per hour)

Then kW = 0.5 /1000 x 0.4 x 1.225 x 5,026 x 16 ^3 
kW = 5,044

For a location where wind blows an average of 7 hours per day, then hours per year is 

3) hrs/y = 7 x 365  = 2555

If the average sales price is $0.075 per kWh, then

$ benefits per year = 5,044 x 2,555 x 0.075  = $967,000 (rounded to thousands)

We can then proceed to the cost side of the analysis, having established that a 5 MW wind turbine at that location would produce revenue of almost $1,000,000 per year. 

For an investor, seeking a minimum return on his money of 10 percent before taxes, a simple method of screening a project is to determine the number of years required to payback the investment.   Using 10 year payback period, then the investment can be:

4) Inv = 10 * 1,000,000 = $10,000,000 

A check on the investment per kW of turbine output shows 

5)  $/kW = 10,000,000 / 5,000  = 2,000 (approximately)

This result, $2,000 per kW, compares favorably to that published by California Energy Commission for onshore wind projects with 2009 installation, where the cost was $1,990 per kW.    It should be noted that wind turbine costs have declined considerably since then (only 5 years ago at this writing), with some sources indicating 30 percent decline.   (end update 8/4/14)

The above provides the basic equations for computing wind power output, however, the turbine efficiency and wind speed are critical for individual project performance.   In the US, there are actually few locations, if any, that have wind speed of 16 m/s (36 miles per hour) for 7 hours each day.  Wind speed maps of the US are available; these show a typical range from zero to 10 m/s.   Wind speed is also classified into 7 classes, 1 - 7, with good wind being in class 3 and 4, and excellent wind in class 5.  These classes are for wind speed of 6.4 to 7.5 m/s for class 3 to 4, and from 7.5 to 8.0 m/s for class 5.   In places offshore on both the Pacific and Atlantic coasts, wind averages 9 to 10 m/s.   The great wind corridor from the Canadian border to central Texas, and extending from the Rocky Mountains east approximately 450 miles, has annual average wind speeds of approximately 9 m/s.  

Using a value for class 7 wind, 9 m/s in the above equations, gives 894 kW, a factor of 5.6 times less than 5,044.    

Roger E. Sowell, Esq.
Marina del Rey, California

As always on SLB, comments are welcome however they must be on-topic, non-commercial, and respectful.  All comments are moderated by Roger Sowell.  Comments may not appear right away. 

Copyright 2014, Roger E. Sowell

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