Engineering Expert Witness Blog

     The last few weeks we’ve been discussing some of the technical and environmental drawbacks of alternative sources of electrical energy and nuclear power generation.  This week we’ll take a look at another drawback, that of energy sprawl.

 

     So what exactly is “energy sprawl?”  It’s an easily understand concept, but one that is often overlooked by proponents of the alternative energy movement.  Energy sprawl is simply the amount of land which is taken over by alternative power sources in order to generate a given amount of electricity, and that number is dauntingly large.

 

     For example, let’s revisit the subject of wind turbines.  According to the National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy, each turbine is to be spaced five to ten turbine diameters apart in a wind farm, depending on local conditions.  Now the blades of a 2 megawatt (2 million watt) wind turbine are about 260 feet in diameter, and for our example we’ll space them at the prescribed minimum distance of five diameters.  The math for this one is easy, 260 times five, which equates to spacing of 1333 feet, or just over a quarter of a mile.  That’s right, if you build a wind turbine farm with a whole bunch of these 2 megawatt turbines, they’ll have to be spaced  a minimum of a quarter mile apart.  You’ll need a lot of acreage.

 

     So based on the calculations above, we’d have to build a wind farm where each 2 megawatt turbine is surrounded by a circle of empty land 1333 feet in radius.  We know from geometry that the area of a circle can be calculated by multiplying pi, that is 3.1416, times its radius squared, and this translates into a minimum area of about 5.6 million square feet per 2 megawatts of power generated, or about 2.8 million square feet per megawatt.  Just to put this into perspective, a football field has an area of 57,564 square feet.  So what we’re actually talking about here is a little more than 48 football fields worth of land per megawatt of electricity generated!

 

     Let’s turn our attention now to solar power generation.  We want to generate electricity with their photo-voltaic (PV) panels, and these panels are made of special materials that convert the sun’s energy directly into electricity.  Great concept, but here again we’re talking a lot of land.  According to the NREL, it’s estimated that 6.4 acres are required to generate 1 megawatt of electricity using PV panels.  Since one acre equals 43,560 square feet, we’d need a total of 278,784 square feet of land area per megawatt.  After we’ve done the math we discover that this equates to almost five football fields of area per megawatt of electricity generated.

 

     We’ve now established that loads of land space is required to operate multiple options for alternative energy, and you’re probably wondering how this all compares to land usage for fossil fuel (i.e. coal, oil, natural gas) and nuclear power generation.  Well, a typical 1000 megawatt coal fired power plant occupies about 148 million square feet.  This translates to around 148,000 square feet per megawatt, which is just over two and a half football fields per megawatt.  As for a 1000 megawatt nuclear power plant, we’re talking about 28 million square feet that’s typically occupied by an operating plant, and that translates to almost 28,000 square feet per megawatt, or a little less than half of a football field per megawatt.

 

     Math established, it’s a hands down victory for fossil fuel and nuclear plants compared to wind turbine and solar energies when it comes to land usage.  Last time I checked tillable land acreage was going down, not up, around cities where electricity demand is highest.  Do we start pushing farther outward to build wind turbine and PV farms on vast expanses of land currently occupied by forests or used to grow our food?  Which would you rather do, eat or have electricity?

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