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October 2014 Brief: Volume 21, Number 29

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Use the Most Productive Energy Source Possible


by Deborah D. Thornton



An important part of the energy discussion, which gets confused in the global-warming debate, is that different sources of energy are appropriate for different needs. Gasoline and diesel fuel made from oil are the most reliable, efficient, cost-effective way to power vehicles and other motorized equipment. We also have a reliable, safe, and easily replicable delivery system. When you need a car or truck to run, you turn it on and it runs, aside from a stray breakdown.


Even before it becomes gasoline, oil is a critical input for making plastic and many other chemistry-driven products, all benefiting humankind. Important health and safety products such as Plexiglas, artificial limbs, aspirin, and rubbing alcohol are oil based. And recreational and convenience products such as scotch tape, soccer balls, guitar strings, pacifiers, fabric softener, hair color, lipstick, and shaving cream might not be “necessary” to our existence, but undeniably make the world a better and more comfortable place.


Another “evil” fossil-fuel-based energy source is coal. Many things are made from coal-powered energy. For example, steel is necessary for safe and secure factories, offices, and homes, yet we can’t produce steel without coal. Should coal really be an enemy of the environmentalists?


A key consideration in this environmental discussion must be the amount of power generated by the source. Is a power source effective? Does it produce more energy to do work than it consumes? In order to be effective, an energy source must generate, and we must be able to capture and use, more power than is used in consuming it. This is called “energy density” and “power density.” As high school physics teaches, “energy” is the ability or capacity to do work, and “power” is the rate of doing that work.[1] In order to be economically useful, the energy and power produced by something needs to be high. The energy produced by many historical sources (wood) and renewable sources (ethanol, wind, and solar) is generally very low. These are not very dense or economically productive power sources. This is often ignored by environmentalists who want to end fossil-fuel use.


Most current renewable fuel sources have low energy and power numbers – hence the problems. For example, the power density of wind is only about 1.2 watts per square meter (W/m2).[2] The largest off-shore wind field, the London Array in the ocean south of England, only has a power density of about 2.5 W/m2. Those wind turbines standing in the Iowa cornfields are not any better.


Because current solar panel technology is very ineffective at converting sunlight into electricity, the power density of solar power is only about 5 W/m2. Even in the desert, with sunlight shining all day, every day, energy from the sun originally has a power density of only about 200 W/m2. The energy captured by solar panels is only a tenth of that, about 20 W/m2. The power density of sun in Iowa is about 170 W/m2 at its June/July peak, which because of panel placement and continuity issues results in a captured power density of about 5 W/m2.[3]


Yet some activists claim Iowa can be the next solar king, claiming that a solar array in Iowa can produce a “comparable amount of electricity as one located in Miami, Houston, (or) Atlanta.”[4] The interesting thing to note is that photos of solar panels show acres and acres across good Iowa farmland, which certainly can be used for more productive purposes. There are still starving children in the world. At least farmers can still grow crops near the bottoms of wind towers.


Power Density in Watts per Square Meter


A similar problem exists in using Iowa crops to make bio-fuels such as ethanol – the power density is low (0.05 W/m2). Some argue that converting grain food to animal food is an inefficient use of crops and a poor way to feed people. If feeding animals is bad, converting corn to ethanol is an even more inefficient use of our crops.[5] Only government subsidies make it economically viable. If Legislators and business people want to support the diversion of corn to make ethanol, fine – but they must make informed decisions and understand the issues.


In contrast, the power density of natural gas is 28 W/m2 and that of modern gas and coal-fired power plants often near 1,000 W/m2. Even a small propane-powered home generator has a power density of almost 1,000 W/m2.[6] If, as a consumer, you are comparing the bang for your buck from solar, wind, or ethanol – the power density factor will overwhelmingly indicate that gas, coal, or propane should be used for electricity and heat generation. However, most people don’t know or think about “energy density” and “power density” when they turn on the lights or start their cars – they just want them to work.


These facts lead to the conclusion that we must bring the discussion of power density to the forefront of energy sector economics and planning. Just as we all appreciate cars which get better gas mileage and cost less to run, we must consider the amount of power we get from original sources when choosing that energy source, and choose the most productive source.


If Iowans truly want to “go off the grid,” help the environment, and be energy efficient, they should invest in home generators and use propane or natural gas. They should encourage the use of oil and coal, not discourage it. Finally, they should not use ethanol or install solar panels or wind turbines.


[1] “Work, Energy, Power” definitions, Hyper Physics, <> accessed on June 27, 2014.
[2] Robert Bryce, “The Real Problem with Renewables,” Forbes, May 11, 2010, <> accessed on June 27, 2014.
[3] Robert Wilson, “The Future of Energy: Why Power Density Matters,” The Energy Collective, August 8, 2013, <> accessed on July 6, 2014.
[4] “Solar Energy in Iowa,” Iowa Environmental Council, p. 3, <> accessed May 15, 2014.
[5] Robert Bryce.
[6] Robert Wilson.


Deborah D. Thornton is a Research Analyst with Public Interest Institute, Mount Pleasant, Iowa. Contact her at


Permission to reprint or copy in whole or part is granted, provided a version of this credit line is used:"Reprinted by permission from INSTITUTE BRIEF, a publication of Public Interest Institute." The views expressed in this publication are those of the author and not necessarily those of Public Interest Institute. They are brought to you in the interest of a better-informed citizenry.




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