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Diversity in energy conversion

Thomas Devine, professor, materials science and engineering | March 28, 2011

The three biggest challenges confronting the world today and far into the future are the production of adequate amounts of nutritious food, the provision of clean water, and the supply of inexpensive and clean energy.  Arguably, the latter is the most important since energy makes possible the production of food and potable water. The recent devastating oil spill in the Gulf of Mexico, the deadly explosions in coal mines (e.g., in the U.S. and China), and the threat of core meltdowns in the endangered nuclear reactors in Japan, have focused considerable attention on how best to supply energy.

I express our challenge as  “supplying energy,” and not, for example, “producing energy.”  We were all informed in grammar school that energy can neither be created nor destroyed (although Einstein informed us of the interchangeability of mass and energy (E=mc2)).  Thus, when we speak of fossil energy, we are referring to the conversion of the chemical energy that is locked in coal, natural gas, and oil to heat or mechanical or electrical energy.  When we harness nuclear energy, we are converting nuclear energy to thermal, or electrical energy.  Solar energy involves the conversion of the sun’s energy to heat or electrical energy.

No process of energy conversion is 100% efficient, and some processes are more efficient than others.  For example, the direct conversion of chemical energy to electrical energy, such as occurs in a fuel cell, takes place with high theoretical efficiency. The hydrogen-oxygen fuel cell, which has been employed in almost all manned space flights, has a theoretical efficiency of 83%. In all methods of energy conversion the actual efficiency is less than the theoretical efficiency, and in the case of fuel cells, the actual efficiencies are in the range of 50-60%. In contrast, the conversion of solar energy to electrical energy occurs with an actual efficiency in the range of 10-15%. There are fuel cells and solar cells that convert energy at higher efficiencies than the values I have cited.  However, these devices generally require the use of expensive materials and/or methods of fabrication, which, temporarily at least, preclude their use in practical methods of energy conversion.

The conversion of mechanical energy to electrical energy, such as occurs in a gas or steam turbine, is very efficient.  However, obtaining the mechanical energy is often inefficient.  Any process that involves temperature changes is subjected to thermodynamically imposed limitations on its theoretical efficiency.  Thus, the conversion of chemical energy in coal to electrical energy and the conversion of the chemical energy stored in gasoline to mechanical energy in a combustion engine have theoretical efficiencies of approximately 30%.  Remember, the actual efficiencies are always less than the theoretical efficiencies, so some motor vehicles, for example, exhibit actual efficiencies of only 10%.

Converting energy from one form to another is only one of several contributors to the total cost of supplying energy in a usable form.   Four factors contribute to the overall cost: (1) the acquisition of the primary form of energy, for example, drilling for oil or mining of coal; (2) the conversion of the primary energy form to the desired form, for example, the conversion of nuclear energy to electrical energy; (3) the transportation of the usable energy from its point of conversion to its point of use. Finally, there is the all-important but ill-defined category that I’ll refer to as (4) “the cost of cleaning up the mess.”  The latter includes the costs associated with oil spills; deaths and injuries to workers, such as coal miner’s black lung, radiation sickness of power plant employees, and events such as explosions of oil refineries and natural gas transmission lines; injuries and deaths of members of the armed forces, who secure/defend sites of primary energy; adverse consequences to the health of people living in the vicinity of any energy conversion plant; environmental damage associated with the acquisition of the primary source of energy, such as water contamination associated with the capture by hydraulic fracturing of natural gas trapped in shale.

When all factors are considered there is no clear winner to the title of “the best source of energy.”  The correct response to our need for energy is “all of the above,” recognizing that what might be appropriate for one country (or one region of a country) might not be optimum for other locales.  In going forward we need to keep all options on the table and we need to aggressively improve the circumstances associated with each type of primary energy.  For example, let’s build new, safer, and more efficient nuclear power plants (but not within 50 miles of a major metropolis) and let’s get rid of the aging plants that have serious technical limitations; let’s bite the bullet and swallow the costs associated with carbon capture and sequestration at plants that convert fossil fuels to heat and electricity; let’s build the costly plants that will convert coal to gasoline (via Fischer-Tropsch reaction) at prices far cheaper than the current cost of crude oil;  let’s develop more environmentally sensitive methods for tapping our vast reserves of coal and natural gas; let’s push harder on each type of “alternative” energy conversion: fuel cells, wind, solar, hydro, geothermal, and wherever possible get the work out of the laboratories and into the construction of pilot plants and small-scale energy-supplying facilities.

President Obama has referred to this as our “sputnik moment.”  It was “us” in the form of the federal government (NASA), not private corporations, which were (and are) focused on maximizing profits, that accomplished our successful response to the original sputnik moment. We did not get to the moon by focusing on profits and a profit-driven approach will not solve our energy crisis. Utilities and private corporations will not spearhead the development of abundant, cheap, and clean energy. There are too many risks of failure. The supply of adequate amounts of safe, clean, usable energy can only be met by a suite of methods, each of which is performing far better than at present. It’s “our” problem and “we” need to solve it.  We, in the form of big government, need to take the lead, assume all risks and costs, and advance all options.

Comments to “Diversity in energy conversion

  1. I agree that we should pursue clean energy but until the costs come down for the average homeowner, it isn’t affordable. With the ever increasing fossil fuel costs, more of an effort should be made to utilize other alternative forms in a way that benefits the whole of society. Just conserving on what we use doesn’t solve the problem of an outdated electrical grid and energy sources that are polluting our earth.

    • Comprehensive and great discussion about our now and future,my dear Prof. is really a surgent matter to discover new energies.
      As i am still a postgraduate student ,stuudying in China university of geograsciences,of geologic engineering ,who is specialized in melt drilling.What we can try to take into consideration is make best of resouce in relatively deeper place.As we know,so far ,it hassnot drill through the crust,the shallowest part of our plant,yet .However,melt drilling perhaps can provide us inspiring belief in the future.
      Melt drilling is not only clearer for its special approches to drilling,but also can utilize the heat from deeper more effcient.what is more,it is likely to find some new energies that we can harness as the drilling hole downer. if you are interested in,no better things can exist in my world from then on!
      -Zhijun Li China

  2. Excellent summary Prof. Devine, and your recommendations must be given highest priority for fast track implementation of our best, immediately achievable solutions because the window of opportunity is closing as Washington politicians continue to marginalize global warming, the U.N. scientific community continues to fail to communicate, with the totally unacceptable consequence being that the public considers global warming to be at the bottom of the priority list.

    One of the greatest lessons in history, as documented by our greatest 20th century historians Will and Ariel Durant, was their conclusion:
    “When the group or a civilization declines, it is through no mystic limitations of a corporate life, but through the failure of its political or intellectual leaders to meet the challenges of change.”

    Indeed, we are experiencing the decline and fall of civilization today, especially with 7 billion people and increasing failures to produce paramount requirements, as you stated:
    “nutritious food, the provision of clean water, and the supply of inexpensive and clean energy” that are imperative to perpetuate even our current levels of quality of life.

    Time has run out for “construction of pilot plants and small-scale energy-supplying facilities,” it is imperative that large-scale hybrid (fission and/or fusion) plants be constructed as the highest priority, immediately. Berkeley is the only university in the world with the intellectual and national lab resources to make this happen, making Berkeley the only hope that our youngest generation has to provide them with an acceptable quality of life by preventing the door from closing on or about 2050.

    So I most strongly urge you to reverse the decline of our civilization by providing intellectual leadership to encourage Obama and politicians around the world to put Global Warming back at the top of the list before short term disasters close the door on long term survival of our civilization.

  3. I think saving energy is definitely needed in our future. That’s why I do what I can for the environment such as recycle, use energy efficient light bulbs, and use my soda maker instead of buying soda at the stores.

  4. I want to talk about two of the best forms to implement a clean, renewable energy source to power our homes and so contribute to the welfare of ourselves and therein of all human beings and all living creatures: the Active Solar Energy. Having a Home Solar Energy System is, without any doubt, a way to help oneself, our planet Earth and humankind by utilizing just a tiny little part of energy that our Sun passes us freely and the cost of setting up such a system is not as expensive as some would make us think, particularly when we talk about thermal systems to get warm water or heating systems.

  5. As we all know, there’s no way (anymore) of escaping from these problems. We are facing the consequences of actions taken WITH conscience of what could happen in the future. However, I think that one problem said on the begging is quite wrong (“…the production of adequate amounts of nutritious food”). The real thing is distribution of food and not production. We probably produce enough food to feed almost everyone in the world but not everyone have access to this food. Just some food for thought!

  6. What I disagree with in this article is the approach that we should pursue all avenues of energy creation. Our first priority should be to pursue clean energy. Permafrost is melting at an alarming rate which will release vast amounts of methane (20x more powerful than CO2 as a greenhouse gas) accelerating greenhouse warming. We have to slow down the warming to at least give ourselves a chance to adapt to a changing world.

    — John McGraw

  7. Solar energy transformation may not be as efficient as one would like, but as long as the sun burns, we will be able to harness it.( Unlike coal, gas, diesel, nuclear etc.)

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