Opinion, Berkeley Blogs

Diversity in energy conversion

By Thomas Devine

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.