Food for thought on the limits of energy innovation.

Byline: Vaclav Smil

PRESIDENT Barack Obama has promised an energy revolution in the world's largest economy, with renewable sources of power and "green" technologies breaking America's -- and ultimately the world's -- dependence on conventional fuels.

The environmental, strategic, and economic benefits -- including lower use of carbon-emitting fossil fuels, less reliance on politically volatile oil-and-gas exporters, and the creation of millions of well-paid jobs -- are uncontroversial. But how realistic is this vision?

There is only one kind of primary energy (energy embodied in natural resources) that was not known to the first high civilisations of the Middle East and East Asia and by all of their pre-industrial successors: isotopes of the heavy elements whose nuclear fission has been used since the late 1950s to generate heat that, in turn, produces steam for modern electricity turbo-generators. Every other energy resource has been known for millennia, and most of them were harnessed by pre-modern societies.

The fundamental difference between traditional and modern uses of energy consists not in access to new or better energy resources, but in the invention and mass deployment of efficient, affordable, reliable, and convenient "prime movers," devices that convert primary energies into mechanical power, electricity, or heat. History could be profitably subdivided into eras defined by the prevailing prime movers.

The longest span (from the first hominids to the domestication of draft animals) is made up of the age when human muscles were the only prime mover. Then came the addition of draft animals and gradual supplementation of animal prime movers by mechanical prime movers, such as sails and wheels, that capture natural energy flows.

A fundamental break with this millennia-long pattern came only with widespread adoption of the first practical mechanical prime mover able to convert the heat of fuel combustion -- James Watt's improved steam engine, designed in the 1780s. More efficient versions of this prime mover dominated the modernisation of the Western world until the first decade of the twentieth century.

During the 1830s, the first water turbines marked the beginning of the end of the waterwheel era. The next two key milestones came during the 1880s, with the invention by Benz, Daimler and Maybach of the gasoline-fuelled Otto-cycle internal combustion engine and the patenting of Charles Parsons' steam turbine. The 1890s witnessed the arrival of Rudolf Diesel's inherently more efficient version of the liquid-fuelled internal combustion engine.

There is only one more prime mover to add to this sequence. The gas turbine was conceived at the beginning of the twentieth century, but its first working prototypes (both stationary and for flight) came only during the 1930s, and began to be rapidly diffused in the 1950'.

Today's most ubiquitous mechanical prime mover -- installed in nearly a billion road and off-road vehicles, water vessels, airplanes, and countless machines and tools -- is the gasoline-fuelled internal combustion engine, fundamentally unchanged since the 1880s.

Economic globalisation would have been impossible without the diesel engines that power enormous crude and liquefied natural gas tankers, bulk cargo vessels transporting iron ore and grain, and massive container ships: some of them now have unit capacities close to 100 MW, but their basic design was mastered within two decades of Diesel's test of his final engine prototype in 1897.

Most of the world's electricity is generated by steam turbines in fossil-fuel-burning and nuclear power plants, and, except for much larger capacities and higher efficiencies, Parsons would recognise in them every key feature of his invention, now more than 120 years old. And intercontinental flights would be an even greater trial without the gas turbines invented in the 1930s by Frank Whittle (who thought about turbofans, now the dominant commercial design, even before he built the first turbojet) and Joachim Pabst von Ohain.

These realities offer three obvious but under-appreciated conclusions about the mechanical prime movers that are the foundations of our economic progress. First, because of their large numbers and their associated (and often expensive and extensive) infrastructures, prime movers are remarkably inert. There has been little real innovation ever since these prime movers were first commercialised more than a century ago (water turbines, steam turbines, internal combustion engines) or more than 50 years ago (gas turbines).

Second, any transition to new prime movers is an inherently prolonged affair, taking decades to accomplish. Even today, for example, there are few indications that steam turbines will not continue to generate the bulk of our electricity in the decades ahead, or that gas turbines will be replaced anytime soon. Recent developments show that even automotive internal combustion engines will not yield to electric motors or fuel cells as rapidly as many enthusiasts have hoped.

Finally, the wider the scale on which an energy prime mover is deployed, the longer it will take for substitutions to appear. A century ago, the world used coal and a relatively small volume of oil at the rate of 0.7 TW, but in 2008 established commercial energies -- fossil fuels and primary (water and nuclear) electricity -- flow at the rate of nearly 15 TW. Obviously, this scale limits the speed with which new prime movers can be introduced to replace any significant share of the old devices.

For example, if 20 per cent of the world's electricity were to be generated by wind turbines, then, considering their inherently low load factor of about 25 per cent (compared to 75 per cent for thermal stations using steam turbines), we would need to install new capacity of some 1.25 TW in these machines. Even with large 3 MW turbines, this would require more than 400,000 new tall towers and giant triple blades. That is a task for many decades.

n Vaclav Smil is Professor of Environment and Geography at the University of Manitoba.

Project Syndicate, 2009

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