Status of Energy Technologies

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Until the advent of the industrial revolution in the 18th century, humans used mainly animal power and mechanical power provided by wind and water. During the eighteenth century wood became the primary energy source used for cooking, space heating, and to fuel the industrialization. As forests diminished, coal became the primary fuel for powering steam locomotives. New applications were also found in the form of coke in casting and smelting, and as town gas for lighting. Coal consumption increased throughout the nineteenth century and peaked as petroleum was being discovered as a more convenient fuel that could be transported in pipelines and used directly in internal combustion engines (Figure 1). As new petroleum resources were discovered and better techniques were developed for refinement, petroleum found more and more applications in a wide variety of technologies (including pharmaceutical, petrochemical, and other industrial sectors) and still dominates the energy market as the fuel of choice. As a result of the rapid industrial growth, it is estimated that 30% of all stocks of nonrenewable energy (including fossil fuels) was used in the twentieth century. Although most of nonrenewable energy resources remain, the reign of fossil fuel is not expected to last much longer. It is believed that world oil has already peaked or is soon to peak in its production, and will be depleted by the end of this century. Use of nuclear fission is closely following the trend of fossil fuel as uranium reserves deplete, nuclear waste piles up, and problems associated with reactor safety make nuclear technology increasingly less attractive.

 US Energy Consumption (Quads) by Source, 1635-2000
Figure 1: US Energy Consumption (Quads) by Source, 1635-2000
 Energy sources: past, present, and future
Figure 2: Energy sources: past, present, and future

As energy becomes more scarce, the pressure to find alternative sources and switch to more efficient technologies increases. Although there have been major efforts to promote renewable sources of energy, most cannot compete economically with fossil and nuclear energy sources - yet. However, much research is being done and many have great hopes that renewable resources will play an ever-increasing role in meeting our energy needs during this century. Nuclear fusion remains a dream for the future and is not expected to be commercially plausible until the last decades of this century (Figure 2). (1)

In the following chapters we will study some of these resources and how they will play a role in reaching our energy goals. New technologies are being developed to harness wind, biomass, tidal energy, and ocean currents, as well as thermal gradients in the oceans and under the ground. New materials are being found to produce cheaper photovoltaic, thermo-photovoltaic, and fuel cells. The next decade may prove to be one of the most interesting eras for energy enthusiasts. In fact, some economists proclaim, energy and the environment (as well as biotechnology and information technology) will become the most dominant sector affecting the economy in this century. Among the changes occurring in various energy sectors are:

Hydropower is going through major changes. The traditional methods of hydropower generation were waterwheels and hydroelectric plants. Although hydroelectric energy has already been exploited to its maximum potential in the United States and much of the industrialized world, small-scale hydro projects may serve as valuable resources in most of the developing countries. Research efforts are also underway, and some demonstration facilities have been built, to show the potential to harness the rise and fall of tides, underwater currents, and the motion of ocean waves.

Wind is another significant source of power. New advances in manufacturing processes have allowed the manufacture of lighter and stronger blades. Power electronics have also developed to a stage where variable-speed wind turbines with sophisticated control strategies have resulted in wind turbine designs with a wider range of operation and higher efficiencies.

Biomass is not only the source of all our food, but can also be used to generate energy. Although biomass is a renewable resource, it is not clean and, if burned, produces the same type of pollutants as fossil fuels. However, unlike fossil fuel, biomass does not produce greenhouse gases, and the overall emission is lower. Newer technologies allow higher productivity and cleaner burning. Genetically modified crops can be produced that are tailored to yield high heating values and burn with considerably less pollution.

Geothermal resources include hot water, steam, magma, and dry rock. With today’s technology only hot water and steam reservoirs can be economically exploited, but works are underway to exploit the earth’s natural thermal gradients. Geothermal heat pumps are available that use the relatively uniform temperature in shallow ground to provide winter heating and summer cooling with a payback time of only a few years.

Solar is another potentially huge, clean, and renewable source of energy, capable of producing both heat and electricity. Flat panel solar collectors are becoming increasingly more efficient and economical. For higher temperatures applications concentrators such as parabolic and dish collectors are manufactured with lighter yet durable materials. For electrical power generation, solar energy can be concentrated by means of a large array of mirrors and dishes (called a heliostat) that can heat up water in a receiver or be used to run a Stirling engine. Alternatively, electricity can be generated directly by photovoltaic cells which are becoming more and more efficient and at a cost of only a fraction of what they were just a few years ago. Thin films and organic plastics have been found that could substitute for silicon semiconductors -- the material used to manufacture most photovoltaic chips. Spherical solar cells are also being introduced in the market, which collect light from all directions, resulting in significantly better collection efficiency.

Hydrogen is considered by many to be the fuel of the 21st century, as much as wood was in the eighteenth, coal was in the nineteenth, and fossil fuel was in the twentieth century. Hydrogen is the cleanest of all fuels, whether it is burned or used to power a fuel cell. The only byproducts are heat and water vapor. The hydrogen technology is still in its infancy, and may still face unanticipated problems.

Nuclear Fission is the most controversial source of energy. Although power generated is clean and the cost is comparable to electricity generated by fossil fuels and hydroelectric plants, the unresolved issues of nuclear waste disposal and safety associated with these plants are daunting. In light of the terrorist attacks of September 11, 2001, these safety issues have taken an even higher priority. Work is being done to design safer reactors. One such design is called a Pebble Bed Reactor, designed originally by Germans and perfected by South Africans. Small grains of uranium, 0.5–mm in diameter, are placed in microspheres covered by layers of porous carbon and silicon graphite coating. Thousands of these microspheres are packed into pebbles, and then the pebbles are arranged in modular forms. The design is considered inherently safe, because fuel can never reach the melting temperature. Thus, the danger of meltdown scenarios similar to those in Three-Mile-Island and Chernobyl are considered highly unlikely. Furthermore, the graphite will act as a casket to contain the radioactive material even after the fuel is burned, eliminating the possibility of any radiation leak.

Nuclear Fusion is still considered the ultimate source of energy. About forty years ago, many had predicted that by the year 2000 fusion reactors would be operational producing cheap, clean, inexhaustible energy. Today, we are still coping with many of the same problems we were facing in the 1960s. The current prediction is that fusion may become practical only in the second half of this century. Time will tell whether we have to revise our predictions again.


(1) “Careers in renewable energy”, DOE/GO-102001-1130, January 2001 (

(2) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

Further Reading

Meadows, D. H., et al., The Limit to Growth, Universe Books, 1972. Also see, The Limit to Growth: The 30-Year Update, Chelsea Green Publishing Company, 2004.

Diamond, J., Collapse: How Societies Choose to Fail or Succeed, Penguin Group, USA, 2004.

Cleveland, C. J., Encyclopedia of Energy, Elsevier Direct Science, 2004.

The International Journal of Energy, Science Direct Elsevier Publishing Company.

Applied Energy, Elsevier Publishing Company.

Journal of Energy Resource Technology, ASME International.

The Energy Journal, The quarterly journal of the IAEE’s Energy Education Foundation, (

External Links

Energy Citation Database, US Department of Energy (

Environmental Protection Agency (

US Department of Energy (

The NIST Reference on Constants, Units, and Uncertainty (

The Club of Rome (

The Sierra Club (