Energy for the 21st Century

Energy issues continue to be of critical interest at American Association of Physics Teachers meetings. Bill Halsey of Lawrence Livermore National Laboratory made this clear in his discussion of "Energy Alternatives to Compete with Current Fossil Fuel Technology" on August 3rd in Sacramento. "Energy is the driving force," he said, "and within that carbon dioxide is the big gorilla." Halsey then went on to show just how big a gorilla carbon dioxide can be. Of our residential and commercial energy, he pointed out, three quarters is electrical, generated from coal, natural gas, and nuclear; the remaining quarter is direct use of natural gas.

Our industrial energy is one third electrical, one third natural gas, and one third oil; the industrial sector of our economy, Halsey added, represents our most efficient use of energy. In contrast, all our energy for transportation comes from oil, and it represents our least efficient use of energy. Halsey's conclusion: "Transportation must change." If it doesn't, he went on, our continued reliance on fossil fuels for transportation alone will double the generation of carbon dioxide in the twenty-first century. And if we are to limit carbon dioxide to twice its pre-industrial level while doubling energy supply every 40-50 years, he said, we will need a fifteen-fold increase of carbon-free energy by the century's end.

Although the world's energy future will also be influenced by population and living standards, even with "conservation" and improved efficiency, the intensity of energy use cannot be reduced to zero. In fact, Halsey noted, the rate of increase in energy demand (1.5-2%/yr) is currently outpacing improvements in efficiency (1%/yr). And because of infrastructure, our energy mix can't be changed quickly: new technologies need twenty years of research and development, another twenty years to be fully marketed, then yet another twenty years to make a dent in the market, he observed. Because even carbon-free generators of electricity depend on fossil fuels for manufacture of their equipment, they too are sources of carbon dioxide.

Halsey presented the life cycle carbon dioxide intensity in units of kg carbon dioxide per megawatt hour (electric) for electrical energy sources as follows: hydroelectricity, 18; nuclear fission, 22; solar, 59; wind, 125; liquid natural gas, 653; oil, 686; and coal, 990. To limit carbon dioxide to double its pre-industrial level, Halsey said, this must decrease by 50% by 2050 and by 75% by 2100.

Halsey went on to list the ways to reduce carbon dioxide: efficiency improvements (which could account for a 20% decrease), switching from coal to natural gas (50% decrease), gasifying coal (also a 50% decrease), and carbon dioxide capture and sequestration. Future use of fossil fuels, he added, must also take into account their long-term limits: 10-40 years for oil, 20-40 years for natural gas, and 100-200 years for coal. Halsey concluded by listing the prognoses for carbon-free energy sources.

Wind is the current "hot" renewable, he observed, currently growing at 16% per year, but presently generating the equivalent of only six electric power plants. Yet Halsey expected that it could generate 20% of our electricity in 50 years. With cost reduction, he added, solar could generate another 10% of our electricity in the same time frame. Halsey was less enthusiastic about other energy sources considered to be "renewable." Biomass presently consists largely of dung, and he observed that more people today still burn it than burn natural gas. There are "advanced" biomass sources, such as alcohol produced from specially-grown crops, but Halsey stressed that they are highly land intensive. And hydroelectric and geothermal technologies he classified as "mature," meaning that they are presently producing pretty much all that they can.

Halsey then went on to nuclear technologies. They began with great promise, he observed, but then faltered. Yet they are still generating the cheapest electricity. New designs and technologies, including advanced fuel cycles, including the use of fast neutrons to fission actinides (but not necessarily "breed" actinide fuel) can play an important role. And without advanced nuclear fuel cycles, Halsey cautioned, nuclear fission's contribution will be limited. Halsey's parting words: "Over-reliance on a single energy source is risky. We need to try everything that looks promising."

One energy source that currently does not look promising but could still play a significant role in our energy future is nuclear fusion. In a talk on "Fusion -- the Ultimate Energy Source?" (which he subtitled "The Agony and the Ecstasy"), John Perkins, also of Lawrence Livermore National Laboratory, observed that we have spent fifty years unsuccessfully trying to make nuclear fusion a viable energy source, and success always seems to be 30 years in the future. But the reward of unlimited energy is so great, he added, that it is important to persist in achieving it. Fusion occurs on the Sun because of gravitational confinement, Perkins said.

Fusion has been achieved on Earth in thermonuclear weapons, but not without nuclear fission. Two approaches have been used to achieve peaceful nuclear fusion: magnetic confinement and inertial confinement. The next step in magnetic confinement is the $3.2 billion International Thermonuclear Experiment Reactor, which is designed 400 megawatts (thermal) with an energy gain of 10 in 400 second pulses, once the six participating groups of nations decide where to build it.

The immediate future of inertial confinement is the National Ignition Facility at Livermore, which has arranged 192 infrared lasers to ignite the fusion of deuterium and tritium in a small pellet. The project is two-thirds built, Perkins reported, and the target date for trials is 2010. It, too, is designed to achieve an energy gain of 10, and when this is achieved, Perkins said, nuclear fusion will no longer be 30 years away. Perkins closed by observing some advantages of nuclear fusion over nuclear fission. Unlike fission, nuclear fusion is free of the threat of proliferation of nuclear weapons. Perkins observed that fusion can also get us off the steam cycle for generating electricity, by using alternative conversion technologies like magnetohydrodynamics. Furthermore, he concluded, fusion is the only energy source that can take us to the stars.