CREDIT: SOLAR MILLENNIUM

The end of the age of fossil fuels may be in sight, but what comes after is still a bit of a blur. There are numerous alternatives to coal, oil, and natural gas from electricity generated by solar farms to biofuels brewed from plants. Scaling up these alternative sources of energy, however, has proved a challenge. This special issue explores the progress that researchers are making in developing better alternatives, and the technical, political, and economic pitfalls associated with scaling them up.

As Kerr (p. 780) notes in a News feature, alternative energies have big shoes to fill. Fossil fuels are widely used in part because they have some unique advantages over other sources of energy. A coal-fired power plant, for instance, can keep running when the Sun isn't shining or the wind dies down, and fossil fuels typically get more energy out of a hectare of land or a liter of raw material than the alternatives. It took about a century to build the energy system that runs on fossil fuels, though, and Kerr reports that it could take just as long to develop alternatives. Still, both Kerr and Cho (p. 786) report that there is potentially more than enough energy available from the Sun, wind, and other renewable sources to replace fossil fuels. Clery (p. 782) reports on one ambitious multinational effort to harness renewable sources to generate electricity in North Africa and then transmit the power across the Mediterranean Sea to Europe. Service (p. 784), however, reports on how high hopes in the United States for one emerging alternative, cellulosic biofuels, have waned because of technical and economic setbacks. Kintisch (p. 788) notes that even a relatively mature alternative technology, wind power, is now encountering public opposition owing to the environmental and aesthetic impacts of wind turbines.

Such grand visions rest in part on vigorous continuing research. Three Perspectives take an in-depth look at how researchers hope to scale up biofuels development successfully. Somerville et al. (p. 790) survey the most promising land crops for large-scale development, and Wijffels and Barbosa (p. 796) discuss algae: a source that holds promise because of both its high content of lipids (which more closely resemble petroleum than sugars do) and its low land-area requirements. Richard (p. 793) considers the changes in transport and processing infrastructure that will be necessary to ship biofuels from field to fueling station.

Finally, nuclear power is a perennial player in the carbon-neutral energy discussion. Grimes and Nuttall (p. 799) review a two-stage approach to the expansion of fission-based electricity generation, with the upcoming 20 years focused on shoring up current technology, followed in later years by the design and construction of next-generation plants that reprocess spent fuel for greater efficiency and waste minimization. Together, all of these pieces show that interest in scaling up alternatives remains high and that many attractive new energy sources exist despite the considerable challenges involved in their development.