Scientists, including chemists and chemical engineers, have also been pursuing the direct capture of solar energy, either for heating or for directly generating electricity.³ One plan would cover significant amounts of arid desert and other surfaces such as rooftops with photovoltaic cells that directly convert solar energy into electricity. At the present time, photovoltaics can convert as much as 30% of the incident sunlight to electricity. The technical challenge, however, is to devise materials and manufacturing processes for photocells that are cheap, long lasting, and efficient in the conversion of light to electricity; ways are also needed to collect, store, and distribute the energy when and where it is needed. These problems have not yet been completely solved. A related advance is the invention of electrically conductive polymers, which are not metals. Alan J. Heeger, Alan G. MacDiarmid, and Hideki Shirakawa received a Nobel Prize in 2000 for opening up this important new area of science.

In an alternative way to take advantage of the sun’s energy, photocells are under development using sunlight to drive chemical transformations, perhaps even producing chemicals that in turn could be used to generate electricity. For example, the photochemical generation of hydrogen, by splitting water, could be combined with a hydrogen fuel cell in this way. This area strongly depends on basic research in photochemistry.

An alternative to solar energy is provided by nuclear energy—currently the source of 7% of the world’s total energy and 20% of U.S. electrical energy. Chemists and chemical engineers have devised the processes for producing the nuclear fuels from crude uranium ores. In many countries nuclear power plants are major sources of electricity (as much as 75% in France), but one of the problems is nuclear waste. A typical nuclear energy plant produces 20 metric tons of radioactive waste each year. Chemists and chemical engineers are working to devise methods to separate the radioactive material from the inert material in which it is produced. If this is successful the volume of radioactive substances to be handled will be much less, and some of the purified radioactive materials may be available for other uses (including medical diagnostics and treatment). As another approach, converting the waste products to tough ceramics could make them stable for very long periods of time. The development of safe methods for dealing with radioactive waste—together with public acceptance of them—pose a challenge to which chemists and chemical engineers can respond.⁴