Cheaper solar power is on the horizon.
Solar cells have a well-deserved reputation for being too expensive. But a steady drop in costs, along with high electricity prices and government subsidies around the world, have led to a boom in the solar market. And while advances in conventional silicon cells will continue to play a major role in continuing this boom, emerging technologies will also play an important role. A number of companies are developing efficient solar cells based on microscopically thin layers of semiconductor material; they're also developing fast, high-volume manufacturing methods that could cut costs. (See "Large-Scale, Cheap Solar Electricity.") Meanwhile, others are developing similarly inexpensive manufacturing for mirrors and lenses to concentrate sunlight, which reduces the amount of expensive photovoltaic material needed. The concentrators make it feasible to use ultra-high-efficiency (and expensive) solar cells originally developed for use in space. (See "Cheap, Superefficient Solar.") This month one manufacturer of such cells set a new record by producing cells that convert 40.7 percent of the energy in sunlight falling on them into electricity. At the same time, others are developing advanced solar cells that mimic photosynthesis or harness nanocrystals to make better cells. (See "New Solar Technologies Fueled by Hot Markets.")

Clean coal technologies get mixed up in politics.
Coal will be a major source of electricity for a long time, especially in places such as China and the United States. That's because it's cheap. The problem is that burning coal emits huge amounts of carbon dioxide. While President Bush supports research into new technology that can reduce such emissions, the fact is that good technology, such as gasification, burning coal in pure oxygen, and methods for sequestering carbon dioxide, exists now that could make a big difference. (See "Simpler and Cheaper Clean Coal Technology" and "The Dirty Secret.") At this point, cleaning up coal is more in the hands of policymakers than in the hands of researchers.