How it works: Hydrogen from natural gas and oxygen from the air react to generate pollution-free, noiseless energy. The most promising kind of fuel cell used for vehicles - the proton exchange membrane, or PEM - uses an electrochemically active platinum catalyst.
Emissions: Squeaky-clean water vapor.
Technical hurdles: To cut costs, scientists now use 30 times less of the pricey platinum. But even with a cheaper catalyst there are obstacles to fuel-cell penetration - namely, the lack of working refueling systems and the demands of storage. A refueling scheme requires the conversion of natural gas to hydrogen, either at the filling station or on the fly; neither scenario has been realized. The problem is that storing the highly combustible element once it's converted requires a lot of space - who wants to drive a big, clunky car that could blow up in a fender bender?
Cost per kilowatt: $2,000 (the internal combustion engine, without muffler or engine control, costs $30 per kW).
Key players: International Fuel Cells, Ballard Power Systems, H Power.
Technical hurdles: That means really cooled: Even so-called high-temperature superconductors require the über-Nordic temperatures of liquid nitrogen to become nonresistant. So the challenge is twofold. First, come up with compounds that make good wire but can take the heat - a Japanese team at Aoyama-Gakuin University recently showed that the very cheap magnesium diboride can superconduct at around -234öC, as opposed to the -253öC required by older materials. Second, find a way to maintain that temperature along the length of the wires - researchers are using metallic silver sheaths wrapped around wires for carrying the coolant. Detroit Edison is using ceramic wires made of bismuth, strontium, calcium, and copper oxide to upgrade an area that will serve 14,000 homes.
Key players: American Superconductor, Intermagnetics General Corporation.
Emissions: None. And they're silent.
Technical hurdles: Photovoltaics are widely used as a power source for communications satellites, but here on Earth they're generally too costly to compete with traditional sources. Meanwhile, as demand grows, the industry will likely exhaust its supply of crystalline silicon - scrap from the semiconductor industry. It will have to find new sources of silicon or identify new materials. There are several thin-film technologies under development, all of which may one day be cheaper than crystalline silicon, but which have yet to achieve comparable efficiency levels.
Cost per kilowatt: $7,000-$9,000.
Key players: BP Solar, Kyocera Solar, Siemens Solar.
Emissions: Carbon dioxide and water, small amounts of nitrogen oxides, and, with some fuels, carbon monoxide.
Technical hurdles: Greater deployment of microturbines will require smarter ways of incorporating new sources into the growing grid. The current network was designed to handle large numbers of consumers getting power from a small number of central producers. Each microturbine, by contrast, serves small groups of consumers on a small portion of the grid. When these sections require maintenance, technicians will need to cut off both the microenergy sources and the central ones feeding affected areas. As more and more small generators are connected, the more complex grid will require better monitoring and control of energy flows.
Cost per kilowatt: $700-$1,500.
Key players: Capstone Turbine, Honeywell.
STATE OF THE ART
Fuel Cell
Superconductive Cable
Photovoltaic Array
Microturbine
