Obviously, an electric aircraft needs juice if it's going to soar -- and that's the big challenge. How do you provide an airplane with enough electricity to power it without weighing it down too much? That's the real advantage of fuel: By and large, an electric battery just can't supply as much power as its weight in gasoline can produce. Still, it hasn't stopped designers from trying. These are the three basic varieties of electric aircraft:
Battery-powered: This design entails hooking the plane up with the appropriate supply of onboard battery power. In addition to playing a role in the first electrically powered flights of the late 19th century, batteries continue to power many of the radio-control planes used by hobbyists today. These two facts are not unrelated: It's much easier to use batteries in a tiny, unmanned plane or an airship elevated by hot air. As batteries introduce a great deal of weight to an aircraft, the reality of a piloted battery-powered airplane had to wait for fuel-cell technology to advance sufficiently. The first manned battery-powered flight took place on July 16, 2006, when students at Tokyo Institute of Technology launched a light plane powered by 160 AA batteries [source: BBC News].
Solar-powered: To deal with the problem of battery weight, designers in the 1970s took to the skies with solar power. These planes didn't rely solely on battery power, but instead used it in conjunction with the endlessly renewable resource of the sun. However, the amount of energy from solar radiation is still rather puny compared to a gallon of jet fuel, rendering solar aircraft both slow and light. The main upside is that they can, in theory, stay airborne for years at a time -- either as unmanned, low-flying satellites or tethered to the ground like kites. For more information, read How Solar Aircraft Work.
Wireless power transmission: Another method of delivering power to an electric aircraft is power beaming or wireless power transmission (WPT) This technology involves using either a ground-based laser or microwave emitter to send energy through the air to a receiver-equipped airplane. Microwave power transmission (MPT) was first used in 1964 to power a miniature helicopter -- and for a whopping 10 hours [source: Dickinson]. In 2002, NASA researchers successfully demonstrated the use of spotlights and laser beams to provide small, unmanned solar craft with necessary energy. While research into this technology continues, scientists believe it may one day allow solar-equipped aircraft to fly through the night in certain areas. For more information, read How Wireless Power Works.