In his 2009 novel, “Hidden Empire”, Orson Scott Card wrote that there would never be a battery-powered airplane.
The trouble with such sweeping predictions as Card’s is that, once you challenge the ingenuity of scientists and engineers, they find a way to prove you wrong. Take, for example, the solar-powered airplane currently being tested by the Swiss.
This airplane, which uses electric motors driven only by solar power, came out as a prototype (HB-SIA) in 2009, and showed itself capable of flying a distance of 350 meters (1148 feet), albeit at only one meter off the ground.
Sometime this year, however, that same prototype, designed by Lausanne, Switzerland-based Solar Impulse SA, is expected to make a non-stop flight of 36 hours, overnight, using only the stored power of solar panels.
The HB-SIA’s wingspan is enormous; at 63.4 meters (or 208 feet) it rivals both the Boeing 747 and the Airbus A340. Its weight, at 1.6 tonnes, is only a fraction; the Boeing tips the scales at more than 333 tonnes. The HB-SIA achieves its slimmed-down profile via honeycomb carbon fiber structural elements, which provide superior strength with less density than aluminum.
The four electric engines run off 11,628 photovoltaic cells made by San Jose, California-based SunPower Corp. These cells take up 200 square meters (2152.78 square feet) of space on the wings and horizontal tail portion, and have a conversion efficiency of 22 percent, which is about the highest rating on the market today, rivaling Sanyo’s claim for 23 percent efficiency.
The engines output about 6 kilowatts, or 10 horsepower. This is equivalent to the power used by engines installed by Orville and Wilbur Wright on their Wright Flyer at Kitty Hawk, N. Carolina, in 1903. The fact that the two kinds of engines are so closely matched in power ratings makes for a curious synchronicity, coming as it does at the beginning of the history of manned flight and its 21st century solar version.
Averaging about 70 miles per hour, the HB-SIA stores power in a series of lithium polymer rechargeable batteries weighing less than half a tonne and providing an energy density of about 220 watt-hours per kilogram (Wh/kg). This is well above the standard for the industry, which is about 150 Wh/kg – a limitation that is integral to Li-ion energy storage in general, according to Ecogeek founder and green guru Hank Green, although lithium-air (oxygen) batteries may alter that paradigm.
Solar Impulse is funding the construction and ongoing testing of HB-SIA through its foundation, which operates under the auspices of the Swiss Confederation as a public utility body, aimed at finding ways toward a fossil fuel-free world.
In 2013, funding will be directed toward the larger HB-SIB, which – with its wingspan of 80 meters (about 263 feet) – will attempt to circle the earth in 25 days (and five stops for human refueling) using nothing but solar power.
Bite your tongue, Scott.
