Advances in Solar-Powered Flight
The extent to which solar cell and battery technology has advanced was well demonstrated by the aircraft, Solar Impulse, which recently flew across America powered entirely by sunlight. The airplane used monocrystalline silicon solar cells, chosen for their ratio of efficiency to weight, to capture solar energy and convert it into electrical power. While solar-powered planes will not be replacing conventional aircraft for the foreseeable future, the advances in technology are noteworthy and valuable to other alternative energy applications.
The Solar Impulse has a wingspan of more than 63 meters, but only weighs 1,600kg. These long wings serve two main purposes – providing lift and, along with the tail, providing 200 square meters of surface area for the huge number of solar cells needed to harness the power of the sun. These solar cells are the lightest in weight and thinnest (135 microns) silicon photovoltaics, but they still account for up to twenty-five percent of the Solar Impulse’s mass. During the hours of the day when sunshine is at its strongest, the solar cells enable the aircraft to charge its batteries while climbing to its peak altitude of 9,000 meters. Because the airplane is shaped like a glider, when the sun is no longer providing power, the pilots are able to shut the engines off and glide, sometimes for several hours, before switching over to using energy stored in the batteries. The Solar Impulse has managed to stay airborne for 26 hours using this method.
In addition to the flight across America, from San Francisco to New York, the Solar Impulse has also completed flights in Europe and from Europe to North Africa. The next goal is a trip around the world, but as pilot André Borscheberg notes, while technology is able to sustain 24 hours flights, the pilot is not. There is only space for one pilot in the current aircraft, with very little room to move about and next to no room for essential equipment such as a parachute and oxygen. To make a trip around the world, the aircraft will need to be larger in order to allow the pilot space to move around and catch some sleep. No doubt these, and other, obstacles will be overcome as technology keeps advancing.