A brief look at the capabilities of solar aircraft...
In late June/early July, Solar Impulse 2 set the world records for the longest and farthest flights in a solar-powered craft when it flew over 3,500 miles in approximately 80 hours - the longest non-stop solo flight without refueling in history.
While the aviation industry has been flirting with the idea of solar-powered planes like the Swiss-made Solar Impulse 2 since the seventies, the idea of solar aircraft is still a new phenomenon. The technical limitations of these platforms have restricted them to more obscure applications, with many functioning similar to low-altitude satellites. However, technology has advanced, and these fascinating vehicles represent a new horizon for the aviation industry, as described here by Cleantech Solutions founder Salman Zafar.
A solar aircraft operates, as its name suggests, on solar cells instead of internal combustion engines. They will typically have a large number of solar cells placed on the airframe. These cells take the sun's rays and use them to produce electricity, and that electricity powers the on-board engines.
As mentioned, there are significant limitations to the technology itself. The most glaring of these has to do with power output; solar cells simply cannot produce as much power as the engines in conventional airplanes. A square foot of solar cells, for instance, produces a minuscule amount of energy when compared to combustion engines, three to six times less power than is used by a sixty-watt light bulb, and solar cells as a whole are only ten to twenty percent as effective as jet engines. The result of this is that aerospace engineers often attempt to cover the airframe with as many cells as possible while also trying to keep the weight as low as possible; many solar-powered airplanes exhibit decidedly unconventional designs. NASA's Helios, for instance, is shaped like a flying ruler, and it even bends.
Conventional airplanes, those powered by combustion and jet engines, greatly exceed the capabilities of their solar counterparts in terms of speed, distance, and maneuverability. When it comes to longevity, however, the amount of time that an airplane can remain airborne, solar airplanes have a distinct advantage. Because solar energy constitutes a renewable energy source, it can be said that a solar airplane run off of an infinite power plant. Props and jets need to land in order to refuel, but solar aircraft can stay in the air for as long as their batteries have juice.
There are a few very worthwhile environmental benefits that come with using solar energy for aviation. Solar-powered crafts emit no exhaust, while airplanes alone reportedly produced five hundred million tons of carbon dioxide in 1992, which accounted for two percent of all human emissions that same year. Their ability to stay airborne for greater amounts of time also makes them a greener option for surveillance or data collection applications. Meanwhile, jet airplanes emit exhaust directly into the atmosphere, directly contributing to air pollution and ozone depletion.Sarah Smith