SWATI SAXENA RTICLE A EATURE F There have been many efforts to build and fl y a solar-powered aircraft that does not guzzle conventional fuels. Although some headway has been made, there is still a long way to go. batteries or fuel cells are used for this The Solar-Powered Aircraft purpose. They can be re-charged during Developments’ “Solar One” is a British the day. mid-wing, experimental, manned solar- Solar Plane History powered aircraft designed by David Solar plane history dates back to the Williams was the third solar-powered 1970s when the 27 lb (12 kg) unmanned aircraft to fl y. A motor-glider type AstroFlight Sunrise, the result of an USA aircraft originally built as a pedal- HE world’s fi rst offi cial fl ight in a ARPA (Advanced Research Projects powered airplane to attempt the Channel solar-powered, man-carrying aircraft T Agency) contract, made the world’s fi rst crossing, the airplane proved too heavy took place on 29 April 1979. Technologists solar-powered fl ight from Bicycle Lake, to be successfully powered by human have been trying since long to look for a dry lake bed on the Fort Irwin Military power and was then converted to greener ways of fl ying aircraft. And what Reservation, on 4 November 1974. solar power, using an electric motor can be greener than harnessing the energy The improved Sunrise II fl ew on driven by batteries that were charged of the sun to power aircraft. 27 September 1975 at Nellis Air Force before fl ight by a solar cell array on the A solar powered plane converts Base. wing. The maiden fl ight of “Solar One” solar energy into electric energy through Larry Mauro built the Mauro Solar took place at Lasham Airfi eld; Hampshire solar panels, which is used to turn the Riser and accomplished the world’s on 13 June 1979. propellers. The solar panels are made fi rst offi cial fl ight in a solar-powered, The “Gossamer Penguin”, a up of photovoltaic cells, which convert man-carrying aircraft on 29 April 1979. smaller version of the human-powered sunlight into electricity. Photovoltaic cells The aircraft used photovoltaic cells that “Gossamer Albatross” was completely are made up of semiconductor materials produced 350 watts at 30 volts, which solar-powered. The US company, such as silicon and cadmium telluride. charged a Hughes 500 helicopter battery, AeroVironment, built it in 1979. A second When this material comes into contact which in turn powered the electric motor. prototype, the Solar Challenger, fl ew 262 with sunlight, the absorbed energy excites The aircraft was capable of powering km (163 mi) from Paris to England. On 7 the electrons and generates electricity. the motor for 3 to 5 minutes, following a July 1981, the aircraft, under solar-power, Solar planes need a source of energy 1.5-hour charge, enabling it to reach a fl ew 163 miles from Cormeilles-en-Vexin to power them at night. Usually electric gliding altitude. Airport near Paris across the English Science Reporter, JULY 2016 34 FEATURETURE ARTICLERTICLE FROM A SOLAR CELL TO A PV SYSTEM Solar Module Solar Cell Electricity Meter AC Isolator Fusebox Inverter PV-System Battery Charge Controller Generation Meter DC Isolator Solar Array Solar Panel Cabling Mounting Tracking System Diagram of the possible components of a photovoltaic system Photovoltaic cells are Military aircrafts need to be fast, quiet of them are also not launched in the made up of semiconductor and agile. Fuel effi ciency is not of primary conventional way. Some are launched by materials such as silicon importance in military applications. hand with a running toss into the air. and cadmium telluride. Solar planes on the other hand are Commercial and military airplanes mostly used for surveillance. The shape of use air-breathing engines for propulsion. When this material comes these planes is very different as well. Solar One, two or four engines are used on into contact with sunlight, planes have high aspect ratio (length/ these planes. Whereas, several electric the absorbed energy excites span) wings as compared to commercial propellers (up to 14) power solar planes. or military aircrafts. They are closer to sail The cruising speed of Helios is no the electrons and generates planes in their wingspan. more than 27 miles per hour while Boeing electricity. Next, let’s compare the weight 747-400 cruises at 567 miles per hour. The of different planes. NASA’s Helios farthest fl ight for a solar plane has been Channel to RAF Manston near London, solar plane weighs nearly 929 kg while 163 miles per hour. fl ying for 5 hours and 23 minutes. Boeing 747-400 weighs nearly 397000 kg Solar planes, however, win in the Designed by Dr. Paul MacCready the with cargo and F-22 weighs 37875 kg. category of longevity. Regular planes Solar Challenger set an altitude record of Commercial airplanes need to transport need to be re-fueled and hence they need 14,300 feet. passengers and cargo and therefore to be grounded. There have been instances Comparison they need to have big fuselages and are of re-fueling aircrafts using another plane There are some basic differences between very heavy. Military airplanes carry one while in fl ight but it is a very expensive traditional planes such as Boeing 747 or or two people and need to have high task. Solar planes can remain in air for the military aircraft F-22A raptor and maneuverability. Therefore, they are as long as the batteries continue to get the solar powered planes. A commercial lighter. charged by solar energy. plane, such as Boeing 747-400, transports Solar planes are even lighter as The amount of solar energy per hundreds of passengers from one location they are powered only by solar energy square foot of panels in an hour is very to another with decent fuel mileage. and cannot fl y if made very heavy. Most less as compared to the energy produced 35 Science Reporter, JULY 2016 FEATURE ARTICLE Solar planes can help with reconnaissance and can observe a particular spot for days. Satellites can do some of these tasks but solar planes are closer to the ground and can see more detail with less expensive cameras. They are less expensive as compared to a Pathfi nder-Plus/HTML/ED02-0161-2.html) Pathfi satellite and can be moved (Source: http://www.dfrc.nasa.gov/Gallery/Photo/ as needed. Pathfi nder-Plus in fl ight over Hawaii, June 2002 by one gallon (3.78 liters) of jet fuel. Solar kilometers) where they can receive direct satellite and can be moved as needed. panels convert nearly 10-20% of the uninterrupted sunlight. During fl ight, the A solar plane costs nearly 20 million total energy into electric energy used for plane automatically switches between US dollars so they are still very expensive propellers. Since the available power is battery and solar as needed. During as compared to gliders due to the very less, the solar planes are kept very landing, both power sources are cut off so expensive solar panels, which comprise of light so that wind can lift them. They are that it can glide down. They are usually nearly half of the total cost. Boeing 747, on made very thin and light. very slow when coming down due to the other hand, costs nearly 250 million Often carbon-fi ber pipes are used for their lightweight and big wingspan. US dollars. the frame with a strong fabric like Kevlar Solar planes can help with As they are environment friendly, stretched across it. They run on batteries reconnaissance and can observe a solar planes leave no carbon footprint. or fuel cells at night. The solar panels are particular spot for days. Satellites can do And since they fl y at very low speeds, spread all across the wing to utilize the some of these tasks but solar planes are there is no threat to birds. entire open surface area. closer to the ground and can see more But one of the disadvantages is that Solar planes prefer to fl y above detail with less expensive cameras. They solar planes need favorable weather the clouds in the Stratosphere (12 to 20 are less expensive as compared to a conditions for takeoff. They can’t stay in Cumulus clouds or turbulent layers of the sky. Let’s have a look at some solar planes. NASA Pathfi nder, Centurion and Helios (United States) NASA’s Pathfi nder, Pathfi nder Plus, Centurion, and Helios were a series of solar and fuel cell system–powered unmanned aircraft developed by AeroVironment, Inc. (https://www.avinc.com) from 1983 until 2003 under NASA’s Environmental Research Aircraft and Sensor Technology program (ERAST). Helios/HTML/ED01-0209-3.html) On 11 September 1995, Pathfi nder set an unoffi cial altitude record for solar- (Source: http://www.dfrc.nasa.gov/Gallery/Photo/ powered aircraft of 50,000 feet (15,000 m) during a 12-hour fl ight from NASA Dryden. On 7 July 1997, Pathfi nder raised the altitude record for solar–powered aircraft to 71,530 feet (21,800 m), which was also the record for propeller–driven Helios in fl ight by NASA aircraft. On 6 August 1998, Pathfi nder Science Reporter, JULY 2016 36 FEATURE ARTICLE (Ref.: www.solar-fl ight.com) (Ref.: www.solar-fl Solar Flight Inc.’s solar- Sunseeker II: One seat solar plane by Solar Flight Inc. powered airplane Sunseeker, aerial vehicles. They were built to develop where the Wright Brothers fi rst fl ew.