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Nearly
66% of the petroleum consumed in the United States is burned for
transportation. In 1999, about sixty percent of the crude oil supply was
imported from other countries.
The
pollution resulting from burning vehicle fuels contributes to the
greenhouse effect, acid rain, and smog. Vehicles powered by solar and
other renewable energy resources are possible alternatives to conventional
vehicles powered by internal combustion engines and fossil fuels.
Solar-powered vehicles (SPV’s), such as cars, boats, bicycles, and even
airplanes, use solar energy to either power an electric motor directly,
and/or use solar energy to charge a battery, which powers the motor. They
use an array of solar photovoltaic (PV) cells (or modules made of cells)
that convert sunlight into electricity. The electricity either goes
directly to an electric motor powering the vehicle, or to a special
storage battery. The PV array can be built (integrated) onto the vehicle
body itself, or fixed on a building or a vehicle shelter to charge an
electric vehicle (EV) battery when it is parked. Other types of renewable
energy sources, such as wind energy or hydropower, can also produce
electricity cleanly to charge EV batteries.
SPV’s that have a built-on PV array differ from conventional vehicles
(and most EV’s) in size, weight, maximum speed, and cost. The
practicality of these types of SPV’s is limited because solar cells only
produce electricity when the sun is shining. Even then, a vehicle
completely covered with solar cells receives only a small amount of solar
energy each day, and converts an even smaller amount of that to useful
energy. At present, most SPV’s with built-on PV arrays are only used as
research, development, and educational tools, and/or to participate in the
various SPV races held around the world.
Solar Car Designs
Perhaps the first, totally solar-powered car, the "Bluebird,"
was built by Ed Passerini, in 1977. Mr. Passerini has also built several
other small, lightweight, and relatively low-cost (under $10,000) solar
cars. At the other end of the spectrum, are solar cars equipped with
advanced technology and built with the backing of large automobile
manufacturers, including General Motors (GM), Ford, and Honda. Some solar
cars use silver-zinc batteries, which have several advantages over
traditional lead-acid batteries: they are lighter, are more efficient, and
accept higher rates of charging. However, they are very expensive, and may
only be charged and discharged (cycled) a few times before they become
unusable and require recycling. While most developers use crystalline
silicon cells in their designs, GM has used the higher efficiency, but
more costly, gallium arsenide cells. GM’s Sunraycer has a 90 square-foot
(8.4 square-meter[m2]) curved solar array integrated into the tear-dropped
shaped body of the car. GM spent $8 million developing the Sunraycer.
John Mitchell Systems designed a SPV with a PV array integrated into two
vertical air foils. These act as a sail to provide aerodynamic thrusts. In
tests, the vehicle achieved 30 miles per hour (mph; or 48 kilometers per
hour [kph]) using wind power alone. Ford Motor Co., and others, have
designed tiltable arrays that track the sun.
Advances in lightweight structural materials have also contributed to
improving solar car performance. The Sunraycer has an aluminum chassis and
body made of two lightweight composite materials. While the car is 19.7
feet (6 meters [m]) long, 6.6 feet (2 m) wide, and 3.3 feet (1 m) high;
the chassis weighs only 14 pounds (6.4 kilograms [kg]). The entire shell
weighs less than 100 pounds (43.4 kg). The total weight of the vehicle,
without the driver, is 390 pounds (177 kg).
Integration of PV Cells onto Conventional Cars
Kyocera Corporation developed a prototype solar-assisted electric commuter
vehicle. It is a small, two-seat hatchback, and weighs about 1,200 pounds
(544 kg). With its nickel-zinc batteries fully charged, the car has a top
speed of 40 mph (64 kph) and a driving range of 70 miles (112 km). A 23
square feet (2.1 m2) PV array can extend this range up to 100 miles (160.9
km) on a sunny day.
Two auto manufacturers have introduced models with an optional PV panel
incorporated into a sunroof. The PV panel runs a ventilation fan to cool
the car when parked in the sun. Other potential uses of solar cells are
for vehicle starting battery charge maintenance systems. PV battery
charging arrays have been designed for rear spoilers, and a "solar
wing," a feature similar to a rear spoiler that provides a downward
force on the vehicle to help improve its traction on racetracks and
highways.
PV EV Battery Charging
The Sacramento Municipal Utility District built a PV array that it uses to
help charge several of the electric cars and trucks that it owns. The
array also shelters the vehicles when they are being recharged. Edison EV,
a private company, designs and builds these types of "charge
ports" for EVs.
Solar Powered Bicycles, Boats, and Aircraft
The city of Palm Springs, California, has constructed 16 charging stations
for electric bicycles around the city. The city’s police department and
many commuters use the stations daily. The stations have lockers for
electric bikes with an electrical outlet that is connected to a
pole-mounted PV array. When parked and "plugged in," the array
charges a bike’s battery.
In 1974, two brothers, Robert and Roland Boucher, flew the Sunrise I, an
extremely light-weight, remote controlled, pilot-less aircraft powered by
a PV array on the wings, to a height of 300 feet. The next year, their
more advanced Sunrise II flew to 17,000 feet (5,000 meters). The US Air
Force funded the development of these solar powered aircraft with the
hopes of using them as spy planes. In 1980, the son of Paul MacCready,
piloted a smaller, sun-powered version of the pedal-powered Gossamer
Albatross (which Mr. MacCready had pedaled across the English Channel).
With support from Dupont, MacReady built the Solar Challenger, and crossed
the English Channel on July 21, 1981. It attained an average speed of 50
mph (80 kph), and at about 12,000 feet (3658 meters).
AeroVironment Inc. built the Pathfinder for the National Aeronautics and
Space Administration (NASA) The Pathfinder is a remote controlled, 100
foot (30m) long "flying wing." It weighs less than 600 lbs (273
kg) and is almost completely covered by a thin-film PV array. Electricity
from the array turns small motors that turn 8 propellers to move and steer
the craft. It has flown to 80,000 feet (24,384 meters). It could be the
precursor to solar powered aircraft that can stay aloft for months as
alternatives to space-based remote sensing satellites.
Solar/battery powered boats are another type of SPV. PV (and wind energy)
systems can charge batteries to run small electric lights and appliances,
and even to run electric motors to move the boat itself.
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