|The last two decades have seen the development of solar cars powered by energy from the sun. A solar powered vehicle can only run efficiently when the sun shines, although most vehicles of this type have a battery backup. Electricity is stored in the batteries when the sun is shining and this power can be used when sun light is restricted. The batteries are normally nickel-metal hydride batteries (NiMH), Nickel-Cadmium batteries (NiCd), Lithium ion batteries or Lithium polymer batteries. Common lead acid batteries used in the average car are too heavy. Solar powered cars normally operate in a range of 80 to 170 volts. To reduce friction with the ground the wheels are extremely narrow and there are usually only three. These are expensive to produce and usually seat only one or two people. Currently they are neither a practical nor economic mode of transport- however, with growing developments they are likely to play a part in reducing reliance on fossil fuels in the future. The huge cost of these cars is mainly due to the large number of expensive and delicate photovoltaic solar panels that are needed to power the vehicle, as well as the high cost of lightweight materials such as titanium composites, carbon fibre and fibre glass. Currently, most of these cars, mainly used in races, are hand made by specialist teams and this adds to the expense. A combination of solar power and wind power may prove to be a method of charging the batteries of �electric cars�.
Several teams have developed lightweight solar cars with new materials, combined with efficient design. Few of the developments:
A team at the Delft University of Technology in the Netherlands has developed the Nuna6 vehicle. Tipping the scales at just 320 lbs, the Nuna6 is half the weight of the first Nuna model developed by the team in 2001. It is also the smallest car in the Nuna family, with a length of 14.6 feet. The wind drag of the new solar-powered car is ultra-low- about as much as a side mirror of a truck driving at 62 miles/hour. The body is made from a carbon fiber sandwich structure to maximize stiffness. Intermediate modulus fibers are woven into a weave by a company from Sweden called Oxeon. A fabric called TeXtreme tis used- it is at the moment one of the most advanced fabrics available. The key feature of the fabric is that it is woven with 20 mm tapes, while regular fabrics are woven with rovings. This has a result that the TeXtreme fabric can be much more flat, and the fibers are straighter. This results in a higher stiffness, which is the key to the design because the car is so big and light. The matrix resin is a special polymer from DSM called Turane that is durable and tough and is said to have very good mechanical properties. The structural foam in the composite sandwich is a product called Rohacell� from Evonik Industries. Nuna6 uses foam with densities varying from 0.00112lb/in3 to 0.00397lb/in3. This special aerospace-grade foam is resistant to high temperatures, is easy to form, and has good mechanical properties. It is flat shaped like a large wing to maximise aerodynamic efficiency and provide enough space for solar panels which cover the top of the vehicle. The total energy consumption is 10 times lower than that of a modern electric vehicle. It is so sleek, that the cars total drag is roughly equivalent to that of a side mirror of a truck travelling at 100 km/hour. It has a strong rigid resin formulation which is lightweight while reducing vibration, allowing the car to go much faster with less energy.
The Stanford Solar Car Project has unveiled Xenith, a solar-powered vehicle that boasts several industry-leading technological innovations, including a lightweight carbon composite chassis. The car weighs just 375 lbs which is down to its 4-inch thin chassis that is made of a unique blend of carbon fibre, titanium and aluminium. The vehicle creates less aerodynamic drag than a rider on a bicycle and it can cruise continuously at over 55 miles/hour fueled only by the sun. It features a three-wheel steering system, glass encapsulated solar panels, and a high efficiency electric motor. he vehicle can travel at 55-60 miles/hou under sun power alone, and it can reach higher speeds when using the reserve battery pack. The vehicle is the first solar powered car to use flexible glass for panel encapsulation. The thin, flexible glass gives us a big advantage because of its strength, UV stability and optical clarity.
The National Kaohsiung University of Applied Sciences developed a solar car titled Apollo VI- 4.3 meters long, 1.8 m wide, and 1.1 m high, weighs around 130 kilograms without taking into account the weights of the driver and battery. It uses silicon solar cells for the first time in order to comply with the new regulations. Although the silicon solar cells cost more than NT$1 million (US$33,700), the whole vehicle built at a value of NT$5 million could reach a top speed of 120 km/hour, with the average speed of between km/hour. The tires are low-friction with lightweight rims that are suitable for the long-distance race.
Tokai University has designed a solar car using HIT® solar cells boasting the world's highest level of energy conversion rate, as well as high-capacity lithium-ion batteries provided by Panasonic. HIT solar cells are hybrids of single crystalline silicon surrounded by ultra-thin amorphous silicon layers. With high conversion efficiency, excellent temperature performance, and high energy output per unit area, the cells are ideal for obtaining maximum power within a limited space, greatly lifting the performance of the solar car in the WSC where regulations limit the total area of solar cells that can be installed on the body. Panasonic also provided cylindrical 18650-type high-capacity lithium-ion rechargeable batteries. These high-capacity, long-enduring, and lightweight batteries utilize it's proprietary nickel-based positive electrodes and have the highest level of energy density in the industry. They can operate for long periods of time and can be linked in lightweight battery pack arrays. Also in use are compound solar cells to energize space satellites that boasted a conversion efficiency of 30%, considerably higher than the 20% efficiency level typical of even advanced crystalline-silicon solar cells. The compound materials enable these cells to absorb more of the available light spectrum than silicon but are more expensive to make.