|  | Nuna-II in the 7th World Solar Challenge | |
Space technology behind Nuna II
The Nuon Solar Team’s solar powered racing car Nuna II includes several advanced technologies originally developed by European companies for spacecraft - ultramodern solar cells, high performance batteries and space plastics.
“The Nuon Solar Team with their Nuon II solar-powered car demonstrates once again that innovative space-developed technologies can be the winning card on Earth,” says Pierre Brisson, Head of ESA’s Technology Transfer and Promotion Office, speaking after Nuna II won the World Solar Challenge 2003 in Australia, with a new world record of only 30 hours, 54 minutes.
Back in 2000, ESA’s Technology Transfer Programme formed a partnership with the Dutch Nuon Solar Team to make innovative space-developed technologies available to help the team to build the world’s fastest solar powered car.
“Our car uses the most advanced space developed technologies, provided to the team via ESA’s Technology Transfer Programme,” says Diederik Kinds, an aerospace engineering student at the Delft University of Technology and leader of the Nuon Solar Team. “This enables the car to reach a theoretical top speed of 175 km/h compared to the first Nuna’s top speed of 160 km/h.” The first Nuna set the World record in the World Solar Challenge 2001 - 32 hours, 39 minutes to complete the 3010 km race.
| | European solar cells | |
SMART solar cell technology on Nuna II
Its successor, Nuna II uses three-layered triple-junction gallium-arsenide solar cells developed by ESA through its Technology Research Programme. The first spacecraft to use this new type of solar cell was SMART-1 launched 27 September 2003, and currently en route for the Moon.
“Most important are the solar cells,” explains Kinds, “we use solar cells that harvest up to 20% more energy than those used on Nuna for the 2001 race.”
The efficiency of a three-layered triple-junction gallium-arsenide solar cell is above 24.5 %. This means that 24.5% of available solar energy is captured and converted into electricity. Commercial available cells for generating electricity on Earth such as the ones used in pocket calculators typically have an efficiency of 6% - 18%.
Nuna II is fitted with 3000 solar cells mounted on the top and the sides of the car, covering a total area of 9 m2, which is 1 m2 more than on the first Nuna car. To reach maximum performance the triple-junction gallium-arsenide cells are mounted in three layers, with the result that sunlight not used by the top layer of cells and normally wasted in conventional one-layered constructions passes through to be captured by the second and the third layers.
Solar power even in the shade
Nuna II has also ten ‘maximum power point trackers’ (MPPT) onboard. MPPTs have been used in satellites for years to optimise the output of solar cells even when they are in the shade. ESA’s comet chaser Rosetta will also use MPPTs in order to get the most energy out of the Sun’s light during its ten-years journey to Comet 67P/Churyumov-Gerasimenko.
A chip in the MPPT measures continuously the voltage supplied by the solar cells, compares it with the fixed battery voltage, and then determines the best voltage to charge the battery. In this way the energy from the solar cells is kept high and constant and more than 95% efficiency can be attained.
| | SMART-1 scanning the Moon's surface | |
Space batteries in Nuna II
In poor weather conditions Nuna II runs on batteries, which have been previously charged by the solar cells. A total of 46 Lithion Ion (Li-Ion) battery cells are connected in series to supply 5 kWh of electrical energy.
These highly efficient batteries were originally developed for space applications where reliability is essential. These same batteries providing power to Nuna II during cloudy weather are also used by SMART-1 when out of contact with the Sun.
Aerodynamics improved by lightweight space-plastics
Compared to the earlier Nuna, Nuna II’s aerodynamics have been greatly improved by reducing the overall weight by use of extremely light space plastics. The 5 metre long and 1.8 metre wide Nuna II weighs only 250 kg and the new design is also very low on the road – the top of the cockpit is only 80 cm high.
The main body is made from carbon fibre (CFRP), which has been reinforced on the upper side and on the wheels’ mudguards with aramide.
The same CFRP is commonly used in the space industry for construction of spacecraft and satellite systems, which have to be both lightweight and strong. Aramide is also used in spacesuits to protect against micrometeorites. On Nuna II this material is used to shield the car against the impact of gravel during the race.
Last update: 24 March 2005 | 
