Nuna is the name of a series of crewed solar powered race cars that have won the World Solar Challenge in Australia eight times: in 2001, 2003, 2005, 2007, 2013, 2015, 2017 and 2025. The vehicles are built by students who are part of the "Brunel Solar Team" (formerly Nuon Solar Team and Vattenfall Solar Team) at the Delft University of Technology in the Netherlands, sponsored by Dutch multinational Brunel International (formerly N.V. Nuon Energy).
Nuna
Design criteria To have a good chance to win, the car has to:
collect as much solar energy as possible use as little energy as possible to drive at a certain speed. This means special attention to: the efficiency of transferring electrical energy to the wheels, and minimizing friction, constituted by: air friction (air resistance), and rolling friction, which in turn is affected by the weight, among other things
Solar cells
The solar cells are made of gallium arsenide (GaAs) and consist of three layers. Sunlight that penetrates the upper layer is used in the lower layers, resulting in an efficiency of over 26%. This type of solar cell is among the best available currently. Apart from efficiency, size also matters, so the entire upper surface of the Nuna 3 is covered with them, except for the cockpit. Efficiency is optimal when the cells are hit by the solar rays perpendicularly. If not, output is reduced by roughly the cosine of the angle with the perpendicular.
A solar cell gives a certain amount of current for a certain amount of sunlight. The voltage depends on the load (more precisely the resistance of the load). The power is the product of voltage and current and therefore also depends on the load. Over a certain voltage the current of the solar cell quickly drops to zero, as the graph illustrates. However, the batteries have a fairly constant voltage, which also has a rather different value than that of the solar cells. So a voltage transformation is needed. A special type of DC-DC converter is used to ensure the load resistance presented to the solar cells is such that the solar cells give maximum power, so also at the top of the green line in the graph. This is called a Maximum power point tracker (MPPT). Here too, the goal is to have this conversion achieve maximum efficiency (>97%).
Aerodynamic design
The aerodynamic drag is an important part of the total resistance. Important are the frontal surface area and the coefficient of drag. The shape must be designed to preserve laminar flow, as turbulence causes increased surface drag. The ideal shape is achieved in various stages:
Through computer simulations of the design. Through testing of a scale model in a wind tunnel. For example, liquid paints can be applied to see the flow of air over the surface. The photo shown was taken during one of those tests in the Low Speed Laboratory of the TU Delft. Through testing of the full scale car in a wind tunnel. For this, the DNW Large Low-Speed Facility (LLF) in Marknesse is used. From meteorological data at the area where the contest is to take place, it can be concluded that there will likely be a strong side-wind. The wheel caps of the Nuna 3 are designed such that a sidewind will have a propulsory effect.
Motor
The motor is totally encased in the rear wheel to minimise loss through mechanical transmission from motor to wheel (such as in a normal car in the gear box and cardan). The motor is an improved version of the original 1993 Motor of the Spirit of Biel III by the Engineering School of Biel, Switzerland (now: Berner Fachhochschule Technik und Informatik). The improvements are due to completely redeveloped digital power electronics and control, realized 1999. They allowed for 50% more power (over 2400 W) and a 45% higher torque compared to the 1993 Spirit of Biel II. The efficiency of the total drive system (including the power electronics losses) is also improved and is now over 98%. But as the graph shows this depends somewhat on the speed and increases with speed. The design was initially made to reach its maximum performance at the normal cruising speed of the solar car at around 100 km/h.
The race Winning the race requires not just a good vehicle but also a clever way of driving it, in accordance with the characteristics of the track. Which is why this has been researched for two months prior to the race. Height differences are mapped and linked to GPS data. From this, during the race, the optimal speed can be determined. Despite all testing and other preparations, one uncertain factor remains; the weather. Any clouds would strongly influence the amount of sunlight that can be captured. So any weather changes along the track will have to be constantly monitored. All these data are analysed by a computer model that constantly computes the ideal speed for that moment. This equipment is built into (petrol powered) pilot cars. Through telemetry these constantly receive data about the condition of the batteries and the amount of captured sunlight.
Team Each version of the Nuna has been built by a team consisting of students of the Delft University of Technology. The team has between ten and twenty team members. They take a year off from their studies to design and build a new version of the solar racer from scratch. In 2001 the Nuna 1 was built by the alpha-centauri team. They were provided with guidance from former astronaut Wubbo Ockels. From 2002 until 2019 the team has been called the Nuon Solar Team. Since 2022 the team is called the Brunel Solar Team.
Nuna 1 (2001)
The first Nuna Team (Alpha Centauri Team) was sponsored by Nuon. The team consisted mainly of students from the Delft University of Technology who were guided by former astronaut Wubbo Ockels. It was the first time that the Dutch team participated in the race, and they won the 3021 km long race in 32 hours and 39 minutes, breaking the old record by the Honda-team from 1996 (33 hours and 32 minutes). The average speed was 91.8 kilometer per hour.
Nuna 2 (2003)
Nuna 2 won the race in 31.05 hours averaging a speed of 97.02 km/h for the 3021 km course, breaking the course record of the team's previous Nuna 1.
Nuna 3 (2005)
Nuna 3 was one of the favourites for the 2005 edition of the World Solar Challenge with a pre-race test-drive speed of 130 km/h. The final result was that the 3021 kilometers between Darwin and Adelaide were covered in a record 29 hours and 11 minutes, averaging about 103 km/h. This is still the current record for the World Solar Challenge.
Nuna 4 (2007)
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