solar car
A solar car is a solar vehicle for use on public roads or race tracks. Solar vehicles are electric vehicles that use self-contained solar cells to power themselves fully or partially from sunlight. Solar vehicles typically contain a rechargeable ...
developed by Nuon Solar Team form the
Delft University of Technology
Delft University of Technology ( nl, Technische Universiteit Delft), also known as TU Delft, is the oldest and largest Dutch public technical university, located in Delft, Netherlands. As of 2022 it is ranked by QS World University Rankings among ...
in 2004-2005 for the 2005
World Solar Challenge
The World Solar Challenge (WSC), since 2013 named Bridgestone World Solar Challenge, is an international event for solar powered cars driving 3000 kilometres through the Australian outback.
With the exception of a four-year gap between ...
.
It succeeded the Nuna2, the solar car that scored a second consecutive win for this solar team by winning the
World Solar Challenge
The World Solar Challenge (WSC), since 2013 named Bridgestone World Solar Challenge, is an international event for solar powered cars driving 3000 kilometres through the Australian outback.
With the exception of a four-year gap between ...
for the third time in a row.
Nuna 3 was one of the favourites for the 2005 edition of the World Solar Challenge with a pre-race test-drive recorded top 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.
It has very efficient
solar cell
A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.orbital satellites (as had the previous Nunas), and it has better
aerodynamics
Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...
and is lighter than its predecessors.
It was designed and built by 11 students from different disciplines of the Delft University of Technology, who have partly put their studies on hold for this. They used the high-tech labs and workshops of the University and, as with the Nuna 2, they received advice from
Wubbo Ockels
Wubbo Johannes Ockels (28 March 1946 – 18 May 2014) was a Dutch physicist and astronaut with the European Space Agency who, in 1985, became the first Dutch citizen in space when he flew on STS-61-A as a payload specialist. He later becam ...
, the first Dutch astronaut and professor at the University.
Main specifications
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
Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy n ...
, 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. Because the 2005 race was held in September (as opposed to October or November in previous years) the sun was lower in the sky (it's earlier in spring). To compensate for this, as many cells as possible were placed at the sides, most notably on the wheel caps.
A solar cell gives a certain amount of current for a certain amount of sunlight. The
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...
depends on the load (more precisely the resistance of the load). The
power
Power most often refers to:
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power
* Power (social and political), the ability to influence people or events
** Abusive power
Power may ...
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
Maximum power point tracking (MPPT) or sometimes just power point tracking (PPT), is a technique used with variable power sources to maximize energy extraction as conditions vary. The technique is most commonly used with photovoltaic (PV) solar sy ...
(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 and the streamline. Any deviation from the ideal streamline will cause
turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
, which costs energy. The ideal streamline is achieved in various stages:
#Through computer simulations of the design
#Through testing of a
scale model
A scale model is a physical model which is geometrically similar to an object (known as the prototype). Scale models are generally smaller than large prototypes such as vehicles, buildings, or people; but may be larger than small prototype ...
in a
wind tunnel
Wind tunnels are large tubes with air blowing through them which are used to replicate the interaction between air and an object flying through the air or moving along the ground. Researchers use wind tunnels to learn more about how an aircraft ...
. For example, liquid paints can be applied to see the flow of air over the surface. The photo shows is 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 a German-Dutch wind tunnel in
Emmeloord
Emmeloord is the administrative centre of the municipality of Noordoostpolder, Flevoland, Netherlands. In 2019, it had a population of 26,055.
Overview
At the heart of the Noordoostpolder, where the three main drainage canals Lemstervaart, Ur ...
will be used.
From
meteorological
Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...
data from 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
electromotor
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate for ...
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
Spirit or spirits may refer to:
Liquor and other volatile liquids
* Spirits, a.k.a. liquor, distilled alcoholic drinks
* Spirit or tincture, an extract of plant or animal material dissolved in ethanol
* Volatile (especially flammable) liquids, ...
by the
Engineering School of Biel
Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more specializ ...
, Switzerlan (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
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of t ...
compared to the 1993
Spirit of Biel II
Spirit or spirits may refer to:
Liquor and other volatile liquids
* Spirits, a.k.a. liquor, distilled alcoholic drinks
* Spirit or tincture, an extract of plant or animal material dissolved in ethanol
* Volatile (especially flammable) liquids, ...
. 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.
Test drive
During one of the test drives in the Netherlands the Nuna 3 achieved a speed of 130 km/h. On the first day of the race the car achieved a top speed of 140 km/h. For comparison, the
Sunraycer The Sunraycer was a solar-powered race car designed to compete in the World Solar Challenge, the world's first race featuring solar-powered cars. The Sunraycer was a joint collaboration between General Motors, AeroVironment, and Hughes Aircraft.
...
(the first winner of the Solar Challenge race) attained a top speed of 109 km/h in 1987.
Important opponents
The winner of the
North American Solar Challenge
The American Solar Challenge (ASC), previously known as the North American Solar Challenge and Sunrayce, is a solar car race across the United States. In the race, teams from colleges and universities throughout North America design, build, test ...
from the
University of Michigan
, mottoeng = "Arts, Knowledge, Truth"
, former_names = Catholepistemiad, or University of Michigania (1817–1821)
, budget = $10.3 billion (2021)
, endowment = $17 billion (2021)As o ...
(USA) was considered to be one of the most important opponents. Other important contestants were the
MIT
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...
(also USA) and the Japanese
Ashiya University
is a private university in Ashiya, Hyōgo, Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, w ...
team. In 2005 there were also two other European contestants, the Dutch
Raedthuys Solar Team
The Solutra is the first solar car designed by a group of students, the Raedthuys Solar Team, of the University of Twente. It participated in the 8th World Solar Challenge in 2005 and finished 9th place. Another Dutch team won the race with the ...
from the
University of Twente
The University of Twente (Dutch: ''Universiteit Twente''; , abbr. ) is a public technical university located in Enschede, Netherlands.
The university has been placed in the top 170 universities in the world by multiple central ranking tables. I ...
and the Belgian
Umicore Solar Team
Umicore N.V.. formerly '' Union Minière'', is a multinational materials technology company headquartered in Brussels
Brussels (french: Bruxelles or ; nl, Brussel ), officially the Brussels-Capital Region (All text and all but one grap ...
from
Leuven
Leuven (, ) or Louvain (, , ; german: link=no, Löwen ) is the capital and largest City status in Belgium, city of the Provinces of Belgium, province of Flemish Brabant in the Flemish Region of Belgium. It is located about east of Brussels. Th ...
.
2005 race monitor
*5 August 2005: the team arrives in
Adelaide
Adelaide ( ) is the list of Australian capital cities, capital city of South Australia, the state's largest city and the list of cities in Australia by population, fifth-most populous city in Australia. "Adelaide" may refer to either Greater A ...
.
*2 September 2005: The road permit is granted.
*16 September 2005: During a test drive Nuna 3 strands in the rough next to the road. A defective wheel suspension turned out to be the cause. The damage was limited and repaired after a few days.
*22 September 2005: The Nuna 3 is approved by the organisation.
*24 September 2005: The Nuna 3 qualifies for the 8th starting position, which is better than the starting positions the previous two models got.
*25 September 2005: The Nuna 3 covered 827 km holding first place, leading the next-placed Michigan team by approximately half an hour.
*26 September 2005: On the second day the Nuna 3 covered 835 km, at an average speed of 105 km/h, which is a new single-day record for the World Solar Challenge. The Michigan team is now 132 km behind.
*27 September 2005: Nuna 3 covered 858 km, beating yesterdays record. They extended their lead to two hours. 500 km to go.
*28 September 2005: Nuna 3 arrives as first car in Adelaide, thus scoring a
hat-trick
A hat-trick or hat trick is the achievement of a generally positive feat three times in a match, or another achievement based on the number three.
Origin
The term first appeared in 1858 in cricket, to describe H. H. Stephenson taking three wi ...
. The overall average speed of 103 km/h over 3,010 km means an improvement by 6 km/h of the 2003 record.
This average speed, which could lead to maximum speeds of 140 km/h speeds on downhill section, well exceeding speed limits on the Australian highway, has led to rules changes for future races.