Questions and Answers about Trev
What is it? Why did you do this?
Our aim was to design, build and demonstrate a practical commuter vehicle that runs entirely on non-polluting, renewable energy. Commuting without polluting. We have been building and racing solar cars for many years. Solar racing cars can travel 750 km in a day at sustained speeds of over 95 km/h, powered only by sunlight. But when we get home from a race, we put the solar car back in the shed and then drive relatively short distances to work and back in cars that are heavy, noisy and polluting. If we can drive across Australia on solar energy, driving to work and back on solar energy should be easy.
Why is it called Trev?
Trev is a good Australian name. But if you want it to mean something, it can stand for Two-seater Renewable Energy Vehicle.
Who designed and built the car?
The prototype car was designed and built by staff and students at the University of South Australia. The project involved many UniSA research groups and schools:
- Institute for Sustainable Systems and Technologies
- Centre for Industrial and Applied Mathematics
- Sustainable Energy Centre
- Transport Systems Centre
- Louis Laybourne Smith School of Architecture and Design
- School of Advanced Manufacturing and Mechanical Engineering
- School of Mathematics and Statistics
- School of Electrical and Information Engineering
Where are the solar panels?
Solar racing cars require large panels of high-efficiency solar cells to propel them along the road at 100 km/h. Our car is not as efficient as a solar racing car, and has much less surface area available for panels. If you are going to propel a car using solar energy, the best place to put the cells is somewhere where they will always be facing the sun. We will be using renewable energy sources on the electricity grid to recharge the car's batteries. We will eventually put some solar cells on the roof of the car, to extend the range and to power a ventilation system that will operate when the car is sitting in the sunlight.
How fast does it go?
Trev has a top speed of 120 km/h so that it can be driven with normal traffic on urban highways. The acceleration is 0-100 km/h in about 10 seconds.
Does it have gears?
The rear wheel is driven by a 6000 rpm electric motor through a two-stage belt transmission. The gear ratio between the motor and rear wheel is fixed at 6:1. One of the advantages of an electric motor is that it delivers maximum torque when it is needed, at low speed.
What type of motor does it use?
The car currently uses a brushed DC motor. We are about to change to a permanent-magnet brushless DC motor with a maximum speed of about 6000 rpm. A high-speed motor is lighter and less expensive than the in-wheel type of motor used in solar racing cars.
What type of battery does it use?
Trev uses a 45 kg pack of lithium ion polymer cells—the same type of cells that are used in mobile phones. These cells deliver about five times as much energy as the same mass of lead-acid cells, and are more energy-efficient.
What about hybrid cars and fuel cells?
The automotive industry seems to be working almost exclusively towards fuel-cell cars running on hydrogen. Hybrid cars are seen as an intermediate step.
Hybrid cars generate significantly less pollution than conventional cars. They do this by turning off the engine when the car is stopped, and by using electric power to help the engine run more efficiently. Fuel-cell cars are electric cars powered from hydrogen—the fuel cell converts the hydrogen to electricity without combustion. The conversion from hydrogen to electricity is clean, but the overall efficiency of generating the hydrogen and then converting it to electricity is not much better than the efficiency of a petrol car. Furthermore, the infrastructure required to support hydrogen cars is unlikely to be in place for at least another 20 years.
The automotive industry is trying to make existing cars more efficient. We have a different approach—make an efficient solar racing car more practical. We do not need 1-2.5 tonnes of machinery to transport one or two people around the suburbs. By designing a car with low mass and an efficient electric drive system, we can provide adequate range for commuting using existing battery technologies.
What is the range of the car?
Trev currently has a range of 120 km/h, but we hope to improve this to more than 150 km. While this is less than that of a petrol car, it is more than enough for most commuting. The car will generally be charged overnight, and so start each day with a full range. The running cost will be less than 1/10 of the running cost of a small petrol car.
How long does it take to recharge?
From a conventional household outlet, it takes 3-4 hours to recharge. With a high-power outlet, the battery can be recharged in just over an hour.
Will the battery need replacing?
The battery should last over 250,000 kilometres.
How efficient is the car?
The car will use about 1/5 of the energy of a four-cylinder car. At 60 km/h, the motor output power is less than 2000 W. About half of this power will be used to overcome rolling resistance; the other half will be used to overcome aerodynamic drag.
Won't charging the car cause extra emissions at the power station?
The CO2 emissions from a coal-fired power station recharging a 1200 kg electric car are about the same as the emissions from a 1200 kg petrol car. But our 300 kg, aerodynamic car requires only 1/5 of the energy of a 1200 kg car. The car can also be recharged using green electricity generated from renewable energy sources such as solar and wind, in which case there will be no emissions.
Why two seats?
About 80% of commuter trips have only one person in the car. Fewer than 5% of all trips around town have more than two people in the car.
Occasionally you may need a car that can travel long distances or carry more than two people. Many households have more than one car; the car that is used for daily commuting could be a low-mass, efficient, non-polluting car. Most times, there will be only one person in the car.
Why is the passenger behind the driver?
The tandem seating layout has two main advantages. First, it gives the driver a better view of the road without having to look around the passenger. Second, it allows us to build a more streamlined vehicle, which reduces the power required to propel the car.
Why three wheels?
Why four? Three wheels has several advantages:
- the suspension system is simpler
- the car will have a lower mass than a similar four-wheeled car
- it is easier to meet the requirements for registration with a three-wheeled vehicle.
How much does the car weigh?
The prototype car has a mass of about 300 kg.
The car is built around a low-mass tub built from aluminium honeycomb panels—the same type of panels used for aircraft cabin floors. Non-structural body panels are be made from low-density foam with a fibreglass skin.
How much did it cost?
The prototype car cost us about $40,000 in materials, parts and machining to build. The most expensive item was the battery, which cost around $10000. Custom built motors are also expensive. In mass production, however, this type of car should be significantly cheaper than a conventional car.
How safe is it?
Safer than a motorcycle with a sidecar.
We have taken safety into account in our design. The cabin section of the tub chassis is relatively stiff, and the surrounding structures are designed to crush. There is a trend to view large, heavy cars as being safer, but this is not necessarily the case. Furthermore, heavy cars inflict more damage in a crash. Would you rather be hit by a large SUV or by our car?
Does it have air-conditioning?
A conventional car air-conditioning unit uses enough power to push our car along at 100 km/h. We are investigating more efficient alternatives. We will also use small glass area, solar powered ventilation and insulation to help keep the car at a comfortable temperature.
When can I buy one?
We don't know. Trev was designed as a prototye car. Our aim was to demonstrate the concept of a low-mass, efficient commuter car. We first displayed Trev at the 2005 World Solar Challenge, and in 2007 we drove Trev from Darwin to Adelaide. But we need someone else to take the ideas and produce a commercial version of the car. We are happy to work with anyone that is interested in developing plans, kits or manufacturing prototypes.
Can I build my own?
In July 2009, TREVipedia was launched. The aim of TREVipedia is to coordinate and document the development by enthusiasts of new versions of Trev. Ultimately, we hope that the new designs will lead to a certified "kit car" with standard components, and that TREVipedia will provide information that will help people build their own Trevs.
I know this bloke that built an electric car with generators on the tailshaft...
Our car is designed to operate in a universe where energy is conserved.