Peter has written an article on the future of cars for The Conversation.
Over the weekend our web site Trevipedia.net disappeared, due to an administrative bungle with the domain name. It is back now, but prompted us to consider moving to a Google Site instead of the current MediaWiki site. If you are, or would like to be, a Trevipedia contributor, you can try the new site and let us know what you think.
Earlier this month, Team Trev member Andrew visited Zimbabwe for a week to meet with key stakeholders in our project to develop a solar-powered vehicle for transporting pregnant women to hospital in rural Zimbabwe. His other task was to assess the roads.
The trip was a great success—we now have a much clearer view of the task ahead, and enthusiastic support from the NGO, hospital and health authorities in Zimbabwe.
One of the key outcomes of the trip is a change of name for the project. Nobody wants to travel in an ambulance, and so the vehicle will be called the ‘African Solar Taxi’.
The other major outcome is that we now have GPS paths and lots of video for the roads we will be using. Many of the roads are dirt tracks. Most of the bitumen roads have not been maintained since they were built about 30 years ago; they are wide enough for one car only, and have potholes and rough edges. This means that we will have to build a vehicle that is both lightweight and robust, with four wheels.
You can find out more, and track our progress, on our new blog: africansolartaxi.com.
Earlier this year we were contacted by an organisation in Zimbabwe enquiring about the possible use of solar-powered vehicles for transporting pregnant women from rural villages to health care facilities. Our initial reaction was that off-the-shelf petrol vehicles or golf carts would be more versatile and reliable. But petrol and electricity are too expensive and often unavailable in Zimbabwe.
Zimbabwe has one of the highest maternal death rates in the world. One of the factors that contributes to the high maternal death rate is the difficulty that expecting mothers have in getting from rural villages to health care facilities such as delivery hospitals. Almost half of the births in the Mashonaland Central region are delivered at home without formal medical assistance.
We are currently working to design, develop and demonstrate a system for transporting expecting mothers from rural villages to health care facilities. The system will comprise vehicles that can be used to transport women to and from health care facilities, and a system for scheduling and managing the vehicles to maximise their effectiveness.
Because of the high cost and low availability of fuel or electricity to power vehicles, the vehicles will be powered by human and solar power. Bicycles with trailers are being used in some parts of Africa for patient transport, but speed and range are limited by the endurance of the rider. We will investigate the use of electrically-assisted cargo bikes with trailers, or custom designed low-energy vehicles based on readily-available components, with solar panels for recharging batteries.
The key vehicle requirements are:
vehicles will service villages within 30 km of a health care facility, and travel up to 80 km per day
vehicles must transport the rider, the patient and an accompanying friend
vehicles must be capable of travelling on unsealed roads and tracks at speeds up to 30 km/h.
If you are interested in being involved in this project, contact Andrew: email@example.com
One of the reasons we built Trev was to get people thinking about the energy they use for mobility. Most people appreciate that using tonnes of machinery to transport a 75 kg person uses a lot more energy than necessary. But some people get a little too inspired: Why don’t you put generators on the wheels?
Generators on the wheels is not a bad idea. The electric motors used in most electric and hybrid cars can act as motors converting electrical power to mechanical power, or as generators converting mechanical power to electrical power. Working as a generator, the motor can convert the kinetic (movement) energy of the car into electrical energy, and this energy can be used to partly recharge the battery. But converting the kinetic energy of the car to electrical energy slows the car. It is called regenerative braking, and the braking force that can be achieved is about the same as the driving force that can be achieved by converting electricity to motion.
Regenerative braking cannot convert all of the kinetic energy of the car into electrical energy—some of the energy is dissipated by resistance forces in the tyres and bearings and by aerodynamic drag, and some is dissipated as heat in the motor/generator and in the electronic controllers. But some of the kinetic energy can be converted to electricity and stored for later use—which is better than occurs with normal friction braking, where all of the kinetic energy is dissipated and none of it can be recovered.
But the proponents of generators on the wheels often want to go beyond regenerative braking to generate electricity without slowing the car. Not necessarily perpetual motion, where the generators generate more than enough electricity to power the motors, but enough to reduce the power required from the battery.
It doesn’t work—at least, not in our universe.
To see why it doesn’t work, try writing power values in each of the empty boxes in the diagram below. Suppose the car is travelling on a flat road at constant speed, so the power values are not changing. The total power into the motor must be the same as the total power out of the motor, and the total power into the generator must be the same as the total power out of the generator. It is like Power Sodoku—everything has to add up.
- Write in the power required for propulsion. This is the power required to overcome rolling resistance and aerodynamic drag. Trev uses about 4000 W at 70-80 km/h.
- Write in the motor losses. Losses in an electric drive system are about 10% of the propulsion power.
- Write in how much power will be transferred from the motor to the generator, and generator losses (about 10% of the power into the generator).
- Calculate the ‘battery out’ power and the ‘battery in’ power.
The total energy from the battery is (battery out – battery in). What do you have to do to minimise (battery out – battery in)?
With Zero Race well and truly behind us, and with Trev back in Adelaide, Team Trev is focussing now upon activities closer to home.
First up, we need to get Trev re-registered in South Australia. When we registered prior to departing for Zero Race, the assessor said that we’d need to complete a lane-change test prior to driving on Australian streets again. We’ve upgraded the front suspension over recent weeks and we undertook a successful swerve test last week, so we hope to be back on the road very soon.
Our next plan is to use Trev for urban commuting, which after all is what it was originally designed to do. We plan to install data loggers in the car to record energy use, then share the car amongst team members to commute and use for their everyday driving, one week each.
With Trev out and about on the streets of Adelaide, we expect to get a lot interest in the car once again, which will give us the opportunity to share our story about Zero Race, and more importantly, to demonstrate that if a little green car can drive around the world in 80 days, it is also more than capable of commuting to and from work.