by Andrew Porter
Electric cars are currently touted as the best thing for the environment. But are they really?
The Tesla electric car was recently tested on the Top Gear TV show. Although faster at acceleration than one Lotus sports car, and faster than a Porsche 911 Turbo round a test track, the battery was dead after 80km. A recharge took three hours, and as most household electricity is still generated by power stations burning fossil fuels, the testers concluded the Tesla is not yet a practical alternative to petrol cars.
Unlike the Tesla, the GT Lightning doesn’t use Lithium Ion Batteries. Instead, it uses Lithium Ion Titanate Nano-tube Batteries. Its claimed range of 290km, whilst better than the Tesla, is still limited. But the GT Lightning does have one advantage over the Tesla - its ability to be recharged through a three-phase 415V AC supply. This means a 70% recharge can take as little as four minutes, comparable to refuelling a normal car. However, using domestic supply means a recharge time of three hours, no better than the Tesla.
While both the Tesla and GT Lightning are better than early electric cars, they have yet to reach the performance of conventional cars. In addition, until generating electrical energy cleanly and sustainably is possible, the pollution problem is simply shifted rather than solved.
On Board Generator
For years, railway diesel locomotives have used on board generators to produce electrical energy to power them. In most cases, this uses a diesel engine running at its optimum efficiency in terms of fuel consumption and engine revolution rate. This allows optimum operating efficiency not possible for a variable speed engine, and the use of electric motors means the ideal form of traction. In other words, the internal combustion engine is being used at its most efficient, and so is the electric motor.
PML Flightlink, a British company, has built a modified Mini using this railway-style technology that produces 640 hp. It uses a petrol-driven electrical constant speed generator and electric motors, one for each wheel. The electric motors give maximum torque in starting and low speed, with reduced load on the generator as the vehicle speeds up.
The engine is only a 250cc twin-cylinder 4-stroke petrol engine running at optimum efficiency in terms of fuel consumption and revs. It uses 300V Lithium Polymer batteries and regenerative (energy-capturing) braking to conserve energy. This setup gives a top speed of 240kph, and acceleration of 0 – 96kph in 4.5 seconds!
An average value of 104 miles per gallon of petrol is realistic, and a range of 400 miles can be covered by using battery power alone. In addition, the battery can be recharged using domestic supply. In other words, the car can be used in pure battery mode, or be used when the internal combustion engine operates the electrical generator to recharge the battery and power the electric motors.
Honda FCX Clarity
The next development is to move away from using any form of internal combustion engine or rechargeable battery as both have their limitations. One approach is to use a Hydrogen Oxygen Fuel Cell. Introduce pure hydrogen and pure oxygen into a fuel cell and you get electrical energy with only pure water as waste. Oxygen can come from the air, and hydrogen is the most abundant element in the universe – so this approach makes sense. The Honda FCX Clarity is the first, high efficiency fuel cell car.
The Clarity uses a hydrogen oxygen fuel cell to power the car with two waste products: pure water and heat (or possibly one waste product during cold weather!). As to performance, it offers 118km per gallon of fuel, 450km per tank of fuel and is about three times more efficient than a petrol- engined car. Refuelling takes the same time as a conventional car.
An Ultra-Capacitor is used to store electrical energy that’s used to start the car. Once the fuel cell is operating, regenerative braking adds stored charge to the ultra capacitors. This leaves one remaining problem to solve - finding a source of hydrogen. It must be stressed that taking hydrogen from a hydrocarbon such as petrol defeats the purpose of the fuel cell: removing the need to use fossil fuels. However, there are two ways to solve this problem.
A British company, ITM Power, has produced a prototype electrolyser-based hydrogen producer that can be used in a domestic garage. It uses off-peak electricity to split water into hydrogen and oxygen, which means users can refill their car - and additional energy used to power or heat the home. But this still relies on generating electricity (possibly) using coal or oil.
Solar cells are an alternative, but they are still not efficient enough to be a realistic option. Researchers are confident that algae can be used to produce hydrogen at an efficiency of about 7%. And of course hydroelectric power can be used to produce hydrogen but with water restriction and geophysical problems that come with it.
Electric cars cannot currently match petrol-engined cars. Even if they do eventually reach equivalent performance, they will only be truly better if clean electricity is available for charging. Fuel cell cars match present generation cars in terms of overall performance, but producing hydrogen is still a problem. Once this latter problem has been solved, the fuel cell car can be the clean, pollution free answer.
Bob Cervi, 'Low-cost hydrogen as big as the first computer.' Engineering and Technology, VOL 3, ISSUE 13, 26 JUL - 8 AUG 2008, Page 3, the Institution of Engineering and Technology, Michael Faraday House, Stevenage, Hertfordshire, SG1 2AY, United Kingdom.