Electric Cars

Will They Ever Come? Do We Want Them?

Certainly the low noise levels and the lack of pollution associated with electric vehicles are appealing. We did have battery driven electric cars in the early part of the twentieth century, electric commercial vehicles were quite widely used in the 20's and 30's and the electric milk float survives to this day. We have had promises of electric cars for years, and there have been numerous brave attempts at producing them but they have all fallen by the wayside. Why is that?

Of course, electricity is not an energy source in its own right but has to be produced from a true energy source. Almost 70% of our electricity is generated in coal or gas fuelled power stations, some 28% comes from nuclear power stations and the remaining amount from renewable sources such as hydroelectric and wind power. There is much talk of making more use of renewable sources but there is a very long way to go. To get the prospects of wind power into perspective one needs to appreciate that it would take several hundred wind turbines similar to the one at Swaffham to produce the same output as one average coal fired station, and that assumes the wind to be sufficiently strong.

It is a fact that a fundamental natural law, the second law of thermodynamics, restricts the efficiency of fossil fuelled power stations with the result that present day efficiencies of around 40% are unlikely to be exceeded; thus 60% of the energy released by burning the fuel is lost to the atmosphere. (This is why electricity is such an expensive form of energy for heating one's home or office. It is clearly much better to burn the fuel on site and thereby make use of more than 80% of the energy release). It also means that each power station emits large quantities of greenhouse gases. Nuclear stations are no longer seen as desirable and renewable sources seem unlikely to take up the share of the burden currently taken by nuclear. The situation is all the more difficult because of the dwindling reserves of oil and gas. It has been said that we are approaching the tunnel at the end of the light. This all presents a major dilemma for those responsible for planning our future electricity supply. Let us hope that they do not make the mistake that has been made in California where environmentalists have successfully opposed new power stations to the extent that there is now insufficient capacity to meet peak demands. If all road vehicles were to be battery powered that too would greatly exacerbate the problem since it would require something of the order of a 50% increase in the generating capacity.

Back to electric cars. Although electricity is expensive, the same law that limits the efficiency of a power station also limits the efficiency of automotive engines. So the cost of electricity is not a deterrent in the use of battery-powered cars. So what is? Over the years we have been told that all we are waiting for is a breakthrough in battery technology, the existing lead/acid batteries are too heavy and too bulky, but, if we could find a more compact and much lighter battery, it is said, we would all be driving electric cars. Is that true? Imagine that we have a new battery one tenth of the size and weight of existing batteries (certainly lighter and more compact alternatives do exist), and we plug our car with the new battery into a socket in our garage to recharge the battery overnight. At what rate could we charge? The largest appliance on our normal domestic circuits is the cooker, which might use 6kW at its greatest rate of use. Let us assume that we could charge our battery at this rate for 9hours. We should then have stored 54kWh of electricity in our battery.

A modern motorcar has an engine that is capable of producing a power output of anything from 100kW to 350kW, most of the time that it is in use, however, it is only using a fraction of this output. Nevertheless to drive up the motorway at 70mph probably requires something of the order of 45kW, depending on the size and shape of the car. Our 54kWh of stored energy would enable us to drive at this speed for just 1hour and 12 minutes. Clearly this is not very satisfactory for long journeys and we would need batteries of considerable capacity, and the ability to charge at a much greater rate if battery driven electric cars are going to replace our internal combustion engines. It is interesting to speculate that when we put petrol into our cars, putting say 30litres in one minute, we are effectively recharging our car with useful energy at the rate of approximately 5MW, almost 1000 times the rate at which we could charge a battery powered vehicle using a domestic circuit.

At present then it would seem that, regardless of any developments that might arise in battery technology, the battery powered electric car will always be limited to use for short journeys, mainly in towns where speeds and the corresponding rates of energy use are low. There is a light on the horizon, however, which raises the possibility of electric cars in the future and this is the development of the fuel cell. With the editor's approval I will consider the possibility of the fuel cell powered car in a future issue.

Ron Watts