We’re seeing enthusiasm everywhere for electric cars, with government subsidies being directed both at buyers and manufacturers. The attractions seem to be obvious – clean, emission free transport, seemingly resolving effortlessly the conflict between people’s desire for personal mobility and our need to move to a lower carbon energy economy. Widespread use of electric cars, though, simply moves the energy problem out of sight – from the petrol station and exhaust pipe to the power station. A remarkably clear opinion piece in today’s Financial Times, by Richard Pike, of the UK’s Royal Society of Chemistry, poses the problem in numbers.
The first question we have to ask, is how does the energy efficiency of electric cars compare to cars powered by internal combustion engines? Electric motors are much more efficient than internal combustion engines, but a fair comparison has to take into account the losses incurred in generating and transmitting the electricity. Pike’s cites figures that show the comparison is actually surprisingly close. Petrol engines, on average, have an overall efficiency of 32%, whereas the much more efficient Diesel engine converts 45% of the energy in the fuel into useful output. Conversion efficiencies in power stations, on the other hand, come in at a bit more than 40%; add to this a transmission loss getting from the power station to the plug and a further loss from the charging/discharging cycle in the batteries and you end up with an overall efficiency of about 31%. So, on pure efficiency grounds, electric cars do worse than either petrol or diesel vehicles. One further factor needs to be taken into account, though – that’s the amount of carbon dioxide emitted per Joule of energy supplied from different fuels. Clearly, if all our electricity was generated by nuclear power or by solar photovoltaics, the advantages of electric cars would be compelling, but if it all came from coal-fired power stations this would make the situation substantially worse. With the current mix of energy sources in the UK, Pike estimates a small advantage for electric cars, with an overall potental reduction of emissions of one seventh. I don’t know the corresponding figures for other countries; presumably given France’s high proportion of nuclear the advantage of electric cars there would be much greater, while in the USA, given the importance of coal, things may be somewhat worse.
Pike’s conclusion is that the emphasis on electric cars is misplaced, and the subsidy money would be better off spent on R&D on renewable energy and carbon capture. The counter-argument would be that a push for electric cars now won’t make a serious difference to patterns of energy use for ten or twenty years, given the inertia attached to the current installed base of conventional cars and the plant to manufacture them, but is necessary to begin the process of changing that. In the meantime, one should be pursuing low carbon routes to electricity generation, whether nuclear, renewable, or coal with carbon capture. It would be comforting to think that this is what will happen, but we shall see.
I haven’t read Richard Pike’s piece yet (probably should before commenting), so he may well touch on these points, but additional factors in favour of electric include:
A move from distributed sources of pollution to point sources with increased electric transportation, allowing more efficient pollution management, and a reduction in human exposure to potentially more harmful fresh fumes
The use of electric vehicles as an energy buffer, allowing (in principle) a much more even – and therefore efficient – generation cycle for power stations
The increased feasibility of electricity re-generation from braking etc in electric vehicles.
An incentive to re-design increasingly energy-efficient vehicles from the ground up.
Of course there are also other factors to be considered here that negate some of the advantages – suggesting that, like most things, this is a complex issue desperately in need of some good science.
You’re not doing an apples to apples comparison there. You’re factoring in the cost of delivery for electricity, but you’re not factoring in the cost of delivery for gasoline or diesel. Gasoline doesn’t just appear in our fuel tanks.
Start adding in the efficiency losses you get from drilling for the oil, transporting the oil to the refinery, converting oil to gas, and then transporting the gas to the station, and I’ll guarantee your numbers would look a bit different.
Andrew, your points are good ones – the fact that a fleet of battery cars in effect is a distributed storage system may be helpful for coping with the peaks and troughs of an energy supply with more renewables.
Richard, you’re right, and to account for this life cycle analysis people talk about “well to wheel” analyses. By the same token, though, coal doesn’t mine itself and deliver itself to the power station, and it’s going to make a big difference whether the gas burnt in a British power station has come from the North Sea, or Kazakhstan or Qatar. Losses in long distance pipelines typically amount to a percent or so of the transmitted gas, which is important because methane is so much more potent a greenhouse gas than carbon dioxide. All of which underlines the point that one really needs to do a systems level analysis.
Jeepers Richard,
This statement is causing you a lot of confusion:
“Petrol engines, on average, have an overall efficiency of 32%, whereas the much more efficient Diesel engine converts 45% of the energy in the fuel into useful output.”
I think that the above statement is true to the extent that you limit your analysis to just the efficiency of fuel for moving a piston, but the goal is person from point A to point B. So if you look at how efficient a form of transportation is you need to calculate the minimum energy to needed to move the mass of a person X distance in some unit of time. (Mass x {distance/ time}^2). If you do that car (gas or diesel) are only 1-4% efficient in moving people from point A to B.
(Electric cars are typically lighter; use regenerative breaking, more aerodynamic, and don’t have losses in the mechanical transmission.)
Jim, of course if people changed from their heavy and inefficient petrol engined cars to light, small, aerodynamically ideal electric cars that would save energy. But then, we’d save lots of energy if everybody just went out and got a Toyota Yaris. Your argument is similar to Andrew’s argument, that the virtue of electric cars is that it permits a fresh start, allowing people to design more efficient cars from scratch. Maybe there’s something in this, but you could just as well argue that the same effort devoted to reengineering ICE powered cars would deliver the same benefit; yes, regenerative braking is a cool feature but you can achieve this in a hybrid.
I productivity gain out of nowhere. Backwards compatible and so simple:
http://cleantechnica.com/2009/04/29/wind-turbine-output-boosted-30-by-breakthrough-design/
I thought wind was stuck at 8cents/kWh and stuck waiting for banking techniques and technologies. For charging cars at night when loads are smallest and when winds are strongest the banking is probably not important. Obviously power generation technologies will green. Anthropic reasoning. Either they will or we will have more simple and fundamental concerns than debating vehicle power sources (can UK really repel hoardes of refugees like in the movie “Children of Men”?).
Hi everyone,
As a follow up to Philip’s post, it is interesting about the targets for renewables.
Is the issue pricing? (i.e 5 cents per kW/h)
Or is it minimising output of CO^2?
In some sense, pricing is a moving target due to inflation. Sure Oil prices have fallen, but notice that the price of consumer goods have fallen at best 1 – 2 %. Over the next 20 years it appears that due to returns to scale in renewables they should become competitive. It this good though?
The question is that there are large inputs for all renewables and there is the danger that the goal of reducing CO^2 emmissions are sacrificed for price?!!!
Finally, there is the issue of creativity. The problem is that constraints like transmission could be a problem in picking a particular technology.
It could be that a particular form of Wind generation is very effiecient, but due to relatively low voltages inefficient to transmit.
Zelah
The win for electric cars is not that they’re efficient now, but that they use a fungible energy source. Want to switch from coal to nuclear? Nuclear to solar? You don’t have to scrap and replace all the cars. Thus, electric cars invite improvement.
Richard Pike’s figures for internal combustion engine efficiency are for optimal speed and power conditions, not for a real world drive cycle. Petrol engines may get 32% in optimal conditions but will be lucky to reach 20% on average, since they run well away from optimal most of the time. Pike’s argument is therefore invalid – there is an efficiency gain, in addition to all other benefits mentioned
I find the human psychology angle in this very interesting. Especially when looking at the cars that are currently in fashion such as 4x4s/hummers. But I have the feeling that things have started to change from the situation that was described in the film ‘Who killed the electric car?’ Or am I wrong? From an ex-design-student’s point of view I find the Tesla cars very interesting – they seem to have produced the first electric car to appeal to some of the staunchest petrol heads.