There is no doubt that electric vehicles are here to stay, at least for private passenger use and at least in cities. And there is no doubt that battery technologies will improve, and that costs will come down. This article takes a looks at the CO2 emission characteristics of currently available fully electric vehicles (EV’s), and the implications for the UK national electricity grid if EV’s were to be widely adopted, displacing internal combustion engine (ICE) cars. The CO2 emissions performance of EV’s is compared to diesel engine cars.
There is an increasing volume of published material on the pro’s and cons of electric versus internal combustion engines (ICE’s), some good and well presented, but some of it misleading. Proponents of electric cars often use unreasonable comparisons, confirmation bias, and special pleading to advance their case for the wide spread adoption of electric cars or to justify their choice of vehicle.
This includes giving little attention to ‘real world’ power usage in electric cars, making comparisons solely with petrol and not diesel cars, implicitly or explicitly assuming electrical production solely from renewable sources and ignoring renewable sources of liquid fuels (in particular, biodiesel) .
EV Energy Usage and Range
The Tesla Model S is used as an example EV, specifically the 2015 Tesla Model S, with the 85kWhr battery pack. The reason for picking this car is that right now this is the only model that comes close to having a reasonable range and is of a size comparable to a mid sized or larger car suitable for longer distance driving. Its energy performance is taken to be a reasonable definition of what is presently feasible for a larger EV.
Electric cars from the other manufacturers (e.g. Nissan Leaf, Peugeot, BMW i3, Renault Zoe, Ford Focus, Mercedes Benz B class) have claimed ranges of 60 to 155 miles, though the achievable ranges under real conditions will be significantly lower. These cars seem to be aimed at short and intermittent urban or city driving. Total sales of EV’s in the UK in 2015 were around 9000 (out of a total of 2.6 million cars).
From the Tesla website (12) the range for a full battery charge varies from 219 to 256 miles at a constant 70 mph, and depending on whether the air conditioning (a/c) is on. At a constant 45 mph, 40 C and the a/c off, Tesla claim a range of 420 miles.
Constant speed is of course not a good reflection of real world motoring. Similarly few people will drive in winter with the heater off and whilst a summer run along a country lane might be nice with the window open, most motoring is done with the windows closed and the air conditioning on.
The realistic basis is therefore with the a/c on. At 70 mph, the Tesla website gives 219 to 242 miles per charge (again, depending on the ambient temperature). Most people do not want to risk running out of fuel (be it electricity or diesel); personally I get a bit twitchy if the remaining range falls below about 60 miles, but let’s be generous and say a 20 mile reserve is a reasonable precaution. This drops the practical predicted range at 70 mph to between 199 to 222 miles.
According to US official figures (1) the energy usage for the S model is 38 kwhr/100 miles, for both ‘city’ and ‘combined’ driving, slightly lower at 37 for ‘highway’. The all-wheel drive version has better figures, but is also more expensive.
But what is the real world figure, for actual driving ?
(Just some notes on units :
T = Tera (trillion)
G = Giga (billion)
M = Mega (million)
k = kilo (thousand)
h or hr = hours
W = Watts = power, or rate of energy supply = 1 Joule/second
Whr = watt hours, a measure of total energy, 1 kWhr = 1 kW for 1 hour = 3.6 MJ
EV01-0116
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