How green is my i3?

[FrancisJeffries]

I’m doubtful whether electric cars help Global Warming much at all – after all, most of the electricity at present comes from coal, oil, or gas-fired power stations whose thermal efficiency and transmission losses deliver less horsepower to the road than petrol-driven cars (which have comparable thermal efficiency and transmission losses from oil well to tank). So let's do some "back-of-the-envelope" (i.e. approximate) sums.

On average, CO2 emissions for UK-generated power were reported as 545g/kWh (Autocar, 2 November 2011). The average takes into account wind and nuclear contributions. (For interest’s sake, coal-fired stations produce about 900g/kWh, oil-fired produce 740g/kWh and gas-fired produce 390g/kWh (see http://www.esru.strath.ac.uk/EandE/Web_sites/01-02/RE_info/C02.htm and http://www.parliament.uk/documents/post/postpn268.pdf). The gas-fired figure probably doesn’t take into account the gas transport CO2 emissions, which are also incurred at compression and de-compression. Likewise, the generation figures do not include electric transmission losses incurred before it gets to your socket - which can be in the range 5-10%. However, as renewables and nuclear come on stream, the mains electricity generation average CO2 emissions are bound to fall.

Now the i3 is said to manage about 3.6miles/kWh. Give it the benefit of the doubt and call that 6km/kWh. So the actual CO2 emissions for the i3 running purely on mains-supplied electricity are 545/6 g/km. That's about 91g/km - not so very different from the quoted (N.B. quoted!) figure for quite a few modern petrol cars.

It's much the same story when running on the Rex: Let's assume ("back-of-the-envelope" sums again) that the car does about 13km/litre of fuel. (That's about 36mpg, reflecting a petrol range of about 70 miles - seems about right.) Exeter University quote 2.31kg/litre of petrol, so we'll get about 2.31/13km kg/km = 177g/km. That's quite a bit worse than some cars, but not as bad as many! Have a glance at http://people.exeter.ac.uk/TWDavies/energy_conversion/Calculation%20of%20CO2%20emissions%20from%20fuels.htm
I'm not clear whether they are doing the real-world sums or listing quoted figures for typical cars. I suspect the former.

The BMW’s claimed emission figure of 0g/km (and 13g/km for the Rex version) is evidently calculated ignoring the CO2 emissions for electricity! On the other hand, the lack of pollution while driving the car in towns will be a significant advantage. Power stations will still be gushing pollutants and CO2, of course, but at least they are out in the countryside – not in our backyard!

 

[MikeS]

Mine’s grey - and I will use PV to charge it :evil:

 

[fdl1409]

True, if you use power from coal fired plants, electric cars are not much better. Still they reduce local pollution and noise.

But: you have every chance to produce your own clean power. I will install a PV system on my roof, somewhere between 16-20kW, in the next months. My production of 12-15.000 kWh per year is 3 times as much as I need for the i3 AND household power demand. I will kick out my gas condensation boiler some time in the next few years, first do some insulation and then install a brine/water heat pump. Even including heating I will still produce more than the total power needed - I will have a plus energy house. PV Prices are very low now, a few thousand Dollars/Euro/Pound are enough to cover the demand of an i3 and more that that. You only need the grid for virtual storage.

Frank
Germany

 

[BrianStanier]

Your back-of-envelope figures are close to those from http://www.owningelectriccar.com/national-grid-electric.html. The i3 BEV should be a little more efficient than the Leaf which they estimate as 85gm/km. My figures after only a week of our Rex are slightly better than we were getting from the Leaf so it too should be around that figure.

 

[Stevei3]

Hi Francis,

if you like these kind of calculations, google on 'well to wheel'. As can be seen via the link 'Brainstanier' provided, there is much more energy involved in getting your gas/diesel car happy than meets the eye. Pumping, refining and distributing fuel, and, in general, higher maintenance requirements have a significant impact on the co2 emissions of your ICE equipped car at the bottom line. It seems that the effort it took to produce the battery for your typical electric car is more than worth it, from a co2 point of view. How our E-car will fare if you take other polluting effects of battery production and/or oil production into consideration is a whole different matter I'd love to do some more digging into. Any tips/leads anyone ?

Tom wrote an excellent piece about the energy requirements of the oil economy: http://bmwi3.blogspot.nl/2014/05/volts-for-oil-gas-cars-burn-coal-too.html

Regards, Steven

 

[I33t]

The zero CO2 claims are a sleight of hand repeated by each of the electric car makers. They can justify the claim because no CO2 is generated from the consumption of fuel from the battery, but we all know that electricity comes from somewhere!

If you care about CO2 production from your EV, the simple answer is to source your power from CO2 free sources by installing enough PV or wind to charge the car, or by buying power from greenpower electricity providers.

There is also the point that the production of the i3 is apparently low CO2 compared to conventional vehicles, so there is more to it than just the fuel...

 

[amateurish]

Your analysis is not correct because you are comparing "tailpipe" emissions of ICE cars with total emissions of EVs.

The figures of 0 CO2 and 13 CO2 for the i3 are "tailipipe" figures and so directly comparable to the emission figures normally quoted for ICE cars.

If you want to look at the CO2 generated by electricity generation, then you will need to compare it with the total CO2 generated by the extraction, refining, transportation etc of diesel or petrol.

 

[FrancisJeffries]

I should, perhaps, have admitted that I do have a 3.35kW solar PV array so, provided I charge the car when the sun is shining, I'll get paid to drive around! :lol:

But my general point was about the total CO2 issue. The tailpipe emissions are as the manufacturers claim, of course, so that's OK, then. I can have guilt-free hedonism in the i3 - when I get the damned thing!

 

[viking79]

My i3 will be orange most likely, don't think they make a green version.

Seriously though, I would rather have 0 tail pipe emissions as it prevents Smaug err smog in a city and let the plant (and regulations) producing power worry about how little emissions are produced in the generation of the electricity. Nothing is more irritating than a diesel truck that has been modified to make it belch black smoke, which causes asthma and respiratory issues.

Honestly though, I am not buying an EV to be "green", but rather since I prefer electric vehicles. They are lower maintenance, quieter, cleaner, fast, etc. Lithium Ion batteries as used in the i3 aren't as bad on the environment to produce as something like a Nickle battery, like NiMH or NiCd.

As stated, why are you comparing tailpipe emissions of petrol/gasoline vehicle to production emissions of the EV? Hardly a fair comparison. Producing gasoline from crude oil is an energy negative process. The crude oil had more energy then the gasoline created from it and also took energy to produce, but we do it because the gasoline burns better and cleaner in the cars. We drive an EV because it doesn't have any tailpipe emissions to pollute the local area, and electricity can be generated in large quantities inexpensively and cleanly from the right sources (nuclear). Hydroelectric is also effective, but can have environmental impact in downstream locations since you are damming water flow. Also, an EV can help consume some of the excess night time electricity to help level the demand and make it easier for power plants.