How Long Is Your Tailpipe?

Monday 16th May, 2011
There are constant disputes between Electric Car fans and their sceptics regarding the true emissions that these vehicles create. We have seen adverts banned by the ASA for claiming "zero emissions" from electric cars and the motor industry is now forced to wave around odd phrases like "zero emissions whilst driving" which don't really capture the whole picture. As usual, I'm going to try and fill in the gaps to try and explain why it's all so complicated.

Let's start at the basic level, the cars. We all know that a car like a Golf GTi is likely fuelled by Petrol. We know that a Ford Transit fan is fuelled by Diesel. But what is a Nissan LEAF fuelled by? If you answered Electricity, not only are you wrong but you're proving how complicated this is. Electricity isn't a fuel, it's actually just a form of energy.

You may remember, from science classes at school, that there are many different forms of energy in the Universe. Energy cannot be created nor destroyed, merely converted from one form to another. The concept of "wasting" energy to a scientist makes no real sense but you can, of course, end up with a shortage of one form of energy and a surplus of another.

So which form of energy makes the LEAF move? If you said electricity, you're wrong again. Kinetic energy is what makes a car move. But which form of energy is the kinetic energy made from? Nope, wrong again, not electricity. The kinetic energy is actually derived from Magnetic energy, in the motor, which is itself powered by electric energy. But where does this electricity, temporarily stored in the batteries, come from? In most cases...it comes from FUEL.

"Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. A fuel contains energy, mostly heat, that can be released and then manipulated." states the Wikipedia article. This is basically chemical energy and examples include the petrol for the Golf I referenced above, diesel for the Transit and other things like wood, coal and natural gas. To extract the energy from these, we usually burn them. So back in our Golf GTi. The chemical energy, from the petrol in the tank, is burned in the engine to make heat. This heat expands the contents of the engine cylinder, creating kinetic energy from the pistons that turn the wheels.

Notice that, in either the Golf or the LEAF, the wheels aren't driven directly by fuel - it can't be. Fuel is not energy, it's a form of stored energy, and to use it we have to convert this fuel from chemical energy into kinetic energy either directly or indirectly. In the Golf, this is done using the onboard engine under the bonnet. This creates those all too famous CO2 emissions from the exhaust pipe. In future hydrogen fuel cell vehicles, as the name implies, hydrogen is the fuel and energy is converted on board from chemical hydrogen and oxygen to electrical energy, which powers a motor to create magnetic energy and turn the wheels with the kinetic energy output from it. It still has an exhaust pipe but, in this case, the only emission is water...so these are also often referred to as zero emissions. In the case of the LEAF this isn't done on board, so it doesn't need a tailpipe, but without fuel to generate that electrical energy in a power station, your EV isn't going anywhere. So the EV fans are keen to convince people that their cars are "zero emission" but, in reality, this is only because the fuel that powers them isn't actually carried or converted on board. I find this misleading and so did the ASA when they banned numerous adverts that claimed it.

Many EV fans are slowly accepting that the "zero emissions" claim is perhaps a bit unrealistic but feel that including the emissions generated outside the electric car is a bit unfair and biased in favour of the old petrol and diesel cars. They argue that if we look at the emissions created from generating the electricity, then we should look at the emissions generated by petrol stations, oil refineries etc. They argue that petrol comes from Crude Oil which creates a lot of emissions when being refined, when being pumped and when being drilled. In reality, this cuts both ways though...let's look in a bit more detail.

Petrol comes from a petrol pump, powered by electricity, adding to emissions in a power station. It gets to the petrol station in a fuel tanker, that uses diesel..from a petrol station. The tanker brings it from the oil refinery, which uses a lot of electricity, adding to emissions in a power station. The oil arrives at the refinery in barrels by truck or train, which have their own emissions footprint. The oil is pumped in from rigs in the North Sea which also create numerous emissions during the process. All these places have workers which also need to get from home to work which means more emissions. It all adds up and there is no denying that the process of getting some petrol or diesel into your tank is a complex one. This is the "long tailpipe" argument.

Likewise, however, there are loads of emissions from the generation of electricity. A large proportion of electricity in the UK comes from coal fired power stations - they burn coal chucking the fumes out of a chimney. The coal, like the oil, has to be delivered by train or truck. Most of the coal even comes from Russia these days, a massive transport footprint. Some power stations are powered by natural gas which again needs to get to the generators by pipeline or tanker, often from the North Sea like the oil. Drilled like the oil, the same footprints as the oil. Some electricity comes from wind turbines which, at first glance, look clean but if you look a little closer you'll realise they are enormous, need to be made in and transported from a factory and also need massive foundations to be dug and filled with concrete which itself has a massive footprint from the extraction and transport of materials required to create it. Nuclear power looks reasonably emission free, from the outside, but again it needs to be powered from refined uranium, in a plant with thick concrete walls etc. Solar panels provide a small, almost insignificant contribution to the National Grid, but even these need to be made in a factory from raw materials that all need to be transported etc.

So where do we draw the line? Well, that's up to you but I think we need to be realistic and put the line in a similar place for each type of vehicle. This, for me, is by looking at the emissions generated from the fuelling of each vehicle. Not the energy used, but the fuel emissions. So this means, for a petrol or diesel car, it's what comes out of the tailpipe. That fuel only goes to one place, it's used to power the car. Every bit of emissions that comes out of the tailpipe is directly attributable to driving the car, the energy derived from it doesn't go anywhere else...it's a no brainer.

An EV is powered by electricity which also cannot be used for anything else. If you use 24kWh of electricity to fully charge a LEAF, those 24Kwh were only used to power the LEAF and so we can look at the emissions generated by the power station to create those units from fuel. Of course this varies across the grid as it uses a mix of sources - at time of writing that is 40.8% from natural gas, 31.7% from Coal, 20.5% from Nuclear, 4.6% from wind and 2.4% from hydro. Some, like the wind and hydro, don't use fuel so can be regarded as zero emissions from my perspective. Others, like gas and goal, have very high emissions. So what they do is take an average which, as I type, is 550g of CO2 for every kWh of electricity generated. So this means that our Nissan LEAF will generate 24 x 550g of CO2 when you fully charge it which means 13,200g of emissions for 100 miles, or in the familiar form 82.5g/km. This means that it is almost as high as many Petrol/Diesel cars, in terms of CO2, and worlds away from the claimed zero.

So, moving forward, I'm going to refer to the emissions generated from the fuelling, not the powering, of each vehicle as "Stage One" emissions. Over time, as the National Grid cleans up its act and switches to more renewable sources, those Stage One emissions for EVs will go down and likely be significantly less than those for standard ICE vehicles. In fact, this may even change if we progress to better systems of measuring emissions from cars. The current standard test is largely regarded as inaccurate and it's apparently fairly easy for a car manufacturer to make the CO2 output look low during the standard test but actually be much higher at other times to create a car that's more fun to drive. I personally believe that Stage One emissions for an EV are better than any ICE vehicle at urban speeds up to around 40mph on a warm day. Above those speeds, or on very cold days, I feel that a petrol hybrid is the better option by far. Diesels can also have low CO2 but, as I've mentioned many times, the other emissions from those vehicles are a particular concern that I would choose to reserve for freight vehicles.

What I'd like to see in future is standard emissions testing that measures the CO2 output of each ICE vehicle at idle and then at 10,20,30,40,50,60 and 70mph. We could also measure the electricity consumed by an EV at the same speeds and convert that to a CO2 equivalent as I did above. That way we could then give each car an energy rating, like the sticker on a new Fridge/Freezer, that shows how efficient it is on urban, extra urban and motorway journeys. If you mainly drive short journeys around town, you would focus on a car that had a green rating for urban travel and look towards an EV. If you mainly munch motorway miles, you'll look at something like a petrol hybrid or perhaps even a diesel which would be green rated there. If you do a big mix of both, then a plug-in hybrid will likely have a green rating in both areas and be the best of both worlds.

So that's my perspective on the tail-pipe argument, feel free to share yours below.

Comments/Trackbacks [13]