Electric Car Emissions MK1

8/4/2019 Electric Car Emissions MK1

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ELECTRIC CAR EMISSIONSAlasdair Fairbairn 21/08/11

While it is very simple to find out the CO 2 emissions from a diesel or petrol car, it is

very difficult to get any sensible information on this for an electric vehicle.[EV]Here is how to work it out and compare with other cars.

Diesel and Petrol cars:

The formula for calculating the Grams of CO 2 emitted per Kilometre by thesevehicles is;

g/Km = X /(mpg x 0.3538)

Where X is 2639 for diesel and 2331 for petrol Appendix A gives the details on how these figures were compiled.

Alternatively you can just Google 'Car Emissions' and there are plenty of sites whichill do the calculation for you.

All very simple; so we will move on.

Electric Cars: [EVs]

Sadly, for EVs you will not be able to use this formula as there is very littleinformation freely available on the internet which provides the required informationor a quick answer.

The formula for the EV, however is this:

g/Km = A x B/(C x D) [ A bit more complicated ]

Where:A is the grams of CO 2 per Kilowatt Hour emitted by the power stations insupplying power to the Grid. [This takes into account the fossil/alternativeenergy mix] B is the capacity of the EV battery in Kilowatt Hours.C is the Overall Efficiency of the transmission and battery charging systeminvolved in getting the energy from the the power station to the wheels of

the vehicle.D is the vehicle distance achieved by a fully charged battery in Kilometres

Appendix B gives the details, assumptions and logic behind this formula.



To obtain a broad brush picture of the likely emissions from an EV you can use thefollowing example data. However if you wish to be more specific then you will neto fully understand the principles outlined in Appendix B

Data : Based on the BMW Mini E .

A = 430 grams per Kilowatt Hour. [ you can get this off the internet byGoogling CO 2 grid emissions real time or somesuch. ( treehugger.com does it.)B = 35 Kilowatt Hours [ From BMW ]C = 0.491 [ This comes from multiplying all the various efficiencies of thecomponents in the transmission and charging system. (approx: 48.6%) ]D = 241 Kilometres [ From BMW ]Thus; for the Mini E as an example we have:

g/Km = 430 x 35/(0.491 x 241) = 127.2 grams per Kilometre. Now for comparison we have the 'claimed' emissions for the Mini D as:

104.0 grams per Kilometre

This cross checks with our diesel formula as :2639/(72.4 x 0.3538) = 103.0 grams per Kilometre

[ Note: the Mini D claims 72.4 mpg]

See Figure 1 overleaf:-



Figure 1 gives a perspective comparison of the two power systems. It should be notedthat the Grid emission figures may be equated to the MPG figures of the diesel bymultiplying by 0.2057 [ie: say 352 g/KWH x 0.2057 = 72.4 mpg. T his taken as the

point considered in the calculations above ]The BLUE trace is Diesel and the EV trace RED

The graph is based on an Overall Electrical Efficiency of 49.1%

Fig. 1

200 225 250 275 300 325 350 375 400 425 45070

78

86

94

102

110

118

126

134

142

150Combined CO2 Emissions (EV & Diesel)

Grid emission level in grams/KWh

GKm i

gKm i

Ai

So how do we explain this difference of some 27 grams per Kilometre in favour of theDiesel versus the EV?

1) If you look at the configuration of the two vehicles you will note that whereas the primenergy producer in the diesel lies under the bonnet; in the EV it is located often many milaway in the power station.

2) Also, whilst the route the energy takes to the wheels in the diesel goes through merely tgearbox and differential ; the route for the EV goes through a complex system of energytransforms each with its separate energy loss.3) The result of this is a large difference in efficiency and lost energy.



The extent of this difference in efficiency is, of course, open to challenge and can besubjective. Practical experience and genuine road tests will eventually home in on this.Meanwhile we can but attempt to make sense of the claims made by the variousmanufacturers of the components involved in this EV route.

The overall efficiency is, of course, the multiplication of the efficiencies of the constituentcomponents. In the above case comprising:Efficiencies:Grid Transmission : 0.91Battery charger : 0.9Charging protocol: 0.75Battery usage factor 0.8:Overall efficiency: = 0.91 x 0.9 x 0.75 x 0.8 = 0.491 [ A used above ]

We next come to the question of the actual CO 2 emitted at the power stations. This is a mix

of fossil and alternative fuel sources which is reflected in the official figures.Here we have the SAP figures for the construction industry:[SAP is "Standard Assessment Procedure" ( Whatever that means )], and gives:

For Year 2009 : Grid electricity 517 grams per Kilowatt Hour.For year 2009 Other non Grid electricity: 529 grams per Kilowatt Hour.

We however, have used the 430 g/Km figure, as given on the internet [ A marked difference which perhaps needs explanation. ]

This really does cause a problem; for which is the true figure? - Which reflects the pragmatic situation?The difference is large and would increase the EV emission figure to some 158 grams perKilometre if these figures were to be used.

If we now go to the figures from 'Elexon' the Quango mentioned in Appendix B, we canlook at the detailed analysis of actually what happens in the Grid Network and find thatthere is a large variation in the emission figures depending on circumstances at the time.

The range is from about 270 to 600 g/Kwh and depends on time of day , the month andwind conditions.

The figure of 430 g/Kwh is in fact the mean of the monthly returns over a year.andtherefore should not be taken as valid in the EV context.Why not?Well; - EV owners are constrained in the times that they can charge their vehicles andfurther will not discharge their batteries fully before recharge. And again they do notcontrol the weather or the date or how many other EVs are being charged.

In the summer they may well beat the diesel, if careful; but in the winter they would be bestadvised to bring the Mercedes C class out of the garage if they wish to conserve CO 2emissions.



Finally the only way that EVs can match the diesel equivalent on CO 2 emissions,apart from increasing the efficiency of the energy supply route, is to reduce thefossil fuel content of the generation system to, at the very least, an average of 350grams per Kilowatt Hour emission level [ An 18.6% reduction ]This would require ahuge investment in ' reliable' alternative generation.[i.e..: NOT wind turbines please! - Another thermodynamic disaster]

CONCLUSIONS:

Far from being 'Zero Emission' vehicles, Electric Cars in use, will in factcontribute to an increase in total CO 2 emissions in the transport industry.

A personal view:Statutary Authorities should be made aware of this fundamental thermodynamic fact if the objective to reduce CO 2 Emissions is to beachieved.

Premature implementation of encouragement policies to increae their use inthe current financial and technological situations should therefore beavoided.



APPENDIX A

The Data:1 mile = 1.609 Kilometres x 0.62 = 1 mile1 UKgallon = 4.546 Litres x 0.2199 = 1 UKgallon [ 1 Ukgallon = 1.2009 USgallons]Diesel fuel produces 2639 grams of CO2 per litre. [Petrol @ 2331 grams].

Other data ( etc:)[Relevant ; but referred to later, or of interest. ]

Diesel fuel produces 2639 grams of CO2 per Litre [ Petrol @ 2331 grams]Diesel cycle efficiency circa 40% [Petrol ( Otto cycle) around 36%]Power station efficiency is problematical, as it involves different thermodynamic cycl

Perhaps we can assume here circa 40%? [ Not too relevant as we are primarilyconcerned with the CO2 emission factor ] National Grid Transmission efficiency seems to be accepted at around 91% [ No ideawhere this comes from; but obviously depends on the source to output locationsand the overall route taken between the two ].Battery charging efficiency is a minefield and varies between 6% to above 90%.[One can but assume here that EV technology has sorted this out and generallythe efficiency would be high. It is a 'Caveate Emptor' situation if you buy one of these vehicles. ] Let us take a figure of 80%.Battery efficiency involves the 'state' of the the battery when it is to be charged. Atnear exhaustion it is relatively efficient. However if you top it up after a quick run to

pick up the papers, it can be very inefficient . We take a figure here of 80% [in the faith that EV users will be responsible.] Thus 80%Battery efficiency usage factor depends on the rate at which the energy is taken fromthe battery. [ You can flatten a Tesla EV battery in 50 miles if you want]

The Diesel formula:

The calculation for a diesel car which returns, say, a practical 60 mpg.

60 miles per UKgallon x 1.609 kilometres per mile x 0.2199 UKgallons per LitreEquals 21.23 Kilometres per Litre

Turn this upside down and you have 0.0471 Litres per kilometre.Multiply this by the 2639 grams per Litre emission figure for Diesel and you get:

124.3 grams per KilometreTo simplify this: As 1.609 x 0.2199 = 0.3538 we can write 2639/(mpg x 0.3538)Hence the formula used in the text:- X/(mpg x 0.3538)



APPENDIX B:

The EV formula:At first sight the easiest way to calculate the emissions of an EV is to multiply the batterycapacity by the Grid emission figure and divide by the distance achieved on a full charge.

This gives 35 x 430/241 = 63.5 grams of CO 2 per Kilometre.Now this looks good and many people then jump to the conclusion that EVs are'Green'

But if you ask the question " How many Kilowatt Hours does it take to fully charge up a35 KWh battery"?; then you need to apply an efficiency factor to the charging process;as in normal engineering practice.Thus the answer to the question, taking an efficiency value of say 50% is 35/0.5 = 70.So the actual emissions of our EV above becomes 124.9 g/Km.

Which is not so good.

Thus, putting this factor into our formula and assigning values as:

A as the Grid Emission figure.B as the battery capacity.C as as the overall charging efficiency. - and:D as the Kilometres achieved on a full battery.

We get:- g/Km = A x B / (C x D)We now need to assess the values that we assign to A,B,C and D.To be credible these figures should be either factual or a fair and reasonable estimate.

Grid Emissions [A]:

A look at the actual grid emissions data as monitored by 'Elexon'; which is the bodyresponsible for this; we find that the figure varies wildly [from 207 to 600g/KWh]

The 430 value used in our example is in fact the mean monthly figure over a year.This is not a particularly appropriate figure to use for the EV owner as it gives littleindication of the Emissions generated during any specific charging process.However it does provide a base average for comparison.

The Data may be accessed onhttp://www.earth.org.uk/note-on-UK-grid-CO2-intensity-variations.htmlAnd/Or:http://www.earth.org.uk/_gridCarbonIntensityGB.html[ Unfortunately, (or otherwise), it is not possible to access these figures directly

from Elexon without paying some £3000.00 for the privilege so the data you see isout of date and but a sample ]You need to be wary here as some of the figures include Transmission Losses and somedo not.



Here is a snapshot of the data format you will find for the monthly analysis.The hourly analysis is similar and available on the website for various sample dates andtimes.

UK National Grid Carbon Footprint Sample Analysis by Month

Generally it appears that, if you are a dedicated EV owner you should charge your

batteries in July or August between the hours of 0100 and 0400. As for January? - Perhaps the Merc C-class might better be wheeled out of the garage?The assessment, here, is best left to the indivual EV owner.

Overall Charging efficiency [C]:

There are four main sections in the energy transfer route where we can estimate the process efficiency.

1) Grid Transmission . This is generally accepted as around 91% or a loss of 9%.2) Battery charging equipment is a very variable figure and can range from 6% toover 90% depending on the quality of the equipment; which should involve power factor correction,true sine electronics and battery voltage monitoring.Generally this equipment would be supplied with the vehicle. Say? - 90%?3) Battery efficiency. Again this is variable as it is a function of how the battery ischarged.and is highest when charging takes place from a deep discharge situation. Justtopping up the battery after a say a 10% discharge would be very inefficient.Say? 0.75%?4) Energy extraction from the battery depends on how quickly this happens.Carefuldriving with minimum acceleration would be needed to achieve the claimed rangefigures. You could easily flatten the battery in 100 miles with a heavy foot.Say? 80%?



The overall efficiency is given by the multiplication of these values as: -0.91 x 0.9 x 0.75 x 0.8 = 0.491 or 50% in round terms.

There are rich grounds for heated debate in this area; so perhaps this, again, shouldleft to the individual EV owner to form a view.

Battery Capacity [B] and Range [D]:

As both these items are 'as claimed' there is little to add here except :to note that the battery does deteriorate; particularly if the charging protocol and care is not followeFigures of up to 20% capacity reduction over a 5 year period have been suggested.This, of course would reduce the range and perhaps even the overall efficiency figur

Only practical experience will tell and be reflected in the second values of these veh

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Electric Car Emissions MK1