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Electric cars extended note: 27th APRIL 2011

 

Wp Ref Electric for web 02

INTRODUCTION

In this note Internal Combustion powered vehicles, ICVs, are diesel powered or powered by the MUSIC experimental petrol engine under development by MUSI Engineering.  Improved ICVs would have regenerative braking, zero idling losses (engine off when stationary) and higher engine efficiencies.  Improved electric powered vehicles, EVs, are assumed to have motors mounted on the wheels, thereby eliminating mechanical transmission losses, and higher efficiencies.

The UK Government’s belief that EVs will emit 40% less carbon than ICVs depends largely on Arup/Cenex report for the BERR/DfT with the title “Investigation into the Scope for the Transport Sector to Switch to EVs and Plug in Hybrid Vehicles”, dated October 2008

The Arup/Cenex Paper

That paper, here called the Arup paper, depends on the claims of manufactures rather than on fundamental analysis or vehicle tests.  Further, although the paper claims that the data represents whole of life performance, nowhere is there information on the energy and emission attributable to battery manufacture. Since the latter may amount to between 50% and 100% of the energy transmitted during the lifetime of an electric car’s battery the omission is of overriding importance. 

In contrast our analysis, detailed in Appendix 1, depends on assigning energy efficiencies to the various links in the chain between the refinery, or power station, and the residual energy required to overcome wind resistance.  The efficiency chain is extended to that point because transmission, rolling and braking losses depend on vehicle weight and batteries make EVs heavier than equivalent ICVs. 

The product of the efficiencies provides the overall efficiencies.  The ratios of the overall efficiencies of EVs to ICVs provide the relative performance of the different vehicle types. The carbon emission per KWh of primary energy divided by the overall efficiencies provides an index enabling the emissions to be compared.  Additionally, the efficiencies were normalised so as to take account of the greater weight of the EV.  That procedure avoids the problems inherent in comparing the often wild claims of manufactures, which may in any case relate to vehicles with different performances and carrying capacities.

The Arup Paper A key finding of the ARUP paper is: “EVs have the potential to offer significant carbon dioxide and greenhouse gas emissions reductions compared to conventional petrol/diesel fuelled internal combustion engines. This applies over a full life cycle, taking account of emissions from power generation and emissions relating to production and disposal. Based on the current UK grid mix there are already significant benefits of the order of approximately 40% reduction; these benefits have the potential to become much greater with further decarbonisation of the UK power mix”.

However, instead of providing the fundamental data upon which calculations should depend there is generalised reference to the GaBi4 suite and to the claims of manufacturers. Consequently we lodged a Freedom of Information request that included the following:

  1. The percentage of the energy burnt in power stations that reach end users, namely “the plug”.
  2. The CO2 per KWh of primary burn.
  3. The ratio of the energy delivered to the drive chain to the energy taken from the plug for the presumed EV.
  4. The assumed thermal efficiency of the presumed internal combustion engine.
  5. The energy used to manufacture and scrap an electric car’s battery divided by the energy that the battery may deliver during its life.

In summary, the response, see attached, is that the GaBi4 grid mix for 2010 delivers 31% of the primary burn to the plug, rising to 50% in 2030 and that the carbon emissions are in the paper referred to, when they are not [1], further, with regard to efficiencies we read:

We [Arup] did not look at individual element losses within the vehicle, only the overall efficiency figures as supplied by manufacturers.”

And with regard to the energy and emissions associated with battery manufacture and scrappage:

We [Arup] could find no quantitative data on the energy required to manufacture a lithium ion battery. Neither was there any data available on the energy required for recycling the battery”.

We are astonished. After all, (a) without knowledge of the energy used to manufacture batteries how can anyone calculate the whole of life carbon emissions and (b) manufacturers’ claims are notoriously optimistic, as illustrated by the

Further, section 6 of the Arup paper cited above “demonstrates” that the cost of running EV will be less than that for an IC powered vehicle. However, the costs assigned to petrol and diesel include tax thereby exaggerating in favour of the E.g by a factor of two to three.

Against that background we regard the ARUP paper as an inadequate basis for national policy.

ELECTRIC CAR BATTERIES – ENERGY USED IN MANUFACTURE

A paper by Samaras, C. and Meisterling [2]  citing table 6 of a paper by Rydh, C.J. and, Sanden [3] suggests that 1700 MJ are required to manufacture 1kWh of battery capacity.  Converting to consistent units yields 472 kWh per kW h of capacity. Figure 1 of the first of those references suggests that the emissions attributable to the manufacture of a battery are of the order of one eighth of the emission due to usage during the battery life.  Similarly, Table 3 of the second reference suggests that a li-ion battery, at 100% Depth of Discharge, the DOD, has a life of 2,800 to 5,000 cycles and, at a 50% DOD, 7,000 cycles. The latter provides a ratio of energy to manufacture to the energy transmitted of 472/3500 or of 1 to 7.4. 

However, Samaras and Meisterling assumed that the batteries in HEVs and PHEVs last the lifetime of the vehicle and the figure given by Rydh and Sanden for Li-Ion battery life (14-16 years) is perhaps optimistic, given the available evidence - even in terms of shelf life. 

Our view is that such lives may arise in hybrid vehicles, when the battery is perhaps seldom discharged significantly and where use is light.  Battery life depends on factors that include the rate of discharge, the depth of discharge, the temperature range that the battery is subjected to and the extent to which the battery is subjected to high power surges. 

The anecdotal evidence below to do with fully electric cars suggests (a) a battery life of at best 3 years (b) vehicle ranges that are at best half those claimed by manufacturers, suggesting that the battery has to be recharged at half DOD, i.e. when only half discharged.  Taken together the implication is that the battery may transmit 500 to 1000 times its full capacity during its life.  If so the energy required to manufacture has the range 50% to 100% of that transmitted during the battery’s lifetime. We have used that range in our calculations.

ANECDOTES

  1. An electric car provided to a journalist for tests was alleged to have a 70 mile range.  The journalist decided to be safe and planned a 50 mile trip only to find the specially prepared car failed at 37 miles.
  2. A user of a G-Wiz found that the battery expired after 2 years and 3 months instead of after the hoped for 5 years.
  3. Jeremy Clarkson of Top Gear found that the Tesla ran out of power after 55 miles on his test track rather than after the 220 miles claimed by the manufacture.
  4. An electric Ford Transit sized van provided to a manufacturer, who wants to remain anonymous, was alleged to have a range of 100 miles.  The manufacturer found that on the level, and with no load, the vehicle managed 60 miles, but that on hills in Wales in managed six (yes six).
  5. Adverse weather conditions are said to reduce battery performance by 40% to 50%

SUMMARY RESULTS

The values below are averages from a range of operating conditions. They show that the EV, far from emitting less carbon than the competing ICV is likely to emit more – between 50% and 100% more than the experimental MUSIC. 

Table 1 Emission ratios: EVs emissions divided by ICV emissions.

Battery energy

(X)

(A)

(B)

Notes

Existing diesels and EVs

0.69

1.03

1.37

(X) Energy used in battery manufacture ignored

(A) Energy used in battery manufacture set to 50% of that transmitted during the battery’s life

(B) Energy used in battery manufacture is set equal to that as transmitted during battery’s life.

Improved diesels and EVs

0.81

1.22

1.63

MUSIC and improved EVs

0.97

1.46

1.95

The data at (X) is from spread sheets (A) or (B).  The data under (A) or (B) are from the corresponding spread sheets.  The range of conditions in the spread sheets represents congested urban running through to the open rural road.  There are also efficiency ratios which compare energy consumptions.   The excel versions enable readers to carry out sensitivity tests.  Click here for sheets (A) and here for sheets (B).

We also found that, at today’s prices and void of tax, the resource costs of electricity for the EV would be substantially above that for the competing ICV.  The comparisons are in Tables 4 of the relevant spread sheets.

OTHER ISSUES

Subject to carbon capture Coal fired generation emits double the carbon of the industry average.  Large scale electrification would extend the life of coal fired power stations.  Hence, there is a case for assigning coal fired emissions to the EV.  If that were is accepted as the correct approach then the EV would be seen as an environmental disaste; think china.

Apart from the emissions issue, the government has not addressed the problems of disposing of e.g. 30 million lithium-ion batteries or the problem of sourcing the lithium should there be a surge in global demand.

If oil ran out then the options would be the electric route or the synthesis of hydrocarbon fuel, which has by far the greater energy density.  However, if oil and other fossil fuel failed within 10 or 20 years then the energy shortage would be so acute that motoring would be the preserve of the truly wealthy or essential services. Not only would oil prices rise but also that of electricity.

RECOMMENDATION.

Investment in EV’s should be discontinued at least until:

  1. Field tests have established the ratio of the energy required to manufacture a battery to the energy transmitted by the battery during its life when in real-life use.
  2. An appraisal of the potential improvements to ICVs has been carried out. 

In support of our conclusion we cite the paper to Ingenia by Professors David Cebon and Nick Collings of Cambridge University originally available here http://www-cvdc.eng.cam.ac.uk/Ingenia-letter but also on our site here.


[1] Subsequent inquiry provided the GaBi4 numbers of:  0.62892 kg CO2/kWh in 2010: 0.41128 kg CO2/kWh in 2020: 0.35567 kg CO2/kWh in 2030. The 2010 value is substantially above that the value generally accepted for the UK generating industry of circa 0.5 kg CO2/kWh and above our value of 0.542.  We believe that is because the GaBi4 value includes some of the emissions prior to the burn in power stations

[2] Samaras, C. and Meisterling, K., ‘Life Cycle Assessment of Greenhouse Gas Emissions from Plug-in Hybrid Vehicles: Implications for Policy’, Environmental Science & Technology, Vol. 42, No. 9, 2008, p. 3171

[3] Rydh, C.J., Sanden, B.A., ‘Energy Analysis of Batteries in Photovoltaic Systems. Part I: Performance and Energy Requirements’, Energy Conversion and Management, Vol. 46, 2005,  pp 1957-1979.

 



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