CO2 emissions in the product life of Tesla Roadster and Lotus Elise. A Comparison

Table of Contents

List of tables and figures

Abbreviations and numerical units

1.1 Introduction
1.2 Life cycle assessment methods

2. Energy source: carbon footprint
2.1 Gasoline
2.2 Electricity

3.1 Combustion engine vehicle: carbon footprint
3.1.1 Combustion engine
3.1.2 Efficiency rates
3.2 Electric motor and battery: carbon footprint
3.2.1 Lithium-ion battery
3.2.2 Electric motor and regenerative braking
3.2.3 Efficiency rates

4. Comparison of the environmental impact of EV and ICEV

Bibliography

Tables

Erklärung

Bewertung der Seminararbeit

Würdigung

List of tables and figures

1.2.1 Life cycle stages of an average combustion engine vehicle focusing on production of fuel and the car

1.2.2 Life cycle stages of an average battery electric vehicle focusing on production of fuel and the car

26 2.1.1 Assumptions of automotive energy resource availability in the future

2.1.2 View on the different Life Cycle Assessment types for vehicle efficiency

2.1.3 Energy return on energy investment (EROI) for different energy sources/systems

2.1.4 Energy gains and direct/indirect energy investments of the U.S. oil and gas industry with combined EROI

2.1.5 CO₂ emissions of different car types at various life cycle stages in g/km

2.2.1 Construction of a silicon photovoltaic cell

3.1.1.1 Functionality an components of an ICE cylinder

3.1.1.2 Components of the ICE of a gasoline fueled Golf A4 and components of the IM with 55kW

3.1.1.3 The CO₂ emissions of different life stages of various vehicles (only LW ICEV considered)

3.1.1.4 Energy consumption and emissions of components of the LW ICEV given in percent (only CO₂ of total emissions considered)

3.1.1.5 Comparison of the Global Warming Potential of vehicle production (column three) of a ICEV and BEV

3.2.1.1 Technical data of a common lithium-ion battery

3.2.1.2 Energy density of different battery types for electric vehicles

3.2.1.3 Kg CO² equivalent for a 300kg lithium-ion battery pack with 100Wh/kg

3.2.2.1 Functional principle of an electric induction motor

3.2.2.2 Depiction of voltage and power waves

3.2.3.1 Efficiency rates of an electric vehicle and a fuel-cell car

3.2.3.2 Right graph: Efficiency rates of the electric motor with car assumptions based on Tesla Roadster without continuously variable transmission (CVT) (lower dotted line)

4.1 The emissions of the Tesla Roadster and Lotus Elise at different life cycle stages given in g/CO₂ per km with a life expectancy of 100,000 km for the battery and 150,000 for both car types

Abbreviations and numerical units

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1.1 Introduction

This paper intends to find out whether the electric vehicle Tesla Roadster or the combustion engine vehicle Lotus Elise has a better environmental impact.

The two specific cars have been chosen in order to give a more realistic comparison of the two different propulsion methods. Both car models are light weight sports vehicles, which means that both technologies are highly efficient for the purpose of meeting the needs of the drivers. Both cars can be taken as representatives of the most highly developed technology available for both electric motor and fuel motor today. Another reason to compare these two cars is that they have the same chassis. (Vehicle Platform Elise) This means that their size and amount of frame material are also similar. Since they are both sports cars and need to reduce weight, similar materials in terms of frame, tires and interior may be used. For a well-founded life cycle assessment both cars need to be comparable on the same premises, which is given in our case. For the two car types only the carbon emissions arising during the production of the engine need to be evaluated, because the manufacturing emissions of the other car parts are likely to be the same.

In order to evaluate which car is more environmentally friendly, an economic method called life cycle assessment (LCA) will be applied. LCA measures, among others, CO₂ emissions. The factors for both cars accounting for the emissions will be chosen and specified further; and relevant economic terms will be explained. In the subsequent chapters the emissions arising during gasoline and electricity production and the efficiency rates will be evaluated. For electricity generation a specific technology will be chosen. Findings of different scientific studies will be considered and related to the specific case of this paper.

Our focus lies on evaluating emissions and efficiency for both engine and battery production. The operating principles of the engines and the battery will be explained as well for reasons of comprehensibility. Other studies will also be taken into account. Finally the findings of this paper will be summarized and depicted in an own figure. A conclusion and an outlook to the future will be provided at the end of this paper.

In the course of the reasoning graphs and tables will be referred to, which can be found in the appendix. This structure has been chosen to provide a smooth text flow, since numerous figures are applied. Sources of information are mainly scientific economy books and internet publications. Official websites of the companies Tesla and Lotus have also been consulted.

Calculations made are based on equations given in different books, and both generic and specific calculations are listed. Simple unit calculations and percentage calculations will not be explained in detail. Abbreviations used are explained when they are used for the first time. For better understanding a list of abbreviations has been provided.

In the course of writing this paper numerous information sources had to be found, because a life cycle assessment of two different car types requires an investigation of various topics from different areas. The economic appliances and some technical studies in the cited books were of great help. The paper has mostly benefited from the book Energy for Sustainability from John Randolph and Gilbert M. Masters, which gives a broad perspective on all energy related topics. Furthermore personal contact was important for the issuing of this paper. An interview with the Tesla Roadster showroom team in Munich on October 29, 2012, was undertaken and gave an idea of the energy friendly company philosophy. An e-mail contact with Mech. Eng. Marcel Gauch provided information about lithium-ion-battery production and overall emissions of different car types. Laborious was the process of finding applicable internet publications, because recent research, especially about electric vehicles, has not been printed yet. The familiarization with new topics was time intensive, because life cycle assessment involves several vehicle life stages.

In the following, the economic basis for the comparison of an electric and a combustion engine vehicle will be explained.

1.2 Life cycle assessment methods

In order to determine which alternative power train is the most beneficial for our future world different comparisons with conservative engines have been made. As mentioned before it would not be appropriate to compare a small city e-car with a big SUV. Moreover the upstream activities of a product should not be neglected. It has to be considered that all the components of a product are manufactured as well, causing pollution. In addition, the disposal of products needs energy, the so-called down stream activities. (Frankl Chap 2.1) Eventually we have arrived at a totally different view of the final products. Without further examination we would of course assume that the electric car would have the least emissions and thus would be the most eco-friendly car. But now we have to take into account every stage in the product chain, which needs energy and hence emits pollutants. (See Table 1.2.1 and 1.2.2)

In economic terms this so-called Life Cycle Assessment (LCA) means:

“Products are regarded as carriers of pollution: they are not only a potential source of pollution and waste during their use; they are also a cause of resource depletion, energy consumption, and emissions during their life starting with the extraction of the raw materials and ending with their disposal.” (Frankl 1)

Investigating the lifelike environmental effects of a car is necessary because only then we have reasonable data to conclude which car is the real victor of the contest. Now the question arises whether the production of electric motor, electric battery and electricity will not match or even outrun the emissions of the components of the combustion engine car. In LCA there are different scientific ways to approach this issue. This will be explained for the specific case of the paper as follows.

Especially for automotive studies LCA guidelines have been introduced: (Gesellschaft 45 ff..)

1. LCA´s applications. In this first step a base reference for the existing products has to be developed. This is done by evaluating scientific books and web pages to extract reliable data for this study. Furthermore, the companies Tesla Motors and Lotus Elise were consulted (personal interview). Mainly general information will be applied; the reasons for this will be explained in step three.
2. Goal definition. The intention of the LCA has to be explained. In this case the environmental impact of the automobiles Tesla Roadster and Lotus Elise are compared in order to determine whether either the electric model or the fuel driven model has less emission in terms of upstream activities.
3. Inventory. The steps of the life cycle considered in the study have to be defined. This section again consists of different units and is a complex description of the LCA limitations.

In LCA impact assessment is mandatory. (Frankl 25) For this study, the ecological impact of the various impact categories at hand was chosen. The next step is to define the term environmental impact. Can we even measure the damage done to our planet occurring in our industrialized world? In which categories should be put cleared forests, extinct species, polluted rivers? There have been approaches to estimate a price for this damage but those environmental dollars cannot that easily be compared to private dollars. In addition it would be very tiresome to examine the complex system of environmental impacts of a product. During fossil fuel combustion greenhouse gas emissions arise, and this is why they are a major concern of this paper.

The overall oil consumption has declined in most sectors except for transportation. (Randolph 25) Even though efforts to reduce oil consumption have been taken the total oil use has significantly risen; therefore petroleum is the largest energy source with 40 %. Hence “any effort to reduce energy demands, oil imports, and carbon emissions must focus on transportation [...]” (Randolph 18) The global air pollutant CO₂ can more easily be measured than complex impacts on our ecosystem, and it can be expressed in metric units. The amount of CO₂ can be added up, which will be done at the end of the study. It can provide a proper base for a comparison between the two types of cars. This so-called carbon footprint is nowadays often used in LCA and “[…] has become a useful overall indicator of environmental impact of energy use.” (Randolph 206)

Although this LCA is limited, it is still complex and data intensive because every production and disposal step of the two cars has to be taken into account. Referring to the LCA standard ISO 14040 a so-called screening or steamlined LCA is possible. (Frankl 28 ff.) It allows to select a key issue of the production cycle and to exclude life cycle stages, system inputs or outputs and impact categories. This procedure is reasonable, because different products with similar processes are often compared, and the modification of a few core studies is only necessary. This case study focusses on upstream activities. The production of the common components of the cars will be neglected.

A further possibility to simplify this specific LCA is that generic modules rather than specific data is applied. The simplification is necessary because access to company-internal data is not completely given, and it would be outside the framework of this case study to calculate every relevant database.

4. Production phase. The parts of the car production focused on have to be listed. In this production phase embodied energy arises which is “the energy it takes to develop, process, manufacture, and transport the materials used in a building or other product.” (Randolph 167) In this case the energy for development is neglected. The energy can then be transferred into the corresponding amount of carbon dioxide. For the model Tesla Roadster the units of CO₂ will be evaluated for the power train with controller and battery. The emissions arising in the process of the electricity generation will also be evaluated. In the case of the Lotus Elise the manufacturing of the engine and the refining of petrol will be taken into consideration for the emission rate only. More accurate information will be given in chapter two and three.

5. Use phase. The numbers of lifetime mileage, vehicle weight and fuel consumption need to be stated. Next to the mandatory data mainly the calculation of CO₂ emissions arising during the average drive cycle of each car has relevance. The calculation will be done in chapter four.

Life cycle assessment provides an overall picture of the product impacts and hence provides a reasonable base for comparison in different sectors. “It forces us to look at the full range of energy, economic, and environmental impacts from 'cradle to grave'.” (Randolph 166) LCA provides numerous benefits in helping industry to reach sustainable decisions for the future.

2. Energy source: carbon footprint

2.1 Gasoline

Conventional fuel driven cars are the standard means of transportation today. They all rely on gasoline or diesel, both extracted from crude oil. The problem with this resource is not only that during the combustion process a lot of CO₂ emissions arise, but also that it is a limited resource. Depending on different assumptions oil will only last for 30 to 40 years, while other energy sources are limitless, such as solar power. (Table 2.1.1) Another aspect to consider is that the fuel we fill in our cars at the gas station has to be processed and delivered. A major point of life cycle assessment is that it investigates the whole life cycle of a product. Naturally the first emissions caused by an internal combustion engine vehicle (ICEV) already arise at the oil platform. These carbon emissions are often ignored, but to access full environmental impact, well-to-wheel (WTW) assessment is necessary, which means to:

“[...] compare full energy, economic, and environmental costs for different transportation options from the fuel wellhead to the vehicle or passenger miles traveled.” (Randolph 167)

The WTW assessment consists of numerous steps that can be subsumed under the emissions for the production (well-to-tank) and combustion of fuel (tank-to-wheels). An overview over the different assessment types is given in Table 2.1.2.

First of all we need to clarify what stages are needed in order to provide gasoline at our gas stations. The crude oil is pumped up at the wellhead, then transported to the refinery where it is processed, and finally it is transported to the gas station. (Randolph 534) The processing of crude oil is a complex chemical process, which is very energy intensive. Generally oil consists of hydrocarbon chains of different lengths. For the production of gasoline the shorter chains need to be extracted by means of fractional distillation. Oil is pumped into a distillation tower and is heated up. The vapors condense on different levels in the tower. After this process, other chemical changes are invoked in the gasoline, for which high temperature and pressure are necessary. (How gasoline is made) It should have become clear that the production of the fuel type of a vehicle is paramount for the energy demands of a car.

Now the question arises whether we have already come to the point where we need more fuel combustion to produce fuel than can be used for driving our cars. A useful indicator to find out whether we put more energy in than we get out is the energy return on energy investment (EROI):

“It indicates how much energy other than direct fuel energy input must be invested to get a unit of useful energy.” (Randolph 173)

The EROI is used to measure the energy of drilling for oil, pumping it up and processing it, in sum all the energy that the oil industry needs to produce gasoline. It can be measured for energy per unit produced over a certain period of time, mostly a year. The higher the ratio of the EROI, the more energy is gained in comparison to investment. If it is less than one, more energy input is needed than we get out. The EROI is calculated as follows. (Randolph 173 f.)

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The EROI value depends on data sources used by a study, but overall it can be claimed that the EROI for U.S. oil and gas production has mostly fallen, since the time oil drilling has started. The decline indicates that the increased search for oil wells to meet the high demands significantly lowers the energy output compared to the input. The authors of Energy for Sustainability give us a data table of different EROIs (Table 2.1.3). It shows that for U.S. oil and gas production in the year 2000 the EROI is 20 to 1, and for U.S. gasoline production it is 7 to 1. The value of oil and gas production is quite high, but the authors tell us that for new discoveries it will be about 8 to 1. A further study gives us an idea about how these values are calculated and how much energy is actually consumed and produced in the U.S. oil and gas industry annually. Numbers are given in Petajoules (PJ) and Exajoules (EJ) in Table 2.1.4.

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In the study of Guilford et al. the EROI is calculated with both direct and indirect input. In our study only the indirect input has been taken into account and we have therefore arrived at different values. Nevertheless our value is higher than the value for U.S. Gasoline production of 7 to 1. For a comparison of the EROI with the one of the electricity of the EV the latter number will be applied. Here the special chemical modifications to get the gasoline to drive a car are taken into consideration, and thus it is more accurate.