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A Low-energy vehicle is any type of vehicle that uses less energy than a regular fossil fuel vehicle.
An energy analysis extends beyond just the operating efficiency and emissions. A Life-cycle assessment involves production and post-use considerations. A cradle-to-cradle design is more important than a focus on a single factor such as energy efficiency.
Higher efficiency can be achieved by changing the vehicle's design, and/or by modifying its powertrain. Energy consumption as low as 5-12.5 kWh/100 km (180-450 kJ/km) is achieved directly by battery electric microcars. When comparing the efficiency of electric cars with IC cars the efficiency of the power generation has to be considered, for example the distribution efficiency for Europe is about 40%, so the overall energy consumption of electric cars lies in the range 0.45 to 1.1 MJ/km. (Average energy efficiency of US plants 33% US DOE (ref to follow) US grid transmission loss 9.5%, UK grid transmission loss 7.4 (ref Wikipedia national grid entry) - transmission losses not included in electric car efficiency figure.) By the year 2050, consumption levels of 1.6 l/100 km (0.64 MJ/km) in diesel-fuelled cars and 2 l/100 km (0.7 MJ/km) in petrol-fuelled cars are deemed feasible. The energy consumption figures for petrol and diesel cars also need to be increased by 18% to represent the oil used in processing and distributing oil-based fuel, to 0.75 MJ/km for diesel, and 0.82 MJ/km for petrol.
To put these consumption figures into perspective a consumption of 1000 km/litre (2350 mpg US) is 0.0344 MJ/km, excluding distribution energy. At 20 km/h it would take 50 hours to travel 1000 km, so with a 20% efficient internal combustion engine it would need to attain and keep this speed using just 38.2 watts.
- 1 Motivation
- 2 Physical background
- 3 Size and performance of various vehicles
- 4 Buying Behaviour
- 5 Fleet Management and Low Energy Consumption
- 6 See also
- 7 References
- 8 External links
Reducing global energy demand might help to reduce access conflicts over oil reserves and/or environmental damage when trying to produce fuel from natural or other fossil sources. Existing published consumption figures tend to underestimate the consumption seen in practice by 20 to 30%. The reason is partly that the official fuel consumption tests are not sufficiently representative of real world usage. Auto makers optimise their fuel consumption strategies in order to reduce the apparent cost of ownership of the cars, and to improve their green image. Even one of the most fuel efficient two seater on the market - the Smart MHD consumes two or three times more energy per km than a cabin based ultralight two seater would - proven by the 1l prototype by VW. Pilot vehicles have proven that a feasible target may lie in the range of 1-2 l/100 km, or lower, or 10 kWh/100 km electricity. Available electric LEVs already use substantially less energy than available cars, e.g. 4–8 kW·h/100 km for the Twike,. Here the challenges are increasing range and lifetime of batteries, crash worthiness, passenger comfort, performance and reducing the price (which is currently about twice that of a cheap conventional four seater).
Energy Efficiency in MJ per km or kWh per 100 km: It is more straightforward to express energy efficiency in MJ (Mega-Joule) per km because terms like MPG (Miles Per Gallon) and litres per 100 km do not take into account what type of fuel is used and thus the numbers will be distorted for different fuel types. Diesel contains 38.7MJ per litre, Gasoline 34.6MJ per litre and Bio-Diesel 30.5MJ per litre, whereas LPG contains only 22.2MJ per liter which is why the number of litres consumed go up drastically when converting a gasoline car to LPG. This does not mean that the energy consumption goes up; it only means that there is less energy in a litre of LPG. Ethanol also contains much less energy per litre than gasoline. To compare electricity and gasoline its easier to use kWh/100 km since 1l gasoline holds around 10kWh.
Energy demand may be kept low by:
- lower parasitic masses (compared to the average load) causing low energy demand in transitional operation (stop and go operation in the cities) where P stands for power, for the total vehicle mass, a for the vehicle's acceleration and v for the vehicle's velocity. Extreme masses will go down to 300 kg from today's 1100 kg to 1600 kg. Five seaters of the sixties had 625 kg. Japanese sub-compact cars have 500–600 kg. Further mass reduction is possible by adapting the maximum number of passengers to the average occupancy rate and having removable seats. Two-seater microcars have less than 400 kg, single-seaters less than 300 kg. Further reductions are possible with very light construction, e.g. Twike. The crash protection is certainly a problem in current traffic conditions, but the low energy vehicles are driven mainly at low velocities in cities.
- low cross-sectional area and mirrors replaced by cameras causing very low drag losses especially when driven at higher speed where F stands for the force, for the cross-sectional area of the vehicle, for the density of the air and for the relative velocity of the air (incl. wind). Two seating places in a tandem (back-to-back or forward-facing in line) arrangement drastically reduce the cross-sectional area down to 1 m². The drag coefficient Cd of the vehicle may be as low as 0.15 for very good vehicles.
- low rolling resistance due to smaller and high pressure tires with optimised tread and low vehicle mass driving the rolling resistance where stands for the rolling resistance coefficient, g for acceleration due to gravity and for the vehicle mass. Advanced driver assistance and ABS could prevent safety problems caused by the small tires, but current light weight vehicles do not possess these systems. Values of down to 0.0025 are possible but are more usually 0.005 to 0.008 for cycle-type tires and 0.010 to 0.015 for car tires.
Technological support for low energy operation may also come from driver assistance systems since driving style can be adapted to achieve lower energy consumption. Energy management becomes possible with hybrid vehicles with the possibility to recuperate braking energy and to operate the internal combustion engine (ICE) at higher efficiency on average. Hybrid power trains may also reduce the ICE-engine size thus increasing the average load factor and minimising the part load losses. Purely electric vehicles use up to 10 x less energy (0,3 to 0,5MJ/km) than those with combustion engines (3 to 5MJ/km and up to 10MJ/km for SUVs) because of the much higher motor and battery efficiencies.
Size and performance of various vehicles
Average data for vehicle types sold in the U.S.A. compared to an advanced vehicle concept, the Honda Insight:
|Type||Width||Height||Curb weight||Combined fuel economy||Percent||Occupancy rate 2005 Florida|
|SUVs||73.5 in 187 cm||70.7 in 180 cm||4242 lb 1924 kg||19.19 mpg 12.25 l/100 km||328%|
|Minivans||75.9 in 193 cm||70.2 in 178 cm||4275 lb 1939 kg||20.36 mpg 11.55 l/100 km||309%||1.67|
|Family sedans||70.3 in 179 cm||57.3 in 146 cm||3144 lb 1426 kg||26.94 mpg 8.73 l/100 km||234%||1.35|
|Toyota Prius||66.7 in 169 cm||57.6 in 146 cm||2765 lb 1254 kg||56 mpg 4.2 l/100 km||112%||n.a|
|GM Volt||70.8 in 180 cm||56.3 in 143 cm||3790 lb 1720 kg||60 mpg 4.0 l/100 km||105%||n.a.|
|Honda Insight||66.7 in 169 cm||53.3 in 135 cm||1850 lb 839 kg||63 mpg 3.73 l/100 km||100%||n.a.|
|Audi A2||65.9 in 167 cm||61.1 in 155 cm||1973 lb 895 kg||71 mpg 3.0 l/100 km||81%||n.a.|
The drag resistance for an SUV, compared with a family sedan with the same drag coefficient, is approximately 30% higher, and its increased mass means that the acceleration forces has to be 35% bigger for a given acceleration. This gives a 40% increase in fuel consumption. The last column in the table demonstrates that with the exception of the Prius and the pick-ups all the alternatives have roughly the same potential fuel usage per passenger IF they were fully occupied. However the fuel usage per passenger really depends on the occupancy rate of each type. In 2000 the occupancy rate was only 1.6 in practice, decreasing each year, averaged across all vehicle types and journey types, and 1.2 for commuting.
Whilst in many countries fuel efficiency is regulated (USA, Japan, Taiwan, South Korea, China) by law, in others there is a non perfect market, where producers tend to avoid prominence of high consumption figures in ads and thus make the procurement decisions less fact based. It is one of the reasons that energy efficient vehicles were not establishing themselves on the market in high volumes. Literature also sees higher child occupancy with SUVs. Reasons for the buying behavior are:
- Low fuel cost
- Sizing on the safe side
- Marketing driven buying
Low fuel cost
In some countries fuel cost is very relevant but not the main cost (11,000 km at 8l/100 km and 1€/l gives 73€/month only). This is lower than the investment costs per month for younger cars and leads to heavier usage of the vehicle. The technical term is least cost optimisation. If the cost operating the vehicle one km more is small then there is the tendency with the user to choose the car instead of public transport.
Sizing (Vehicle/Engine) on the safe side
If you are unsure about the final size of your family or the distances you normally drive you want to be on the safe side. Because of the big annuity or leasing rate, people tend to plan in advance and buy bigger cars. People also think that SUVs are safer for their children, but see the misconceptions section below for a discussion on this.
Marketing driven buying
There is an effect on purchasing decisions (exclusive of rational considerations, emotionally laden, and influenced by perceptions of luxury appointments or particular performance features) which is deliberately aimed at by much vehicle advertising. To avoid giving the potential customer information on which to base a more rational decision, the ads contain only marketing emphasis as desired by the marketing department concerned.
Effect of vehicle size and engine power
Vehicles with a higher number of seats have a better fuel economy if they are fully occupied. But you don't save fuel if you drive an SUV commuting to work alone, equally, you don't save fuel if you all drive separately to the same work in hybrids. The logic leads immediately to the coach or bus public transport because here the average occupancy rate in operation (in % of the seating capacity) is much higher than for the average SUV or Minivan because its a public system. Rideshare experience is very bad because of the reluctance of people to enter someone else's car. It has also to be said that the image build up for minivans has pushed back older vehicle concepts equipping estate vehicles with a third seat row. This way you avoid the high mass and big height of a minivan. Other statements often heard are:
- A stronger engine consumes less petrol because it works under less stress
- Heavier vehicles are safer
The fuel consumption of an engine is depicted as a 3dimensional map where the consumption is shown against RPM and torque. Normally the smallest consumption is seen in the upper middle part of the diagram. For diesel engines this region is bigger to lower torque and extends to higher RPM. The choice of engine power for a given vehicle should consider the typical application - for non transient low velocity operation this leads to lower power requirements, at the cost of reduced acceleration and top speed. A hybrid electric concept allows an even lower power internal combustion engine, but the added weight pays only off if operating in stop and go conditions frequently or generally at low power, if using a series hybrid electric concept.
In a collision the occupants of a heavy vehicle will, on average, suffer fewer and less serious injuries than the occupants of a lighter vehicle. An accident in a 2000 lb (900 kg) vehicle will on average cause about 50% more injuries to its occupants than a 3000 lb (1350 kg) vehicle.
Fleet Management and Low Energy Consumption
The EU- sponsored RECODRIVE project has set up a quality circle to manage low energy consumption in fleets. This starts with energy aware procurement, and includes fuel management, driver information and training and incentives for all staff involved in the fleet management and maintenance process. Vehicle equipped with gear shift indicators, tire pressure monitoring systems and downsized internal combustion engines and for stop'n go operation also hybrid electric power trains will help to save fuel.
- All-electric vehicle
- Green vehicle
- Low-carbon economy
- Low-rolling resistance tires
- Miles per gallon gasoline equivalent
- Plug-in hybrid
- Strategies for Managing Impacts from Automobiles, US EPA Region 10, retrieved May 22, 2012
- "European Union’s End-of-life Vehicle (ELV) Directive", End of Life Vehicles (EU), retrieved May 22, 2012
- http://themes.eea.europa.eu/Sectors_and_activities/energy/indicators/EN19%2C2007.04/fig1a.gif/view European power generation efficiency 2004
- SRU German Advisory Council for the Environment, Reducing CO2 Emissions from Cars http://www.lowcvp.org.uk/assets/reports/Reducing_CO2_Emissions%20Aug%2005.pdf p.5 feasible targets for fuel consumption
- http://www.calcars.org/calcars-technical-notes.pdf slide 2 85% well to tank efficiency
- Real-world emissions as well as the fuel consumption under the MCC (Milan City Cycle) were much higher - almost double - those obtained under the European type approval test cycle, Ref: JRC>IES>>13202
- http://www.edmunds.com/advice/fueleconomy/articles/105503/article.html On-line ref for differences between EPA and actual fuel consumption
- Roche, Schinkel, Storey, Humphris & Guelden, "Speed of Light." ISBN 0-7334-1527-X p176 Michelin measured rolling resistance
- Auto Channel, 2008 New Cars, 2008 New Car Buyers Guides, 2008 New Car Pictures, 2008 New Car Videos, 2008 New Car Reviews, 2008 New Car Pricing, 2008 New Car Buyers Guide, 2008- 1993 Car reviews, Hybrids, Compare Cars, The Car Channel, Compare New Cars, 2008 Toyota Camry Hybrid, 2007 Honda; 2007 Honda Accord; 2007 Honda Civic; 2007 Hybrids; 2007 New Car Pricing, 2007 Car Reviews, 2007 Car Specifications, 2007 Car Fuel Info, 2007 Car Comparisons, Used Car Prices, 2006 Car Reviews, Automotive News, Automotive, Total Ownership Costs (TOC), Pennysaver Autos; Used Vehicle Classifieds, Auto Industry News, Everything for the auto enthusiastic, and more on The Auto Channel
- Fig. 8-5 AVO Trend by vehicle type http://www.dot.state.fl.us/Research-Center/Completed_Proj/Summary_PL/FDOT_BD015_14_rpt.pdf
- InsightCentral, encyclopedia featuring the measures shown for the Honda Insight
- Car occupancy: by trip purpose, 1998-2000: Social Trends 32
- Petroleum Conservation Research Association (PCRA)New Delhi http://www.energymanagertraining.com/Presentations/3L_Auto/02Pune/02PCRA_Transport.pdf
- SUVs: The High Costs Of Lax Fuel Economy Standards for American Families Public Citizen June 2003 http://www.citizen.org/documents/costs_of_suvs.pdf
- J K Galbraith, The New Industrial State, extensive example from automotive industry of requirement to control end user choice
- ...males were significantly less likely to switch to becoming passengers or to car-pooling. from http://www.pinnacleresearch.co.nz/research/vehicle_occupancy.pdf
- website Rewarding and Recognition Schemes for Energy Conserving Driving, Vehicle procurement and maintenance
- http://www.wired.com/cars/futuretransport/magazine/16-01/ff_100mpg WIRED article including images of Aptera Motors' vehicle
- VW Lupo driven with 2.5 l/100 km in Australia 94 mpg U.S.
- Toyota ES3 2.7 l/100 km in the FIA ECO-Test 87 mpg
- Mitsubishi i-concept car tested at 3.8 l/100 km 62 mpg