Low-energy vehicle

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A Low-energy vehicle is any type of vehicle that uses less energy than a regular vehicle. The 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/100km (180-450 kJ/km) is achieved directly by battery electric microcars. The energy efficiency of the power generation has to be considered when comparing the efficiency of electric vehicles with hydrocarbon powered ones, for example the distribution efficiency for Europe is about 40%,^[1] so the overall energy consumption of electric cars lies in the range 0.45 to 1.1 MJ/km. Looking to 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.^[2] The energy consumption figures for petrol and diesel cars should be increased by 18%^[3] 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.

1 Motivation
2 Physical background
3 Facts
- 3.1 Models in Production
4 Outlook
5 Buying Behaviour
6 Fleet Management and Low Energy Consumption
7 See also
8 References
9 External links

[edit] Motivation

3 l-vehicle courtesy Greenfleet

LEV Twike

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%.^[4]^[5] 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/100km, 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,^[6]. 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 100km: 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/100km since 1l gasoline holds around 10kWh.

[edit] Physical background

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) ${P_{accel}= m_{vehicle} \cdot a \cdot v }$ where P stands for power, $m v e h i c l e$ for the total vehicle mass, a for the vehicles acceleration and v for the vehicles 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.^[7] 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 ${F_{drag}= A_{cross} \cdot C_d \cdot \frac {v_{air}^2 \rho_{air}} {2} }$ where F stands for the force, $A c r o s s$ for the cross-sectional area of the vehicle, $ρ a i r$ for the density of the air and $v a i r$ 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 C_d 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 ${F_{roll}= \mu_{roll} \cdot m_{vehicle}\cdot g }$ where $μ r o l l$ stands for the rolling resistance coefficient, g for acceleration due to gravity and $m v e h i c l e$ 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 $μ r o l l$ down to 0.0025^[8] 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. Maximum ranges are improving with new LiIon electrochemical storage batteries. It is not likely that purely IC powered vehicles will match the energy efficiency of EVs especially in transient operation. Hybrid electric vehicles will have to reduce the IC-size to beat them.

[edit] Facts

Some newer examples of efficient commercially available internal combustion-propelled vehicles:

Audi A2 (3l) 1.16 MJ/km (3.0 L Diesel/100 km / 94 mpg UK / 78 mpg US) (discontinued)
VW Lupo (3l) 1.16 MJ/km (3.0 L Diesel/100km / 94 mpg UK / 78 mpg US) (discontinued)
Toyota Prius 1.45 MJ/km (Hybrid) (4.2 L/100 km / 67 mpg UK / 56 mpg US)
Honda Insight 1.49 MJ/km Hybrid vehicle (4.3 L/100 km / 65 mpg UK / 54 mpg US) (discontinued)
Honda Civic Hybrid 1.59 MJ/km (4.6 L/100 km / 55 mpg UK / 46 mpg US)
Citroen C3 1.94 MJ/km Stop & Start (5.0 L Diesel/100 km / 56 mpg UK / 47 mpg US)

Average data for vehicle types sold in the U.S.A.^[9] compared to an advanced vehicle concept, the Honda Insight:

Type	Width	Height	Curb weight	Combined fuel economy	Percent	Occupancy rate 2005 Florida^[10]
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
SUVs	73.5 in 187 cm	70.7 in 180 cm	4242 lb 1924 kg	19.19 mpg 12.25 l/100 km	328%	(1.35 light trucks)
Honda Insight^[11]	66.7 in 169 cm	53.3 in 135 cm	1850 lb 839 kg	63 mpg 3.73 l/100 km	100%	n.a.
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.

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,^[12] and 1.2 for commuting.

Vehicles with a higher number of seats have a better fuel economy if they are fully occupied. You don't save fuel if you drive a 7 seater commuting to work alone, equally, you don't save fuel if 4 of you each drive a Honda Impact to work instead of sharing a lift in a Minivan. 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^[13].

[edit] Models in Production

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In practice we have not seen much on the market focusing on low propulsion energy demand. The battery electric GM EV-1 and the hybrid electric Honda Insight are no longer in production as well as the 3l Lupo from VW. In Germany as internal combustion vehicle the Jetcar (car) may be bought. There are however several relevant scientific competitions such as the Shell Eco-Marathon, Automotive X Prize and Solar car racing.

Triggered by congestion charging in London and other environmental incentives in Europe a few Battery electric vehicles have arrived on the market, such as the REVA G-Wiz and the MEGA City NICE.

Consumption of some low energy vehicle in production (note that this varies depending on speed and driving conditions, so not all numbers are directly comparable):

Model	Consumption in kWh/100 km*	Consumption and Fuel	estimated average CO₂-Emission	Motor	Comment
CityEl	3,5–5,5	Electricity	0 g/km direct Emission; 22–36 g/km (grid power Germany)	2,5 or 3,5 kW Electric motor	1seat
Startlab Open	7			4 kW	2seat
Twike	< 8	< 8 kWh/100 km Electricity (no official test figure)	0 g/km direct Emission; <52 g/km (grid power Germany)	5 kW Electric motor	2seat
Tesla Roadster	15	Electricity, approx ca. 1.74 l gasoline per 100km in city traffic	0 g/km direct emission	185 KW	two seater cabriolet 0 to96 km/h (60 mph) in 4 seconds
REVA		electric	0 g/km direct emission;	13.2 kW DC	2+2seater
VW Lupo 3L TDI	29,3	2,99 l/100 km Diesel	79 g/km	1,2 l; 45 kW	(1999–2005) innovative technologies like electric hydraulic coupling, stop'n go mode, light wheels etc. failed to prove economy with low fuel price.
Audi A2 1.2 3L TDI	30,38	2,99 l/100 km Diesel	81 g/km	1,2 l; 45 kW	(1999–2003) similar to the VW Lupo but bigger Aluminium chassis
Smart Fortwo mhd	32,34	3,3 l/100 km Diesel	88 g/km	0,8 l, 33 kW Microhybrid	(2008 till now) 2seater
SEAT Ibiza Ecomotive		3,8 l/100 km Diesel	g/km	l, kW	(2008) 4seater
smart cdi	37,24	3,8 l/100 km Diesel (RL80/1268/EWG)	100 g/km	0,8 l, 30 kW	(2000–2007) 2seater, consumption in practice 3.5 to 4.7 l/100 km
VW Polo BlueMotion	37,24–39,2	3,8–4,0 l/100 km Diesel (RL80/1268/EWG)	99–104 g/km	1,4 l; 59 kW	Modell 1,4 TDI (BlueMotion); since July 2007 from 4,1 l/100 km reduced to 3,8 to 4,0 l/100 km Diesel (RL80/1268/EWG)
Kia Eco C’eed	38,22	3,9 l/100 km Diesel	g/km	1,6 l, kW	(2009) 4seater
Toyota Prius	38,27	4,3 l/100 km high octane gasoline (RL80/1268/EWG)	104 g/km	1,5 l; 57 kW + Electric 50 kW	Hybrid electric; 2004er and 2006er Model (Prius 2)
Citroën C1 HDi55	40,18	4,1 l/100 km Diesel (RL80/1268/EWG)	109 g/km	1,4 l; 40 kW
Citroën C1; Peugeot 107; Toyota Aygo	40,94	4,6 l/100 km high octane gasoline (RL80/1268/EWG)	107 g/km	1,0 l; 50 kW	since 2005 produced by TPCA
Honda Civic Hybrid	40,94	4,6 l/100 km high octane gasoline (RL80/1268/EWG)	107 g/km	1,3 l; 70 kW + Electric 15 kW	(2006 till now) Hybrid electric
Citroën AX Diesel	41,16 und 44,1	4,2 und 4,5 l/100 km Diesel on average	111 g/km, 120 g/km	1,4 und 1,5 l mit 37 bzw. 40 kW	was one of the most efficient low cost high volume vehicle in the 9oies weighting only 720 kg.
Daihatsu Cuore, Daihatsu Trevis	42,72	4,8 l/100 km low octane gasoline (RL80/1268/EWG)	112 g/km	1,0 l; 43 kW
Opel Astra Eco4	43,12	4,4 l/100 km Diesel	116 g/km	1.7 DTI 16V; 55 kW out of production
Mini Cooper D 2007	43,12	4,4 l/100 km 2008 makes have 3,9 l/100 km Diesel	118 g/km	1.6d (TDCI) 16V; 80 kW	in production since 2007
*conversion factors: Diesel=9,8 kWh/l; petrol=8,9 kWh/l

[edit] Outlook

In the near future several low energy vehicles may be in production.

Aptera Motors Typ-1 with three wheels, a claimed C_d of 0.11, and a claimed energy usage of 6 kWh/100km, is due in late 2008.
Loremo LS (for low resistance mobile) turbodiesel car, which claims C_d of 0.20 and 157 mpg, is due in 2009.
VW's 1l car, and the Daihatsu UFE III are examples of working prototypes which may show up in future.

[edit] Buying Behaviour

Whilst in many countries fuel efficiency is regulated (USA, Japan, Taiwan, South Korea, China^[14]) 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
Misconceptions

[edit] Low fuel cost

In some countries fuel cost is very relevant but not the main cost (11,000 km at 8l/100km 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.

[edit] 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 ^[15]

[edit] Marketing driven buying

There is a certain room free of intelligence and full of emotion and tendency towards luxury. This may be seen in the emotional marketing campaigns of the car brands. To avoid information given to the customer the ads contain only marketing speech bypassing also CO2 labelling requirements this way.

[edit] Misconceptions

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^[16]. 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 misconception often heard are:

A stronger engine consumes less petro because it works under less stress
Heavier vehicles are safer

The fuel consumption of a motor is depicted in a shell diagramm where the consumption is shown over RMP and torque. Normally the smalles consumption is seen in the upper middle part of the diagramm. For diesel engines this region is bigger to lower torque and extends to higher RPM. Misconceptions result from the fact that people do not know this facts. It is true that operating a very small engine at maximum power all the time results in a suboptimal fuel economy, but the maximum power is seldom necessary if you don't drive highway all the time. So the choice of the engine power should consider the typical application and deduct the power needed- for non transient low velocity operation this leads to lower figures. A hybrid electric concept allows even lower power for the internal combustion engine. But the added weight pays only off if you operate in stop'n go conditions frequently or generally at low power if you use a serial hybrid electric concept.

The SUV case had lead to a couple of investigations. If we exclude behavioural influences we see a high variance in vehicle safety depending on the make. This is also caused by inherently unsafe concepts like a high centre of gravity. But in General only energy absorption in Joule counts. Here optimisation of the crash absorbers, aluminium structures or foams help to achieve high energy absorption while reducing the weight.

[edit] Fleet Management and Low Energy Consumption

The EU- sponsored RECODRIVE project^[17] 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.