Electric vehicles

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The REVA electric car was launched in June 2001 in Bangalore and is exported to the UK as the G-Wiz. The G-Wiz's electric motor has a peak power of 13 kW, and can produce a sustained power of 4.8 kW. The motor provides regenerative braking. It is powered by eight 6-volt lead acid batteries, which when fully charged give a range of "up to 77 km." A full charge consumes 9.7 kWh of electricity. These figures imply a transport cost of 13 kWh per 100 km.

Manufacturers always quote the best possible performance of their products. What happens in real life? The real-life performance of a G-Wiz in London is shown in figure 20.21. Over the course of 19 recharges, the average transport cost of this G-Wiz is 21 kWh per 100 km - about four times better than an average fossil fuel car. The best result was 16 kWh per 100 km, and the worst was 33 kWh per 100 km. If you are interested in carbon emissions, 21 kWh per 100 km is equivalent to 105gC02 per km, assuming that electricity has a footprint of 500 g C02 per kWh.

Now, the G-Wiz sits at one end of the performance spectrum. What if we demand more - more acceleration, more speed, and more range? At the other end of the spectrum is the Tesla Roadster. The Tesla Roadster 2008 has a range of 220 miles (354 km); its lithium-ion battery pack stores 53 kWh and weighs 450kg (120Wh/kg). The vehicle weighs 1220 kg and its motor's maximum power is 185kW. What is the energy-consumption of this muscle car? Remarkably, it's better than the G-Wiz: 15 kWh per 100 km. Evidence that a range of 354 km should be enough for most people most of the time comes from the fact that only 8.3% of commuters travel more than 30 km to their workplace.

I've looked up the performance figures for lots of electric vehicles -they're listed in this chapter's end-notes - and they seem to be consistent with this summary: electric vehicles can deliver transport at an energy cost of roughly 15 kWh per 100 km. That's five times better than our baseline fossil-car, and significantly better than any hybrid cars. Hurray! To achieve economical transport, we don't have to huddle together in public transport - we can still hurtle around, enjoying all the pleasures and freedoms of solo travel, thanks to electric vehicles.

Figure 20.20. Electric vehicles. From left to right: the G-Wiz; the rotting corpse of a Sinclair C5; a Citroen Berlingo; and an Elettrica.

14 16 18 20 22 24 26 28 30 distance (miles)

Figure 20.21. Electricity required to recharge a G-Wiz versus distance driven. Measurements were made at the socket.

14 16 18 20 22 24 26 28 30 distance (miles)

Figure 20.21. Electricity required to recharge a G-Wiz versus distance driven. Measurements were made at the socket.

Figure 20.22. Tesla Roadster: 15kWh per 100km. www.teslamotors.com.

Figure 20.22. Tesla Roadster: 15kWh per 100km. www.teslamotors.com.

yh rg W

S00 -750 -700 -650 -600 = 550 ü 500 ü 450 = 400 = 350 -300 -250 -200 -150

Walk 0

Earthrace "eco-boat" (4 passengers)

Jet-ski

Hydrogen car (BMW)

Learjet (S passengers)

Helicopter

Ocean liner

Range Rover

Ocean liner (full)

Hovercraft Hydrogen fuel-cell car (Honda)

Cessna 310 (6 passengers)

Figure 20.23. Energy requirements of different forms of passenger transport. The vertical coordinate shows the energy consumption in kWh per 100 passenger-km. The horizontal coordinate indicates the speed of the transport. The "Car (1)" is an average UK car doing 33 miles per gallon with a single occupant. The "Bus" is the average performance of all London buses. The "Underground system" shows the performance of the whole London Underground system. The catamaran is a diesel-powered vessel. I've indicated on the left-hand side equivalent fuel efficiencies in passenger-miles per imperial gallon (p-mpg). Hollow point-styles show best-practice performance, assuming all seats of a vehicle are in use. Filled point-styles indicate actual performance of a vehicle in typical use.

See also figure 15.8 (energy requirements of freight transport).

Boeing 747

Boeing 747 (full)

Catamaran

Turboprop

150 200

This moment of celebration feels like a good time to unveil this chapter's big summary diagram, figure 20.23, which shows the energy requirements of all the forms of passenger-transport we have discussed and a couple that are still to come.

OK, the race is over, and I've announced two winners - public transport, and electric vehicles. But are there any other options crossing the finishing line? We have yet to hear about the compressed-air-powered car and the hydrogen car. If either of these turns out to be better than electric car, it won't affect the long-term picture very much: whichever of these three technologies we went for, the vehicles would be charged up using energy generated from a "green" source.

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