I

Specific Energy & Power

CAPACITORS

i. Iff1

Specific Energy (Wh/kg)

Fig. 7. Main characteristics of energy storage systems

Source: PSI

Specific Energy (Wh/kg)

Fig. 7. Main characteristics of energy storage systems

After hybrids, fuels cells might be an option. Fuel cells do have superior efficiencies; however, they cannot be run directly on fossil fuels. Commonly, one is talking about hydrogen, which has to be produced based on natural gas, electrolysis or biomass. An alternative is methanol, which is presently not looked at with too much enthusiasm — considering the problems with hydrogen (low density), there is a chance methanol will come back. Figure 8 shows a scheme of a low-temperature polymer fuel cell, the type most likely to be used in cars in a decade or two.

O2 - electrode (cathode) H2 - electrode

O2 - electrode (cathode) H2 - electrode

(anode)

Fig. 8. Scheme of a polymer fuel cell (PEM)

] electrolyte ] catalyst

Source: IMRT ETH Zurich, 2005

Fig. 9. The ETH Zurich PAC-Car

Polymer fuel cells, operated with hydrogen and air, achieve at lower loads efficiencies in excess of 50% — the best values of gasoline engines at higher loads are around 35%. But as mentioned earlier, hydrogen needs to be produced. ETH Zurich together with a number of partners produced a new world record with the PAC-Car: on 1 litre of gasoline equivalent the car shown in Figure 9 travelled 5385 kilometres. The fuel cell, produced by the PSI, was run on hydrogen. Here again, the idea is to stretch the limits to the extreme as pointed out with the ETH Zurich Hybrid III. The PAC-Car data are as follows: length 2.78 M, width 0.57 M and height 0.61 metres. Drag coefficient: 0.09, frontal area: 0.254 m2 and rolling resistance: 0.0015. Weight: 30 kg, power: 900 Watt.

Figures 10 and 11 show efficiencies of powertrains, tank-to-wheel and well-to-wheel. These data do have to be taken with a grain of salt — they give rough indications and do not pretend to be very accurate. Most important is the observation that a fuel cell, compared to an advanced hybrid powertrain in the context of well-to-wheel efficiency (taking into account the energy needed to produce hydrogen based on natural gas), is losing quite a bit of its glamour. This means hydrogen and fuel cells hardly make sense, if the hydrogen is not produced in a sustainable manner.

At this point a general remark about the energy consumption of cars is due. More and more, the psychology of the driver is a very important factor when it comes to fuel consumption. The customer asks for a fun-to-drive car and a car is more and more an expression of lifestyle — how to impress the neighbour. Fun-to-drive as a first priority translates into power per unit of weight. With a given car weight and the time envisioned to achieve a car

15 10

15 10

4).

3f~

2l

1

1

1

1

1

1

1

1

1

1) Original SI-engine

2) Hybrid III

3) w/o Supercaps

4) w Supercaps (recuperation)

SI CI today

SI CI 2010

SI CI CH2 Fuel Cell Hybrid today 2010 2010

Hybrid III (ETH/VW)

1) Original SI-engine

2) Hybrid III

3) w/o Supercaps

4) w Supercaps (recuperation)

SI CI today

SI CI 2010

SI CI CH2 Fuel Cell Hybrid today 2010 2010

Fig. 10. Efficiencies of different powertrains, tank-to-wheel cN ^

Fig. 10. Efficiencies of different powertrains, tank-to-wheel

SI CI today

SI CI 2010

SI CI Hybrid 2010

CH2 Fuel Cell today 2010

SI CI today

SI CI 2010

SI CI Hybrid 2010

CH2 Fuel Cell today 2010

Fig. 11. Efficiencies of powertrains well-to-wheel speed of, say, 100 kilometres per hour starting from rest, defines the power needed with a given engine type. Figure 12 gives an indication of what the consequences are of "fun to drive."

Vehicle B is a standard European car of the upper-middle class with the same specific power as car C, being a sports utility vehicle (SUV). Both have about the same acceleration of 0-100 km/hour; the fuel consumption of the SUV is double that of reference car B. The empty weight of the SUV

Vehicle

Mass kg

Power kW

Spec. power kW/100 kg

Consumpt. l G,D/100 km

A

1250*

107

8.6

4.3

B

1320*

110

8.3

7.4

C

2480*

220

8.9

14.9

D

12'000*/40'000

330

2.8/0.8

35

A: Hybrid; B: reg. Car; C: SUV. (A, B, C: All cars with 5 seats) Accel.: 8.9-10.9 s for 0-100 km/h D: Heavy truck (Diesel). *: weight empty G: gasoline; D: diesel

A: Hybrid; B: reg. Car; C: SUV. (A, B, C: All cars with 5 seats) Accel.: 8.9-10.9 s for 0-100 km/h D: Heavy truck (Diesel). *: weight empty G: gasoline; D: diesel

Fig. 12. The consumer decides about fuel consumption is 2480 kg; the total weight with a passenger is some 2'550 kg. This means, with one person, one moves basically the wrapping only. A look at car D, a truck, illustrates what it means to move goods in a most economical way: the empty weight is 12,000 kg; fully loaded it is 40,000 kg. The acceleration is certainly not breathtaking. Now let's have a look at fuel consumption: it is amazingly low. All of this means that "fun to drive" and psychology result in high energy consumption figures. The situation can be improved by using a hybrid powerplant, demonstrated with car A, a Prius by Toyota. Or in other words, "fun to drive" is possible by applying advanced hybrid technology, which results in lower energy consumption.

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