Family car: comparing material energy with use energy

Here we move up in scale. Argonne National Laboratory, working with the U. S. Department of Energy, has developed a model (GREET) to eval­uate energy and emissions associated with vehicle life. Table 7.9 lists the

Table 7.9 Material content of a conventional family car and one made of lightweight materials

Material

Conventional ICE vehicle, kg

Lightweight ICE vehicle, kg

Material energy Hm MJ/kg*

Carbon steel

839

254

32

Stainless steel

0.0

5.8

81

Cast iron

151

31

17

Wrought aluminum (10% recycle content)

30

53

200

Cast aluminum (35% recycle content)

64

118

149

Copper/brass

26

45

72

Magnesium

0.3

3.3

380

Glass

39

33

15

Thermoplastic polymers (PU, PVC)

94

65

80

Thermosetting polymers (polyester)

55

41

88

Rubber

33

17

110

CFRP

0.0

134

273

GFRP

0.0

20

110

Platinum, catalyst (Table 6.3)

0.007

0.003

117000

Electronics, emission control etc (Table 6.4)

0.27

0.167

3000

Other (proxy material: polycarbonate)

26

18

110

Total mass

1361

836

*From the data sheets of Chapter 12 and Tables 6.3 and 6.4.

bill of materials for two of the vehicles they analyze: a conventional mid­sized family car with an internal combustion engine (ICE) and a vehicle of similar size made of lightweight materials, with the biggest differences italicized in bold. The total mass is shown at the bottom of the columns. "Lightweighting" reduces it by 39%.

The data sheets of Chapter 12 provide the embodied energies of the materials. Fuel consumption scales with weight in ways that are ana­lyzed in Chapter 9; for now we use the results that a conventional car of this weight consumes 3.15 MJ/km; the lighter one consumes 2.0 MJ/km.1 There is enough information here to allow an approximate comparison of embodied energy and the use of the two vehicles, assuming both are driven 25,000 km per year for 10 years.

The bar charts of Figure 7.11 show the comparison. The input data are of the most approximate nature, but it would take very large discrepancies to change the conclusion: the energy consumed in the use phase of both vehicles greatly exceeds that embodied in their materials. The use of light­weight materials increases the embodied energy by 43% but reduces the much larger fuel-energy consumption by 37%. The result is a net gain: the sum of the material and use energies for the lightweight vehicle is 30% less than that of the conventional one.

8 X 105

0

FIGURE 7.11

family car.

T MJ/km = 2.86 liters/100 km = 95.5 miles per U. K. gallon = 79.5 miles per U. S. gallon.