FROZEN HEAT | Volume 2

Hydrogen to carbon ratio of global primary energy

100 Percent (logarithmic scale) Share in total primary energy

Percent (logarithmic scale)

100

Coal

Oil

Carbon free age

Traditional biomass

10

10

Gas

Methane age Oil age

Gas H/C = 4

1970

Oil H/C = 2

1

Renewables

1

Nuclear

Coal age

1935

Coal H/C = 1

1860

0.1

0.1

Pre industrial age

Wood H/C = 0.1

0

1860 1880 1900 1920 1940 1960 1980 2000 0

Source: Marchetti, 1985;WEC, 1998 and IEA, 2012 1800 1850 1900

1950

2000 2050

2100

Sources:WEC, 1998; IEA, 2012; Grubler and Nakicenovic, 1988.

Figure 1.3: Global primary energy substitution 1860-2009, expressed in fractional market shares. Sources: WEC (1998), IEA (2012), Grubler and Nakicenovic (1988).

Figure 1.4: Hydrogen to carbon ratio of global primary energy, 1860- 2009. The ratio is expressed in fractional shares of hydrogen and carbon in average primary energy consumed. Source: Marchetti (1985), WEC (1998), IEA (2012).

In 1985, Marchetti presented the concept of the hydrogen to carbon ratio (H/C), which can be used as a proxy for environ- mental quality (Marchetti 1985; Ausubel 1998). Firewood has the highest carbon content and lowest H/C ratio, with about one hydrogen atom per ten carbon atoms. Among fossil ener- gy sources, coal has the lowest H/C ratio at roughly one hydro- gen atom to one carbon atom. Oil has, on average, two hydro- gen atoms to one carbon atom, and natural gas or methane, four hydrogen atoms to one carbon atom. Figure 1.4 shows the changes in the H/C ratio resulting from global primary energy substitution in the period from 1860 to 2009 and the continu- ous decarbonization from 1860 to 1970. At this point, the H/C ratio has become approximately constant. Many energy analysts agree that this trend points to a future increasingly fuelled by natural gas, which could serve as a bridge towards a low- to no-carbon long-term energy outlook

(Nakicenovic et al. , 2011; MIT 2010). That is consistent with the dynamics of primary energy substitution, as well as with the steadily decreasing carbon intensity of primary energy and the increasing hydrogen to carbon ratio. As non-fossil energy sources are introduced into the primary energy mix, new energy conversion systems will be required to provide low- to no-carbon energy carriers, in addition to growing shares of electricity. Ideal candidates might be conversion systems with carbon capture and storage tech- nologies. With the implementation of such technologies, the methane economy would lead to a greater role for energy gas- ses and, over time, hydrogen. An analysis of primary energy substitution and market penetration suggests that natural gas could become the dominant energy source and that the methane economy could provide a bridge toward a carbon- free future (Grubler and Nakicenovic 1988, IPCC 2007).

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 17