Year	% of total fuel combustion
1971	22.678120262758963
1972	22.75918841702581
1973	21.794137094996692
1974	20.271771643449274
1975	20.30630058720838
1976	18.69441676814643
1977	19.176681155714654
1978	22.025710946630305
1979	19.999232275152586
1980	20.0650641604916
1981	19.650505396607844
1982	20.07374732924392
1983	20.609451423343536
1984	19.84008166042872
1985	19.19691786509017
1986	19.29912810194501
1987	18.30001574059499
1988	19.422170915104054
1989	19.336285907609035
1990	18.941461935092505
1991	19.762929727763293
1992	20.91364167740775
1993	19.637650978758856
1994	19.348129660991773
1995	20.467005652927313
1996	20.384678165297352
1997	21
1998	19.712266532054514
1999	21.083682657972364
2000	21.12548218742909
2001	20.654563586500757
2002	20.90707721999254
2003	20.96865027219824
2004	20.68006969050369
2005	20.920005448424824
2006	20.704181804127696
2007	20.703379270583422
2008	20.695673209842415
2009	21.842627684533472
2010	22.57381788147842
2011	23.32834460098742
2012	23.321077016933497
2013	23.884472875827345
2014	22.850307482325515