Year	% of total fuel combustion
1971	7.5
1972	7.547169811320756
1973	6.642066420664207
1974	6.761565836298933
1975	6.907894736842104
1976	6.896551724137931
1977	7.624633431085044
1978	7.2864321608040195
1979	7.945205479452054
1980	10.914454277286136
1981	12.040133779264213
1982	11.486486486486486
1983	8.55614973262032
1984	9.880239520958085
1985	11.147540983606559
1986	12.662337662337663
1987	13.114754098360656
1988	15.359477124183007
1989	15.358361774744028
1990	14.814814814814813
1991	15.053763440860216
1992	14.440433212996389
1993	12.837837837837837
1994	12.297734627831716
1995	12.26993865030675
1996	11.886304909560724
1997	10.251046025104602
1998	10.351966873706003
1999	8.370702541106128
2000	9.004739336492893
2001	8.30670926517572
2002	9.09090909090909
2003	10.29126213592233
2004	10.70110701107011
2005	9.98278829604131
2006	10.8348134991119
2007	9.00900900900901
2008	11.320754716981131
2009	9.797297297297296
2010	10.305958132045088
2011	7.679180887372013
2012	7.3604060913705585
2013	9.25925925925926
2014	8.556149732620321