Year	% of total energy
1960	3.0777318498275013
1961	2.9689718585503777
1962	2.8151149269034823
1963	2.6743346657606684
1964	2.5604985581149573
1965	2.4540170458753483
1966	2.3721607703395415
1967	2.2516127458828654
1968	2.2094250879716864
1969	2.1249872906784075
1970	2.3810339489919703
1971	2.587895248099443
1972	2.5186617754887823
1973	2.4241629932786597
1974	2.4996288952967864
1975	2.5108784271727487
1976	2.509735395650333
1977	2.5405744606978047
1978	2.6437823886926903
1979	2.69245089443536
1980	2.8304306139346402
1981	2.933616457707152
1982	3.144364893517142
1983	3.311951108592855
1984	3.4267925726892448
1985	3.3845846391540206
1986	3.4075169193098067
1987	3.4909727043921532
1988	3.4059155747347076
1989	3.373504811392931
1990	2.3848647268361276
1991	2.422513819751442
1992	2.5085806640967667
1993	2.388816654064019
1994	2.363572278156311
1995	2.456356430204213
1996	2.4111247315875617
1997	2.3621941049868562
1998	2.435060029267465
1999	2.68544323107717
2000	2.6742842341205826
2001	2.516154906266645
2002	2.478059320378765
2003	2.6241247238004677
2004	2.668753381873843
2005	2.8196044048809035
2006	2.9745726791707465
2007	3.09822254167256
2008	3.283989310857652
2009	3.466266839919541
2010	3.661408415273848
2011	3.6641494088899793
2012	3.894183899129358
2013	4.006242821829681
2014	3.993753382760643
2015	3.935214174007865