Year	% of total energy
1960	3.1748062911757517
1961	3.0796393715892236
1962	2.9601446789873007
1963	2.8645500015455654
1964	2.78350691952641
1965	2.6686135320804407
1966	2.588774846809637
1967	2.426013645911075
1968	2.448732904984039
1969	2.374511041452687
1970	2.2596844153958444
1971	2.2121560981135344
1972	2.2111064813094963
1973	2.1674846995196804
1974	2.2327864927968792
1975	2.223350015181372
1976	2.379648297033043
1977	2.4711166957685484
1978	2.661109491496173
1979	2.81669954835829
1980	3.019309907620651
1981	3.129385704344946
1982	3.312588436713414
1983	3.5166444900788565
1984	3.775230180228072
1985	3.6695985428088043
1986	3.755109266084801
1987	3.961695575172626
1988	3.7726169111747248
1989	3.541547286629442
1990	1.4328283620318067
1991	1.5246987762882607
1992	1.785499982366615
1993	1.4106827130856159
1994	1.376093650541377
1995	1.5827292398520778
1996	1.5158225782714776
1997	1.4334425849121992
1998	1.5624788368860558
1999	2.1893105294063315
2000	2.1793445197315306
2001	1.9197865723130763
2002	1.7185564379115483
2003	2.008311362907394
2004	2.1172211407701114
2005	2.3044470362686997
2006	2.5413873184583737
2007	2.5751109807492036
2008	2.831691834733527
2009	2.930978555476053
2010	3.204616658982303
2011	3.2984451395916077
2012	3.560646645661551
2013	3.672007535687285
2014	3.6900665601661595
2015	3.6210347459051646