Year	% of total energy
1971	62.45600634077426
1972	63.34430528554053
1973	62.0136969546456
1974	67.70959722443497
1975	65.22640034301436
1976	74.37512286696146
1977	73.23989597899349
1978	73.00885404684976
1979	72.13977915901876
1980	70.47086278637417
1981	70.91282237489241
1982	69.65016723271822
1983	68.64663453364889
1984	69.07794189332785
1985	69.63405008811573
1986	68.02217777585955
1987	65.88534159181108
1988	66.87497733178166
1989	70.05100450642018
1990	66.41361492301345
1991	66.77272530479549
1992	65.2772635537262
1993	63.15818166063738
1994	59.31713701479323
1995	55.51464517126023
1996	52.681134237525505
1997	50.43592204689047
1998	48.77342236150981
1999	48.38349905949102
2000	46.667208842802296
2001	44.40842433869412
2002	40.66791035559723
2003	40.01012568183587
2004	35.71306345733715
2005	33.830294928386415
2006	32.92120492267146
2007	30.5283987922847
2008	28.49595183081049
2009	26.091405120053846
2010	23.468688947530474
2011	23.730523539340812
2012	23.56824823990844
2013	23.82023834321584