Year	% of total energy use
1971	5.323867581835544
1972	5.827313193386791
1973	6.072941361998606
1974	6.474480251444486
1975	6.824907296122252
1976	7.457685078269832
1977	8.135932683579094
1978	8.403940499706069
1979	8.96804894405729
1980	9.737277736421145
1981	10.296315662990004
1982	10.929798759757311
1983	11.445322616538594
1984	12.180058282645737
1985	12.540336474496597
1986	11.613781289023175
1987	11.527433144236833
1988	12.121205446899063
1989	12.431715804879289
1990	12.411946970074172
1991	12.434752852218326
1992	12.57095161583868
1993	12.724210723552625
1994	12.481790721146133
1995	13.02302229239267
1996	12.798434055462279
1997	12.940570407801658
1998	13.158315719448147
1999	12.878408386279986
2000	13.712333710325453
2001	12.957041179844975
2002	13.245851015028393
2003	13.759840719199618
2004	13.239111612376508
2005	13.337350265883096
2006	13.721022701035901
2007	13.562582370233853
2008	12.90939716325823
2009	13.79550183067927
2010	12.700438357227187
2011	13.491612403251196
2012	12.650740564591429
2013	11.498104237890935
2014	10.809087327787147