Year	% of total energy
1971	80.39137380191694
1972	80.93368202616638
1973	84.40022603334218
1974	82.71419210794544
1975	83.01154206046235
1976	81.5045030741477
1977	81.21234360322048
1978	81.50294340821378
1979	81.35894780890244
1980	80.366859023268
1981	80.57730300141435
1982	80.34011369789181
1983	80.84450642889583
1984	79.50420289016165
1985	79.33930878796883
1986	78.08275229768626
1987	82.73351498920867
1988	83.22484203563188
1989	83.70739373316992
1990	78.55091446522658
1991	78.61984970668378
1992	78.27388536267223
1993	77.25479636786879
1994	76.7706891518474
1995	74.74091595827625
1996	73.58565295588167
1997	73.37949139159775
1998	72.74062155479045
1999	71.76526497378939
2000	70.22657363088194
2001	73.45409638908471
2002	72.63318504484305
2003	68.88440760875127
2004	66.72776612871883
2005	67.25813099822236
2006	66.59713375142667
2007	64.22790976280463
2008	66.583012377667
2009	70.22063150794772
2010	71.76268900783333
2011	70.23084610527263
2012	64.2510459246224
2013	60.57726875093758
2014	52.13502892357543