Year Hours 1955-01-01 36.9977047146402 1956-01-01 36.7911290322581 1957-01-01 36.9150744416873 1958-01-01 37.0390198511166 1959-01-01 37.1216501240695 1960-01-01 37.0803349875931 1961-01-01 36.8324441687345 1962-01-01 36.3986352357320 1963-01-01 36.6052109181141 1964-01-01 36.5019230769231 1965-01-01 36.1300868486352 1966-01-01 36.1094292803970 1967-01-01 35.9235111662531 1968-01-01 35.9441687344913 1969-01-01 35.6343052109181 1970-01-01 35.0765508684864 1971-01-01 34.7666873449132 1972-01-01 34.9112903225806 1973-01-01 35.0765508684864 1974-01-01 34.4155086848635 1975-01-01 34.1263027295285 1976-01-01 34.6014267990074 1977-01-01 34.9939205955335 1978-01-01 35.0972084367246 1979-01-01 34.9732630272953 1980-01-01 34.1263027295285 1981-01-01 34.1263027295285 1982-01-01 33.5478908188586 1983-01-01 33.5685483870968 1984-01-01 33.9403846153846 1985-01-01 33.9816997518610 1986-01-01 34.0849875930521 1987-01-01 34.1469602977667 1988-01-01 34.3122208436725 1989-01-01 34.2915632754342 1990-01-01 34.0849875930521 1991-01-01 33.6924937965261 1992-01-01 33.4859181141439 1993-01-01 33.3206575682382 1994-01-01 33.7338089330025 1995-01-01 33.7338089330025 1996-01-01 33.6305210918114 1997-01-01 33.7338089330025 1998-01-01 33.4239454094293 1999-01-01 33.4652605459057 2000-01-01 33.6511786600496 2001-01-01 32.9488213399504 2002-01-01 32.4943548387097 2003-01-01 32.8661910669975 2004-01-01 32.8248759305211 2005-01-01 33.0521091811414 2006-01-01 33.1500000000000 2007-01-01 33.2500000000000