Year	Hours
1970-01-01	1902
1971-01-01	1871
1972-01-01	1813
1973-01-01	1769
1974-01-01	1758
1975-01-01	1689
1976-01-01	1698
1977-01-01	1674
1978-01-01	1655
1979-01-01	1647
1980-01-01	1670
1981-01-01	1643
1982-01-01	1652
1983-01-01	1648
1984-01-01	1642
1985-01-01	1627
1986-01-01	1630
1987-01-01	1595
1988-01-01	1577
1989-01-01	1559
1990-01-01	1546
1991-01-01	1541
1992-01-01	1561
1993-01-01	1562
1994-01-01	1554
1995-01-01	1546
1996-01-01	1536
1997-01-01	1549
1998-01-01	1564
1999-01-01	1573
2000-01-01	1585
2001-01-01	1588
2002-01-01	1579
2003-01-01	1577
2004-01-01	1579
2005-01-01	1579
2006-01-01	1586
2007-01-01	1570
2008-01-01	1573
2009-01-01	1544
2010-01-01	1546
2011-01-01	1548