| Year | MJ m2/d (Kcal m2/d) |
| 1993 | 19.2 (4589) |
| 1994 | 17.5 (4183) |
| 1995 | 19.2 (4589) |
| 1996 | 17.5 (4183) |
| 1997 | 17.3 (4135) |
| 1998 | 17.5 (4183) |
| 1999 | 18.4 (4398) |
| 2000 | 16.1 (3848) |
| 2001 | 19.6 (4684) |
| 2002 | 19.3 (4589) |
| 2003 | 18.3 (4374) |
| 2004 | 18.5 (4422) |
| 2005 | 18.8 (4483) |
| 2006 | 18.5 (4398) |
| 2007 | 18.1 (4326) |
| 2008 | 18.8 (4469) |
| 2009 | 18.3 4374) |
| 2010 | 18.7 (4469) |
| 2011 | 17.9 (4278) |
| 2012 | 17.9 (4278) |
| 2013 | 18.4 (4398) |
| 2014 | 18.5 (4422) |
| 2015 | 17.9 (4278) |
| 2016 | 18.5 (4422) |
| 2017 | 18.6 (4445) |
| 2018 | 17.9 (4278) |
| 2019 | 18.8 (4493) |