On 16 Nov 2006 12:09:52 -0800 Will wrote :
However, when their surveyor came to measure up he said that the
west-facing roof was inadequate and the panels would have to be sited
on the gable-end wall (facing south).

You might want to download SAP2005 from www.bre.co.uk/sap2005

You can leave 95% of it to people like me, but Appendix H will give you
some hard numbers. Table H2 gives solar radiation as 724W/m2 on a
vertical south facing panel, 886/829 for a west facing panel pitched at
30/45 degrees.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk