atmospheric radiation scattering/absorption

lurksalot

I am still trying to assess the ability of the sun to heat a house through glass and I am a bit stuck .
Most solar flux /radiation measurements I have found are based on a total of direct and diffuse radiation on a horizontal surface and then formulated for vertical surfaces with some cosine functions depending on orientation.
Now, at for example , a latitude of 53deg between October through to May (inclusive, being the UK heating season ) the total values are around 180Kwhrs/sqmtr for North and 490 Kwhrs/sqmtr South .
My issue is that the measured North figure will be purely be diffuse radiation and thus basically the energy would be from the visible portion of the spectrum ie light . On the basis that 97% of the solar power is in the visible and near IR range and that radiation diffused through H2O will have been absorbed and radiated at a higher wavelength , that the resultant 180Kwhrs on a North facing vertical face would be the energy of the visible light ?
Also on the basis that the energy from the sun is approx 45% visible light and 50% near IR would it be reasonable to assess that even on full disc sunshine only 50% of the insolation value could be used to calculate heat benefit ?
This probably sounds a bit daft but any clarification of my limited understanding of this would be of great benefit
Many thanks Kev

lurksalot

Any Help is appreciatted