The new 645 watt solar panels beautifully installed by Onboard Solar.
The rusty looking mark down the side is, in fact, tar residue. The flue above the roof was not insulated and the tar/creosote was condensating in the inside and, via the roof mounting, running across the roof and down the side. I cured it by installing an insulated chimney but getting the stain off will be a nightmare.
