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I have a large loft with a gable end facing due South on the Sussex coast. There is a small (0.45sqm) window. I would like to install solar panels for water heating on the floor of the loft angled up towards the window at a distance of a couple of metres back.The object being to avoid panels on or visible from the exterior. Does anyone have experience of how much solar energy could be collected by this method?
Just to expand on that.. The widely quoted figure for the amount of energy reaching earth is 1000W/sqm. You have a window about 0.25 sqm so around 250W of energy is coming in the window. Solar panels are 40-60% efficient I believe so that's around 100 to 150 watts output. However the panel would either have to track the sun or be much larger than the patch of sunlight falling on the floor. If it's much larger you might loose all that heat from the part of the panel that's not illuminated.
Thanks, Tuna & CWatters, for that feedback, particularly the energy figures. it seems that the area of the sunlight patch is relevant and will vary according to the distance of the panel behind the window. My loft gets extremely hot in Summer, and I wonder if that might counteract the heat loss from the part of the panel in comparative darkness. In addition, the proposed system would have a circulating pump which would continuously pass the liquid through the sunlit area of the panel. Tracking the sun daily would be complicated, but a method of tracking the seasons by alternative vertical postions of the panel, could be practicable. If all else fails, I do have a fallback option:- Because the gable end is timber framed tile hung, a larger window could be fitted for a reasonable cost.
To sum up, do you consider that the principle of placing the panel some distance behind a (suitable sized) window is sound?
<blockquote><cite>Posted By: Harry</cite> My loft gets extremely hot in Summer, and I wonder if that might counteract the heat loss from the part of the panel in comparative darkness.</blockquote>
You could consider the whole roof as a collector and fit an air-water heat pump. It would be useless in the winter, though.
> it seems that the area of the sunlight patch is relevant and will vary according to the distance of the panel behind the window.
A fixed amount or energy will be coming in the window. If the panel is further away that energy is spread out slightly more but it's still roughly the same amount of energy. The collector should be as close to the window as possible to reduce the size of the collector needed and the it's losses.
>To sum up, do you consider that the principle of placing the panel some distance behind a (suitable sized) window is sound?
Well I guess it might work in a green house. Solar panels are typically behind glass but the gap is kept small and sealed to reduce convection losses. The extra layer of glass (the greenhouse) would cause some light to be blocked and some reflected.
Don't know how feasible it is, but since there are many people who build their own, would it be worth making your own panel with the box made to look like a window frame? If it is, you could use the existing windows glass for glazing the box.
Deffinately not worth it. The glass used in solar collectors is not ordinary glass. It's very low iron oxide and more often than not the glass surface is frosted. Together, this gives improved solar energy penetration through the glass with reduced losses and reflection back. With the sun having to penetrate your roof window first would mean a huge reduction in available energy.
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