question

[Magnus]

I have moved into an attic flat with large south facing windows in the roof. I'm wondering if a solar pannel will work effectively if it is behind a double glazed window? I think my landlord would not be too happy with me fixing it to the roof.

[skeptik]

I have moved into an attic flat with large south facing windows in the roof. I'm wondering if a solar pannel will work effectively if it is behind a double glazed window? I think my landlord would not be too happy with me fixing it to the roof.

You mean PV? Dont see why not . I have a solar powered pocket calculator on the table next to me and it works fine on the light coming in through the double glazing next to the table. Might be a small loss of efficiency from whats absorbed by the window glass, which you'd have to keep clean.

... and its going to make your room a lot darker!

[clv101]

All that'll happen is the efficiency will drop a bit since your double glazing will reflect a couple of percent at each air/glass interface. You might also lose a bit of defuse light since the window frame will mask some of the sky, this masking effect might also shorten your solar day a bit... I'd guess maybe 15-20% less energy behind a window than it would have collected.

[Ballard]

Should work fine as long as your windows are relatively old and have not been fitted with solar control glass.

Solar control glass looks like normal glass but is more reflective, like having a very fine mirror coating on the glass. Modern south facing windows often have this glass fitted to prevent solar gain. They should really be designed from a passive solar viewpoint to maximise solar gain in the winter, and minimise it in the summer.

I'm rambling...

[mikepepler]

All that'll happen is the efficiency will drop a bit since your double glazing will reflect a couple of percent at each air/glass interface. You might also lose a bit of defuse light since the window frame will mask some of the sky, this masking effect might also shorten your solar day a bit... I'd guess maybe 15-20% less energy behind a window than it would have collected.

I agree - you might expect a 10% loss for every pane of glass it passes through, though maybe less if it's expensive glass?

As said above, it does make your room darker, but when it's actually sunny that's probably not a problem. You might want to rig up some way of easily moving it out of the way when it's cloudy. Keeping it indoors saves you a lot of hassle with wiring and waterprrofing, and next time you move, you'll have the kit all ready to try outdoors if you can.

[Magnus]

Thanks for the info. Yes it will darken the room but I work nights on a regular basis and have to black out the windows during the day anyway.