Conservatory Ventilation

Hi,     I have a large conservatory with no roof ventilation (polycarbonate panels). It is north facing so doesn't suffer from the unbearable heat build up of others but does get hot in summer.
I was thinking of adding 4 of these solar powered vents. Once switched on they can be forgotten, but they don't work at night (some expensive models have a battery backup which do).
Any thoughts? They would have to fitted from the inside, I hope I can get someone to position the external part from the outside using a stick whilst I attach it. Waterproofness is obvious concern as is heat loss in the winter.
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