Solar Powered Fan ventilation myths and half truths
Solar powered fans are rated according to fan displacement at maximum speed in free air conditions.
That is a fan in a tube, with nothing on top and nothing below, at maximum speed which would be ostensibly at full light and not necessarily driven by the solar panel accompanying the fan when presented to you as a product.
The minute the flow encounters resistance, like the cap on a solar fan roof ventilator or the free air available on the intake side, performance values are well short of those claimed. Add the variances of light available on the day you can reduce those ratings further again until they are only a fraction of what is claimed possible.
The solar panel is the energy side of this equation so look at the life expectancy as claimed by the manufacturer or the marketing company. There’s no point to going to the trouble of installing the unit just to find some months later that you have is a solar powered lemon because if the warranty doesn’t cover the labour you’re going to be up for the same costs again and again….or until you, or someone else, falls off the roof.
And after all of that, remember…if you don’t have a roof ventilator that works at night….which is when you really need it for the evening purge….then you don’t have the product that benefits you most.
Yes there are products out there that offer you solar during the day and switch over to 240vac at night through a transformer and a switching chip which are more things that will go wrong sooner than later. So the question then becomes…who is going to maintain it and at what cost?
Sounds good doesn’t it, in the meantime you’ve acquired an education, at a cost, albeit one you didn’t need.
This is where the calibre of guidance sought is important, and having an open mind whilst seeking it.
There are, by design, solar powered products that use a fan during the day and revert to natural flow at night, however the air entering the attic void (replacing that which is exhausted) needs to be able to enter freely through high flow eaves vents such as the Condor type.
You can exhaust heat from the roof void using a fan….but the fan is not on the roof!
No fan manufacturer in the world will guarantee their fans (other than belt driven) to operate continuously in temperatures above 65 degrees which means that there will be failures, especially with the cheaper products, that translate into repairs and/or replacement.
The question then is simple….is that what you want……or would you prefer a simpler approach to achieving a better result in ventilating your roof?