This was just a little project someone asked me to do, provide forced ventilation for a small garden shed. There's not much else to say about this, at each gable end of the shed there's now an air vent and over one vent sits a 12cm computer fan, rated at 12V. It's fed power directly from a pair of small solar panels mounted on an adjustable stand to be positioned pointing towards the most sunshine.
The panels are just glued to an angled piece of plywood, screwed onto a length of broom handle, the whole being painted for outdoor resilience. The blocks are to be fixed to the side of the shed and a screw in each will then anchor the post in position once it has been adjusted.
It won't run all the time or indeed, everyday, but will change the air in the shed several times an hour when it does so provides the ventilation to prevent damp air accumulating.