Too much engineering, but might be something to play with. You could have a roof turbine running a main drive shaft, with your ceiling fans ran off of it.

The easy way would be a solar chimney.

It would work but the features would be less than with a regular electric fan. Questions are: How would you change the speed of rotation of the fan for low medium and high settings? Also how do you maintain a constant speed?But it would probably have to also be built into the structure of the house and wouldn't be portable.But if you just don't want to open up the windows because it would let cold air out then you might try better insulation and the energy saved from good insulation could then be used to power a fan.

Nice concept. Hydraulics are most efficient when used for high pressure, low flow-rate applications. A direct mechanical drive would be simpler and avoids the risk of messy fluid leaks.

You would have a governor and a linear transmission. It could possibly be done purely mechanically or with the assistance of electronics.

I'd say "open the windows," but I could see this working in larger/divided buildings.

There's another way that this could work. Bernoulli's principle says that higher wind speed equals lower air pressure, which is why chimneys force air upwards through them as wind blows across there tops. So supposedly you could make a solid state vent built into the house, that just uses the same principles as chimneys, and creates air current just like a fan. They say some ancient structures incorporated this into there designs for natural air flow down passage ways.

Looks like a practical idea. A old British invention during thedays of Raj in India - A Punka . This could be slightly modifiedto suit your idea. It is not a conventional fan. It was a bambooweaven sheet quite rigid fixed to the roof which was manupulated by a man pulling the string to fan air on to the office table. If thisPUNKA could be coupled to cam and connected to a windmill - you couldget air when the windmill moves. When there is no wind you willhave to use power.

This comment which I made to my idea of a coiled generator is relevant to your idea of a windpowered solar fan.It is a workable idea - I always had the old punka (a kind of ceiling fan)in mind - a British invention of the Raj. It is possibleto harness the wind energy to wind a huge coil and use it when you need. The beauty of this idea is that the cam based punka is thatthe shaft can be brought out of the building and coupled to a wind mill quite easily.

I think the simplest system would be to use a vertical axis wind turbine on the roof that rotates a shaft that passes straight down through the roof, and has the ceiling fan attached directly to it. Thus, the turbine and fan would simply be on the same shaft. I don't know if this set up would work that well, (it might tend to turn too fast) but it would certainly be simple. You should probably use a very low, wide turbine to produce high torque and low RPMs.

If you want to control its speed, you could connect a generator to the shaft in the attic. The generator could act as a regenerative brake, slowing the fan and generating usable electricity. You could also use the generator as a motor to run the fan on windless days, but you would want to disconnect the turbine somehow to avoid wasting power blowing air outside. Actually, a one way bearing could do this automatically.

To prevent rain water from running down the shaft, you could have a tube anchored to the roof that runs up around the shaft, and another slightly larger tube attached to the shaft above the smaller tube that wraps around the top few inches of the smaller tube. The larger tube spins with the shaft, while the smaller one is stationary. The larger tube would act as an inverted cup, keeping water out of the smaller tube.

To control the speed, you could incorporate gears in the shaft that would vary the speed of the fan blades.

Adding gears would increase the cost and complexity. It would also add drag which might reduce the likelyhood of it turning at all in light winds.