I got one of these Vornado Energy Smart fans last summer that has a high-efficiency brushless DC motor that runs off 24VDC transformer that plugs into the fan with a standard barrel connector. It's expensive but it does move air well and can be dialed down to really low speeds to reduce noise and energy consumption.

Today I made up a DC power cord and played with running it off of 12V batteries and power supplies through a DC converter to measure the fan's current draw. At full speed it pulled 2.2A x 24.0V ~ 53W from the converter, which corresponded to 4.2A x 13.8V ~ 58W from the power supply I was using. At about 75% fan speed, which seems like the sweet spot in terms of noise and air flow, the fan pulled 1A x 24V = 24W. I have the exact same design with the traditional AC motor and it pulls 72W from the wall socket at full speed, although the DC model feels like it may move a bit more air at top speed.
You could hook up two deep-cycle 12v batteries in series with a 24V solar charge controller and then run the fan directly off batteries with no conversion losses from a DC-AC inverter or a DC-DC converter.