The solar powered fan does not seem to be running at full capacity. Why?

The solar fan will speed up and slow down depending on the angle of the sunlight on the solar panel.

The solar fan will speed up and slow down depending on the angle of the sunlight on the solar panel. Even though the sun may be up, it may not be high enough to provide the energy required to generate current flow through the panel. This will cycle through the day as the sun tracks across the sky and repeat itself. It will also change depending on the season (i.e. it will slow down in the wintertime due to the lower rise and shorter duration).