1. your location might help
2. how powerful are those solar cells? They need to be at least 4W as the inverter won't be 100% efficient and if you're lucky 80% (those little ones will not be)
3. Panels are never near their rated peak output.
To run a 12V 0.25A fan, you will need 1A at 3V, even if your converter is 100% efficient. Likely, your converter will be no better than ~75%, so that means ~1.3A. I would be very surprised if your bitty panels put out more than 50mA in bright sunlight.
Hello, I am in Southern Michigan. Not 100% sure on the power of the solar cells. I just know they power on a little LED, which I presume is 1.5v. My other option was to maybe get a better solar panel, but clearly they arent that efficient for the size, so I might resort to this 5V .25A 1.25W fan here: Evercool 70mm X 15mm 5 Volt Fan - ( EC7015M05CA) - FrozenCPU.com with that option, I wanted to see if I can run it on those solar cells with a step up, or just get one of these: https://www.futurlec.com/Solar_Panel.shtml (6V 400mA) for $20
true, but if I buy the 5v 1.25W fan, and just used one of those panels, I should be fine. All I need it to do, is run during the day, or most of it. Its for a fan aspirated radiation shield.