Home made powered foundation vents? Computer fans and solar power?
CFM: Cubic Feet per Minute. It is the same unit for both. 

Note that computer fans are not rated or listed for such use or permanent installation and might not like getting wet. 

I don't doubt that such a setup would work but I would test it first with some power adapters (12VDC, common for 120mm fans) before looking at solar panels. As the exact power requirements will depend on the voltage and amperage of the fans, until this is known it is not possible to say if a 20W solar panel would be sufficient for a single fan.