Can one wire solar cells to a computer to model data?
A USB only communicates in the digital domain as far as I know. If you need to enter the analog domain, or ADC (Analog to Digital Converter), then your best bet is probably to hook up an Arduino through the USB port and then listen to an Analog Input on the Arduino. Then you can let the Arduino send that information to your computer. 

There are some Analog to Digital Converters for USB out there, I just googled and they are... not the cheapest, and the software they come with are probably hush hush. If you use an Arduino instead you can use open source software and get a lot of help from the community. 

Maybe this thread on the Arduino Forum will help you in the right direction.
I know it's not good practice to answer with links, but considering the question was how to do it, and this is just a follow-up answer in the right direction I feel that it's okay. Shoot me if you feel different with a thumb down button. http://forum.arduino.cc/index.php?topic=14524.0