RPCoyle:
Why would you need a fan and heat sink? I don't think any of the components get that hot, and it would require a lot more power to drive the fan.
The fan is not likely for the Arduino circuit, but for the solar dryer function. I am assuming what he is talking about is something like a solar food dehydrator, where airflow is critical to removing the moisture from the food being dehydrated. And he probably want to add temperature control to allow the device to maintain the appropriate temperature range for the specific type of food being dried.