•A solar powered "fan" is easy to install and has no moving parts.
Attach a 10-15ft upright pipe between 6-10inches in diameter to the side of your house where it will get maximum sun exposure. Cap it to keep out rain and screen it for bugs. Run an air duct (flexible plastic in 4-6inch diameter works well.) to the air outlet on your composting toilet. Paint the upright pipe black.
This will work all night just on the temperature differential between the house and the night air, but during the day draws more than enough air to evaporate excess moisture from the pile and keep it aerated.