Desiccants need regeneration once having absorbed humidity. My idea is to span the inlet to a ventilation system with sheet desiccant material to remove evening humidity, and having that sheet exposed directly to the sun during the day to regenerate the desiccant. Perhaps the sheet holder can be constructed within a semi solar cooker (mirrored) configuration to speed the process.
For those familiar with the material, would this work?
If you are using Silica Gel you would need to get above the boiling point of water to effectively remove the moisture.
The recommended temperature for regenerating Silica Gel is 100 to 140 degrees celsius. A concentrating type solar cooker can achieve that. The flat plate types have a hard time getting over 70 degrees celsius.
I would suggest a damper and vent to allow the humid air to vent while the desiccant is regenerating.
The other suggestion would be a desiccant wheel running between a hot duct (regenerative) and your cold duct.
Snippet source: https://www.eng-tips.com/viewthread.cfm?qid=216148