8.4.13 
Should I switch off the fan in the night, if I do not have a Solar-Panel?
In the first night it is better to leave the fan running (high humidity). Later may be it is better to be off in the night if there is risk of cooling down the product too much. 

Should I paint all sides inside black of the dryer?
You can do that, increases the performance of the dryer a bit if the grid is not full with product. 

Which products should be covered to protect from sunlight?
The Plants with Chlorophyll (leaves), that could bleach

Drying in 2 Layers?
Is possible but lower layer will dry more slow, due to not being exposed to sunlight. So may be changing the layers from time to time. And all drying will take longer. Better is one layer completely full. 

13.4.13
in Info_food_eng you find more Information about making fruit-Bread, cakes and more now

17.4.13 
drying timber / wood : is quite interesting, because dried timber is stored sun-energy because it has a higher energy during burning. 

25.4.13
The solar module should be sized so that, even with an overcast sky, there should be a little flow of air in the dryer.
You can make other sizes of dryer, but
• The ratio of black area to drying surface should be 1:1. 
• The height should be maintained approximately, even if the drier is longer or wider
• Keep Fan-Size per square meter black area 40-50 m3/h air (about one fan)

4.6.13
see extra Document "drying food" for a lot of new information