Seven years ago, I built a solar dehydrator. It has worked very well. But I also noticed that the design had one issue. That is, the fruit in the bottom tray always took longer to dry. Resulting in having to swap trays around to improve drying time for all items in the dehydrator. The issue was of course that the air entering at the bottom was at ambient air temperature, and had to be heated in the box. Thus the lower part of the box was cooler than the upper part.

The solution was of course to build a preheater, to warm up the air before it entered the box. Which this year I finally got around to doing. While the idea is simple, I of course always over engineer things, so the actual construction took much longer than I expected. But I am still very pleased by the results both aesthetically and functionally. And drying efficiency has been improved.

Photos below showcase the design and installation (the preheater is attached with hinges and easily removable).