In a humid environment, with an abundance of fruit at certain times of the year, what is the best method for drying fruit slices for later use? I don't want to use any type of equipment that needs power/active heating (like an oven)... is it possible to simply slice the fruits and leave in the sun/air?
Unless you have some other constraint you've failed to mention, it's what they are made to do. When we had a gas oven with a standing pilot, that kept the oven warm enough to use as a crude dehydrator; now I just use a common electric heat & fan model.
images are examples, not endorsements.
I saw an episode of Good Eats where Alton Brown uses a regular box fan and air conditioning filters to dehydrate jerky. Looks like the same can be applied to fruit according to his Food Network Post. Not sure if this would work in a humid environment though.
Special equipment: 1 box fan, 4 paper air-conditioning filters, 2 bungee cords, 6 (14 by 14-inch) plastic dehydrator sheets In a large mixing bowl, combine the lemon juice and water. Set aside until ready to use. Peel, core and dice the fruit into 1/2-inch cubes, with the exception of the strawberries. Slice the strawberries 1/8 of an inch thick. Place the fruit into the lemon water and allow to soak for up to 2 minutes. Remove and drain thoroughly. Lay 1 (14 by 14-inch) plastic dehydrator sheet on 1 of the air-conditioning filters. Place the fruit on the plastic dehydrator sheet and cover with another plastic sheet. Repeat this process with remaining plastic sheets and two more filters, stacking on top of the first one. Top these with the remaining empty filter. Next, lay the box fan on its side and lay the filters on top of it. Strap the filters to the fan with two bungee cords. Stand the fan upright, plug in and set to high. Dry for 42 to 48 hours. When dry, the fruit should be pliable but not sticky. You should not be able to squeeze moisture from the fruit. If using a commercial dehydrator, follow the manufacturer's directions. Remove the fruit from filters and store in an airtight container in a cool dry place. Recipe courtesy of Alton Brown, 2007