We work in Burkina Faso where moringa produces leaves from May/June to October during our rainy season (800-900 mm). Last year we established a moringa plot of about 150 trees and began drying the leaves for powder. The frustrating thing is that the rainy season is very humid, so drying the leaves in the shade is very difficult, possibly taking a week or more of spreading it out (on a plastic mat, tarp or sheet), gathering it in for the rains and the nights, spreading it out again, etc. Another promoter of moringa in Burkina said he has used his gas oven. Though it works, to do it at low temperatures either requires very small batches or lots of turning. Then too, ovens are not affordable by most villagers, and it seems a pity to waste the fossil fuel where there is so much sun. Perhaps others have had similar experiences and might appreciate a village-level technology solar dryer that we have used this year to very good effect.
We start with a woven plastic mat of 1.5 x 3 meters and spread the moringa leaves (most stems removed) 1-3 cm thick. On each side of the long sides of the mat we place two long boards which support two pieces of corrugated metal roofing, just 5-8 cm above the plastic mat. The two short sides are left open to let air pass, and if it is windy, some rocks may be needed to hold the roofing in place (Figure 4).
Depending on how thickly the leaves are spread, and on how sunny or cloudy the day happens to be, it may be helpful to turn the leaves once or twice. In our experience, one day of decent sunshine from 9 am to 3 pm can dry leaves for a kilo of powder. Temperatures under the tin can get above 50ºC, but of course the leaves are still in the shade and the quality of the resulting powder can been seen in its bright green color. From a physics standpoint, the metal roofing blocks the vitamin-destroying UV rays of the sun. The bottom surface of the hot tin dries the leaves both by infrared radiation and by warm-air convection. Black paint on the top surface of the tin could increase both effects.