Non-Edible Sweet Potato

BEASI is looking at a feedstock for ethanol production and other fuels in Cameroon. This plant is a very efficient crop, needing little water and nitrogen. They are very high yielding, as well as biotic and abiotic stress resistant. We are working with a start-up bioenergy company (CAREnergy, LLC) in the US that developed a non-edible giant sweet potato variety that meets those qualifications.

These are very dry sweet potatoes, which are not in the food markets. The BEASI team targeted this nonedible sweet potato to be a dedicated energy crop for bio-ethanol production in Cameroon. This is a variant of the sweet potato that has been specifically bred for high starch content. Industrial sweet potatoes are very different from food varieties of sweet potatoes and grow to enormous sizes, some over 20 pounds.

These tuber yields translate into enough starch to produce 1500-1800 gallons of ethanol per acre. This represents the highest ethanol yield per acre for any available feedstock. Sweet sorghum is the closest to this sweet potato tuber with ethanol yield per acre of about 1100 gallons. Sugar crops, like sugar cake, yield 600 gal/acre and corn 300 gal/acre. Switch grass yields 320 gal/acre and another cellulose crops average 350 gal/acre. This data demonstrates the HUGE potential of these giant potato tubers as feedstock for bioethanol production.

These sweet potatoes are extremely well suited to the growing conditions throughout the southeast, northwest, and littoral areas of Cameroon. They are drought resistant and grow well in sandy loam soils, and as a result will not compete for land with food crops. In addition, the sweet potatoes are extremely heat tolerant and need very little water and fertilizer to grow, far less than corn.

Since these sweet potatoes are bred for biofuel production, unlike table-top varieties, the appearance is not critical for downstream application and commercialization and they may be planted and harvest mechanically. This attribute will significantly reduce the farmer’s production costs and allow farmers to grow these sweet potatoes on a commercial scale.

Image: Flow scheme for the bio-ethanol production by processing sweet potato and associated co-products.