That traditional biomass stove in paper's figures is perhaps the worst stove imaginable. Its efficiency could below 10%. Better designed stove has efficiency above 30% and has much less indoor air pollution.

That being said, the more I read it, the more I like this PV steam cooker. It is simple and easy to scale up by adding more PV panels and more sands. Although Ghana is close to the equator, I wonder whether it worth to steer the PV panels during the day.

Edit, efficiency measured by energy transferred to boiling water or cooking vs energy released from burning biomass.