They were in the process of developing an energy storage system for that purpose when they realized that their idea was better suited to grid-scale energy storage.
And on the other hand….
Specifically, he teaches them that the food and bathroom waste they produce every day can be transformed by a biogas digester into fuel to clean and cook plus a compost to fertilize crops.
One flame in a room.
There once were 10s of 1000s in old rural China; so simple, so common, but now?