Lamp oil. Charcoal and other fuels are expensive. Solar power is a wise investments which pays for itself in a short time. Couple this with simple 'solar ovens' and the poorest folk can have better lives.

The lead-acid batteries as pictured in the article are the weak link in the system.

Many NGOs now refuse to support these sorts of projects.

Under heavy use lead-acid batteries don't last long, just a few years, and become a serious environmental hazard if they are not properly recycled. Presumably the "solar mamas" are educating people about that risk and are now using LiFePO4 Lithium Batteries, which have their own recycling issues.

Purchasing replacement batteries might also be an economic burden to many users. A 100AH battery sells for $100-$200 here in the U.S.A..

There no reason that we, as a world civilization, can't connect everyone to an electric grid. My great grandparent's ranch, which is about as far as way from civilization as one can get in the 48 United States, got electricity as part of FDR's New Deal. Local men were hired to install and maintain the lines.

My great grandma was always suspicious of electricity. When me and my siblings visited her home we were not allowed to touch the light switches or turn on my great grandfather's "damnedradio." The damned radio was the primary reason my great grandfather enthusiastically signed onto rural electrification. Powering vacuum tube radios with batteries was a very expensive hobby.

I've inherited my great grandmother's Aladdin oil lamp, a mantle type, that she used frequently because she preferred the light it made to electric light. It was only smokey when you lit it. But it was expensive too. The mantles are fragile. You can still buy replacement mantles today, $299 for a pack of 12 from Lehmans , $25 for one. Smokeless oil lamps are not cheap to operate.