As a solar panel was raised onto the roof of their ­mud-brick home in a Tanzanian village in sight of Mount Kilimanjaro, Akida Saidi and his wife felt giddy at the prospect of entering a new era. In a place where most residents make do with pit latrines instead of ­toilets and till their fields of maize and pigeon peas with hoes, suddenly having electricity would catapult them into the 21st century.