lutful... of ideasPremiumReviews:
reply to SparkChaser
Re: GravityLight: lighting for developing countries. I have to do some calculations but maybe hand-cranked pulleys can be used to pull up a much bigger weight (rocks/bricks/water containers) to store much higher potential energy.
Another option could be a small enclosed flywheel assembly which is spun up to very high rpm using hand cranked mechanism. Yet another option is a heavy pendulum on a low friction pivot?
However, the cost of the mechanics of such battery-less systems need to compare well against locally made and recycled lead-acid batteries which are quite cheap.
*** Rural solar is quite feasible for developing countries. The country where I was born has millions of "solar home systems" ... see my old post ( »Re: Solar Training ) for a photo montage of rural female entrepreneurs (often with just grade 5 education) assembling the charge controller PCBs and installing these systems.
Google image search shows many more examples: »www.google.ca/search?q=banglades···&bih=676