4. GravityLight
This wonder-gadget-which you can get for less than $10- requires no batteries or sunshine and is instantly available anytime. How does it work? Well load a weight on one side and allow it to fall naturally under gravity. The weight can be anything from sticks and stones to other domestic objects.The kinetic energy of the weight is harnessed by a series of small gears into electrical energy and the light is turned on. Simple as that.
This eco-friendly GravityLight not only costs nothing to run but also powers electrical devices such as radios and reading lights.