http://naturalhomes.org/offgrid-gravity-light.htm?a=earthenbuilt
GravityLight is a revolutionary new approach to storing energy and creating illumination. It takes only 3 seconds to lift the weight which powers GravityLight, creating 30 minutes of light on its descent. For free.
GravityLight is a revolutionary new approach to storing energy and creating illumination. It takes only 3 seconds to lift the weight which powers GravityLight, creating 30 minutes of light on its descent. For free.