It is amazing how technology has given us the tools to create energy from pretty much anything. The gravity light is an amazing invention that uses gravity to power a light. Originally started as a crowdsourcing project on Indiegogo, it now has been tested in many countries effectively delivering a half hour of light from the gravitational force on a bag of dirt.
If that’s not enough, you can 3D print sand in the desert with solar energy. The Solar Sinter, the invention of Markus Kayser, systematically melts sand using a Fresnel Lens. Fresnel lenses, which used to be fairly common, are the front part of a rear-projection TV. Here’s how to salvage one. How hot can a Fresnel lens get? Try melting a rock at 3800F.
scott thorp 
sir, iwant to know sand bag can charge inverter battaries with hight of four story building.
I’m sure it can do that. I’d contact the designers at info@gravitylight.org. The website is http://gravitylight.org/. Good luck.