Tommy Mitchell’s solar cellphone charger in Bryant Park in Manhattan. Once charged, he says, it can operate for a whole week without sun. – NYTimes.com.

Pacing around his Brooklyn apartment, Tommy Mitchell paused to eye his machine with frustration. On top was an 85-watt solar panel that he realized he had just installed upside down.

A solar-powered cellphone charger, it looks like an oversize white iPad on stilts, with eight charging wires sprouting like tentacles from the middle. Once charged, the machine, which sits on a huge battery, can run a whole week without sun, he said.