4:55 The former mine, now managed by Michigan’s Department of Natural Resources, has been vacant for years. Most recently state police used the area, known as 7 Mile Pit, as a shooting range. Now, Roberts is trying to develop the site into a solar farm that could power a few thousand homes, at the very least, he said. “Hopefully we can do much better than that.” He’s the founder of a renewable energy company called Circle Power, and officially started working on the project this fall. It’s part of a growing effort to build up the state’s solar capacity. That’s as efficiency gains make solar cheaper than conventional sources and many of the state’s coal plants retire, which generate nearly a third of Michigan’s electricity.