Gravel being added to a grid system - Paul Maguire/Shutterstock Gravel grid systems comprise a network of interlocking plastic modules that hold the surface layer of gravel on top of a base layer.

More than 10,000 proposed solar, wind, and battery projects are currently waiting in line to connect to the U.S. electric grid—more than enough to hit a target of 90% clean energy by 2035. But many of ...