For most people, electricity only flows one way (into the home), but there are exceptions — people who use solar panels, for instance. In those cases, excess electricity created by the solar cells travels back out into the grid to be distributed elsewhere. And in some states, people can be paid for this excess electricity. The practice is called “net metering” (referring to the total or “net” amount of energy used). It all started in the 1970s when an engineer named Steven Strong hooked his solar panels up to the electric grid and fed electricity up the line without asking the permission of the power company. For a while it was a relatively non-controversial practice, but there are now big political battles being fought over it. We adapted this doc from the NHPR program Outside/In.