If you’ve done any solar work, you know the interconnection process with the utility is where projects go to stall for weeks and months. The process varies by utility, but the basics are: you submit an interconnection application, the utility reviews it for technical feasibility, approves or conditionally approves, then after installation you get a permission to operate (PTO) letter before you can turn the system on. Some utilities do this in two weeks. Some take six months.
The technical stuff the utility is reviewing: will the solar output affect voltage on their distribution line, do they need to upgrade the transformer or service entrance, does the system meet their anti-islanding requirements. Modern grid-tie inverters all include anti-islanding as required by UL 1741.
Net Energy Metering (NEM): the billing policy that allows solar customers to receive credit for excess power sent to the grid. California just went through the NEM 3.0 transition, which drastically reduced the export credit rate and changed the economics of residential solar dramatically. Know the NEM policy in your utility territory before you help a customer make a solar purchase decision - the economics are very different depending on the utility and state.