The single biggest driver of solar payback after the federal credit — how your utility credits the power you export back to the grid.
Full retail net metering
Every kWh you export cancels out a kWh you consume at the retail rate. The strongest policy for homeowner economics — solar-only sizing usually wins.
Net billing
Exports are credited at a wholesale or avoided-cost rate, well below retail. Batteries typically improve payback under net billing because you use more of your own generation on-site.
Avoided cost / no mandate
The utility pays only what it would have paid a wholesale generator — usually 2–4¢/kWh. Size conservatively and pair with storage to maximize self-consumption.