On sunny afternoons, your panels may produce more electricity than your home is using. That extra power usually flows to the grid, and how your utility credits it has a big effect on what solar is worth to you.

Some utilities credit exported power at or near the retail rate you pay. Others credit it at a much lower rate, or use time-of-use pricing where the value of electricity changes throughout the day. Rules differ from state to state and can change over time, which is why a quote built on outdated assumptions can look better than reality.

Ask the installer which billing arrangement your utility currently offers new solar customers and how their savings estimate accounts for it. You can also call your utility directly and ask about connection fees, minimum monthly charges and any waiting period for approval. If export credits are low in your area, a battery may be worth discussing, though it adds cost.