If you’ve started looking into home solar, your inbox is likely full of proposals promising “Zero Down,” “Free Solar,” and “Guaranteed Savings.” Comparing these proposals against each other — let alone understanding what you’re actually buying — can be exhausting. Here is how to cut through the sales gimmicks and evaluate a residential solar quote on the metrics that actually matter.
1. Price per watt: the only true cost comparison
Ignore the monthly payment pitch. Ignore the “net cost after incentives.” The single most reliable way to compare hardware costs across proposals is price per watt (PPW): the gross system cost divided by the total system wattage (in watts, not kilowatts).
In California, a fair price per watt for a quality solar-plus-storage system from a reputable installer typically ranges from $3.50 to $5.00/W depending on system size, equipment tier, and installation complexity. If a quote comes in significantly below this range, scrutinize the equipment. If it’s significantly above, ask what premium features justify the difference.
2. Battery sizing: the most common corner-cut
Many volume installers will include a single, undersized battery in their proposal just to check the “includes storage” box. We routinely see proposals where the included battery wouldn’t run the home’s air conditioning for two hours, let alone provide meaningful backup during a multi-day outage or optimize time-of-use savings.
How to check battery sizing
Look at the battery’s usable capacity in kWh and compare it to your daily energy consumption (which you can find on your utility bill). A home consuming 30 kWh per day needs at least 10–15 kWh of usable battery capacity to meaningfully shift peak consumption and provide several hours of backup. If the proposal includes a 5 kWh battery for a home that uses 40 kWh per day, the storage component is cosmetic.
3. Equipment quality: who made it?
The proposal should clearly identify the panel manufacturer, model, and wattage, as well as the inverter and battery manufacturer and model. If the proposal lists generic descriptions like “Tier 1 panels” or “premium inverter” without naming specific manufacturers, that’s a red flag. You should be able to look up the exact equipment and verify its specifications, warranty terms, and reputation.
4. Labor warranty: the overlooked protection
Equipment warranties cover manufacturing defects. But what about the installer’s work? Roof penetrations, electrical connections, conduit routing, and mounting hardware are all installed by the contractor, not the manufacturer. If a roof leak develops around a mounting bolt three years from now, the panel manufacturer’s warranty won’t cover it.
You want an installer who guarantees their workmanship for at least 10 years — covering roof penetrations, electrical work, and mounting hardware. If an installer won’t stand behind their own work for a decade, consider what that says about their confidence in their installation quality.
5. Savings projections: check the assumptions
Every solar proposal includes a savings projection showing how much money the system will save you over its lifetime. These projections are only as good as their assumptions. Ask to see the utility rate escalation assumption (what annual rate increase they’re projecting), the NEM export rate assumptions, and the degradation rate of the panels over time. If any of these inputs are unrealistically optimistic, the projected savings won’t materialize.
A good solar proposal should make you feel informed, not confused. If you can’t understand what you’re buying after reading it, that’s a problem with the proposal — not with you.