Start with the cash-equivalent solar price
Before comparing monthly payments, identify what the solar system would cost without financing. Divide the solar-only installed price by the DC array size in watts to get a useful cost-per-watt comparison.
- Keep batteries separate when comparing solar $/W.
- Ask whether roof work, service-panel upgrades or trenching are included.
- If a loan price is much higher than the cash price, identify dealer fees or other financing costs.
Check system size and production separately
A larger kW system is not automatically a better proposal. Compare the proposed DC size with the annual kWh production estimate and your actual annual electricity use.
- Look for the production model, roof orientation and shading assumptions.
- Compare first-year kWh, not only panel count.
- Check whether the proposal assumes an unrealistically high future electricity price.
Read the equipment line items
The quote should identify the exact panel model, inverter architecture, battery model if applicable and major balance-of-system equipment. Generic labels such as premium panel are not enough for a serious comparison.
Separate warranties
Panel product and performance warranties are manufacturer terms. Inverter and battery warranties are separate. Installer workmanship and roof-penetration coverage are also separate. Ask who handles service if a component manufacturer approves a warranty claim but labor is not covered.
Verify utility and incentive assumptions
A proposal can show attractive savings while using the wrong export credit, an expired incentive or a simplified electricity escalation rate. Compare the proposal against the current utility tariff and program rules for the service address.