Solar panels: costs, savings and payback

How rooftop solar becomes useful electricity

Photovoltaic modules produce direct-current electricity. An inverter converts that output into alternating current for household loads. Electricity used at the time it is generated avoids a purchase from the utility; surplus energy goes to the grid or an optional battery. A kilowatt measures the system’s power rating, while a kilowatt-hour measures energy delivered over time. A 6 kW array does not produce 6 kW all day.

Start with twelve months of electricity use, roof age and an estimate of shading. Request a production report that identifies roof orientation, tilt, shading losses and inverter assumptions. A roof needing replacement soon can turn a cheap solar bid into an expensive remove-and-reinstall project. Separate that cost before comparing proposals.

A worked example: the export rate changes the answer

Assume a $17,400 installed system produces 7,700 kWh in its first year. These are example inputs, not a local quote. If 40% is used at home at $0.16/kWh and 60% is exported at $0.05/kWh, annual electricity value is (3,080 × $0.16) + (4,620 × $0.05) = $723.80. Simple payback is $17,400 ÷ $723.80, or about 24 years before maintenance, financing and degradation.

If every generated kWh instead has a $0.16 value under the applicable tariff, the same system yields $1,232 per year and a 14.1-year simple payback. This is why you should read the actual utility tariff. A salesman’s production estimate alone does not tell you the bill reduction. Fixed monthly charges usually remain.

Compare ownership and financing on the same basis

Ask for a cash price and a financed price for identical equipment. List interest, loan fees, maintenance, monitoring fees and inverter replacement assumptions. A low monthly payment can conceal a longer term or a higher principal. For a lease or power-purchase agreement, compare payment escalation, roof-work responsibilities, transfer requirements when selling the home, and purchase options.

For your own sensitivity check, reduce production 10%, increase the installed price 10%, and use a lower export rate. Run the calculator again with electricity escalation set to zero. If the project only works with aggressive price increases, describe it as a bet on future rates rather than a dependable near-term saving.

When a battery belongs in the proposal

Evaluate the solar array and battery as separate purchases. Storage may shift exports into evening self-consumption or provide outage protection, but it adds equipment cost and energy losses. Ask what equipment enables operation during a grid outage: ordinary grid-connected solar is not automatically backup power. Confirm the backed-up circuits, continuous output and usable energy.

Reduce avoidable consumption first, but include realistic future loads such as an EV or heat pump. Oversizing for hypothetical use can produce low-value exports; undersizing before an imminent electrification project may force a costly second installation.

Before you request a quote or buy

• Annual production report with shade and loss assumptions
• Written utility export tariff and interconnection requirements
• Roof work, permits, electrical upgrades and warranties itemized
• Cash price alongside financing terms for the same system
• Conservative savings case without unconfirmed rebates

Frequently asked questions