The Solar Savings Calculator estimates annual solar generation, annual electricity-bill savings, and simple payback from system size, average sun hours, electricity rate, days, and installation cost.
Calculation method
The calculator uses a simplified production model to estimate generation and savings.
The default period is 365 days. A payback value is shown only when both installation cost and annual savings are positive.
Worked example
For a 5 kW system, 4.5 sun-hours per day, an electricity rate of 12,000 installation cost:
- Generation:
5 x 4.5 x 365 = 8,212.5 kWh/year, rounded by the tool to 8,213 kWh. - Annual savings:
8,212.5 x $0.30 = $2,463.75. - Simple payback:
$12,000 / $2,463.75 = 4.87 years.
Interpreting the result
This is a gross energy-offset estimate. Actual savings depend on self-consumption, export credits, system losses, shading, orientation, maintenance, tariffs, and seasonal production. A payback period is not a financing APR or a guarantee of investment return.
Frequently Asked Questions
What sun-hours value should I use?
Use a representative daily equivalent from a local solar assessment or a trusted irradiance source. Do not treat peak-sun-hours as the same thing as total daylight hours.
Does the calculator include feed-in tariffs?
No. It multiplies generation by the electricity rate you enter. Model exported energy separately when your tariff pays a different rate.
Why is the payback result blank?
The tool leaves payback blank when installation cost is zero or annual savings are zero. It also rejects negative cost and invalid numeric inputs.
Limitations
The model does not account for inverter efficiency, degradation, battery storage, financing, taxes, rebates, export limits, or time-of-use billing. Use an installer quote and current tariff data for a purchase decision.