California Solar Payback Calculator accuracy and testing

Formula source

• Net cost = installed cost - incentives. Yearly savings = annual production x electricity value, adjusted by utility value escalation and solar degradation until cumulative savings reaches net cost.

Test cases

Known limitations

• Planning estimate only; not tax, legal, insurance, utility, financial, or real estate advice. Verify current local rules, policies, rates, exemptions, caps, exceptions, official notices, utility tariffs, insurance declarations, and qualified advisors before relying on any result. This does not promise savings, net billing treatment, tax credit eligibility, interconnection approval, system performance, or insurance treatment.

Assumptions

• All rates, caps, windows, premiums, and charges are editable planning examples.
• No live local tax, utility, rent, legal, insurance, or program rate is fetched or guaranteed.
• Calculations run client-side in the browser and are based only on the values entered.

Unit handling

• Installed Cost accepts values in $.
• Incentives or Credits accepts values in $.
• Annual Production accepts values in kWh.
• Electricity Value Preset accepts one of the configured options.
• Electricity Value accepts values in $/kWh.
• Utility Value Escalation accepts values in %/yr.
• Solar Degradation accepts values in %/yr.
• Analysis Period accepts values in years.
• Estimated Simple Payback is displayed in years.

Rounding rules

• Number displays use up to 2 decimal places in the calculator UI.
• Input precision follows configured step values where provided.

Version history

Change log