The formula
A worked example
Of 480 kWh, using 60% at home avoids 72.00 at 0.25/kWh. Exporting the remaining 192 kWh at 0.05/kWh adds 9.60; total estimated energy value is 81.60.
What this estimate includes
This is energy value, not profit or investment return. It excludes installation costs, finance, maintenance and taxes. Monthly net metering, export limits and time-varying tariffs require a different model.
Common questions
Is this the same as a payback calculator?
No. It estimates the value of energy in one period. It does not subtract system cost or model investment returns.
Can I assume 100% self-consumption?
Only if all modeled generation is actually used on site. Household demand timing, export constraints and storage losses affect the achievable share.
Further reading
PVWatts: detailed site-specific solar modeling. Background reference; these tools are independent and are not endorsed by the source organization.