Net Metering Calculator
Solar Production and Household Usage Rarely Match Hour by Hour
A solar array generates most of its power in the middle of the day, while household consumption often peaks in the morning and evening — so most solar homes are simultaneously buying grid power at some hours and exporting excess power at others. Net metering nets these two flows against each other over a billing period, charging for imported power and crediting for exported power, often at different rates.
The Formula
Grid Export (kWh) = max(Energy Generated − Energy Consumed, 0)
Net Bill = (Import kWh × Import Rate) − (Export kWh × Export Rate)
A negative net bill means the export credit exceeds the import cost — the utility owes a credit rather than a payment. Many utilities pay a lower rate for exported power than they charge for imported power, which is why the import and export rates are entered separately.
Where This Is Useful
- Estimating a solar bill — project the net amount owed or credited for a billing period once generation and consumption are known.
- Sizing a system against net metering rules — when export credit is lower than the import rate, oversizing a system for full offset may pay back more slowly than sizing closer to actual consumption.
- Comparing utility net metering policies — running the same generation and consumption figures against different import/export rate structures shows how much a utility's specific policy affects the bottom line.
Worked Examples
| Scenario | Generated | Consumed | Grid import | Grid export | Net result |
|---|---|---|---|---|---|
| Surplus month | 900 kWh | 750 kWh | 0 kWh | 150 kWh | $15.00 credit |
| Deficit month | 600 kWh | 900 kWh | 300 kWh | 0 kWh | $45.00 owed |
How to Use This Calculator
- Enter Energy Generated in kWh for the billing period.
- Enter Energy Consumed in kWh for the same period.
- Enter the Grid Import Rate per kWh.
- Optionally enter an Export Credit Rate per kWh — defaults to the import rate if left blank.
- Select Calculate to see grid import, grid export, and the net amount owed or credited.
Related Calculations
Check total system production feeding into this bill with the Solar Panel Output Calculator, or see the overall payback timeline with the Solar Payback Period Calculator.