Calculator Inputs
Use the responsive grid below. Large screens show three columns, medium screens show two, and small screens show one.
Example Data Table
| Input | Sample Value | Meaning |
|---|---|---|
| Peak Import | 280 kWh | Grid energy purchased during peak hours. |
| Off-Peak Import | 520 kWh | Grid energy purchased during off-peak hours. |
| Peak Export | 140 kWh | Solar energy exported during peak hours. |
| Off-Peak Export | 210 kWh | Solar energy exported during off-peak hours. |
| Peak Import Rate | 0.22 | Charge applied to each imported peak kWh. |
| Off-Peak Import Rate | 0.12 | Charge applied to each imported off-peak kWh. |
| Peak Export Credit Rate | 0.14 | Credit earned for each exported peak kWh. |
| Off-Peak Export Credit Rate | 0.08 | Credit earned for each exported off-peak kWh. |
| Fixed Monthly Charge | 18 | Standing monthly utility charge. |
| Meter / Service Fee | 6 | Additional recurring service cost. |
| Tax Percentage | 7.5% | Tax applied to the positive pre-tax subtotal. |
| Minimum Bill Floor | 12 | Lowest payable amount after credits and tax. |
| Solar Generation | 760 kWh | Total solar energy generated for the period. |
| Self-Consumed Solar | 410 kWh | Solar energy used directly onsite. |
Using the sample values above yields a final bill near 119.97 and export credits near 36.40.
Formula Used
Peak import cost = Peak import kWh × Peak import rate
Off-peak import cost = Off-peak import kWh × Off-peak import rate
Gross import cost = Peak import cost + Off-peak import cost
Peak export credit = Peak export kWh × Peak export credit rate
Off-peak export credit = Off-peak export kWh × Off-peak export credit rate
Total export credit = Peak export credit + Off-peak export credit
Pre-tax subtotal = Gross import cost − Total export credit + Fixed charge + Meter fee
Tax amount = max(Pre-tax subtotal, 0) × Tax %
Final bill = max(Pre-tax subtotal + Tax amount, Minimum bill)
Net metering savings = Bill without export credits − Final bill
Self-consumption % = Self-consumed solar ÷ Total solar generation × 100
Solar export share % = Total exported solar ÷ Total solar generation × 100
Grid dependency % = Total import ÷ Estimated site load × 100
How to Use This Calculator
- Enter the imported electricity for peak and off-peak periods.
- Enter exported solar energy for both time windows.
- Fill in utility import rates and export credit rates.
- Add fixed charges, meter fees, tax percentage, and minimum bill.
- Enter solar generation and self-consumed solar for operational metrics.
- Press Calculate Net Metering to view the result above the form.
- Review the chart, billing breakdown, and savings indicators.
- Use the CSV or PDF buttons to export the calculated report.
Frequently Asked Questions
1. What does time-of-use net metering mean?
It means imported and exported electricity is valued differently depending on the hour or tariff block. Peak periods usually cost more, while off-peak periods cost less. Net metering applies credits to exported solar energy based on those time windows.
2. Why are peak and off-peak values entered separately?
Separate entries improve bill accuracy. Utilities often apply different prices to daytime, evening, or overnight usage. Splitting imports and exports by period shows whether your solar system reduces expensive peak consumption or mainly offsets cheaper off-peak energy.
3. Which export credit rate should I use?
Use the exact credit rate from your utility tariff or interconnection agreement. Some utilities credit at retail, some at avoided cost, and others at a special net metering rate. If peak and off-peak export credits differ, enter both values separately.
4. Can export credits make my bill negative?
That depends on the utility program. Some carry credits forward, while others enforce a minimum monthly bill. This calculator protects the final amount with the minimum bill field, so you can model utilities that never allow a payable bill below a fixed floor.
5. Why include a fixed charge and meter fee?
Many utility bills include non-energy charges that remain even when solar offsets imported electricity. Adding those items prevents underestimating the true monthly cost and helps you compare tariff plans more realistically.
6. What is self-consumed solar?
Self-consumed solar is the portion of generated energy used onsite before it reaches the grid. Higher self-consumption often improves savings because that energy avoids retail import rates instead of earning a lower export credit.
7. How often should I update the inputs?
Update inputs every billing cycle or whenever utility rates change. Seasonal load shifts, tariff revisions, battery use, and solar production changes can all affect the outcome. Monthly updates usually give the clearest planning view.
8. Does this calculator replace my official utility bill?
No. It is an estimation and planning tool. Real bills may include riders, fuel adjustments, demand charges, taxes, or credit carryovers not shown here. Always compare the result with your actual tariff schedule and utility statement.