Calculator Inputs
Example Data Table
| Scenario | Consumption kWh/mo | Solar kWh/mo | Import Rate | Export Rate | First-Year Net Savings | Simple Payback |
|---|---|---|---|---|---|---|
| Compact Residential | 900 | 700 | $0.16 | $0.08 | $1,084 | 9.6 years |
| Balanced Residential | 1,200 | 1,000 | $0.18 | $0.10 | $1,744 | 6.8 years |
| High Export Profile | 1,500 | 1,650 | $0.20 | $0.11 | $2,282 | 6.1 years |
These examples are illustrative. Use your local tariff, fixed charge, and credit rules for more accurate engineering and financial planning.
Formula Used
1) Baseline bill without solar
Baseline Monthly Bill = Fixed Charge + (Monthly Consumption × Import Rate × (1 + Tax Rate))
2) Solar energy flow
Self-Used Solar = min(Monthly Solar Generation × Self-Consumption Ratio, Monthly Consumption)
Exported Solar = Monthly Solar Generation − Self-Used Solar
Grid Import = Monthly Consumption − Self-Used Solar
3) Monthly bill with net metering
Export Credit = Exported Solar × Export Rate × Credit Realization
Solar Bill = max((Fixed Charge + Grid Import × Import Rate × (1 + Tax Rate)) − Export Credit − Other Monthly Bill Savings, 0)
Monthly Savings = Baseline Monthly Bill − Solar Bill
4) Long-term savings and payback
Net Upfront Cost = Installation Cost + Interconnection Cost − Incentives
Annual Production Factor = (1 − Degradation)Year−1
Annual Rate Factor = (1 + Tariff Escalation)Year−1
Lifetime Net Savings = Sum of annual net savings − Net Upfront Cost
This model estimates engineering-style financial performance by combining load offset, exported energy credits, utility escalation, system degradation, and recurring ownership costs.
How to Use This Calculator
- Enter your average monthly electricity consumption in kWh.
- Enter expected monthly solar generation from design or monitoring data.
- Set the self-consumption ratio to reflect daytime on-site use.
- Add your retail import rate, export credit rate, taxes, and fixed monthly charge.
- Include extra monthly savings if solar lowers demand-related charges.
- Enter installation cost, incentives, interconnection fees, and yearly maintenance.
- Choose degradation, tariff escalation, and the analysis period.
- Press Calculate Savings to see the result summary, chart, and annual table.
- Use the CSV or PDF buttons to export the calculated output.
Frequently Asked Questions
1) What does net metering savings mean?
It is the reduction in your electricity cost after on-site solar offsets imported energy and exported surplus earns bill credits. The calculator combines both effects.
2) Why is self-consumption important?
Self-consumed solar usually replaces electricity at the full import rate. Exported energy may receive a lower credit, so higher self-consumption often improves total savings.
3) Why include credit realization?
Some utilities reduce, expire, or settle credits differently from the headline export rate. Credit realization lets you model that practical loss.
4) Does the calculator include fixed utility charges?
Yes. Fixed monthly charges stay in both baseline and solar scenarios, because many utilities continue charging them regardless of exported energy.
5) What does tariff escalation do?
It increases future electricity rates year by year. Rising tariffs typically make avoided purchases and exported credits more valuable over time.
6) Why model annual degradation?
Solar modules slowly lose output over time. Degradation reduces future self-use and exports, so it lowers long-term savings slightly.
7) Is payback the same as profit?
No. Payback shows when cumulative savings recover the initial net cost. Profit or net savings continues accumulating after that point.
8) Can I use this for commercial projects?
Yes, for early engineering screening. For final decisions, add time-of-use tariffs, demand charges, financing, and utility-specific settlement rules.