Calculator inputs
Enter your assumptions. Percent fields accept 6 or 0.06.
Tip: Use export rate for buyback or net metering credit.
Example data table
Sample assumptions to illustrate typical outputs.
| Scenario | Solar size | Battery | Retail rate | Export rate | Upfront cost | Year 1 net | Payback |
|---|---|---|---|---|---|---|---|
| Example | 6.0 kW | 10.0 kWh | $0.18 | $0.06 | $18,050 | $1,850 | 9.7 yrs |
Your results will differ based on local production, tariff structures, and replacement timing.
Formula used
- Year-1 solar generation: G₁ = SizeₖW × ProductionFactor
- Year y generation: Gᵧ = G₁ × (1 − Degradation)^(y−1)
- Self-used energy: Sᵧ = Gᵧ × SelfConsumption%
- Exported energy: Eᵧ = max(0, Gᵧ − Sᵧ)
- Solar savings: Vᵧ = Sᵧ×Rateᵧ + Eᵧ×ExportRateᵧ
- Battery TOU value (simple): Bᵧ = (UsablekWh×Cycles)×Spread×Efficiency
- Net savings: Netᵧ = (Vᵧ + Bᵧ) − O&Mᵧ − Replacementsᵧ
- NPV: NPV = −Upfront + Σ(Netᵧ / (1+Discount)^y)
- IRR: discount rate where NPV equals zero.
How to use this calculator
- Set your currency, retail rate, and export credit.
- Enter solar size and local production factor.
- Adjust self-consumption to match your profile.
- Add battery details and TOU assumptions, if relevant.
- Include incentives, O&M, and planned replacements.
- Click Calculate ROI, then export CSV or PDF.
If you have a detailed utility plan, set TOU spread to your real peak-offpeak difference.
Disclaimer: This tool provides estimates for educational planning and budgeting.