Calculator Inputs
Use the fields below to estimate battery economics, financing impact, backup value, and long-term project returns.
Example Data Table
| Scenario | Usable Capacity | Net Project Cost | Year 1 Benefit | Simple Payback | 20-Year ROI |
|---|---|---|---|---|---|
| Small Home Backup | 9.6 kWh | $7,900 | $1,020 | 8.1 years | 118% |
| Balanced Self-Consumption | 13.5 kWh | $9,380 | $1,430 | 7.2 years | 176% |
| Large Time-Shifting System | 20.0 kWh | $13,800 | $2,040 | 7.8 years | 168% |
These example figures are illustrative. Local tariffs, incentives, financing, battery cycling, and outage value can materially change the outcome.
Formula Used
Gross Installed Cost = Battery Cost + Inverter Cost + Installation Cost + Electrical Upgrade Cost
Net Project Cost = Gross Installed Cost − Flat Rebate − (Gross Installed Cost × Incentive %)
Source Energy Cost per kWh = (Solar Charge Share × Export Tariff) + (Grid Charge Share × Off-Peak Tariff)
Value Spread per kWh = Peak Import Tariff − Source Energy Cost per kWh
Annual Shifted Energy = Usable Capacity × Cycles per Day × 365 × Utilization × Round-Trip Efficiency × Degradation Factor
Annual Gross Benefit = (Annual Shifted Energy × Value Spread × Tariff Escalation Factor) + Demand Savings + Backup Value
Annual Net Cash Flow = Gross Benefit + Residual Value − O&M − Loan Payment − Replacement Cost
ROI % = Total Net Profit ÷ Net Project Cost × 100
NPV = Sum of discounted cash flows, including the initial outlay
LCOS = Discounted lifecycle costs ÷ Discounted lifetime stored energy delivered
How to Use This Calculator
Enter all installed costs, including battery, inverter, labor, and upgrade work. Then add rebates or tax credits to estimate the net project cost.
Define battery performance using usable capacity, cycles per day, utilization, efficiency, and degradation. These drive how much energy the battery can shift each year.
Enter your electricity economics next. Use the peak import tariff, off-peak charging rate, and solar export tariff to model opportunity cost and arbitrage value.
Add demand savings, backup value, maintenance, financing, and replacement assumptions. These fields allow a more realistic lifecycle cash flow model.
Press Calculate ROI. The calculator shows results above the form, including payback, NPV, IRR, LCOS, yearly cash flow, and a Plotly graph.
Use the CSV button to export the full yearly table. Use the PDF button to save a clean report with the same result table.
Frequently Asked Questions
1. What does ROI mean for a solar battery?
ROI measures how much profit the battery system produces relative to its net installed cost. It reflects bill savings, backup value, financing, maintenance, replacements, and residual value over the selected project life.
2. Why is the export tariff included?
Charging a battery with solar energy can mean giving up export revenue. The export tariff captures that opportunity cost, which makes the storage value estimate more realistic for net billing or feed-in programs.
3. What is the difference between payback and NPV?
Payback shows when cumulative cash flow becomes positive. NPV goes further by discounting future cash flows, helping you compare a battery investment against your required return or alternative uses of capital.
4. Why can a battery have strong backup value but weak ROI?
Backup value can be important during outages, but it may not fully offset high installed costs, modest cycling, limited tariff spread, or expensive financing. Reliability value and financial return are related, but not identical.
5. What does LCOS tell me?
LCOS is the discounted cost per delivered kilowatt-hour from storage. It helps compare battery economics with export compensation, grid energy, or alternative technologies under consistent lifetime assumptions.
6. Should I include a replacement year?
Yes, if you expect the battery to need major refurbishment or replacement before the project ends. Including that cost gives a more realistic lifecycle model, especially for long evaluation periods.
7. How do cycles per day affect results?
Higher cycling generally increases savings because more stored energy is shifted through the battery. However, extreme cycling can accelerate degradation, so realistic operating patterns matter for credible ROI estimates.
8. Can this calculator work for commercial sites?
Yes. Add realistic demand savings, tariffs, financing, and backup value assumptions. Commercial outcomes often depend heavily on demand charge reduction, tariff complexity, and available cycling windows.