Calculator Inputs
Plotly Cash Flow Graph
Example Data Table
| Scenario | Net Cost ($) | Year 1 Net Savings ($) | Simple Payback (Years) | Analysis Period |
|---|---|---|---|---|
| Small Home Battery | 7,500 | 1,120 | 6.70 | 15 years |
| Medium Solar Storage | 9,500 | 1,460 | 6.51 | 15 years |
| Large Time-of-Use Setup | 13,800 | 2,140 | 6.45 | 15 years |
Formula Used
1) Net system cost
Net System Cost = Battery Cost + Installation Cost - Incentives
2) Effective daily shifted energy
Effective Daily Shifted kWh = Usable Capacity × Daily Cycles × Round Trip Efficiency
3) Arbitrage savings
Annual Arbitrage Savings = Effective Daily Shifted kWh × 365 × (Peak Rate - Off-Peak Rate)
4) Solar self-consumption savings
Annual Self-Consumption Savings = Effective Daily Shifted kWh × 365 × (Peak Rate - Export Rate) × Self-Consumption Gain
5) Year 1 net savings
Year 1 Net Savings = Arbitrage Savings + Self-Consumption Savings + Demand Savings + Outage Value - Maintenance
6) Simple payback
Simple Payback = Net System Cost ÷ Year 1 Net Savings
7) Discounted cash flow
Discounted Cash Flow = Yearly Net Savings ÷ (1 + Discount Rate)Year
8) NPV
NPV = Sum of Discounted Cash Flows - Net System Cost
How to Use This Calculator
- Enter your battery equipment price and full installation cost.
- Add all rebates, credits, or local storage incentives.
- Use usable capacity, not gross battery nameplate capacity.
- Enter realistic round trip efficiency and average daily cycling.
- Input your off-peak, peak, and export tariff values.
- Add expected self-consumption improvement and demand savings.
- Include annual maintenance and any resilience value from backup power.
- Set escalation, degradation, discount rate, and analysis years.
- Press calculate to review payback, NPV, ROI, and yearly cash flow trends.
- Use CSV or PDF export for reporting and comparison.
Frequently Asked Questions
1. What does payback mean for a solar battery?
Payback is the time needed for cumulative savings to recover the net upfront battery cost. It helps compare storage investments using energy bill reductions and other yearly benefits.
2. Why does round trip efficiency matter?
Round trip efficiency shows how much stored energy is returned after charging and discharging losses. Lower efficiency reduces usable shifted energy and delays the payback period.
3. Should I include incentives and rebates?
Yes. Incentives directly reduce your net system cost. Lower upfront cost usually shortens payback and improves lifetime return metrics such as ROI and NPV.
4. What is tariff arbitrage in this calculator?
Tariff arbitrage means charging when electricity is cheaper and using stored energy when rates are higher. The wider the rate spread, the stronger the savings potential.
5. Why include battery degradation?
Battery degradation reduces effective storage performance over time. Including it gives a more realistic long-term forecast instead of assuming identical yearly savings forever.
6. What is discounted payback?
Discounted payback adjusts future savings for the time value of money. It is stricter than simple payback because future dollars are worth less today.
7. Can backup power value be counted?
Yes. If outages cause measurable inconvenience, spoilage, downtime, or safety risks, you can assign a yearly resilience value and include it in the analysis.
8. Is a shorter payback always better?
A shorter payback is attractive, but not the only metric. Compare NPV, lifetime savings, degradation, tariff assumptions, and backup benefits before deciding.