Model daily shifting and demand charge savings quickly. Include incentives, maintenance, and degradation over years. Get a realistic plan that fits your household budget.
| Scenario | Capacity (kWh) | Cycles/day | Peak / Off-peak ($/kWh) | Solar share | Year-1 net savings |
|---|---|---|---|---|---|
| Starter home | 7 | 0.8 | 0.25 / 0.12 | 50% | $420 |
| High spread rates | 10 | 1.0 | 0.35 / 0.10 | 60% | $1,050 |
| Small business | 20 | 1.0 | 0.30 / 0.14 | 40% | $1,680 |
The largest savings usually come from the difference between peak and off‑peak pricing. When the spread is $0.20 per kWh and round‑trip efficiency is 90%, each delivered kWh avoids about $0.20 − ($0.10/0.90) ≈ $0.09. Multiply that by annual delivered energy to estimate arbitrage potential. Seasonal tariffs and weekend schedules can change the effective spread, so validate the hours you plan to discharge. Even small rate errors compound when cycled daily. Use your last twelve bills for monthly calibration.
Usable energy is capacity times the usable percent, not the nameplate rating. A 10 kWh unit at 90% usable provides 9 kWh per cycle. At one cycle per day, year‑one delivered energy is roughly 9×365 adjusted for degradation. Increasing cycles can raise savings, but only if you have enough peak load to offset.
If solar would otherwise be exported, storing it has an opportunity cost equal to the export credit. With a $0.06 export credit, 90% efficiency, and $0.28 peak price, the net value per delivered kWh is about $0.28 − ($0.06/0.90) ≈ $0.21. Higher export credits reduce this benefit and may favor exporting instead.
For customers billed on peak kW, even small reductions add up. A 0.5 kW reduction at $12 per kW‑month yields 0.5×12×12 = $72 per year, before degradation. If your tariff has higher demand charges, accurate peak‑shaving estimates become as important as energy shifting assumptions.
Simple payback divides net upfront cost by year‑one net savings, but it ignores discounting and future degradation. NPV discounts each annual net cashflow using your chosen rate, then subtracts upfront cost after incentives. A positive NPV indicates the savings stream beats your hurdle rate, while the discounted break‑even year shows when the investment turns positive.
If the peak and off‑peak spread is small, or efficiency is low, the off‑peak energy needed to recharge can cost more than the peak energy you avoid. Check your tariff hours and update rates.
Efficiency converts charging energy into delivered energy. Lower efficiency means you must buy or forgo more kWh to deliver the same output, reducing net savings in both grid arbitrage and solar shifting.
Use a realistic value based on load and operating rules. Many homes cycle around 0.5–1.0 daily, while some programs or peak‑shaving strategies can increase cycles during high‑price seasons.
The calculator reduces benefits over time using a simple linear degradation rate. It approximates year‑one output at mid‑year capacity and scales future cashflows similarly. Manufacturer warranties may differ.
Incentives reduce the net upfront cost, improving payback and NPV. They do not change operational savings unless they require specific dispatch behavior or program participation that alters cycling.
Set demand reduction and the demand charge rate to zero. The results will then reflect only energy shifting, solar shifting, and any backup value you assign, minus annual operating and maintenance costs.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.