| Scenario | Nominal (kWh) | DoD (%) | Efficiency (%) | Cycle life | Upfront cost | Upfront / usable kWh |
|---|---|---|---|---|---|---|
| Home storage (typical) | 10.0 | 90 | 92 | 4000 | $4,950 | $550.00 |
| High-usage system | 20.0 | 85 | 90 | 6000 | $9,800 | $576.47 |
| Budget pack | 5.0 | 80 | 88 | 2500 | $2,200 | $550.00 |
- Nominal kWh (if using voltage × amp-hours): Nominal kWh = (Voltage × Amp-hours) ÷ 1000.
- Usable capacity (initial): Usable kWh = Nominal kWh × (DoD ÷ 100).
- Effective cycles: Effective cycles = min(Cycle life, Cycles/day × 365 × Years).
- Final capacity fraction: Final = min(EOL %, 1 − Calendar degradation × Years).
- Delivered energy (year t): Delivered = Usable kWh × Efficiency × Annual cycles × Mid-year capacity fraction.
- Upfront cost per usable kWh: Upfront ÷ Usable kWh.
- Levelized cost per delivered kWh: (PV costs − PV residual) ÷ PV delivered energy.
- Pick the currency and choose how you will enter capacity.
- Enter DoD, efficiency, and realistic usage cycles per day.
- Set service life, cycle life, and degradation assumptions.
- Add upfront, annual maintenance, and optional replacement values.
- Press Calculate to see results above the form.
- Download CSV or PDF to share with stakeholders.
What cost per usable kWh means
Cost per usable kilowatt-hour converts a battery’s sticker price into an energy capacity metric engineers can compare across chemistries and vendors. The calculator divides total upfront spend by initial usable energy, where usable energy equals nominal kWh multiplied by depth of discharge. For example, a 10.0 kWh pack at 90% DoD provides 9.0 kWh usable, so a 4,950 cost yields 550 per usable kWh.
Inputs that move results most
Upfront cost is only half the story; throughput determines long-run value. For stationary storage, published pack prices often span 200–600 per kWh, but integration, controls, and commissioning can add 10–30% in practice. Higher cycles per day increases delivered energy until the cycle-life ceiling is reached. Round-trip efficiency shifts delivered kWh directly: moving from 88% to 92% raises delivered energy about 4.5% at the same cycling. DoD changes both usable capacity and stress; many designs target 80–95% depending on warranty and thermal limits.
How degradation is represented
Two effects are combined: cycle aging and calendar aging. Effective cycles are capped at the specified cycle life, while calendar degradation reduces capacity linearly each year and is limited by the end-of-life threshold. The calculator uses a mid‑year capacity fraction to estimate annual delivered energy, then averages across years. This provides a pragmatic planning curve when detailed electrochemical models are unavailable.
Why discounting changes comparisons
Levelized cost per delivered kWh uses present value: future maintenance, replacements, and residual value are discounted using the selected rate. A higher discount rate reduces the weight of later energy delivery and increases the levelized figure, especially for long-lived systems. Discounting is essential when comparing a low-cost pack with shorter life against a higher-cost pack that delivers energy over many years.
Interpreting outputs for engineering choices
Use “upfront per usable kWh” for procurement benchmarking and “levelized per delivered kWh” for lifecycle economics. If you pay for grid energy, enabling loss-energy costing adds the discounted cost of efficiency losses based on your electricity price. When results are close, test sensitivity by adjusting DoD, cycles per day, and degradation rate; these three parameters often dominate variance more than small price changes.
What does “cost per usable kWh” represent?
It is the upfront total cost divided by initial usable energy. Usable energy equals nominal capacity multiplied by depth of discharge. It helps compare packs with different sizes and operating limits.
What is the difference between usable and delivered kWh?
Usable kWh is the energy you can discharge from the pack at the start of life. Delivered kWh accounts for round‑trip efficiency and degradation over time, so it better reflects lifetime energy output.
How do I choose cycles per day?
Use measured or expected operating patterns. A backup system may average 0.05–0.2 cycles/day, while daily solar shifting can be 0.7–1.0. The calculator also caps total cycles at the cycle-life limit.
Why is a discount rate included?
Discounting converts future costs and future energy delivery into today’s value. It makes long-lived benefits less dominant and enables fair comparisons between options with different lifetimes, maintenance profiles, or replacement timing.
When should I enable loss-energy costing?
Enable it when charging energy has a meaningful price and you want efficiency differences reflected in economics. The tool estimates loss kWh from efficiency and multiplies by your electricity price, then discounts those costs over time.
How do I model a mid-life replacement?
Enter a replacement cost and the year it occurs. The calculator discounts that expense to present value and includes it in levelized cost, letting you compare designs that require inverter, module, or auxiliary replacement.