Plotly graph
Calculator inputs
Example dataset
| Cycle | Energy In (kWh) | Metered Out (kWh) | Aux (kWh) | Useful Out (kWh) | RT Efficiency (%) | Buy Price | Loss Cost |
|---|---|---|---|---|---|---|---|
| Cycle 01 | 120.000 | 104.000 | 1.500 | 102.500 | 85.42 | 0.1900 | 3.33 |
| Cycle 02 | 200.000 | 176.000 | 2.000 | 174.000 | 87.00 | 0.2100 | 5.46 |
| Cycle 03 | 75.000 | 63.500 | 0.800 | 62.700 | 83.60 | 0.1700 | 2.09 |
| Cycle 04 | 150.000 | 131.000 | 1.200 | 129.800 | 86.53 | 0.2300 | 4.65 |
| Cycle 05 | 95.000 | 83.000 | 1.000 | 82.000 | 86.32 | 0.2000 | 2.60 |
Formula used
- Useful Out (kWh) = Discharge Out − Aux (if deducted)
- Self-discharge Loss (kWh) = Energy In × (Self%/100)
- Effective Out (kWh) = max(0, Useful Out − Self Loss)
- RT Efficiency (%) = (Effective Out ÷ Energy In) × 100
- Loss (kWh) = Energy In − Effective Out
- RT Efficiency (%) = Charge% × Discharge% × Conversion% × (1 − Aux%) × (1 − Self%)
- Projected Out (kWh) = Planned In × (RT%/100)
- Loss Cost = Loss kWh × Buy Price
- Delivered Cost/kWh = Input Cost ÷ Useful Out
How to use this calculator
- Select Energy-based if you have measured charge and discharge kWh.
- Enter auxiliary consumption only when it reduces usable discharge.
- Add the buy price to quantify loss cost and delivered cost per kWh.
- Optionally add a sell price to estimate net margin on discharged energy.
- Press Calculate. Review results above the form.
- Use Download CSV or Download PDF for reporting.
Round-Trip Efficiency as a Delivered Energy Ratio
Round-trip efficiency converts metered charge energy into usable discharge energy. If 100 kWh is charged and 88 kWh is delivered, efficiency is 88%. Finance teams use this ratio to translate purchased electricity into “delivered” energy for budgets, tariffs, and contract guarantees. Track it by cycle and by month to spot drift from temperature, aging, or control changes.
Loss Components You Can Separate
The calculator lets you separate three common loss buckets: auxiliary consumption, self-discharge, and conversion loss. For example, 120 kWh in, 104 kWh metered out, and 2 kWh auxiliary deducted yields 102 kWh useful out before self-discharge. A 1% self-discharge adjustment removes 1.2 kWh from useful output. In planning mode, charge, discharge, and conversion efficiencies multiply, then auxiliary and self-discharge reduce the total.
Delivered Cost per kWh for Pricing
Delivered cost is input cost divided by useful output. With a buy price of 0.20 per kWh, charging 100 kWh costs 20.00. At 86% round-trip, useful output is 86 kWh, so delivered cost becomes 0.233 per kWh. This metric is useful for comparing storage against alternatives like demand response, peak contracts, or generator rental, because it internalizes losses.
Arbitrage Margin and Break-Even Spread
When you also enter a sell price, net margin estimates arbitrage performance for the cycle. A simple break-even spread approximation is buy price × (1/efficiency − 1). At 0.20 buy and 86% efficiency, the spread is about 0.033 per kWh. Any sell price above 0.233 per kWh improves gross margin; higher efficiency lowers the required spread.
Cycle Reporting and Governance
Cycle labels, notes, and exports support audit-ready reporting. Keep one naming convention across sites, include metering scope in notes, and export monthly summaries to reconcile invoices. Use a stable baseline efficiency and flag deviations of 3–5 percentage points for investigation. Pair the chart with maintenance logs to explain changes. For time-of-use tariffs, repeat runs by period to quantify savings and confidence levels today.
FAQs
It is the percentage of charge energy that returns as usable discharge energy for one full cycle, after any selected deductions and adjustments.
Deduct it when auxiliary loads are measured separately and reduce energy available to your load. Leave it unchecked if your discharge meter already reports net delivered energy.
Losses mean you purchase more energy than you can deliver. The calculator divides total input cost by useful output, so lower efficiency increases delivered cost.
Use Energy-based mode for real cycles with metered kWh in and out. Use Efficiency-based mode for planning, proposals, or sensitivity analysis when components are estimated.
A practical break-even sell price is the delivered cost per kWh shown in results. If sell exceeds that value, the cycle margin becomes positive, all else equal.
Save the cycle label, metering scope, key inputs, and prices with each export. Store the CSV or PDF alongside invoices, dispatch logs, and meter screenshots for traceability.