Downloads
Run the calculator first to enable exports.
Calculator Inputs
Large screens show three columns, then two, then one.
Example Data Table
Sample inputs and outputs for reference.
| Scenario | Daily energy (kWh) | Gen kW | Battery kWh | Battery share | Year‑1 savings | Payback |
|---|---|---|---|---|---|---|
| Warehouse | 120 | 30 | 40 | 35% | $4,900 | 5 yrs |
| Clinic | 60 | 20 | 30 | 45% | $3,200 | 4 yrs |
| Small factory | 220 | 60 | 80 | 30% | $7,800 | 6 yrs |
Formula Used
- Annual energy = Daily kWh × 365
- Generator runtime (hours) = Generator kWh ÷ (Generator kW × Loading)
- Fuel liters = Generator kWh × Fuel rate (L/kWh)
- Fuel cost = Fuel liters × Fuel price
- O&M cost = Runtime hours × Maintenance per hour
- Battery usable kWh = Battery kWh × DoD × (1 − Reserve)
- Battery to load = min(Daily kWh × Share, usable kWh) × 365
- Charge energy = Battery-to-load ÷ (Roundtrip eff × Inverter eff)
- Hybrid generator kWh = Direct-to-load + Charge energy
- NPV = Σ Cashflowy ÷ (1 + Discount)y
How to Use This Calculator
- Enter your site’s daily energy, average load, and peak demand.
- Fill generator rating, typical loading, fuel rate, fuel price, and maintenance cost.
- Provide battery size, DoD, reserve, and efficiency assumptions.
- Set battery energy share to reflect your dispatch strategy.
- Choose financial assumptions, then click Calculate.
- Review savings, payback, and NPV. Export CSV or PDF if needed.
Hybrid dispatch performance
Battery share shifts generator output away from low‑efficiency, part‑load operation. In this calculator, annual generator kWh equals direct‑to‑load kWh plus charging kWh. Charging kWh grows when roundtrip efficiency or inverter efficiency falls, so aggressive battery dispatch can backfire. Use the plot to see whether fuel escalation makes hybrid savings widen over time. If peaks are high, keep reserve higher and treat battery share as a ceiling.
Fuel and runtime analytics
Generator runtime is computed as generator kWh divided by rated kW times average loading. Lower loading increases hours and maintenance cost, even if energy stays similar. If your measured loading is below 50%, consider resizing, adding load management, or increasing battery share to keep the generator closer to an efficient band. Track fuel rate in L/kWh from logged data, because nameplate curves differ in the field.
Battery utilization and life
Usable battery energy is capacity times depth of discharge times one minus reserve. Annual cycles are battery‑to‑load kWh divided by usable kWh. A higher battery share reduces fuel but accelerates cycling and thermal stress. The replacement year estimate converts cycle life into years using your modeled cycles per year, then applies replacement cost percent. Validate cycle life at your chosen DoD and temperature range before relying on the estimate.
Capital planning and financing
Upfront cost equals generator capex plus battery and inverter capex for the hybrid case. The cashflow model escalates fuel and O&M annually, then discounts each year to compute NPV. A negative NPV difference (Hybrid − Baseline) indicates the hybrid plan is cheaper on a present‑value basis under your assumptions. If you finance the battery, reflect debt service outside this model and keep discount rate aligned with your hurdle rate.
Decision metrics for stakeholders
Use year‑1 savings for quick screening, then validate with payback and NPV. Payback is calculated from undiscounted cumulative savings against extra capex. Export CSV for models and PDF for review. For sensitive loads, confirm peak headroom and battery runtime at average load as risk controls. When costs cross, review escalation inputs and replacement timing to explain the turning point.
FAQs
What does “battery energy share” represent?
It is the target portion of daily load served through the battery path. The model caps it by usable battery energy after DoD and reserve, then accounts for charging losses through efficiencies.
Why can hybrid generator kWh be higher than load kWh?
Because the generator must supply both the direct load and the energy needed to charge the battery. Roundtrip and inverter losses mean charging requires more kWh than the battery later delivers.
How is generator runtime calculated?
Runtime equals annual generator kWh divided by generator kW times average loading. If loading is low, runtime rises, increasing maintenance cost even with similar delivered energy.
How is battery replacement estimated?
The calculator converts annual battery-to-load energy into cycles per year using usable kWh. Replacement year is cycle life divided by cycles per year, rounded up, then applied with the replacement cost percentage.
What does negative NPV (Hybrid − Baseline) mean?
It means the hybrid scenario has a lower present-value cost than the baseline under your discount rate and escalation assumptions. It does not guarantee cash availability or financing feasibility.
How should I choose the discount rate?
Use your organization’s hurdle rate or weighted cost of capital for comparable projects. For riskier fuel logistics or uncertain runtime, consider a higher rate, then test sensitivity by running multiple scenarios.