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Microgrid System Sizing Calculator

This calculator develops a preliminary microgrid size from peak site load and resilience requirements. It estimates firm generation capacity for the critical load, then calculates battery energy needed for the selected autonomy period after accounting for renewable contribution and discharge efficiency. The result provides a starting point for feasibility studies and vendor discussions. Final sizing requires an hourly load profile, renewable resource data, equipment power limits, dispatch logic, fault studies, and reliability criteria.

Microgrid design requirements

kW
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hr
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Result
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Preliminary microgrid size
Critical load—
Firm generation capacity—
Required nominal battery energy—

1. Enter site peak load
Use the maximum demand relevant to the microgrid design boundary.

2. Identify the critical fraction
Enter the portion of peak load that must remain served during islanded operation.

3. Add generation margin
Allow for uncertainty, equipment derating, and moderate future growth.

4. Set battery autonomy
Choose the number of hours the battery should support the residual critical load.

5. Credit firm renewable output
Enter only the renewable contribution considered dependable during the design outage.

6. Apply battery efficiency
Use the expected discharge-path efficiency to convert required delivered energy into nominal energy.

7. Review both outputs
Treat generation kW and battery kWh as preliminary targets for chronological validation.

Critical load = Peak load × Critical-load fraction
Firm generation capacity = Critical load × (1 + Design margin)
Residual battery-supported load = Critical load × (1 − Firm renewable contribution)
Required nominal battery energy = Residual load × Autonomy hours ÷ Battery efficiency

This simplified model sizes generation and storage independently and does not optimize their interaction.

What the result means

The main display summarizes recommended firm generation capacity and nominal battery energy for the entered critical-load and autonomy assumptions.

Check battery inverter kW, generator step-load response, minimum loading, renewable variability, starting currents, and black-start sequence separately.

Given: 1,200 kW peak load, 60% critical load, 20% generation margin, 4 hours autonomy, 15% firm renewable contribution, and 90% battery efficiency.

Calculation:
Critical load = 1,200 × 0.60 = 720 kW
Generation capacity = 720 × 1.20 = 864 kW
Residual load = 720 × (1 − 0.15) = 612 kW
Battery energy = 612 × 4 ÷ 0.90 = 2,720 kWh

Result: Preliminary sizing is 864 kW of firm generation and 2,720 kWh of nominal battery energy.

Why can generation capacity and battery capacity both cover the critical load?

They address different design functions in this simplified model. Generation capacity covers sustained power, while battery energy provides the entered autonomy for residual load.

What counts as firm renewable contribution?

Only renewable output considered dependable during the design event should be credited. For conservative resilience sizing, this may be much lower than average renewable output.

Does the battery energy include a depth-of-discharge limit?

No separate depth-of-discharge input is included. Reduce the efficiency-equivalent usable fraction or increase nominal capacity in a detailed model to reflect it.

Should motor starting loads be added to peak load?

Starting and transient requirements should be studied separately because short-duration power and voltage response may govern inverter or generator selection.

Can this replace an hourly microgrid simulation?

No. Hourly or subhourly simulation is needed to test renewable variability, storage cycling, dispatch, fuel use, curtailment, and loss-of-load risk.