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Hybrid Inverter Sizing

Recommend hybrid inverter for PV + battery + backup.

Electrical

Inputs (SI units)

Sum of steady-state loads (lighting, electronics, resistive heating) on the backup circuit.

Rated power of the largest motor/compressor load requiring starting current.

Inrush multiple of a motor's rated power during start (typ. 3–6× for compressors/pumps).

Fraction of connected loads running simultaneously at peak — avoids oversizing to worst-case sum.

Total installed PV nameplate power feeding the inverter's MPPT inputs.

Datasheet maximum PV array capacity the inverter's MPPT stage can accept (typically 1.2–1.5× AC rating).

Usable battery energy connected to the inverter's DC battery port.

Battery bank nominal voltage — must fall within the inverter's battery voltage window.

Lowest DC battery voltage the inverter's battery port accepts.

Highest DC battery voltage the inverter's battery port accepts.

Manufacturer continuous charge/discharge C-rate limit, used to derive max battery power.

Typical short-duration surge multiple a hybrid inverter can deliver above its continuous rating.

Results

Recommended hybrid inverter
5 kW
Theoretical required rating
5 kW
Diversified continuous load
3.2 kW
Motor starting surge requirement
4.5 kW
Battery DC power / current
5 kW / 104.2 A
✓ PASS — PV array 6 kWp within inverter max PV input 9 kWp.
✓ PASS — Battery voltage 48 V within inverter window 40–60 V.
✓ PASS — Continuous rating with 2× surge covers required surge 6.2 kW.
✓ PASS — Selected inverter 5 kW covers continuous demand 3.2 kW.

Engineering Recommendations

  • →Confirm the inverter datasheet's surge current curve (duration vs multiple) rather than assuming a flat surge factor.
  • →Check that the battery's BMS communication protocol (CAN/RS485) is supported by the chosen hybrid inverter.
  • →Engineering-grade preliminary calculation. Final design must be verified against project-specific site conditions, manufacturer datasheets, applicable standards and utility requirements.

Detailed Calculation Log

Loads: continuous=4 kW, surge=1.5 kW ×3, diversity=80%.
PV 6 kWp vs inverter max PV 9 kWp -> OK.
Battery 48 V vs inverter window 40-60 V -> OK.
Selected 5 kW hybrid inverter for theoretical requirement 5 kW.

Save & Load Project

Designs are stored privately in this browser — nothing is uploaded.

Engineering Formula

  • P_inv ≥ max(PV/1.2, Load, Battery-C-rate)
  • Battery C-rate (0.5C) = Bat × 0.5

Hybrid inverter must simultaneously feed backup loads AND absorb PV/charge battery. Sized to the largest of the three streams.

Step-by-step Calculation

  1. 1.Diversified continuous loadContinuous × diversity3.2 kW
  2. 2.Motor surge requirementSurge load × start factor4.5 kW
  3. 3.Total surge requirement(Peak−Surge) + Motor surge6.2 kW
  4. 4.Required continuous ratingmax(peak, surge load)3.2 kW
  5. 5.Battery powerBat kWh × C-rate5 kW
  6. 6.Battery currentP_bat×1000 / V_bat104.2 A
  7. 7.Theoretical inverter ratingmax(continuous, battery power, surge/surgeMultiple)5 kW
  8. 8.Standard selectionnext(STD_INVERTER_KW, theoretical)5 kW

How to use this calculator: Hybrid Inverter Sizing

Recommend hybrid inverter for PV + battery + backup. The example below is calculated by this page's real engine from the displayed inputs.

  1. 1Confirm that the Hybrid Inverter Sizing matches the quantity or design check you need.
  2. 2Enter Continuous connected load, Motor/surge load, and Motor starting factor using the units printed beside each field.
  3. 3Check every value before calculating, especially decimal points and measurement units.
  4. 4Calculate, then follow the substituted equations in the worked example and compare the result with any stated limit.
  5. 5Read the assumptions, warnings and cited references before using the result for a financial, medical or engineering decision.

Input guide and example values

Use values from the same measurement basis and time period. Conditional fields appear only when the related option is selected.

InputExample valueWhy it matters
Continuous connected load4 kWSum of steady-state loads (lighting, electronics, resistive heating) on the backup circuit.
Motor/surge load1.5 kWRated power of the largest motor/compressor load requiring starting current.
Motor starting factor3 ×Inrush multiple of a motor's rated power during start (typ. 3–6× for compressors/pumps).
Load diversity factor80 %Fraction of connected loads running simultaneously at peak — avoids oversizing to worst-case sum.
PV array capacity (STC)6 kWpTotal installed PV nameplate power feeding the inverter's MPPT inputs.
Inverter max PV input9 kWpDatasheet maximum PV array capacity the inverter's MPPT stage can accept (typically 1.2–1.5× AC rating).
Battery capacity10 kWhUsable battery energy connected to the inverter's DC battery port.
Battery voltage48 VBattery bank nominal voltage — must fall within the inverter's battery voltage window.
Inverter min battery voltage40 VLowest DC battery voltage the inverter's battery port accepts.
Inverter max battery voltage60 VHighest DC battery voltage the inverter's battery port accepts.
Battery max continuous C-rate0.5 CManufacturer continuous charge/discharge C-rate limit, used to derive max battery power.
Inverter surge capability2 ×Typical short-duration surge multiple a hybrid inverter can deliver above its continuous rating.

Formula inputs & variables for Hybrid Inverter Sizing

These are the named quantities used by this calculator. When the source formula does not define a mathematical symbol, OneCalcApp keeps the real input label instead of inventing one.

Variable / inputUnitMeaning in this calculation
Continuous connected loadkWSum of steady-state loads (lighting, electronics, resistive heating) on the backup circuit.
Motor/surge loadkWRated power of the largest motor/compressor load requiring starting current.
Motor starting factor×Inrush multiple of a motor's rated power during start (typ. 3–6× for compressors/pumps).
Load diversity factor%Fraction of connected loads running simultaneously at peak — avoids oversizing to worst-case sum.
PV array capacity (STC)kWpTotal installed PV nameplate power feeding the inverter's MPPT inputs.
Inverter max PV inputkWpDatasheet maximum PV array capacity the inverter's MPPT stage can accept (typically 1.2–1.5× AC rating).
Battery capacitykWhUsable battery energy connected to the inverter's DC battery port.
Battery voltageVBattery bank nominal voltage — must fall within the inverter's battery voltage window.

How the Hybrid Inverter Sizing works

The Hybrid Inverter Sizing uses Continuous connected load, Motor/surge load, Motor starting factor, Load diversity factor, PV array capacity (STC), Inverter max PV input, Battery capacity, Battery voltage, Inverter min battery voltage, Inverter max battery voltage, Battery max continuous C-rate, and Inverter surge capability to calculate Recommended hybrid inverter, Theoretical required rating, Diversified continuous load, Motor starting surge requirement, and Battery DC power / current. Its engine applies P_inv ≥ max(PV/1.2, Load, Battery-C-rate); the worked values below come from that same live calculation rather than a separately typed example.

With Continuous connected load 4 kW, Motor/surge load 1.5 kW, Motor starting factor 3 ×, Load diversity factor 80 %, PV array capacity (STC) 6 kWp, Inverter max PV input 9 kWp, Battery capacity 10 kWh, Battery voltage 48 V, Inverter min battery voltage 40 V, Inverter max battery voltage 60 V, Battery max continuous C-rate 0.5 C, and Inverter surge capability 2 ×, the main worked-example result is Recommended hybrid inverter = 5 kW.

How each Hybrid Inverter Sizing input is used

Continuous connected load

The Hybrid Inverter Sizing worked example uses Continuous connected load = 4 kW. This value is passed directly into the calculation, with an allowed minimum 0.1. Sum of steady-state loads (lighting, electronics, resistive heating) on the backup circuit.

Motor/surge load

The Hybrid Inverter Sizing worked example uses Motor/surge load = 1.5 kW. This value is passed directly into the calculation, with an allowed minimum 0. Rated power of the largest motor/compressor load requiring starting current.

Motor starting factor

The Hybrid Inverter Sizing worked example uses Motor starting factor = 3 ×. This value is passed directly into the calculation, with an allowed minimum 1 and maximum 8. Inrush multiple of a motor's rated power during start (typ. 3–6× for compressors/pumps).

Load diversity factor

The Hybrid Inverter Sizing worked example uses Load diversity factor = 80 %. This value is passed directly into the calculation, with an allowed minimum 10 and maximum 100. Fraction of connected loads running simultaneously at peak — avoids oversizing to worst-case sum.

PV array capacity (STC)

The Hybrid Inverter Sizing worked example uses PV array capacity (STC) = 6 kWp. This value is passed directly into the calculation, with an allowed minimum 0.1. Total installed PV nameplate power feeding the inverter's MPPT inputs.

Inverter max PV input

The Hybrid Inverter Sizing worked example uses Inverter max PV input = 9 kWp. This value is passed directly into the calculation, with an allowed minimum 0.1. Datasheet maximum PV array capacity the inverter's MPPT stage can accept (typically 1.2–1.5× AC rating).

Battery capacity

The Hybrid Inverter Sizing worked example uses Battery capacity = 10 kWh. This value is passed directly into the calculation, with an allowed minimum 0.1. Usable battery energy connected to the inverter's DC battery port.

Battery voltage

The Hybrid Inverter Sizing worked example uses Battery voltage = 48 V. This value is passed directly into the calculation, with an allowed minimum 1.2. Battery bank nominal voltage — must fall within the inverter's battery voltage window.

Inverter min battery voltage

The Hybrid Inverter Sizing worked example uses Inverter min battery voltage = 40 V. This value is passed directly into the calculation, with an allowed minimum 1. Lowest DC battery voltage the inverter's battery port accepts.

Inverter max battery voltage

The Hybrid Inverter Sizing worked example uses Inverter max battery voltage = 60 V. This value is passed directly into the calculation, with an allowed minimum 1. Highest DC battery voltage the inverter's battery port accepts.

Battery max continuous C-rate

The Hybrid Inverter Sizing worked example uses Battery max continuous C-rate = 0.5 C. This value is passed directly into the calculation, with an allowed minimum 0.05 and maximum 3. Manufacturer continuous charge/discharge C-rate limit, used to derive max battery power.

Inverter surge capability

The Hybrid Inverter Sizing worked example uses Inverter surge capability = 2 ×. This value is passed directly into the calculation, with an allowed minimum 1 and maximum 4. Typical short-duration surge multiple a hybrid inverter can deliver above its continuous rating.

Hybrid Inverter Sizing formulas and result interpretation

Formula 1: relationship used

In the Hybrid Inverter Sizing, P_inv ≥ max(PV/1.2, Load, Battery-C-rate). The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 2: relationship used

In the Hybrid Inverter Sizing, Battery C-rate (0.5C) = Bat × 0.5. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Recommended hybrid inverter

For the displayed Hybrid Inverter Sizing worked example, Recommended hybrid inverter is 5 kW. Verify Continuous connected load, Motor/surge load, and Motor starting factor and their units before relying on this output.

Theoretical required rating

For the displayed Hybrid Inverter Sizing worked example, Theoretical required rating is 5 kW. Verify Continuous connected load, Motor/surge load, and Motor starting factor and their units before relying on this output.

Diversified continuous load

For the displayed Hybrid Inverter Sizing worked example, Diversified continuous load is 3.2 kW. Verify Continuous connected load, Motor/surge load, and Motor starting factor and their units before relying on this output.

Motor starting surge requirement

For the displayed Hybrid Inverter Sizing worked example, Motor starting surge requirement is 4.5 kW. Verify Continuous connected load, Motor/surge load, and Motor starting factor and their units before relying on this output.

Battery DC power / current

For the displayed Hybrid Inverter Sizing worked example, Battery DC power / current is 5 kW / 104.2 A. Verify Continuous connected load, Motor/surge load, and Motor starting factor and their units before relying on this output.

Hybrid Inverter Sizing accuracy, checks and limitations

  • Hybrid Inverter Sizing units check: confirm Continuous connected load (kW), Motor/surge load (kW), Motor starting factor (×), Load diversity factor (%), PV array capacity (STC) (kWp), Inverter max PV input (kWp), Battery capacity (kWh), Battery voltage (V), Inverter min battery voltage (V), Inverter max battery voltage (V), Battery max continuous C-rate (C), and Inverter surge capability (×) before calculating.
  • Hybrid Inverter Sizing result check: compare Recommended hybrid inverter, Theoretical required rating, Diversified continuous load, Motor starting surge requirement, and Battery DC power / current with the substituted formula steps and the displayed rounding precision.
  • Hybrid Inverter Sizing: Use this result for preliminary design and cross-checking. Confirm the applicable code edition, manufacturer data, site conditions and qualified-engineer approval before final design or installation.

Understanding the result

Read the main result together with supporting checks, assumptions, limits and intermediate values.

For a manual check, repeat the first equation, confirm the units and change one input at a time.

Common mistakes when using Hybrid Inverter Sizing

  • Do not mix units for Continuous connected load (kW), Motor/surge load (kW), Motor starting factor (×). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
  • Do not replace the displayed P_inv ≥ max(PV/1.2, Load, Battery-C-rate) relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
  • Do not treat Recommended hybrid inverter = 5 kW from the worked example as a universal answer. It belongs to the displayed example inputs and must be recalculated for the actual case.

When the Hybrid Inverter Sizing is useful

Hybrid Inverter Sizing is designed for cases where Continuous connected load, Motor/surge load, Motor starting factor, Load diversity factor are known and you need Recommended hybrid inverter, Theoretical required rating, Diversified continuous load. The page keeps the live calculator, calculation method and worked example together so the result can be checked instead of treated as a black-box number.

Use the calculator for the scope described by its inputs and notes. The displayed method is P_inv ≥ max(PV/1.2, Load, Battery-C-rate). If the real project or decision needs factors that are not represented here, treat the result as an estimate and add the missing checks separately.

Continuous connected load and Motor/surge load: what changes the answer

The worked example uses Continuous connected load = 4 kW, Motor/surge load = 1.5 kW, Motor starting factor = 3 ×, Load diversity factor = 80 %. With those values, Recommended hybrid inverter is 5 kW. Changing an input should be interpreted according to that field's unit, range, option and hint rather than by the number alone.

For this calculator, the main input roles are: Continuous connected load (kW): Sum of steady-state loads (lighting, electronics, resistive heating) on the backup circuit. Motor/surge load (kW): Rated power of the largest motor/compressor load requiring starting current. Motor starting factor (×): Inrush multiple of a motor's rated power during start (typ. 3–6× for compressors/pumps). Load diversity factor (%): Fraction of connected loads running simultaneously at peak — avoids oversizing to worst-case sum.

How to sanity-check a Hybrid Inverter Sizing result

Start by confirming the entered values and units, then compare the substituted working with the displayed formula or calculation steps. Pay particular attention to Recommended hybrid inverter, because it is the first worked-example output shown by the live engine.

Finally, compare the result with the assumptions, warnings and related calculators on this page. A nearby calculator can be useful as a cross-check when it measures the same workflow from a different input or output direction.

Next logical calculator

Continue with Battery Backup Calculator

Battery Backup Calculator covers the same practical workflow from a related calculation angle, making it a useful cross-check after Hybrid Inverter Sizing.

Open Battery Backup Calculator

Standards, source trail and limitations

References show the method used. Check the current local edition, amendments and project specification before a regulated decision.

Design Assumptions

  • • Single-inverter topology.
  • • 0.5C battery charge/discharge.

Engineering Tips

  • ◆Choose inverter with ≥ 2 MPPTs for split-roof arrays.

Warnings

  • ▲Some hybrids limit backup power to 70% of AC rating — check spec.

Standards & References

IEC 62109-2IEEE 1547.1

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