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Inverter Sizing

Recommend inverter AC rating from PV DC and DC/AC ratio.

Electrical

Inputs (SI units)

Sum of all module Pmax at STC

1.1–1.3 typical for IEC/NEC climates

Results

Required AC capacity (theoretical)
10 kW
From target DC/AC ratio
Selected standard inverter
10 kW
Next catalogue size ≥ 10 kW required
Number of inverters
1
Installed AC capacity
10 kW
Final DC/AC ratio
1.2
Cold string Voc
1,090.48 V
Hot string Vmp
693.04 V
Max strings per MPPT (current-limited)
1
Estimated clipping-risk fraction
37.34 %
✓ PASS — Array DC power (12 kWp) within a sound envelope of inverter max DC input (11 kW).
✕ FAIL — Cold Voc (1,090.48 V) EXCEEDS inverter max DC voltage (1,000 V) — reduce modules per string.
✕ FAIL — String voltage falls outside the MPPT window (200–850 V) at some operating temperature.
✓ PASS — String Imp (10.5 A) is within the MPPT max current (16 A).
✓ PASS — Final DC/AC ratio 1.2 is within the normal 1.0–1.35 design band.
⚠ WARNING — Estimated clipping risk 37.34% may cause measurable energy loss at peak irradiance.

Solar PV decision support

PV design decision summary

This section organises the existing calculator output into design checks, governing criteria and comparison cases. Core solar formulas and the calculator's original results are unchanged.

Solar PV sizing & array decision support v3 · 2026.08

Review required

2 explicit checks did not pass. Review the inputs, assumptions and applicable limits before using the result.

3 pass1 review2 fail1 info

Governing criterion

Voltage compatibility

✕ FAIL — Cold Voc (1,090.48 V) EXCEEDS inverter max DC voltage (1,000 V) — reduce modules per string.

Structured directly from this solar calculator's own runtime alert.

Design checks

Solar engineering check 1

pass

✓ PASS — Array DC power (12 kWp) within a sound envelope of inverter max DC input (11 kW).

Structured directly from this solar calculator's own runtime alert.

Voltage compatibility

fail

✕ FAIL — Cold Voc (1,090.48 V) EXCEEDS inverter max DC voltage (1,000 V) — reduce modules per string.

Structured directly from this solar calculator's own runtime alert.

MPPT compatibility

fail

✕ FAIL — String voltage falls outside the MPPT window (200–850 V) at some operating temperature.

Structured directly from this solar calculator's own runtime alert.

DC/AC ratio review

pass

✓ PASS — Final DC/AC ratio 1.2 is within the normal 1.0–1.35 design band.

Structured directly from this solar calculator's own runtime alert.

Solar engineering check 6

review

⚠ WARNING — Estimated clipping risk 37.34% may cause measurable energy loss at peak irradiance.

Structured directly from this solar calculator's own runtime alert.

Inverter DC/AC ratio review

pass

1.20

Inside the preliminary 1.10–1.30 band described by this calculator. Manufacturer input limits still govern.

Calculated inverter AC requirement available

info

10 kW

Final equipment selection must use a real inverter rating and then verify DC voltage, MPPT current, thermal derating and grid-code requirements.

Next design actions

Engine recommendation 1

Use 1 × 10 kW standard inverter(s) — chosen because it is the smallest catalogue rating meeting the required 10 kW AC capacity.

Engine recommendation 2

Balance string counts evenly across all MPPT inputs to minimise mismatch.

Engine recommendation 3

Re-check Voc(cold) and MPPT window whenever module count per string changes.

Engine recommendation 4

Engineering-grade preliminary calculation. Final design must be verified against project-specific site conditions, manufacturer datasheets, applicable standards and utility requirements.

Current design output — resolve failed checks

10 kW

From target DC/AC ratio

Equipment selection check

Choose a real inverter and verify all DC input limits

AC kW/kVA sizing alone does not establish string-voltage compatibility, MPPT current capacity or temperature derating.

Methodology & limit

Decision support is structured from the existing solar calculator engine and the current user inputs. PASS/FAIL is shown only where the engine or entered project criteria support an explicit check. Final PV design still requires site survey, exact module/inverter datasheets, structural/electrical design and applicable statutory approval.

Engineering Recommendations

  • →Use 1 × 10 kW standard inverter(s) — chosen because it is the smallest catalogue rating meeting the required 10 kW AC capacity.
  • →Balance string counts evenly across all MPPT inputs to minimise mismatch.
  • →Re-check Voc(cold) and MPPT window whenever module count per string changes.
  • →Engineering-grade preliminary calculation. Final design must be verified against project-specific site conditions, manufacturer datasheets, applicable standards and utility requirements.

Detailed Calculation Log

Inverter DC input limit 11 kW vs array 12 kWp → ratio 1.09.
MPPT window 200–850 V vs string Vmp(hot) 693.04 V / Voc(cold) 1,090.48 V.

Save & Load Project

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

Engineering Formula

  • P_ac = P_dc / (DC/AC)
  • S_ac = P_ac / PF [kVA]
  • Oversizing % = (DC/AC − 1) × 100

Inverters are typically DC-oversized to clip infrequent peaks and lift CUF. 1.10–1.30 is standard for India / IEC climates.

Step-by-step Calculation

  1. 1.Total connected DC capacityΣP_module12 kWp
  2. 2.Required AC capacityP_dc / (DC/AC)10 kW
  3. 3.DC/AC ratio at inverter max DC inputP_dc / P_inv,maxDC1.09
  4. 4.Cold-condition string Vocn × Voc × [1 + β/100×(Tmin−25)]1,090.48 V
  5. 5.Hot-condition string Vmpn × Vmp × [1 + γ/100×(Tmax−25)]693.04 V
  6. 6.String Imp vs MPPT max currentImp ≤ I_mppt,max10.5 A ≤ 16 A → OK
  7. 7.Max strings per MPPT (current-limited)floor(I_mppt,max / Imp)1
  8. 8.Array power achievable on one inverterP_string × strings/MPPT × MPPT count17.56 kWp
  9. 9.Estimated clipping-risk fractionmax(0, (Pdc−Pinv,maxDC)/Pdc)×10037.34 %
  10. 10.Number of inverters⌈Pdc,total / Pdc,per-inverter⌉1
  11. 11.Selected standard inverter ratingnext standard ≥ required AC10 kW
  12. 12.Installed AC capacityP_inv,std × N_inverters10 kW
  13. 13.Final DC/AC ratioP_dc,total / P_ac,installed1.2

How to use this calculator: Inverter Sizing

Recommend inverter AC rating from PV DC and DC/AC ratio. The example below is calculated by this page's real engine from the displayed inputs.

  1. 1Confirm that the Inverter Sizing matches the quantity or design check you need.
  2. 2Enter Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power 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
Total connected DC (array nameplate)12 kWpSum of all module Pmax at STC
Target DC/AC ratio1.2 -1.1–1.3 typical for IEC/NEC climates
Inverter max DC input power11 kWFrom inverter datasheet — DC input limit
Inverter max DC voltage1000 VAbsolute maximum system voltage
Module Voc (STC)49.5 VMeasured or known module voc (stc) used by the calculation engine.
Module Vmp (STC)41.8 VMeasured or known module vmp (stc) used by the calculation engine.
Voc temp coeff β-0.29 %/°CNegative for crystalline silicon
Vmp temp coeff γ-0.38 %/°CMeasured or known vmp temp coeff γ used by the calculation engine.
Lowest expected cell temp-10 °CMeasured or known lowest expected cell temp used by the calculation engine.
Highest expected cell temp70 °CMeasured or known highest expected cell temp used by the calculation engine.
Modules per string20 -Measured or known modules per string used by the calculation engine.
MPPT window low200 VMeasured or known mppt window low used by the calculation engine.
MPPT window high850 VMeasured or known mppt window high used by the calculation engine.
Max current per MPPT16 AMeasured or known max current per mppt used by the calculation engine.
MPPT count per inverter2 -Measured or known mppt count per inverter used by the calculation engine.
Module Imp (STC)10.5 AMeasured or known module imp (stc) used by the calculation engine.

Formula inputs & variables for 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
Total connected DC (array nameplate)kWpSum of all module Pmax at STC
Target DC/AC ratio-1.1–1.3 typical for IEC/NEC climates
Inverter max DC input powerkWFrom inverter datasheet — DC input limit
Inverter max DC voltageVAbsolute maximum system voltage
Module Voc (STC)VMeasured or known module voc (stc) used by the calculation engine.
Module Vmp (STC)VMeasured or known module vmp (stc) used by the calculation engine.
Voc temp coeff β%/°CNegative for crystalline silicon
Vmp temp coeff γ%/°CMeasured or known vmp temp coeff γ used by the calculation engine.

How the Inverter Sizing works

The Inverter Sizing uses Total connected DC (array nameplate), Target DC/AC ratio, Inverter max DC input power, Inverter max DC voltage, Module Voc (STC), Module Vmp (STC), Voc temp coeff β, Vmp temp coeff γ, Lowest expected cell temp, Highest expected cell temp, Modules per string, MPPT window low, MPPT window high, Max current per MPPT, MPPT count per inverter, and Module Imp (STC) to calculate Required AC capacity (theoretical), Selected standard inverter, Number of inverters, Installed AC capacity, Final DC/AC ratio, Cold string Voc, Hot string Vmp, Max strings per MPPT (current-limited), and Estimated clipping-risk fraction. Its engine applies P_ac = P_dc / (DC/AC); the worked values below come from that same live calculation rather than a separately typed example.

With Total connected DC (array nameplate) 12 kWp, Target DC/AC ratio 1.2 -, Inverter max DC input power 11 kW, Inverter max DC voltage 1000 V, Module Voc (STC) 49.5 V, Module Vmp (STC) 41.8 V, Voc temp coeff β -0.29 %/°C, Vmp temp coeff γ -0.38 %/°C, Lowest expected cell temp -10 °C, Highest expected cell temp 70 °C, Modules per string 20 -, MPPT window low 200 V, MPPT window high 850 V, Max current per MPPT 16 A, MPPT count per inverter 2 -, and Module Imp (STC) 10.5 A, the main worked-example result is Required AC capacity (theoretical) = 10 kW.

How each Inverter Sizing input is used

Total connected DC (array nameplate)

The Inverter Sizing worked example uses Total connected DC (array nameplate) = 12 kWp. This value is passed directly into the calculation, with an allowed minimum 0.1. Sum of all module Pmax at STC

Target DC/AC ratio

The Inverter Sizing worked example uses Target DC/AC ratio = 1.2 -. This value is passed directly into the calculation, with an allowed minimum 1 and maximum 1.6. 1.1–1.3 typical for IEC/NEC climates

Inverter max DC input power

The Inverter Sizing worked example uses Inverter max DC input power = 11 kW. This value is passed directly into the calculation, with an allowed minimum 0.1. From inverter datasheet — DC input limit

Inverter max DC voltage

The Inverter Sizing worked example uses Inverter max DC voltage = 1000 V. This value is passed directly into the calculation, with an allowed minimum 50. Absolute maximum system voltage

Module Voc (STC)

The Inverter Sizing worked example uses Module Voc (STC) = 49.5 V. This value is passed directly into the calculation, with an allowed minimum 5.

Module Vmp (STC)

The Inverter Sizing worked example uses Module Vmp (STC) = 41.8 V. This value is passed directly into the calculation, with an allowed minimum 5.

Voc temp coeff β

The Inverter Sizing worked example uses Voc temp coeff β = -0.29 %/°C. This value is passed directly into the calculation, with an allowed minimum -0.6 and maximum 0.2. Negative for crystalline silicon

Vmp temp coeff γ

The Inverter Sizing worked example uses Vmp temp coeff γ = -0.38 %/°C. This value is passed directly into the calculation, with an allowed minimum -0.6 and maximum 0.2.

Lowest expected cell temp

The Inverter Sizing worked example uses Lowest expected cell temp = -10 °C. This value is passed directly into the calculation, with an allowed minimum -40 and maximum 25.

Highest expected cell temp

The Inverter Sizing worked example uses Highest expected cell temp = 70 °C. This value is passed directly into the calculation, with an allowed minimum 25 and maximum 90.

Modules per string

The Inverter Sizing worked example uses Modules per string = 20 -. This value is passed directly into the calculation, with an allowed minimum 1.

MPPT window low

The Inverter Sizing worked example uses MPPT window low = 200 V. This value is passed directly into the calculation, with an allowed minimum 30.

MPPT window high

The Inverter Sizing worked example uses MPPT window high = 850 V. This value is passed directly into the calculation, with an allowed minimum 100.

Max current per MPPT

The Inverter Sizing worked example uses Max current per MPPT = 16 A. This value is passed directly into the calculation, with an allowed minimum 0.5.

MPPT count per inverter

The Inverter Sizing worked example uses MPPT count per inverter = 2 -. This value is passed directly into the calculation, with an allowed minimum 1.

Module Imp (STC)

The Inverter Sizing worked example uses Module Imp (STC) = 10.5 A. This value is passed directly into the calculation, with an allowed minimum 0.1.

Inverter Sizing formulas and result interpretation

Formula 1: relationship used

In the Inverter Sizing, P_ac = P_dc / (DC/AC). 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 Inverter Sizing, S_ac = P_ac / PF [kVA]. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Formula 3: relationship used

In the Inverter Sizing, Oversizing % = (DC/AC − 1) × 100. The quantities in this relationship come from the named inputs or from an earlier calculation step shown in the worked example.

Required AC capacity (theoretical)

For the displayed Inverter Sizing worked example, Required AC capacity (theoretical) is 10 kW. From target DC/AC ratio Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Selected standard inverter

For the displayed Inverter Sizing worked example, Selected standard inverter is 10 kW. Next catalogue size ≥ 10 kW required Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Number of inverters

For the displayed Inverter Sizing worked example, Number of inverters is 1. Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Installed AC capacity

For the displayed Inverter Sizing worked example, Installed AC capacity is 10 kW. Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Final DC/AC ratio

For the displayed Inverter Sizing worked example, Final DC/AC ratio is 1.2. Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Cold string Voc

For the displayed Inverter Sizing worked example, Cold string Voc is 1,090.48 V. Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Hot string Vmp

For the displayed Inverter Sizing worked example, Hot string Vmp is 693.04 V. Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Max strings per MPPT (current-limited)

For the displayed Inverter Sizing worked example, Max strings per MPPT (current-limited) is 1. Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Estimated clipping-risk fraction

For the displayed Inverter Sizing worked example, Estimated clipping-risk fraction is 37.34 %. Verify Total connected DC (array nameplate), Target DC/AC ratio, and Inverter max DC input power and their units before relying on this output.

Inverter Sizing accuracy, checks and limitations

  • Inverter Sizing units check: confirm Total connected DC (array nameplate) (kWp), Target DC/AC ratio (-), Inverter max DC input power (kW), Inverter max DC voltage (V), Module Voc (STC) (V), Module Vmp (STC) (V), Voc temp coeff β (%/°C), Vmp temp coeff γ (%/°C), Lowest expected cell temp (°C), Highest expected cell temp (°C), Modules per string (-), MPPT window low (V), MPPT window high (V), Max current per MPPT (A), MPPT count per inverter (-), and Module Imp (STC) (A) before calculating.
  • Inverter Sizing result check: compare Required AC capacity (theoretical), Selected standard inverter, Number of inverters, Installed AC capacity, Final DC/AC ratio, Cold string Voc, Hot string Vmp, Max strings per MPPT (current-limited), and Estimated clipping-risk fraction with the substituted formula steps and the displayed rounding precision.
  • 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 Inverter Sizing

  • Do not mix units for Total connected DC (array nameplate) (kWp), Target DC/AC ratio (-), Inverter max DC input power (kW). A unit mismatch changes the input magnitude even when the typed number looks reasonable.
  • Do not replace the displayed P_ac = P_dc / (DC/AC) relationship with a different convention without also changing the underlying assumptions; compare like-for-like methods when checking the result.
  • Do not treat Required AC capacity (theoretical) = 10 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 Inverter Sizing is useful

Inverter Sizing is designed for cases where Total connected DC (array nameplate), Target DC/AC ratio, Inverter max DC input power, Inverter max DC voltage are known and you need Required AC capacity (theoretical), Selected standard inverter, Number of inverters. 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_ac = P_dc / (DC/AC). 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.

Total connected DC (array nameplate) and Target DC/AC ratio: what changes the answer

The worked example uses Total connected DC (array nameplate) = 12 kWp, Target DC/AC ratio = 1.2 -, Inverter max DC input power = 11 kW, Inverter max DC voltage = 1000 V. With those values, Required AC capacity (theoretical) is 10 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: Total connected DC (array nameplate) (kWp): Sum of all module Pmax at STC Target DC/AC ratio (-): 1.1–1.3 typical for IEC/NEC climates Inverter max DC input power (kW): From inverter datasheet — DC input limit Inverter max DC voltage (V): Absolute maximum system voltage

How to sanity-check a 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 Required AC capacity (theoretical), 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 Fuse Size Calculator

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

Open Fuse Size Calculator

Design Assumptions

  • • Losses in DC combiners < 2%.
  • • Ambient inverter derating negligible up to 45 °C.

Engineering Tips

  • ◆Pick the next standard AC rating up (5, 10, 15, 25, 40, 50 kW).
  • ◆Balance strings equally across MPPTs.

Warnings

  • ▲DC/AC > 1.35 risks clipping > 3% and voids some warranties.

Standards & References

IEC 62109-1/2IEEE 1547CEA Technical Standards (India)

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