PV string voltage formulas
Formula chart for PV string voltage, temperature adjustment and module-count relationships.
PV string voltage relationships for product records
Use these row summaries to read the calculation relationship before checking the value table.
Coefficient conversion
Convert datasheet percent per deg C into a decimal coefficient.
coeff_decimal = coeff_pct / 100Cold open-circuit voltage
Adjust module open-circuit voltage for cold design temperature.
Voc_cold = Voc x (1 + (coeff_pct / 100) x (T_cold - 25 deg C))Cold operating voltage
Estimate the cold operating point for MPPT review.
Vmp_cold = Vmp x (1 + (coeff_pct / 100) x (T_cold - 25 deg C))Hot operating voltage
Estimate the hot operating point for MPPT review.
Vmp_hot = Vmp x (1 + (coeff_pct / 100) x (T_hot - 25 deg C))String voltage
Scale adjusted module voltage by modules in series.
Vstring = Vadjusted x Nseries
- Module voltage, temperature coefficient, temperature delta and module count relationships.
- Show PV string voltage formulas without replacing product, inverter, DNSP or authority checks.
- AS/NZS 5033, AS/NZS 4777, product and inverter requirements noted for project review.
- Temperature calculations use coeff_pct / 100 and T - 25 deg C context; record Voc_cold, Vmp_cold, Vmp_hot, MPPT window, datasheet, inverter limit and DNSP context.
Temperature-adjusted PV voltage formula rows
Show PV string voltage formulas without replacing product, inverter, DNSP or authority checks.
| Relationship | Formula | Use | Boundary |
|---|---|---|---|
| Coefficient conversion | coeff_decimal = coeff_pct / 100 | Convert datasheet percent per deg C into a decimal coefficient. | Coefficient sign and units must match the current datasheet source. |
| Cold open-circuit voltage | Voc_cold = Voc x (1 + (coeff_pct / 100) x (T_cold - 25 deg C)) | Adjust module open-circuit voltage for cold design temperature. | Compare with equipment maximum voltage and inverter limit before project review. |
| Cold operating voltage | Vmp_cold = Vmp x (1 + (coeff_pct / 100) x (T_cold - 25 deg C)) | Estimate the cold operating point for MPPT review. | Not a complete MPPT compatibility review without inverter datasheet context. |
| Hot operating voltage | Vmp_hot = Vmp x (1 + (coeff_pct / 100) x (T_hot - 25 deg C)) | Estimate the hot operating point for MPPT review. | Product, inverter, DNSP and project requirements still control design decisions. |
| String voltage | Vstring = Vadjusted x Nseries | Scale adjusted module voltage by modules in series. | Final count needs datasheet, inverter, DNSP and authority review. |
- Use current datasheets and inverter limits.
- The calculator owns entered project-specific values.
Formula variables
Use these symbols and units when reading the chart rows.
| Variable | Meaning | Unit | Use |
|---|---|---|---|
| Voc | Module open-circuit voltage. | V | Use the current product datasheet value. |
| Vmp | Module maximum-power voltage. | V | Use the current product datasheet value. |
| coeff_pct | Temperature coefficient percent per degree. | %/deg C | Convert with coeff_pct / 100 before applying T - 25. |
| coeff_decimal | Temperature coefficient as a decimal per degree. | 1/deg C | Derived from coeff_pct / 100. |
| T | Cell or design temperature. | deg C | |
| T_cold | Cold design temperature. | deg C | Use the selected cold design condition. |
| T_hot | Hot design temperature. | deg C | Use the selected hot operating condition. |
| T - 25 | Temperature delta from STC. | deg C | Use the selected cold or hot design temperature. |
| Vadjusted | Temperature-adjusted module voltage. | V | Use Voc_cold, Vmp_cold or Vmp_hot depending on the row. |
| Voc_cold | Cold adjusted open-circuit voltage. | V | Compare with equipment maximum voltage. |
| Vmp_cold | Cold adjusted operating voltage. | V | Compare with the inverter MPPT range. |
| Vmp_hot | Hot adjusted operating voltage. | V | Compare with the inverter MPPT range. |
| Nseries | Modules connected in series. | Use the proposed string count from the design record. | |
| Vstring | String voltage after multiplying by modules in series. | V | Compare with equipment or MPPT boundaries as appropriate. |
| MPPT | Inverter MPPT operating window. | Check current datasheet and DNSP context. |
Worked relationship example
This example shows how one set of entered values reads through the relationship.
PV cold string Voc relationship reading
A module datasheet value is temperature-adjusted before comparing a string with equipment limits.
- Module Voc
- 49.5 V
- Temperature coefficient
- -0.28 %/deg Cconvert to -0.0028
- Cold design temperature
- -5 deg C
- Modules in series
- 12
- Convert coefficientcoeff = coeff_pct / 100 = -0.28 / 100 = -0.0028 per deg C.
- Apply temperature deltaT - 25 deg C = -5 - 25 = -30 deg C.
- Find cold module voltageVoc_cold = 49.5 x (1 + -0.0028 x -30) = 53.7 V.
- Find string voltageString Voc_cold = 53.7 x 12 = 644 V.
Cold string Voc estimateabout 644 V
Compare this estimate with equipment maximum voltage, inverter limits, MPPT range and DNSP/project requirements.
Use the example to read the temperature relationship; product datasheets, inverter limits and approval context still control design decisions.
- Datasheet values are current for the selected module.
- Temperature basis and DNSP context are project-entered records.
Where the PV string chart belongs
Use the chart to understand the formula basis; calculators handle project-specific inputs, warnings and results.
| Item | Value |
|---|---|
| Purpose | Show PV string voltage formulas without replacing product, inverter, DNSP or authority checks. |
| How to use the source | Module voltage, temperature coefficient, temperature delta and module count relationships. |
| Standards and project context | AS/NZS 5033, AS/NZS 4777, product and inverter requirements noted for project review. |
| Where judgement is still needed | Use this chart to understand the relationship behind a calculation; do not treat it as a substitute for entered project values. |
| Before relying on it | Confirm current standards, local authority requirements, DNSP conditions, project documents and manufacturer data before relying on a decision. |
| Context | Applies to | Public boundary |
|---|---|---|
| AS/NZS 5033, AS/NZS 4777 and product context | PV string voltage, module count and inverter compatibility records | The chart does not approve a design or reproduce controlled standards text. |
| Datasheet and inverter limits | Voc_cold, Vmp_cold, Vmp_hot, equipment maximum voltage and MPPT range | Use current module and inverter datasheets before making product or string-count decisions. |
| DNSP and project boundary | Connection context and final design review | DNSP, local authority and project requirements can override worksheet estimates. |
Formula basis for PV string voltage
Review the cited calculator source, module datasheet basis, inverter boundary, DNSP context and Australian project limits before using these PV string formulas.
| Item | Value |
|---|---|
| Source | AUWiring PV string voltage calculator formula notes. |
| Source type | Product and project record model |
| Derivation basis | Derived from AUWiring calculator logic and user-entered module data; no product listing or controlled standards text is reproduced. |
| Last checked | 2026-07-13 |
| Review interval | Annual or when PV calculator formulas, product-data practice or Australian energy-system requirements change. |
| Review trigger | Formula change, standards update, product limit change or project feedback. |
| Version used | R27-2026-07-13 |
| Australian application | Australia; product listings, inverter limits, DNSP and authority requirements govern final decisions. |
Use a calculator for project values
Use the chart to read the formula relationship, then open a calculator when you need entered project values, warnings and result context.