PV string calculator
Modules per string, string current and isolator for PV.
Reads AS/NZS 5033:2021 and AS/NZS 4777.2:2020.
Try a job 8
Each job fills in example values. Replace them with your values.
- Size solar strings for a 600 V inverterThe modules per string for 49.5 V modules on a 600 V inverter at −5 °C.
- Check string fuses on three parallel stringsWhether three parallel strings of 13.9 A modules call for string fuses, and their rating.
- Size strings for a 1000 V inverterThe modules per string for a commercial inverter.
- Size strings for a cold inland siteThe modules per string at a record low of −8 °C, on a 600 V inverter.
- Check a string on a hot roofWhether the hot voltage stays above the tracker's minimum.
- Check two strings need no fuseWhether two strings in parallel need string fuses.
- Check the array current at the inverterThe array's short-circuit current against the inverter input.
- Size strings for a house trackerThe modules per string for a 450 V window.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Module Voc
- 49.5 V
- Module Vmp
- 41.5 V
- Module Isc
- 13.9 A
- Voc temperature coefficient
- -0.27 %/K
- Vmp temperature coefficient
- -0.35 %/K
- Module maximum series fuse
- 25 A
- Cold voltage correction
- Maker’s coefficient, Cl 4.2.1.2(a)
- Record low temperature
- -5 °C
- Record high temperature
- 35 °C
- Cell rise above ambient
- 35 K
- Installation
- Domestic, 1000 V limit
- Modules per string
- 10
- Strings in parallel
- 2
- KI, bifacial factor
- 1
- Backfeed current from the inverter
- 0 A
- String fuse rating
- 0 A
- Inverter maximum d.c. voltage
- 600 V
- MPPT minimum voltage
- 150 V
- MPPT maximum voltage
- 550 V
- Inverter Isc PV
- 0 A
Modules per string
5 to 11
- String maximum voltage
- 535.1V
- String Vmp at the hottest cell
- 349.6V
- Maximum string current
- 17.38A
- Array current to the inverter
- 34.75A
- d.c. isolator, at least
- 34.75 A at 535.1 V
- String fuses
- Not called for
This result is a design aid. Verify it against the current standard.
Calculation steps
- Voc correction, 1 + coefficient × (Tmin − 25 °C)1.08x
AS/NZS 5033:2021 Cl 4.2.1.2
- Module maximum voltage at the coldest cell53.51V
AS/NZS 5033:2021 Cl 4.2.1.2
- Limit for a domestic installation1,000V
AS/NZS 5033:2021 Cl 3.1
- Most modules per string11
AS/NZS 5033:2021 Cl 4.2.1.3.1
- Hottest cell, record high plus the rise70°C
- Module Vmp at the hottest cell34.96V
- Fewest modules per string for the MPPT minimum5
- String maximum voltage535.1V
AS/NZS 5033:2021 Cl 4.2.1.3.1
- String Vmp at the hottest cell349.6V
- String Vmp at the coldest cell458.6V
- Maximum string current, 1.25 × KI × Isc17.38A
AS/NZS 5033:2021 Cl 3.3.3.1
- Fault current from the other strings, (SA − 1) × ISTRING MAX17.38A
AS/NZS 5033:2021 Cl 3.3.3.2
- String fuse window, above 1.2 × ISTRING MAX and at most the module rating20.85 to 25A
AS/NZS 5033:2021 Table 3.1
- String cable current17.38A
AS/NZS 5033:2021 Table 4.2
- Array cable current to the inverter34.75A
AS/NZS 5033:2021 Table 4.2
- d.c. isolator current rating, at least34.75A
AS/NZS 5033:2021 Table 4.3
- d.c. isolator voltage rating, at least535.1V
AS/NZS 5033:2021 Table 4.3
- Smallest conductor4mm²
AS/NZS 5033:2021 Cl 4.4.2.3
- Cable temperature near the modules, record high plus 40 K75°C
AS/NZS 5033:2021 Cl 4.4.2.2
About this calculator
How this is calculated
The tool sizes a PV string. It finds how many modules fit in a string, the string current, the fuses and the d.c. isolator. It reads AS/NZS 5033:2021. It reads the inverter limits from the plate you enter.
- Cold voltage. The tool corrects the module Voc for the coldest cell (Cl 4.2.1.2). The factor is 1 + coefficient × (Tmin − 25 °C). Tmin is the record low.
- Most modules. It divides the voltage limit by the corrected Voc. The limit is the lower of the inverter maximum and the domestic limit in Cl 3.1 (Cl 4.2.1.3.1).
- Fewest modules. It finds the hot cell as the record high plus the cell rise you enter. It then finds the fewest modules that keep Vmp above the MPPT minimum.
- String current. It works 1.25 × KI × Isc (Cl 3.3.3.1). It adds the fault current from the other strings (Cl 3.3.3.2).
- Fuses. A fuse window sits above 1.2 times the string current and at most the module rating (Table 3.1).
- Cable and isolator. It gives the cable currents (Table 4.2), the isolator ratings (Table 4.3) and the smallest conductor (Cl 4.4.2.3).
| Step | Table or clause | What it decides |
|---|---|---|
| Cold voltage | Cl 4.2.1.2 | The module voltage at the coldest cell |
| String length | Cl 4.2.1.3.1 | The most modules in a string |
| String current | Cl 3.3.3.1 and Cl 3.3.3.2 | The current for cable and fuse |
| Fuse window | Table 3.1 | The fuse range |
| Isolator | Table 4.3 | The current and voltage ratings |
Worked example
- 10 modules of 49.5 V Voc, 2 strings, 600 V inverter. The tool gives 5 to 11 modules per string. The string maximum voltage is 535.1 V. The string current is 17.38 A and the array current is 34.75 A. No string fuses are called for.
Limits
- The tool derives the AS/NZS 5033 figures from the text until the Standard is checked. It says so in a warning.
- AS/NZS 5033 sets no cell rise. The tool uses the rise you enter.
- The inverter limits are the ones on its plate. Read them from the data sheet.
- The tool does not size the cable. Use the DC cable size calculator at these currents and at the hot cable temperature.
- Above 120 V, hold the voltage drop from the furthest module to the inverter to 5 % of Vmp.
See also: PV string voltage and temperature, Solar string sizing for a 600 V inverter and PV and inverter basics.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
How does the tool find the most modules per string?
It corrects the module Voc to the record low temperature, by the maker’s coefficient or by AS/NZS 5033 Table 4.1. It divides the lower of the inverter maximum and the 1000 V or 1500 V limit by that voltage, and rounds down.
How does the tool find the fewest modules per string?
It works the module Vmp at the hottest cell: the record high plus the cell rise you enter. It divides the MPPT minimum by that voltage and rounds up. AS/NZS 5033 sets no cell rise, so the 35 K default is AmpSize’s assumption.
When does a string take a fuse?
Where strings run in parallel, the others can feed a fault in one string. The tool adds that current to the backfeed and compares it with the module’s maximum series fuse. Where it is higher, the fuse sits above 1.2 times the maximum string current and at or under the module rating.
Are the AS/NZS 5033 figures verified?
No. They are encoded from the text of AS/NZS 5033:2021, and stay derived until a print of the standard is read. Check each figure against the current standard before you rely on it.
Clauses and tables this tool reads
- AS/NZS 5033:2021 Cl 3.1Maximum voltage of PV d.c. circuits
- AS/NZS 5033:2021 Cl 3.3.3.1Maximum string current
- AS/NZS 5033:2021 Cl 3.3.4.1When strings take overcurrent protection
- AS/NZS 5033:2021 Cl 4.2.1.2PV module maximum voltage
- AS/NZS 5033:2021 Table 4.2Current in PV circuits
- AS/NZS 5033:2021 Table 4.3Switch disconnector ratings
- AS/NZS 4777.2:2020 Cl 7.2.2Inverter ratings marking
- AS/NZS 5033:2021 array limitsPV array voltage, current and cable limits
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