Solar String Sizing Calculator
How many panels can go on one string? Check the inverter window at your coldest and hottest days.
Data: AS/NZS 5033, edition not confirmed. About standard editions
For reference only. Always verify panel and inverter datasheets and comply with AS/NZS 5033 and local installation standards. Cell temperature differs from ambient; adjust accordingly.
Solar Panel Specifications
Panel Preset
Panel Electrical Data (STC)
Negative value, e.g. -0.28
Inverter Specifications
Site Conditions
Coldest expected cell temp (winter dawn)
Hottest expected cell temp (summer peak)
Tip: Cell temperature is typically 20–35°C above ambient. For an ambient range of -5°C to 40°C, use cell temps of approximately -5°C to 75°C. AS/NZS 5033 provides regional temperature data.
Solar warning labels from $10.59 each.
Engraved traffolyte PV and battery warning signs, made in Townsville, posted Australia wide. Order online.
Design solar labelsLabel the array while the numbers are in front of you.
About This Solar String Sizing Calculator
This calculator works out the minimum and maximum number of panels per string based on your inverter MPPT window and site temperatures. Built for Australian solar installers designing residential and commercial systems.
Use it when you need to check string lengths before ordering panels. Enter panel datasheet values and local temperature extremes, and get safe string sizes that keep voltage within the inverter range year-round.
Temperature derating follows the methods in AS/NZS 5033. This is a reference tool. Always verify against current panel and inverter datasheets and your local BOM temperature data.
Questions
- How do I calculate how many solar panels per string?
- Divide the inverter's maximum MPPT voltage by the panel's Voc at the coldest expected temperature to get the maximum panels. Divide the minimum MPPT voltage by the panel's Vmp at the hottest expected temperature to get the minimum. This calculator handles the temperature derating automatically.
- Why does temperature affect solar string sizing?
- Panel voltage increases in cold weather and decreases in hot weather. If you size strings without accounting for cold-temperature Voc rise, you risk exceeding the inverter's maximum input voltage and damaging it.
- What temperatures should I use for string sizing in Australia?
- Use the site's minimum recorded ambient temperature for maximum voltage calculations and the expected cell temperature on a hot day (typically ambient plus 25-30°C) for minimum voltage. Your local BOM data provides the ambient extremes.
- How does temperature affect solar panel voltage output?
- Solar panel voltage changes by its temperature coefficient, typically around -0.27% to -0.35% per degree Celsius for monocrystalline panels. In cold conditions (e.g. 0°C), a panel rated at 41V Voc at STC (25°C) can rise to approximately 44.6V. In hot conditions (e.g. 70°C cell temperature), it drops to around 34.5V. AS/NZS 5033 requires string sizing to account for both extremes. This calculator applies the exact temperature coefficients from your panel datasheet automatically.
- What happens if the string voltage exceeds the inverter maximum?
- If the open-circuit voltage of a string exceeds the inverter's maximum DC input voltage, the inverter's input stage can be permanently damaged. This typically occurs on cold winter mornings when panel voltage peaks. The limit is on the inverter datasheet. The damage is not covered under warranty if the installation exceeds rated limits. This calculator checks your string Voc at the coldest expected temperature against the inverter's maximum to prevent this.
- How do I calculate the minimum number of panels per string?
- Divide the inverter's minimum MPPT voltage by the panel's Vmp at the highest expected cell temperature. For example, if the inverter minimum MPPT is 150V and panel Vmp at 70°C cell temperature drops to 34V, the minimum is 150 / 34 = 4.4, rounded up to 5 panels. If the string voltage falls below the MPPT window, the inverter cannot track maximum power and energy harvest drops significantly. This calculator performs this calculation using AS/NZS 5033 temperature correction methods.