Question 1

How do I calculate how many solar panels per string?

Accepted Answer

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.

Question 2

Why does temperature affect solar string sizing?

Accepted Answer

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.

Question 3

What temperatures should I use for string sizing in Australia?

Accepted Answer

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.

Question 4

How does temperature affect solar panel voltage output?

Accepted Answer

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.

Question 5

What happens if the string voltage exceeds the inverter maximum?

Accepted Answer

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. Most inverters have a maximum input of 600V for residential or 1000V for commercial systems per AS/NZS 5033. 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.

Question 6

How do I calculate the minimum number of panels per string?

Accepted Answer

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.

String Sizing Calculator

Solar Panel Specifications

Panel Preset

Panel Electrical Data (STC)

Inverter Specifications

Site Conditions

About This Solar String Sizing Calculator