# Solar Inverter Sizing Calculator

> Size a solar inverter from array kWp and a DC/AC ratio, and check the maximum panels per string from cold-weather Voc and the inverter voltage limit.

Category: Energy & environment · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/solar-inverter-sizing-calculator

An inverter is sized from the array’s DC rating divided by a chosen DC/AC ratio. Strings must also stay below the inverter’s maximum DC voltage on the coldest morning, when panel voltage is highest.

Also called: String sizing calculator, DC/AC ratio calculator.

## Inputs
- Array size (DC) (unit kWp; default 6.6)
- DC/AC ratio (default 1.2)
- Panel open-circuit voltage (Voc) (unit V; default 49.5)
- Voc temperature coefficient (unit %/°C; default -0.27)
- Lowest expected cell temperature (unit °C; default -10)
- Inverter maximum DC input voltage (unit V; default 600)

## Results
- Inverter AC rating
- Panel Voc at the lowest temperature
- Maximum panels per string
- Cold Voc of that string

## Formula

```
AC kW = DC kWp ÷ DC/AC ratio;  Voc(cold) = Voc × (1 + β × (Tmin − 25));  Max panels per string = ⌊Vmax ÷ Voc(cold)⌋
```

Where:
- β: Voc temperature coefficient as a fraction per °C (negative)
- Tmin: lowest cell temperature, °C
- Vmax: inverter maximum DC input voltage

## Worked example
1. AC rating = 6.6 ÷ 1.2 = 5.5 kW.
2. Voc at −10 °C = 49.5 × (1 + (−0.0027) × (−35)) = 49.5 × 1.0945 = 54.18 V.
3. Panels per string = 600 ÷ 54.18 = 11.07, so at most 11.

**Result:** A 6.6 kWp array at a 1.2 ratio suits a 5.5 kW inverter, with no more than 11 of these panels per string on a 600 V input.

## What the result means

A ratio above 1 slightly clips output on the sunniest hours but makes better use of the inverter the rest of the time. The string limit is a hard safety limit: exceeding the inverter’s maximum voltage can damage it.

## Assumptions and limits
- The temperature coefficient is linear over the range.
- All strings use identical panels.
- Does not check the MPPT voltage window, maximum input current or minimum string length; check them against the datasheets.
- Local electrical codes may require extra margins; a qualified installer must design the final system.

## Questions

### Why does panel voltage rise in the cold?

Silicon cell voltage falls as temperature rises and rises as it falls. On a clear, freezing morning the open-circuit voltage is at its highest.

### Is it safe to oversize the array?

Within the inverter maker’s stated DC limits, yes; the inverter simply caps its AC output. Never exceed the maximum DC voltage or current.

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_Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials._

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/solar-inverter-sizing-calculator