Solar Inverter Sizing Calculator

How it is calculated

The DC/AC ratio is the array's DC rating at standard test conditions divided by the inverter's AC nameplate, so inverter kW = array kW ÷ ratio. The tool then picks a catalogue size: it walks through a built-in list (1.5, 2, 3, 3.8, 5, 6, 7.6, 8, 10, 11.4, 15, 20, 25, 30, 40, 50, 60, 75, 100 kW) and takes the first one that is equal to or larger than the calculated value; above 100 kW it rounds up to the next 10 kW. Finally actual ratio = array kW ÷ standard kW shows what you really end up with. Array size is in kW DC and must be positive; if the ratio is left empty it uses 1.2. Because it always rounds up, the standard size can give a lower ratio than the one you asked for.

Common mistakes

• Entering the array in watts: 10000 instead of 10 describes a 10 MW plant and returns a huge inverter, because the field is kW DC.
• Typing the ratio as the inverter-to-array ratio (0.83) instead of DC divided by AC (1.2): the result would be a larger inverter than intended.
• Treating the standard size as the only option: it always rounds up, so a slightly smaller inverter in the list may match your target ratio better; compare the actual ratio.
• Using the panels' real-world output instead of their kW rating at standard test conditions, which is the figure the ratio is defined against.
• Assuming every manufacturer offers these sizes; the list is only a set of common ratings, so check the models you can actually buy.