Solar Electrical Rules - Updated March 2024

Minimum number of solar panels per inverter 'string'.

Single phase 5-6kW inverters typically need three panels per string minimum.
Three phase inverters usually need double that number of panels.
Insufficient voltage means that the inverter won't be able to start that string up.

Unlikely that there will ever be a problem with single phase, but let's look at three phase.
Let's say you want a 5kW three phase inverter and 15 x 440W panels (6.6kW).
Your roof design shows you can have 10 panels facing North and 5 panels facing West.
That's not usually enough voltage to start up the West facing inverter MPPT.
The North roof panels will work fine, but the West roof won't do a thing.

Sometimes it can be done with just five panels.
Higher voltage panels is one way.
An inverter that needs a lower start-up voltage is another.
Using an optimiser is a third way.
Put an optimiser on one of the North facing panels and run it from the West string.

Maximum number of solar panels per string.
Most of today's popular solar panels are relatively 'low voltage'.
This means you can usually install 13 panels, sometimes 14 panels on a string.
Kudos to Gold Coast Power Solutions for this excellent online calculator.

There are a small number of solar panels that are 'higher voltage'
Trina Vertex S+ for instance, where you might only get 10 panels on a string.
Conversely, the higher voltage will help in the first scenario...perhaps fewer panels to start up.

REC Alpha are higher still, 8 or 9 panels max to a string, and SunPower Maxeon only 6 panels...but
in SunPower's case their voltage is so high and current so low, you can parallel two strings together.
That gives you 12 Maxeon panels.

Solar4Ever have been selling and installing solar in Perth, WA since 2011. If you want a quote please get in touch.

(08) 6102 2527

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This review was written by Andrew MacKeith, Solar4Ever service manager since 2011.