“What size inverter?” sounds like it wants one number. It actually wants two, because an inverter is rated two ways, and the right size comes from matching both of them to two different things: your solar panels and the appliances you actually run. Here is the plain version.
The two ratings
Every inverter has a continuous rating and a surge rating. The continuous rating is the power it can supply all day without strain, the number you mostly size around. The surge rating is a short burst, usually around double the continuous figure for a few seconds, that exists to start motors. Both matter, and for different reasons.
Matching it to your panels
For the solar side, the inverter should roughly match your array, with the panels a little larger than the inverter. The usual sweet spot pairs an array about 15 to 25 percent bigger than the inverter’s rating, so a 6 kilowatt array sits comfortably on about a 5 kilowatt inverter. Go too small and you throw away panel output on bright days; go too big and you have paid for capacity that never gets used. You can read inverter basics under solar inverter.
Matching it to your loads, the part people get wrong
If your system has a battery and backs up the house, the inverter also has to run everything you want on at once during an outage, and start the biggest motor among them. This is where people get caught. A fridge, an air conditioner or a water pump can pull two to three times its running watts for a second or two when it kicks on. If the inverter cannot cover that surge, the appliance just will not start, even though its running watts are small and the rest of the house is barely sipping power. So you size for the surge of the biggest motor on top of everything else running, not for the quiet average.
The Goldilocks point
Too small, and things trip or refuse to start when a motor kicks in. Too big, and you have spent money you did not need to, and the inverter runs less efficiently when the load is light. The right size sits comfortably above your real peak, with enough surge headroom to start your heaviest motor, and no more. Bigger is not better here. Correct is.
So what size is right for you?
It comes down to two things: how big your panel array is, and what you want running, especially through an outage. A home that only backs up lights, fans and a fridge needs a far smaller inverter than one that wants to ride out a cut with the air conditioning on. That is why we size it from your actual loads and array rather than a round number, the same way we approach battery backup sizing.
Related reading
- What an inverter actually does in a solar system for what the inverter is doing in the first place.
- Battery backup sizing: keeping the essentials on through an outage for deciding what the inverter has to run.
- How to size a solar system for your electricity bill for sizing the array the inverter pairs with.
- Battery and inverter support for inverter selection and installation.
What are the two ratings on an inverter?
Continuous power and surge power. The continuous rating is what the inverter can supply steadily all day, and it is the figure you mostly size around. The surge rating is a short burst, usually about double the continuous rating for a few seconds, that exists to start motors like fridges, pumps and air conditioners. Both matter when choosing a size.
How do I match an inverter to my solar panels?
The inverter should roughly match the array, with the panels a little larger than the inverter, commonly about 15 to 25 percent bigger. So a 6 kilowatt array pairs well with about a 5 kilowatt inverter. Too small wastes panel output on bright days, while too big means paying for capacity that never gets used.
Why does a motor’s startup surge matter for inverter size?
Because a fridge, air conditioner or water pump can pull two to three times its running watts for a second or two when it starts. If the inverter cannot supply that brief surge, the appliance will not start, even though its running watts are modest. So a backup inverter must be sized to start the biggest motor while everything else is running.
Can an inverter be too big?
Yes. An oversized inverter costs more than you needed to spend and runs less efficiently when the load is light, which is most of the time. The aim is a size that sits comfortably above your real peak with enough surge headroom to start your heaviest motor, not one chosen to look impressive. Correct beats big.
Does the inverter size depend on whether I have backup?
Very much. A grid-tied system without backup is sized mainly to the panels. A hybrid system that runs the house in an outage must also handle everything you want on at once plus the biggest startup surge, so backing up air conditioning needs a much larger inverter than backing up lights, fans and a fridge.
How do you decide the right size for my home?
By looking at two things: the size of your panel array and the loads you want to run, especially through an outage. We list what needs to run together, account for the largest motor’s startup surge, and match that to the array, so the inverter is sized to your real situation rather than a round number.
The next step
The right inverter size comes from your panels and, above all, what you want running when the power goes. Get a free quote or message us with what you want to keep on, and we will size the inverter to start and run it properly.