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What Size Inverter Do I Need for Solar Panels?

What Size Inverter Do I Need For Solar Panels? Factors You Should Consider When Sizing Your Solar Inverter

The capacity of your inverter can mean the difference between saving money with solar power and saving even more. You win either way but you win more when you get it right, which is likely why you’re asking: What size inverter do I need for solar panels?

The simple answer is that your inverter capacity should be roughly equal to the DC rating or your solar array. For example, let’s say your solar PV system is rated to be 5 kW. Your inverter should ideally be 5000 watts (5 kW), too.

That being said, you also have the option to undersize or oversize your inverter. Other factors also come into play when choosing the right size. I’m talking you through all that today but feel free to tap on the bullets below to jump sections.

Examples of solar inverters in Australia depicted through illustrations.
Examples of solar inverters in Australia depicted through illustrations.

Factors you should consider when sizing your solar inverter

1. The capacity of your solar panel array.

This is the most important factor you should consider when choosing your inverter size. After all, your inverter is in charge of converting the DC electricity from your solar panels to the AC power that your appliances use. So, it has to be capable of handling all that electricity.

This is also the reason why your inverter size should be more or less equal to that of your solar panel capacity.

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2. Where you live.

According to Geoscience Australia, our continent has the highest solar irradiance of any continent around the world. Consequently, this makes Oz the best place to have solar systems.

However, even in Australia, some places are better than others when it comes to solar power. According to the same source, these are the deserts in the northwest as well as the center of the continent.

This is important to consider because this also determines the power output of your solar array. In other words, a system might have a peak power of 6.6 kW in one place but the same system might only produce 5 kW in another.

3. Other factors specific to your home

These include the tilt and orientation of your roof as well as any shading and other environmental factors. Again, these are factors that play a role in how much power your solar system will be able to produce.

Generally, though, you’ll want to avoid south-facing panels because this setting gets you the least power output. The tilt of solar panel systems also depends on where they’re installed but 10-30 degrees is a safe bet in Australia.

A good installer should be able to factor in all these specifics to deduce the inverter size that’s best for you and your home. If you’re having trouble looking for one, we have a network of pre-vetted installers that you can use. We can get you 3 FREE quotes from them right away.

Should you oversize or undersize your inverter?

Well, that depends. Here’s a closer look at their pros and cons so you can decide what’s best for you.

Oversized inverters

The pros and cons of Oversized Inverters of solar panels. A graph shows Australian conditions.
The pros and cons of an oversized solar inverter.

Oversizing your inverter prepares you for upgrades in the near future. So, if you installed a 6 kW array and a 7 kW inverter now, you’d have about 1 kW of wiggle room if you want to expand your solar system in the future.

Another benefit is that your solar inverter won’t be as stressed when your panels are producing their maximum power output. Meaning, it might just last a few years longer.

Consequently, a solar inverter that’s far larger than your array capacity won’t be as efficient. Meaning, you won’t get all the power your solar panels produce and you won’t be maximizing your savings.

And, truth be told, not many Australians add more solar panels to their existing solar systems. Solar technology is moving so fast that your inverter might not be compatible with newer solar panels by the time you decide to expand your system.

Recommended: Should I get more solar panels than I need?

Undersized inverters

Graph showing some of the pros and cons of Undersized Inverters for solar panels. An important consideration when installing a solar system.
The Pros and Cons of Using Undersized solar inverters in Australia.

The best thing about a smaller inverter size is savings. For one, it’s cheaper so you save on upfront costs. Moreover, solar inverters are at their most efficient when they’re operating at near maximum capacity.

For example, let’s say you have a 6 kW system but due to geographical factors and shading, it only produces an average of 5 kW. In this case, an undersized inverter would make sense. A 5 kW inverter won’t cost you as much as its 6 kW counterpart and it functions more efficiently.

That being said, the drawback is that downsizing too much will result in power clipping. This is where your array produces more power than your solar inverter can handle. The losses in total power output eventually outweigh the savings you made upfront.

This brings up the question:

How undersized can a solar inverter be?

There are 2 ways to look at this:

  1. From your installer’s standpoint, and
  2. From your savings standpoint

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Your installer will base his recommendations on the array-to-inverter ratio.

A table that shows a sample of the array-to-inverter ratio.
A table that shows a sample of the array-to-inverter ratio.

To calculate the array-to-inverter ratio, divide the DC rating of your solar array by the AC rating of your inverter. So, if you had a 10 kW array and a 10 kW (10,000 watts) inverter, you’d get a ratio of 1.

That being said, downsizing your inverter is going to increase that ratio. For example:

  • Solar array = 10 kW
  • Solar inverter = 8 kW (8000 watts)
  • Array to inverter ratio = 1.25
An example graph that illustrates the calculation of the array-to-inverter ratio.
A graph that illustrates the calculation of the array-to-inverter ratio.

To minimize clipping (and therefore maximize your power output), your installer will typically only recommend combinations that get you a ratio of less than 1.55.

You can save more if your array capacity isn’t any larger than 33% of your inverter’s.

Relationship between Inverter Capacity, Solar Array Capacity, and Potential Savings
A table that displays the correlation between inverter capacity, solar array capacity, and potential savings.

Meaning, if you had an 8000 watts solar inverter, your array should not be larger than 10.6 kW. Here’s how I computed that:

  • 33% of 8000 watts = 2640 watts
  • Maximum size of solar array = 8000 watts + 2640 watts = 10,640 watts (10.6 kW)

The reason you save more money this way is that this is one of the requirements of the Clean Energy Council. If you go over this, your system won’t be eligible for rebates which significantly increases the upfront cost of your installation.

FAQs:

What size solar power inverter do I need?

The right size solar inverter for you will depend on the size of your solar array, where you live, and other environmental factors. Though, as a rule of thumb, you won’t go wrong with matching your inverter capacity with the capacity of your solar array.

What happens if inverter is too big?

If your inverter is too big, it won’t function as efficiently as it could so your system performance suffers. It does, however, give you more wiggle room if you decide to add more solar panels in the future.

What are the different types of inverters for home use?

The 4 main types of inverters for your home include string inverters, micro inverters, power optimizers, and hybrid inverters.

Conclusion

To get the most out of your entire solar system, pairing your solar array with the right inverter size is crucial. And while many factors come into play when choosing the best solar inverter for your home, here’s a summary of what you should consider:

  • Rule of thumb: You will need an inverter that roughly matches the capacity of your solar panels.
  • If you choose to undersize, you spend less money while gaining better efficiency but an inverter that’s too small also results in power clipping that might outweigh your savings.
  • If you choose to oversize, you spend more money upfront but open up the option to add more solar panels in the future. The catch is the likelihood of lesser efficiency.

If you need help choosing the right solar inverter and solar panel combination, our network of pre-vetted installers can help.