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Module 6: Sizing Your Inverter for Your Solar Power System

You’ve made it to the final step in sizing a solar power system, which is choosing the right power inverter. 

At this point, you know how much power you use, how big your battery bank needs to be, and how many solar panels you should aim for. 

As mentioned in previous modules, your inverter is the component that ties everything together, converting stored DC power into usable electricity for your home, devices, and appliances.

In this final lesson, we’ll break down exactly how to size your inverter so your system actually performs as you want it to. By the end of Module 6, you’ll know:

• Why inverter sizing is important
• How to calculate your inverter power requirements
• How to choose the right voltage and capacity
• What to look for if you plan on expanding your system in the future

Let’s get started.

Why Sizing Your Inverter is Important

The inverter is the bridge between your solar power system and your electrical loads. You can almost think of it as the heart or brain of your system.

It converts the DC (Direct Current) electricity generated by your solar panels into the AC (Alternating Current) electricity that your home appliances and portable devices can actually use. 

If your inverter is too small:

• You won’t be able to run all of your devices and appliances at the same time
• Your system may shut down when you push it beyond its rating
• You’ll limit what you’re able to add in the future.

If your inverter is oversize, you’re just paying more money than you need to.

How to Size Your Power Inverter: Four-Step Method

It sounds complicated, but sizing an inverter can be a straightforward process. 

If you remember the information we covered in the previous lessons, you can size your inverter by following these four simple steps: 

Step 1: Calculate Your Total Power Consumption (in Watts):

Start by determining how much power you need to run at the same time.

This combined wattage of all of your appliances and devices is a crucial number you’ll need to size your inverter, just like it was when you sized your batteries.

If you need help calculating the total wattage of all of your electrical loads, we recommend re-visiting our Power Consumption Calculator.

Let's say you used our calculator and came up with a total power consumption of 1,700 watts. This would be the minimum continuous output your inverter would have to be able to support. 

If you don’t take the time to do this step correctly, there’s a good chance your system won’t be capable of running everything at the same time, which can be frustrating and limiting in real-world situations.

The size of your battery bank will also influence the size of your inverter. We already discussed how this can be calculated in Module 2, but if you need a quick refresher, check out our video: Sizing Battery Capacity for Your Solar Power System

Step 2: Check Your Solar Panel Array Size (in Watts): 

Next, look at the size of your solar panel array. This is the total wattage of all of your solar panels combined together, which you should know by now if you worked through Module 5. 

Let’s say your combined solar array is 2,500 watts, you would want an inverter that could accept at least 2,500W of solar input. 

If you do not have an inverter that can handle this, some of the power your solar panels generate will be wasted. 

⚡Solar Lab Tip: Oversize Your Inverter’s Solar Input

Just like we recommended oversizing your solar panel array, we also suggest oversizing your inverter’s solar input. 

Not only will this ensure that the solar power you panels generate actually ends up in your batteries, it will make it easier to expand your solar panel setup in the future.

Step 3: Determine Your Voltage Requirements (120V vs. 240V): 

Most household appliances and devices run on 120V, but some larger appliances need a 240V input, including:

• Central air conditioners and water heaters
• Washing machines and dryers
• Power tools and some well pumps
• EV chargers
• Electric ovens

Check your appliances ahead of time and consider what you realistically need to run during a power outage. 

Most backup systems will be fine with a power inverter that outputs 120V, but those looking to build a whole home solar power system will need to choose a split-phase inverter that is capable of output both 120V and 240V. Knowing what you need ahead of time can save you a serious headache. 

If you are looking to purchase a portable power station, knowing their output voltage is just as important. 

Most of the smaller and mid-sized units just output 120V, but there are models that have split-phase capabilities, like an Anker SOLX F3800 Plus or EcoFlow DELTA Pro 3

Step 4: Choose the Right Inverter Size

Once you know your power needs, the size of your solar panel array, and your voltage requirements, you can choose an inverter.

Example Inverter Selection

Let’s say that you calculated your total simultaneous load to be 1,700W and you only needed 120V right now. A basic 3,000W inverter would be a smart choice. 

In this scenario, something like an EG4 3000W All-in-One Inverter could be a good fit because it would give you:

• Headroom for startup surges (appliances often surge higher than their continuous wattage when they are first firing up)
• Room for future expansion
• Less strain on the inverter during day-to-day use

Something like that beginner-friendly EG4 inverter would also be a good option because it has a robust 5,000W solar input, which would allow you to build a relatively large solar array. 

You’d also have the option to stack more than one of these inverters to increase your solar input, output power, and even your voltage, as two units wired together enables a 240V output. 

⚡Solar Lab Tip: Oversizing is Usually Cheaper in the Long Run

While smaller components and power stations are almost always cheaper than units with higher input and output ratings, it can be more cost effective to buy bigger components than you need in the beginning, rather than risking needing to replace them in the future. 

You can also save yourself some trouble by choosing an inverter that is stackable, meaning you can wire it together with additional units to increase your output, input, and even voltage.

Grid-Tied vs Off-Grid vs Hybrid Inverters

If your goal is to sell excess solar power back to the grid, you’ll need a grid-tied inverter. Keep in mind that many places are phasing out or reducing incentives for this, so you’ll want to check the policies where you live.

For example, California's NM 3.0 Program has significantly reduced the payments for solar power fed back into the grid. 

For most people, an off-grid or hybrid inverter will be a good choice. If you want to build a fully independent backup or emergency power system, going with an off-grid inverter would work.

If you want a backup power system, but still want to retain the option to charge your batteries with AC power from the grid at night or when the sun isn’t shining, you’ll want to choose a hybrid inverter. 

⚡Solar Lab Tip: Think About Future Expansion Possibilities 

Even if you’re unsure if you’ll expand your system in the future, choosing an inverter with a higher solar input and output capacity can be a good option (within reason). While solar panels are relatively cheap, batteries and inverters are fairly expensive, so you’ll want to avoid needing to replace them in the near future. 

Inverter Sizing Doesn’t Have to Be Complicated 

Sizing an inverter doesn’t require serious electrical experience. Instead, you just need three key numbers:

• Your simultaneous power load (how much power everything you want to run would need to run at the same time)
• Your solar array wattage (the total amount of power all of your solar panels would output if they were running at maximum efficiency)
• Your voltage requirements (whether you will just run 120V appliances, 240V loads, or both)

If you choose an inverter that exceeds your exact current needs, you’ll likely have a system that’s reliable, expandable, and future-proof enough to last for many years. 

You Completed Our Guide to Solar Power Systems!

At this point, you know how to:

• Calculate your power usage
• Size your battery bank
• Build a solar panel array
• Choose the right inverter

You now have the foundational knowledge to design and purchase a real solar power system with confidence (and without getting ripped off). 

If you want to crunch your own numbers, or you just need a quick reference sheet, we have a solar cheat sheet and worksheet below.

Don't forget to bookmark these pages for future reference. We also highly recommend downloading your free PDF version of the course. Not only will this allow you to access the material offline, you'll also get a complimentary Solar Power Cheat Sheet with all of your formulas in one place, and a worksheet you can use to fill in your own numbers.