What Size Solar Inverter Do You Need for Solar Panels?

When you install a solar system, picking the right size for your solar inverter is really important.

You may have heard about making your solar system “oversizing” or “undersizing” than your inverter, but what does that actually mean?

The size of a solar inverter is measured in watts (W) and tells you the maximum power it can handle. Usually, your inverter should match your solar system’s size.

But often, people choose a bigger solar system than the inverter. This can make things more efficient, but you have to make sure it’s not too big compared to the inverter.

That’s why sometimes you see systems like a 6.6kW solar setup with a 5kW inverter. It’s really important to get this balance right.

If it’s too far off, it might not work as well and could even affect whether you qualify for certain solar power benefits from the government.

Also, if your solar system is connected to the power grid, you need to think about how much power you can send back to the grid.

This varies depending on where you live. Some inverters can control this, but not all of them can, and it’s not possible in every area.

We made this guide to help you understand all about sizing your solar inverter right, so you can make the most of your solar investment.

How to Determine the Solar Inverter Size?

While the size of your solar array is a key determinant in choosing an inverter, other factors like your geographical location and specific installation conditions also play a significant role.

It’s important to consult with professionals and use manufacturer guidelines to ensure your inverter is appropriately sized for your solar system.

1. Size of Your Solar Array:
   • The most important factor is the size of your solar panel system.
   • The inverter needs to handle all the power your solar panels produce.
   • Typically, the inverter size should be close to your solar system’s DC rating. For example, a 6 kilowatt (kW) system will likely have an inverter around 6000 watts (W), give or take a bit.
2. Manufacturer Guidelines:
   • Inverter manufacturers provide guidelines on which solar array sizes their products work best with.
   • If you pair their inverter with a solar array outside these recommendations, it might void the warranty.
3. Geography:
   • Your location affects solar panel production.
   • For example, a 6 kW system in Arizona (with more sunlight) will produce more power than the same size system in Vermont.
   • In sunnier and moderate-temperature areas, inverters are often sized closer to the solar array’s total wattage to handle more power. In areas with less sun or where panels are less efficient due to heat, a smaller inverter might be enough.
4. Site-Specific Conditions:
   • How and where your solar array is set up affects its electricity production.
   • Factors like tilt angle, direction (azimuth), shading, and environmental conditions (like dust) impact how much power your panels generate.
   • Solar installers consider these factors and equipment efficiencies to estimate your system’s real-life output, different from standard testing conditions in a lab.
   • Systems with higher derating factors (like those with more shade, non-optimal tilt, or eastward facing) don’t reach maximum energy output and can work with smaller inverters compared to the array size.

How to Calculate The Solar Inverter Size You Need

Staying within the optimal ratio range ensures that your system operates efficiently without overloading the inverter.

Calculating the right size for your solar inverter involves a couple of straightforward steps.

Here’s how you can do it:

Check the DC Rating:

The DC rating of your solar panels is a good starting point.

Typically, this rating is similar to the inverter’s AC output capacity.

The DC rating represents the maximum amount of DC (Direct Current) power your solar panels can produce under optimal conditions.

Understand the Array-to-Inverter Ratio:

This ratio shows the relationship between your solar panel system’s DC rating and the inverter’s maximum AC (Alternating Current) output.

It helps to understand how well the inverter can handle the power produced by the solar panels.

Calculate the Array-to-Inverter Ratio:

To find this ratio, divide the DC rating of your solar panel array by the inverter’s maximum AC output.

For instance:

• If you have a 3 kW solar panel system (3000 watts DC) and a 3,000-watt inverter (3000 watts AC), your calculation is 3000 (DC) ÷ 3000 (AC) = 1.
• For a 5 kW system (5000 watts DC) with a 3,800-watt inverter, it’s 5000 ÷ 3800 = 1.32.
• With an 8 kW system (8000 watts DC) and a 5,000-watt inverter, it’s 8000 ÷ 5000 = 1.6.

Ideal Ratio Range:

Most solar systems have an array-to-inverter ratio between 1.15 and 1.25.

As long as your ratio is below the recommended maximum of 1.33, your solar system should be operating efficiently.

Most Common Solar Inverter Size

Oversizing Your Solar Array

Oversizing the solar array, also known as ‘overclocking the inverter,’ involves using a solar inverter with a lower wattage than the capacity of the solar panel system.

This practice, common in solar PV system installations, enhances efficiency and performance.

Solar panels usually operate below their maximum DC rating, which is why a smaller inverter compared to the array size is often sufficient.

Many inverter manufacturers endorse this approach, assuring its safety and efficiency.

Inverters operate most efficiently at high capacities, and any extra power beyond their capacity is safely ‘clipped’ without causing damage.

Despite seeming counterintuitive, appropriately oversizing the solar array maximizes power generation throughout the day, adapting to the fluctuating levels of daylight.

The strategy aims to reduce the time the inverter operates at low efficiency.

By using a lower-capacity inverter, it reaches its optimal efficiency zone quicker and maintains it for longer periods, thus generating more power, even during peak times when ‘clipping’ occurs.

Most states impose a 5kW limit on power export for grid-connected solar systems. This restriction discourages the installation of larger inverters unless the system includes infrastructure like solar battery storage to utilize the increased output.

Additionally, a smaller inverter is less costly, leading to upfront hardware savings and a shorter solar payback period due to enhanced efficiency.

Regulations allow oversizing a solar array up to a ratio of 1.33, meaning a 5kW inverter can support up to a 6.6kW system. This limit ensures that solar installations effectively contribute to carbon emission reduction.

Undersizing Your Solar Array

Undersizing a solar inverter, in contrast to oversizing, means choosing an inverter that has a lower capacity than the total potential output of the solar panel array.

Essentially, the inverter is not powerful enough to handle the maximum electricity the solar panels can generate under optimal conditions.

Undersizing can be problematic.

If the solar panels are producing more electricity than the inverter can convert, the excess power is not used.

This leads to a loss of potential energy, as the system is not able to utilize all the power generated by the solar panels.

An undersized inverter can become a bottleneck for the system.

Even if the solar panels are performing well, the system as a whole can’t operate at full efficiency due to the inverter’s limitations.

Moreover, consistently operating an inverter at its maximum capacity can lead to increased wear and tear. This might reduce the lifespan of the inverter and potentially lead to more frequent maintenance or replacements.

While an undersized inverter might initially cost less, the loss in potential energy generation can mean lower returns on your investment over time.

The system is not optimized for maximum energy production, which can affect the overall cost-effectiveness of the solar installation.