Inverters are often described as the “brains” of a solar power system. These devices communicate between your solar panels and your home, converting DC (Direct Current) power generated by your panels into AC (Alternating Current) used to run your appliances.

Two main types of inverters live at the heart of most solar power systems: micro-inverters and string inverters, with legitimate advantages and use cases for both.

What is a String Inverter?

A string inverter is a central unit with connection hubs for a “string,” or group, of solar panels. Typically, 6-12 solar panels are connected to one inverter, depending on the wattage of the panels and the capacity of the inverter.

For larger systems, additional string inverters can be added, with the number of solar panels equally balanced between strings for best performance.

What is a Micro-Inverter?

In direct contrast, micro-inverters are small, dedicated inverter units that connect to each solar panel in your system. A 12-panel system would come with 12 micro-inverters, each controlling the output of a single panel, functioning independently from the rest of the system.

Advantages of String Inverters

Simple and Cost-Effective

The main appeal of string inverters is their cost and simplicity. There are far fewer parts in string inverter systems, translating directly to lower costs and a much less complicated installation process.

The simple design also reduces the potential failure points in the system. With fewer parts, there are fewer opportunities for something to malfunction down the line.

In ideal conditions, string inverter systems can perform on par with micro-inverter systems, saving homeowners thousands of dollars on their solar project. They’re a great pick for wide-open systems exposed to complete sunlight.

Long Cabling Runs

Another advantage is the ability to better transmit power over very long cabling runs (300+ feet).

In solar power systems, some of the power generated is lost due to resistance in the wires. String inverters mitigate this by driving high-voltage DC from the array to the inverter. The higher voltage DC is more efficient at conserving power through the cabling run.

String inverters really shine in situations where there’s plenty of open space to build your array, like off-grid or rural properties. You can build a ground-mounted string inverter system anywhere on your property and run the cables back to your home without worrying about efficiency losses along the way.

Drawbacks of String Inverters

Requires Full Sun Exposure

You may have noticed the phrase “ideal conditions” doing some heavy lifting in that last section.

String inverters work best in situations where your solar panels will have full exposure to the sun. Once you start to encounter shade from trees, snow coverage, and other obstacles that can block sunlight from hitting the panels, their performance can start to suffer.

That’s because the output of solar panels in a string are linked together, and the entire string can only produce as much as the weakest panel in a string. So if shade covers one panel and halves its output from 400W to 200W, the entire string of panels drops to 200W as well, effectively cutting your system performance in half.

While the technicalities are beyond the scope of this article, the simple takeaway is that string inverter systems are designed for 100% exposure to sunlight.

While you can buy dedicated power optimizer units for string inverter systems, we find that micro-inverters are better suited for shade mitigation. (See our comparison of power optimizers vs. micro-inverters at the end of the article.)

Advantages of Micro-Inverters

Efficient and Flexible

Micro-inverters solve the inherent design flaw of string inverter systems by isolating the output of each individual solar panel. Every panel is paired with its own micro-inverter, allowing them to operate independently from the rest of the system.

If one panel suffers a drop in production due to shade or faulty equipment, the rest of the system will continue to perform at full capacity. This is a massive boost to the overall performance and reliability of your system where sun obstruction is a concern.

Do you have large trees or neighboring buildings that will cast shadows on your panels throughout the day? Do you expect heavy snow, dust or debris to cover your panels regularly? In scenarios like these, micro-inverters are the ideal pick.

Expandable

The modular nature of micro-inverter systems make them easy to expand should you require more power down the line. You can simply add another panel+micro-inverter (as many as you need) if your energy usage habits change.

String inverter systems are not nearly as expandable. Because the number of panels needs to be equal in each string, you’ll be forced to add an entire new string of panels, or rearrange your existing strings to balance them.

And that’s not to mention the limited inverter capacity. Adding more panels might put you over the threshold your current inverter can handle, forcing you to add another inverter into the mix.

Expanding string inverter systems often leads to a complete re-design from the ground up. Micro-inverters make it much easier to grow (or shrink) your system as needed.

Drawbacks of Micro-Inverters

Higher Initial Cost

For their improved performance and flexibility, micro-inverters come with a higher up-front price tag. Though you’ll have to budget more for your purchase, it’s well worth it in situations where you’re battling shade issues. The improved efficiency in shaded conditions should do more than enough to offset the initial price difference over time.

A Middle Ground: String Inverters With Power Optimizers

We should mention another option that serves as a sort of middle ground between the two: string inverters with power optimizers. If you need to mitigate shade issues, but are insistent on a string inverter system, you can add power optimizers to your panels.

These units accomplish some of the same things as micro-inverters, like per panel power optimization, rapid shutdown, and monitoring. They’re designed to bring string inverters up to speed in less-than-ideal conditions.

These systems come with the same design limitations as any string inverter system. Panel strings need to be balanced, and expansion is a pain due to inverter sizing restrictions. But they do have a use case. If you need the long DC cabling run of a string inverter system, but also need to solve shade issues, power optimizers could be the way to go.

Need Help With Your Solar Project?

Not sure which inverter setup is best for your system? Reach out to our expert design team for help. We’re happy to answer any questions you have on your quest to go solar.