Microinverters vs. string inverters: Which is right for you?

Inverters are the unsung heroes of solar energy systems. Without them, you wouldn’t be able to harness the power of your solar panels to power your home. Solar panels generate direct current (DC) electricity, but most home appliances require alternating current (AC) electricity. Inverters take the DC electricity from your solar panels and convert it to AC electricity usable for your home. 

There are a few different types of solar inverters: String inverters, microinverters, and optimized string inverters (power optimizers + string inverters). Each type caters to different setups, and choosing the right type of inverter for your solar panel system can make a big difference in its cost and performance. 

Usually, your installer will recommend a certain type or brand, but being an informed shopper can help ensure you're getting the right equipment. We'll help you figure out which one is best for your solar panel system.

Solar companies have used string inverter technology for decades. It's an incredibly reliable, tried-and-true technology and is the most affordable option available today. String inverters work best for those with relatively simple roofs that get lots of direct sunlight

Centralized DC to AC conversion

• Easier system maintenance with no electronics on the roof

• Most affordable option

• Only offer string-level monitoring

How it works

In a string inverter setup, an installer will arrange your solar panels into groups connected by wires referred to as a "string”. Multiple strings of panels will then be connected to a single inverter, which is called a centralized inverter. This transforms the DC electricity produced by the panels into usable AC electricity for your home or business.

The main downside of a string inverter is that every panel connected to a string is limited to the output of the weakest panel. Modern solar inverter and panel technology allows individual panels to continue producing power even if a part of the panel is shaded, but without module-level power electronics, string inverters can only optimize power output at the string level, not at the individual panel level. 

String inverter systems aren't the best solution for homes prone to shading throughout the day, as linked panels are limited to the output of the weakest panel (whether due to being partly in the shade or any performance issues). However, their ease of installation and lower prices make them attractive to homeowners and installers.

Microinverters utilize module-level power electronics (MLPE) and are by far the most popular type of inverter on the EnergySage Marketplace, even though they're also usually the most expensive. 

Panel-level DC to AC conversion and optimization

• The power output of each panel is optimized independently

• System size can be expanded easily in the future

• Electronics are all located on the roof

How it works

Unlike string inverters, which convert DC power into AC power for a group of connected panels, microinverters are connected to each individual panel.

Installers usually mount the microinverters onto the back of the solar panel, but they can also be placed next to the panel on your solar racking system.

As a result, microinverters allow you to monitor the performance of individual solar panels.

Power optimizer systems offer many of the same benefits as microinverters and are often a compromise between microinverters and standard string inverters.

Centralized DC to AC conversion + panel-level optimization

• The power output of each panel is optimized independently. Total output isn’t limited by lower-performing panels. 

• Provide both system and panel-level monitoring

• Future system size increases may require an additional central inverter

How it works

Like microinverters, systems with power optimizers have MLPE components. They reduce the impact of shading on panel and system performance, as well as offer panel-level performance monitoring.

Optimized string inverters are able to manage power generation on a panel-by-panel basis, similar to microinverters, but they then send the power to a string inverter to convert the DC power into AC power collectively. 

While optimized string inverters optimize panel output independently, they still convert electricity centrally. Instead of converting the DC electricity to AC electricity at the panel site, they "condition" the DC electricity and send it to a string inverter for conversion.

If your roof experiences shade during the day, the panel-level optimization afforded by power optimizers often results in higher system efficiency – and a better long-term return on your investment – than using a string inverter alone.

If you have a south-facing roof with a single plane and no shade, save some money by choosing a string inverter.

In reality, most roofs aren't that simple. You'll probably want some level of panel-level optimization, but it might not need to be one-to-one microinverters or optimized string inverters. Some microinverters can convert power from four panels instead of just one, which can save you some money.

Why panel-level optimization is often worth it

Here are some reasons you might choose inverters with panel-level optimization.

1. They help improve performance for solar panels on complicated roofs or roofs that experience shade during the day.

2. They can monitor the performance of individual solar panels, meaning you can assess the number of kilowatt-hours (kWh) one solar panel in your array produces versus another.

3. If one microinverter stops working, the entire system's performance isn’t ruined. 

Microinverters vs. optimized string inverters: How do they differ?

Microinverters and optimized string inverters provide many of the same benefits, but they're not the same things. Here are the biggest differences:

Microinverters convert electricity at the panel level

Microinverters convert DC energy into AC energy right at the panel site (typically on the roof). Power optimizers sit behind a solar panel, but they don't convert the electricity independently; the power is still sent to a centralized inverter located elsewhere on your property, like a garage or an attic.

Instead, optimizers "condition" the DC energy and send it to a central inverter that finishes the conversion process. The conditioning process smooths out varying DC voltages generated by the panels so that the centralized inverter can more efficiently convert it to AC energy. However, if your central inverter breaks, it takes down your whole system.

Microinverters often come with better warranties

Both microinverters and power optimizers typically come with 25-year warranties. However,  power optimizers must be paired with a centralized inverter, which typically has a shorter warranty period (around 10 to 12 years). Installers sometimes offer an extended warranty on the centralized inverter, either as part of their package deal or at an additional price.

It can be easier to fix or replace optimized string inverters

Replacing a failed microinverter or a power optimizer on a roof will likely cost more than replacing a string inverter on a ground-level wall, given the labor required to access and work up on your roof. However, no need to worry if your inverter has a strong labor warranty.

Microinverters can limit your battery storage setup

Both microinverters and power optimizers are compatible with battery storage. But, depending on whether you want a DC or AC-coupled battery solution, you may need to use a particular type of inverter. Microinverters typically only work with AC-coupled batteries, for example. It’s best to check with your installer or electrician about which inverters work best with your battery of choice.

Ultimately, you want to pick an inverter that enables your solar panel system to perform well without breaking the bank. Talking to your installer about the inverters they offer and what they think will be the best fit for your system is the perfect place to start.

It's important to remember that microinverters and optimizers aren't the only available options. String inverters are the way to go if you're looking for the most wallet-friendly option and have a south-facing roof with little shade. But if your roof is more complicated, microinverters or power optimizers could significantly increase your savings with solar down the line.