String inverters vs. Power optimizers vs. Microinverters

As you consider a solar panel system for your home, you and your installer must determine what type of inverters will work best for your home solar system. Inverters convert the direct current (DC) electricity your solar panels generate into usable alternating current (AC) electricity. Given the complex power electronics and software contained within, inverters are vital to the ongoing performance of your solar power system. 

Three major types of inverters are available: string inverters, power optimizers, and microinverters. Each has its best use case, and your installer will determine the correct choice for your system.

• Inverters convert your solar panels' direct current electricity into appliance-friendly alternating current electricity that your entire home uses.

• The three main inverter options for residential and commercial solar installations are string inverters, microinverters, and power optimizer systems.

• String inverters are the most commonly installed worldwide.

• Microinverters and power optimizer systems are typically more expensive than string inverters.

• Solar shoppers can use the EnergySage Marketplace to browse solar system components based on price, efficiency, brand, quality, and more.

Three types of inverters are currently available for your solar energy system: string inverters, power optimizer systems (also known as string inverters + power optimizers), and microinverters. Power optimizers and microinverters are often collectively called "module-level power electronics" or MLPEs.

String inverters are the most commonly deployed inverter option globally, making up most of the world's inverter market. However, MLPE technologies are increasingly gaining market share as their costs have steadily decreased.

String inverters are the most cost-effective inverter option available in the United States. Traditionally, a solar installation company would propose a string inverter for your system if your roof had limited shading throughout the day and did not face in multiple directions (such as a gabled roof). However, thanks to recent hardware and software updates from major string inverter companies, string inverters are now applicable in broader circumstances.

How string inverters work

In a string inverter setup, an installer will arrange your solar panels into groups connected by "strings" (hence their name!). You can connect multiple strings of panels to a single, centralized inverter, which transforms the DC electricity produced by the panels into usable AC electricity for your home or business.

Solar companies have used string inverter technology for decades. It's an incredibly reliable, tried-and-true technology, but as with your other inverter technology options, it may not be suitable for certain types of installations. Although modern solar inverter and panel technology allows individual panels to continue producing power even if a part of the panel is shaded, without module-level power electronics, string inverters can only optimize power output at the string level, not at the individual panel level. So, string inverter systems aren't always the best solution for homes prone to shading throughout the day. However, their ease of installation and lower prices make them attractive to homeowners and installers.
One of the most common reasons individual solar panels produce less power (or stop producing power altogether) is shade from nearby objects. If your roof experiences shade throughout the day or in certain seasons, you could either remove the source of the shade (e.g., cut down a tree) or install the panels in a sunnier space (e.g., ground mount or carport installation).

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

How power optimizer systems work

Like microinverters, systems with power optimizers have an individual optimizer component at each panel, the module-level power electronics (MLPE) component. However, 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 than using a string inverter alone. Like microinverters, power optimizers reduce the impact of panel shading on system performance and offer panel-level performance monitoring.

Microinverters, another form of MLPEs, are rapidly gaining popularity, particularly for residential solar panel systems. 

How microinverters work

Systems with microinverters typically have an individual installed on the back of each solar panel. They convert the DC electricity from your solar panels into AC electricity on your roof without a separate string inverter. In most cases, installers mount the microinverters onto the back of the solar panel, but they can also place them next to the panel on your solar racking system.

Microinverters take MLPE to the logical conclusion: While power optimizers aggregate the electricity from your panels and send it to a string inverter for the DC to AC conversion, microinverters make the DC to AC inversion right at each solar panel. As a result, like with power optimizer systems, microinverters also allow you to monitor the performance of individual solar panels.

Similarities between microinverters and power optimizers

Let's start with the similarities between microinverters and power optimizers:

1. Microinverters and power optimizers help improve performance for solar panels on complicated roofs or roofs that experience marginal shading during the day.

2. Both microinverters and power optimizers 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. Typically, solar companies install one MLPE (i.e., microinverter or power optimizer) on the back of each solar panel, so if your system has 20 solar panels, that often means 20 microinverters or 20 power optimizers.

Key differences between microinverters vs. power optimizers

While microinverters and power optimizers provide many of the same benefits, the two technologies also have many differences, as explored in greater detail below:

1. Where direct current (DC) converts to alternating current (AC)

Microinverters convert DC energy into AC energy right at the panel site. While power optimizers sit behind a solar panel, they don't convert the electricity independently; instead, optimizers "condition" the DC energy and send it to a central inverter that finishes the conversion process. The conditioning process fixes the voltage of the DC energy so that the centralized inverter can more efficiently convert it to AC energy. 

2. Warranty

Both microinverters and power optimizers come with 25-year warranties. However, while warranties cover optimizers for 25 years, the centralized inverter they pair with often has a shorter warranty (typically 10 or 12 years). Installers sometimes offer an extended warranty on the central inverter, either as part of their package deal or at an additional price.

Additionally, it's essential to closely examine what a company's warranty terms include (and what they don't!). Does the company cover installation labor, replacement, and shipping parts? And what is the claim process like for getting a warranty processed? These are essential considerations when choosing the type of inverter to install on your property.

3. Maintenance

Over the lifetime of microinverters and power optimizer systems, you need to consider if and how many times they'll fail, as well as the impact of an unlikely failure on the production of your solar panel system. If an individual inverter fails, replacing a 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 on your roof. However, no need to worry if your inverter has a strong labor warranty!

4. Battery options

Both microinverters and power optimizers are compatible with battery storage. However, depending on whether you want a DC or AC-coupled battery solution, you may need to use a particular type of inverter. If you're considering battery storage, talk to your installer or electrician about which inverters work best with your battery of choice.

Which is the right option for your system?

Microinverters and power optimizer systems have similar efficiencies, monitor individual panel performance, and can help maximize energy production on slightly shaded or complicated roofs. But your preferences will ultimately determine which option is best for your home. Talking to your installer about what 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.

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