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String inverters vs. power optimizers vs. microinverters

Last updated 7/16/2020

energy flow from solar panels to a home

If you are considering a solar panel system for your home, one of the key decisions you need to make is the type of inverter to install. Inverters convert direct current (DC) electricity generated by your solar panels into usable alternating current (AC) electricity. Given the complex power electronics and software contained within, inverters are vital to the success of your solar power system.

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Breaking down solar panel inverter technologies: string inverters, power optimizers, and microinverters

There are three types of inverters that are currently available to you for your solar energy system: string (also known as centralized) inverters, power optimizer systems (also known as string inverters + power optimizers), and microinverters. Microinverters and power optimizers are often collectively referred to as “Module-Level Power Electronics” or MLPEs.

String inverters are by far the most commonly deployed option globally and comprise the vast majority of the world’s inverter market, especially for larger scale systems. However, MLPE technologies have gained in popularity and market share over the last five years as their costs have come down.

Key takeaways: String inverters, microinverters & power optimizers
  • Inverters convert the DC electricity that your solar panels produce into appliance-friendly AC electricity.
  • The three main inverter options available for residential and commercial solar installations are string inverters, microinverters and power optimizer systems.
  • Historically string inverters are the most commonly installed worldwide.
  • Microinverters and power optimizer systems are typically more expensive than string inverters.
  • Microinverters and power optimizers allow you to monitor the power production of each individual panel.
     

String inverters

string inverter diagram

String inverters are the most cost-effective inverter option available in the U.S. Traditionally, solar installation companies generally offered systems with string inverters if your roof had limited shading throughout the day and did not face in multiple directions (such as a gabled roof). However, recent hardware and software updates from the major string inverter companies now make them applicable in a wider set of circumstances.

How String Inverters Work

Your solar panels are arranged into groups connected by “strings”, hence their name. Multiple strings of panels can be connected to a single inverter, which transforms the DC electricity produced by the panels into appliance-friendly AC electricity.

String inverter technology has been used for decades. It is a very reliable, tried-and-true technology, though may not be suitable for certain types of installations. Although modern solar 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. This means string inverter systems may not be right for homes that are prone to shading throughout the day. However, their ease of install and lower price point make them attractive to many homeowners and installers.

One of the most common reasons for individual solar panels to produce less power or stop producing power altogether is shading from nearby objects. If your roof is prone to shading 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 where they will not be shaded.

Compare your inverter options

EnergySage’s database of solar reviews has comprehensive information about specific installers, financiers, and equipment manufacturers, including manufacturers of string inverters, microinverters, and power optimizers. If you are looking for a review of MLPE technologies, EnergySage has also developed a comprehensive comparison of micro-inverter and power optimizer options.

Power optimizers

power optimizer diagram

Power optimizers, a type of module level power electronics, offer many of the same benefits as microinverters (as seen below), but tend to be slightly less expensive. Power optimizers are often considered a compromise between more expensive microinverters and the standard string inverter.

How Power Optimizers Work

Like microinverters, power optimizers are devices located at each panel. 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. In scenarios where your roof is shaded, the panel level optimization afforded by power optimizers results in higher system efficiency than using a string inverter alone.

Similar to microinverters, power optimizers reduce the impact of panel shading on system performance, and also offer panel-level performance monitoring. Systems that use optimizers are often more affordable than those that use microinverters.

Microinverters

microinverter diagram

Microinverters, another form of module level power electronics, are gaining popularity, particularly for residential solar systems. Microinverters tend to be more expensive than string inverters or power optimizers, however recent declines in their costs have made them a more competitive option.

How Microinverters Work

Microinverters are installed on each individual panel in a solar energy system. They convert the DC electricity from your solar panels into AC electricity on your roof, with no need for a separate central inverter. In many cases the microinverters are mounted onto the back of the solar panel itself, but they may also be mounted next to the panel on your solar panel racking system.

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

Find a complete list of MLPE manufacturers in our article about microinverter and power optimizer options.

How “smart modules” use micro-inverters and power optimizers

Increasingly, microinverter and power optimizer manufacturers are partnering with solar panel manufacturers to create “smart modules.” Simply put, a smart module is a solar panel with a piece of MLPE equipment already integrated into it. This simplifies installation and cuts down on labor costs for installers. Many of the world’s biggest panel manufacturers now have smart module options available, including LG, Panasonic, and SunPower.

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