String inverters: What you need to know

Inverters are an essential part of any solar panel system – they convert direct current (DC) electricity produced by your solar panels into usable alternating current (AC) electricity. There are a few different types of inverter technologies to consider. String inverters are a tried-and-true inverter technology and one of the oldest options available in the market today.

A string inverter system aggregates the power output of groups of solar panels in your system into "strings." Multiple strings of panels then connect to a single inverter where electricity is converted from DC to AC electricity. This single inverter is typically located in an electronics box that's placed on the side of your house or in your garage. Because panels are connected in strings to the inverter, if one or more panels are underproducing energy (due to shading, dirt, or some other factor), the output of the rest of the panels on that string will be reduced.

A string inverter is typically capable of handling multiple strings of panels attached to it. For example, you may have three strings of five panels each, for a total of fifteen panels on a single string. The size of the string inverter in kilowatts (kW) and the wattage of the solar panels you use will determine how many panels you can string to one inverter without wasting energy. To learn more about solar inverter sizing, check out our blog on the topic.

String inverters are an effective, affordable solution for many solar installations. The solar panel systems that are best suited for string inverters have little to no shading and panels that are on fewer than three separate roof planes. In these scenarios, you don't have to worry about any reduced output on an individual string due to shading, while the ability to connect multiple strings to the same central inverter affords some flexibility in the direction the different strings of panels are facing.

String inverters may not be right for every solar panel installation; similarly, it's not always worth it to pay a premium for power optimizers or microinverters, especially if your home is ideal, or close to ideal, for solar. String inverters are a proven, durable and affordable technology that is worth considering during your solar shopping journey.

When comparing string inverter options, there are a couple of main metrics to keep in mind:

Efficiency

Just like solar panels, string inverters have varying efficiencies. An inverter's efficiency is a measure of how much energy is lost in the form of heat during the conversion from DC to AC electricity. Higher efficiency string inverters lead to higher overall system efficiencies and more solar electricity production.

Size

Solar inverter sizing depends on a number of factors, including the size of your solar array, your geographical location, and other site-specific considerations. Larger string inverters will generally be more expensive but may be worth it to maximize energy production.

Warranties

Product warranties cover problems like manufacturer defects and environmental damage to your inverter system. Check to see if your inverter's warranty term matches the warrantied life of your solar panels.

Price

Although they are not typically the most expensive component of a solar panel installation, it's still important to weigh the price you'll pay for a string inverter. Larger, more efficient string inverters with longer warranties may come with higher price tags but will still likely be less expensive than power optimizer or microinverter options.

Many manufacturers have string inverter products available. Here are a few of the biggest names in the category:

Fronius

Based in Austria, Fronius makes both residential and commercial string inverter systems. They offer three main lines of products: the Fronius Primo, Fronius Symo, and Fronius Symo Advanced series.

SMA

SMA is a German company with residential and industrial solar inverter system offerings. They have main string inverter series (Sunny Highpower, Sunny Tripower, and Sunny Boy) for residential applications and also offer larger central inverters and battery inverter products.

Sungrow

Another string inverter manufacturer option for residential and commercial rooftop solar energy systems is the China-based company Sungrow. According to their website, their string inverter solution has been installed for almost 70 gigawatts (GW) of solar worldwide as of mid-2018.

Delta

A Taipei-based manufacturer, Delta makes a number of energy-related products, including both residential and commercial solar inverters. Their M Series of transformerless, single-phase inverters are the preferred choice of Tesla.

The best way to ensure that your string inverter system is sized and installed appropriately is to work with a qualified, reputable solar installer. You can sign up on the EnergySage Solar Marketplace to receive multiple quotes online from pre-screened, vetted installers. These EnergySage Approved installers will use design tools to make sure your solar array and inverter are set up accordingly, given your electricity needs, solar equipment, property, and geography.