What are string inverter systems?
In the solar power industry, wiring sets of individual panels together is called “stringing”. A string solar inverter converts all of the direct current (DC electricity) in strings of panels into usable alternating current (AC electricity) your home appliances use.
String inverters are also known as “central inverters”. They have been around for decades, are affordable, and get the job done on most small-scale solar installations.
String inverters are best suited for rooftops with uniform southern exposure without any shading issues. That’s because, if a single panel were to become shaded, energy production for the entire string becomes limited by the output of the worst performing panel.
For example, say there’s a large oak tree that obscures one or two of your solar panels in the early afternoon. Because all the panels are tied together in a string, when those two modules are shaded, the output of the other panels will be negatively impacted. It’s sort of like having a hose with a kink in it. Even though there’s a lot of water pressure (electricity), not much juice comes out the other end.
There are a few advantages and drawbacks to using string inverters with your solar PV system. We cover them here so you can confidently proceed with your solar panel system design.
Advantages of string inverter systems
String inverters have a couple of notable advantages over other inverter systems. Here are some of them to consider:
String inverters are affordable. This is because manufacturers have had decades to make their operations more efficient, and you only need a single inverter for most solar installations, compared to microinverters and DC power optimizers, which are used behind every individual solar panel.
Compared to microinverters and DC power optimizers, string inverters cost about $1,000 less on a typical 5kW installation.
One thing to keep in mind though, is that string inverters will need to be replaced after 8 to 12 years, while your solar panel array is warrantied to last 25 years. A replacement will add more cost to your solar energy system.
Replacement is easy
Since you will only need one string inverter for most home installations, troubleshooting problems is pretty straightforward. Your inverter is the piece of equipment most likely to fail over the life of your system.
Being able to switch one unit out at an affordable price is more appealing than having to possibly troubleshoot many inverters or power optimizers behind every one of your solar panels.
Disadvantages of string inverters
Listed below are some issues to take into account with string inverters, since not one type of inverter is going to check all the boxes.
Backup power limitations
When the grid goes down while the sun is up, it’s nice to be able to use all the electricity your solar panels produce to continue to power your home loads. Hybrid inverters have a special feature called “pass-through power”, which directs all of your solar energy to your battery or home circuits when there’s a grid disruption.
In this way, you can still use all of the energy from your solar panels when the grid is down - as long as the sun is in the sky. While you technically don’t even need a battery for a hybrid inverter to operate in pass-through power mode, it helps to have one to have a more reliable energy source in the event it starts getting cloudy. The inverter also shuts off the flow of power to the grid to keep lineworkers safe who may be working to fix the outage.
String inverters, however, do not have this pass-through power function. This can be a frustrating realization if the grid goes down and you thought you had backup power capability with your solar panels.
Unsuitable for system expansion
If you are considering adding on to the size of your solar array at some point down the road, string inverters may not be the best choice. Each string inverter needs to be properly sized to the overall solar array.
To get the best performance out of your string inverter, it needs to be operating near its maximum capacity. Therefore, if you wanted to add on additional solar panels, the inverter would need to be larger than your current one.
An alternative would be to wire your new panels to a separate new inverter which ties into the loads flowing from your other one, but that’s usually just as expensive a process as simply getting a new, larger inverter.
If you’re unsure whether you may want to expand your solar system at some point in the future, microinverters are a better choice. Since they convert DC to AC behind every panel, they are naturally modular. You can simply plop on as many more as you wish and your system is set up to perform.
Limited system monitoring
In our smartphone age, being able to monitor the output of your solar installation can be a nice perk. While many string inverters allow you to view total system performance, you do not have visibility into the performance of each panel.
That level of detail may seem like overkill, but it can be particularly useful if one of your panels were to become damaged, or assaulted by bird poop without you knowing.
Panel level monitoring is available with microinverters and power optimizers.
Your solar panel array is warrantied to last at least 25 years. Unfortunately, most string inverters have warranties of only eight to 12 years.
While string inverter replacement costs are usually modeled into your solar savings estimates, it still sort of feels like you’re buying a car with a 10-year warranty, knowing the engine might go bust in five.
If you’re looking for more peace of mind without future costs down the road, microinverters have 25-year warranties which match the length of your solar system’s lifespan.
Final thoughts on string inverters
String inverters are a great option if you have abundant southern exposure on your roof, and your roof is at a uniform pitch. They are affordable and have stood the test of time over decades of use in the home solar industry. SMA and Fronius are leading manufacturers of string inverters.
To optimize the photovoltaic power your panels produce in partially shaded conditions or if you have a roof that faces different directions you’d like to site panels on, we recommend you use microinverters or DC power optimizers instead. Enphase is a leading manufacturer of microinverters, and SolarEdge leads the market in power optimizers.
For more thoughts on deciding which type of solar inverter system is right for you, visit our guide to choosing the best solar inverter for your home.
- How to choose the right type of inverter for your home
- How solar inverters work in your home solar system
- Solar inverter reviews
- String inverters convert DC electricity from your solar panels to usable AC in your home.
- They work great for non-shaded, south-facing solar installations at uniform pitch.
- They are affordable, and easy to install and replace.
- String inverters have limited backup power and monitoring options, have a shorter warranty than your solar panels, and are not well-suited to system size expansions.
Author: Dan Hahn | Solar Journalist
Dan is a solar journalist and content advisor with SolarReviews. He also works with solar installers and solar nonprofits to develop and execute strategic plans.