How a solar inverter works in your home solar system
The inverter is the hardest-working component of your solar system. Its main job is to convert direct current (DC) flowing from your solar panels into alternating current (AC) your home uses.
Aside from this core function, solar inverters have three other important jobs: voltage tracking, grid communication, and emergency shutoff.
In this article, we’ll briefly explain each of these functions. We’ll also introduce you to string inverters, power optimizers, microinverters, and hybrid aka “battery ready” inverters.
What is the purpose of a solar inverter?
The main purpose of a solar inverter is to convert the DC electricity flowing from your solar panels into usable AC power that your home appliances use. However, they have three other jobs, too.
Ensuring the production of plentiful, clean power
Solar panel inverters are responsible for continually tracking your solar array’s voltage to figure out the maximum power at which your solar panels operate, ensuring the system produces the most and cleanest power at all times.
While off-grid inverters typically rely on cheaper modified sine wave technology, grid tied home solar inverters create a more pure sine wave of AC electricity, to ensure your sensitive home appliances function smoothly and efficiently.
Communicating with the utility grid
Solar inverters need to interface with the grid. Inverters ensure that, in the event of a temporary power outage, no power from your solar panels winds up making it out to the transmission lines outside your home. This prevents lineworkers who may be troubleshooting or repairing wires from getting zapped.
Your inverters also feed power loads into the grid when your home doesn’t need the power or your batteries are full (if you have them connected to your solar system).
Arc detections and hazardous shut downs
Inverters are also required to shut down when they detect a hazardous electrical arc, which is caused by system aging and material degradation within your home’s wiring and solar panels. Some inverters perform better than others at safety shutoff.
According to a PVEL’s 2019 ground and arc fault test, Delta and Fronius inverters had higher accuracy rates of arc detections.
Solar inverter options for your home
There are four main solar inverter options to consider when designing your home solar system:
- String inverters
- Power optimizers
- Hybrid inverters
We’ll introduce you to each of these system types. Note, there is a fifth inverter type, called a “central inverter”, which is essentially the same thing as a string inverter, just that it’s enormous and meant for solar farm applications. We won't go into detail about them here.
In the solar industry, wiring panels together is called “stringing”. There are several different stringing configurations which impact how each system performs.
A string inverter is meant to pair with sets of panels that are simply strung together in sets. All the DC electricity the panels generate gets sent at once down the line to the inverter for conversion to AC. String inverters can handle multiple sets of strings, and based on the size of your solar installation, you may need to have more than one.
If one of the panels were to be shaded by trees at a certain time of day, the productivity of the whole set would deteriorate, because production output is reliant on the performance of the worst producing solar panel.
If your roof has a good southern exposure without shade, you need not be concerned about this issue and you can benefit most from using a string inverter, since they are most affordable and have worked well for decades.
Some smart engineers came up with the idea of solar microinverters to solve system performance problems when a few panels were compromised by shade, damage, or excessive bird poop. Microinverters do the job of converting DC to AC at the back of every single panel.
Even in variable shading conditions, maximum levels of AC electricity flow from your solar panels to your home and electric grid. A study by University of Virginia researchers reported 27% more efficiency in partially shaded solar installations when using microinverters instead of string inverters. Having a component on every panel also allows for individual panel monitoring, alerting you to any unexpected performance issues.
While solar microinverters are more costly, they allow for more easy system expansion than a string inverter. However, when one of them fails, maintenance can become an issue since someone will have to get up on the roof to replace the unit.
Some solar panel manufacturers like LG are integrating solar microinverters with their panels out of the box, to reduce costs for installers. Panel integrated microinverters benefit from much longer 25 year warranties than other inverter types, which are typically only covered for eight to 12 years.
Power optimizers are a lot like microinverters, in that they are affixed to the back of each solar panel and allow for individual panel monitoring. However, they do not convert electricity from DC to AC. Instead, they track the voltage and condition of the DC electricity flowing through your solar array’s strings to ensure optimal production gets sent along to your inverter.
The optimized and conditioned DC electricity gets sent to a modified, smaller inverter which then converts the DC power to AC. Power optimizer setups are more affordable than microinverters, highly efficient, and allow for easy system expansion.
Power optimizers are a great match for battery backup systems, since batteries and solar panels speak the same DC language. The power from your solar panels can directly charge your batteries, avoiding system losses due to conversion from DC to AC, then back to DC again.
With the increased interest in resiliency and energy independence, it’s worth noting that hybrid inverters pair well with home battery backup systems too. Hybrid inverters have the capability to convert DC electricity from your solar panels to AC for your home, and also the ability to convert AC electricity from the grid to DC to charge your battery bank.
They also come with a charge controller to smartly detect when to direct solar energy to your batteries, your home circuits or the grid, or pull electricity from the grid to charge your battery.
Some hybrid inverters have multiple modes, which can be configured to provide power to essential home circuits when the grid is down. Many homeowners select hybrid inverters when going solar without even having a battery backup system installed, since they can be more affordable upfront.
How long do solar inverters last?
String inverters usually last between 10 to 15 years. Some can even last up to 20 years if installed in a cool, well ventilated place out of direct sunshine.
Weather-rated string inverters can last up to 15 years in direct sun. Be sure to check your manufacturer’s spec sheet to see what their recommended installation procedures are.
Power optimizers and microinverters are relatively new technologies, and manufacturers expect them to last beyond their 25-year warranties. Not enough time has passed to see what their actual longevities are.
Next steps for considering solar inverters for your home
Solar inverters are the reason the electricity coming out of your solar panels is useful in your home. As you’ve just learned, you have several options to consider when designing your home solar system with your installer.
We recommend getting multiple solar estimates to connect with installers for their opinion on what type of inverter setup would work best for you.
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.