In the past the most common inverter is a central unit that does the DC-to-AC conversion for a group of solar panels. For a small installation, like a home solar system, you’ll usually need just one central inverter. This type is called a string inverter because the solar panels are wired together in one or more strings, like Christmas lights. This is usually the least expensive inverter option. A string inverter is installed near your meter board with a solar system DC isolator switch.
Now most modern solar installations, an installer will often recommend module-level electronics. There are two types: microinverters and power optimizers, which are also called DC optimizers.
With both types, each solar panel is paired with one electronics package that is bolted to the rack adjacent each panel. That means if your system has 20 solar panels on the roof, you will have 20 MLPE units on the roof. Depending on the manufacturer, there is usually some type of electronics package that is also installed near your electrical panel.
A microinverter is a fully self-contained solar inverter. It’s about the size of a paperback book, and is bolted onto the rack underneath a solar panel. Each microinverter fully handles the DC-to-AC electricity conversion for one solar panel.
The largest player in the microinverter market, by far, is Enphase Energy. They have a large product lineup that is currently on its 8th generation, which has helped the company develop more functionality of their products over the generations.
Both microinverters and power optimizers have the following advantages over cheaper string inverters:
- Better shade tolerance. String inverter-based solar systems can suffer significant power reduction when the array is partially shaded. Both types of MLPEs skirt around this problem.
- Module-level monitoring. With a string inverter, you can monitor the power output of the system as a whole, but it can’t tell you how an individual solar panel in your array is performing. Microinverters and power optimizers change that, and let you see how much electricity each panel in your system is producing in real-time. Even if you aren’t the type of person to obsessively check on your system and geek out on how much electricity you’re making, panel-level monitoring is still useful because it will tell you if one panel in your system is under producing. This could be because of a panel failure, or something like panel cleanliness.
Microinverters, the most advanced inverter option, have some additional advantages:
- Flexible layout and system expansion. With a power optimizer-based system, the DC-to-AC conversion still happens at a centralized inverter unit mounted near your electrical panel. Because of this, there are still constraints on the string layout. For example, an individual string might be limited to a certain total wattage. With microinverters, there are no such limitations, and the solar panel layout can be as crazy as needed to fit your rooftop. While not all homes may need this, it also gives you more options for future expansion. For example, if you decide you want to power an electric car with solar in the future, microinverters will let you add as many panels as you want.
- (Possibly) fewer system failures. In the US market, manufacturers of microinverters and power optimizers have standardized on 25 year warranties. (If you come across a product with less than a 25 year warranty, think twice.) However, with power optimizers, this applies only to the external optimizer unit, not the central inverter. For example, SolarEdge offers a 25 year warranty for the optimizer, but only a 12 year warranty with their central HD-Wave inverter. If the duration of a warranty reflects the manufacturer’s expected lifetime for a product, that means budgeting for an inverter replacement halfway through the lifetime of your solar system. Microinverters, on the other hand, can have a 25 year warranty for the entire unit.