Choosing the type of inverter to install is an important decision in the solar installation process and can impact how your system looks and performs. Inverters convert direct current (DC) electricity made by solar panels to alternating current (AC) used in your home. Two kinds of inverters are used today: string inverters and microinverters. Getting the right inverter depends on your roof and the features you want with your system.
String inverters have been around for decades and are the most commonly used inverter technology available. A string inverter is a medium-sized piece of equipment normally placed by your other home electrical equipment. String inverters work with “strings” or groups of solar panels. The energy produced by these strings is sent to the inverter where it is converted.
String inverters are generally the most cost effective type of solar system and work well if you have a roof that faces only one direction and gets no shade. Panels in a string inverter system are wired in series. This means the system is only as powerful as its lowest producing panel. For example, a leaf falling on a panel from a nearby tree could reduce the efficiency of the entire array. If your roof is shaded during parts of the day or you want to maximize system production by putting panels on multiple roof faces you should consider adding power optimizers.
Power optimizers connect to each panel and are a type of Module Level Power Electronic (MLPE). By tracking the maximum power point (MPPT) of each module, power optimizers boost the performance of the entire system, and allow the system to perform even under partial shade conditions. Unlike a traditional string inverter, power optimizers also come with the ability to monitor each solar panel.
Instead of a central string inverter, microinverters attach to the racking system or are manufactured into the back of the panel. Microinverters convert, optimize, and monitor the performance of each solar panel. Microinverters are often seen as comparable in performance to power optimizers.
Because they are smaller and usually out of sight, microinverters can offer a simpler and cleaner system look. Microinverters are wired in parallel instead of in series so they don’t have a single point of failure. If a microinverter malfunctions the system will still produce from all its other panels until the microinverter is replaced. This is one of the main advantages of microinverters.
While a string inverter system without MLPEs is the most cost effective system you can buy, most homes disqualify for that type of system and most customers want the individual monitoring that comes along with MLPEs. Here we’ll quickly breakdown microinverters and power optimizers.
Microinverters are usually a little more expensive than power optimizers and don’t scale well. A large PV system with string inverters will cost significantly less than a system with one microinverter per panel.
Enphase and SolarEdge, the two leading microinverter and power optimizer companies, both have 25-year warranties on their MLPEs. SolarEdge has a standard 12 year warranty for its string inverter which can be extended to 25 years.
SolarEdge, the biggest power optimizer company in the US has a 99% CEC rated efficiency on its latest string inverter. Enphase, the microinverter market leader, has a 97% CEC weighted efficiency for its new microinverter.
In a study from the National Renewable Energy Laboratory, MLPE’s recovered around 20-30% of shading losses when compared to a traditional string inverter. In this test, the power optimizer system recovered about 2% more power than the microinverter system.
Because microinverters are performing their work on rooftops and contain more parts than power optimizers they have higher heat loss and therefore may break down more often. Most installers will say it’s easier to replace a string inverter on the ground than to replace a microinverter on the roof.
Lastly, some homeowners worry about how their solar system will look. Some of the new string inverters can be as small as a large shoebox but if you don’t want to see an inverter on the side of the house, or don’t have room to hang an inverter, microinverters can be a good option.