The job of the inverter is to produce AC power (alternating current) from a DC power source that is either a PV array or a battery bank. In this article, we will look at two classifications of inverters: String inverters and Micro inverters.
String Inverters
Most residential solar installations require just one string inverter, which is typically mounted on an exterior wall in the vicinity of the home’s electrical meter. These inverters have built in electronics designed to efficiently manage solar input and AC output. Each PV array is connected to a maximum power point tracker (MPPT) on the inverter. The MPPTs monitor their dedicated circuits and dynamically adjust resistance or input voltages to maximize power production.
Inverters of this type come in all different sizes. We identify the name plate size of an inverter by its rated continuous AC output. This means that a “7 kW” inverter is capable of continuously producing 7 kW of AC power from a DC source, such as solar panels. The DC input can, and should, exceed the AC rating of the inverter. That said, we will save DC-to-AC ratio for another post!
Microinverters
Microinverters are exactly what they sound like; a small inverter. They are considered a module level power electronic (MLPE), which means they are mounted on the roof with the solar modules. Microinverters are popular among homeowners because of the reliability they provide. If one microinverter malfunctions, the rest of the system still works. This is not the case with a string inverter, which is a single point of failure.
Typically speaking each solar panel gets its own dedicated microinverter, which converts the DC to AC on the roof. This is great because it allows installers to use normal residential AC wiring to bring solar power down to the service panel.
Each inverter gathers, records, and reports data every 5 to 15 minutes, depending on the manufacturer. This data is displayed in a user friendly interface on cloud based software for homeowners and system administrators to monitor.
Microinverters seem like a better option to most installers and homeowners, but there are some drawbacks. As you can likely imagine, solar installations using microinverters are generally more expensive than string inverter installs. This is due to the cost of not only the microinverters themselves, but also the proprietary cables and combiner boxes associated with this equipment. The second consideration is the limited size options available in microinverters. Solar panels are getting more powerful, but microinverters haven’t done well keeping up with the innovation. For example, a common solar panel size these day is 405W. The most common microinverter is rated for continuous output of 290W. While we do want to oversize inverters to a degree, it is important to recognize that solar panels are outrunning microinverters for the time being.
