Microinverter or String Inverter?

Comparison between micro-inverters and string inverters

• What is a Micro-Inverter – a micro-inverter can also be referred to as a solar micro inverter. It is a piece of electronic equipment used in PV arrays for changing the waveform of current – i.e. changing Direct Current (DC) to Alternating Current (AC).
• What is a String Inverter? – String inverters can also be referred to as centralized inverters. They convert Direct Current (DC) to Alternating Current (AC) but here the inverter is connected to a string of solar panels, instead of individually as does a micro-inverter.

When a micro-inverter might be a better choice than string inverters

Easy to install and use

1. You don’t need an expert to install it for you. Micro-inverters can be easily set-up by you thereby saving you the cost of paying experts to do it for you.
2. It does not require any additional hardware or manual configuration. It is Plug-and-play for the most part.
3. Micro-inverters are connected to an AC source carrying normal household voltages. Whereas, central inverters are connected using multiple strings of thick DC wires from the solar panels to the central inverter through a tunnel.
4. The installations of central-inverters demand 4-8 categories of high voltage DC wires which need to be connected correctly to the inverter.
5. In the installations of string-inverters, the installer has to calculate line losses to determine the size of the wire that will be required to connect it to the panels. Also, the panels, central inverters, and the racking all require different grounding components.
6. Even for the loading of the string-inverters, it requires that the person installing it, design the system to be able to load-balance each strand of panels.
7. In a central-inverter, when a panel malfunctions, it can be hard to determine which panel exactly in the system is malfunctioning without testing each one of them with a micrometer.

Effectiveness (Total System Output)

1. Micro-inverters make the best use of the power output of each individual panel resulting in an additional power of 5-15% per panel on average.
2. Central (String) inverters will not function at 100% if there is shading on even one panel in the array, whereas a micro inverter system will function optimally, and every other panel’s production in the array will not be affected by the one shaded panel.
3. If a panel malfunction in a micro-inverter system, it will not affect the whole system and the exact panel that is malfunctioning can be easily determined.

Safety

1. Micro-inverters are safer to use, whereas string-inverters will expose the installer to hundreds of volts of unsafe DC power while micro-inverters do not.
2. Micro-inverters are safe to handle as they do not produce power when they are not connected to your solar panels. On the other hand, a string inverter needs to be handled safely because they produce power as soon the panels are exposed to light.
3. A string inverter can be wired incorrectly in a lot of ways which could lead to severe damage or even death of the installer.  
4. There is virtually no way a micro inverter can be wired incorrectly because it is plug-and-play.

Durability and Cost Effectiveness.

1. Micro-inverters last for a very long time having an average lifespan of about 32 years and also a longer warranty of 25 years whereas central inverters have a shorter lifespan and a shorter warranty period of 10-12 years.
2. The cost of maintenance for a string inverter can be more as it will need replacement in 10-15 years.
3. Be sure to ask your installer if your warranty will cover replacement of the inverters if and when they expire before the 20 or 25 year mark.

The advantages of a string inverter

There is certainly a lot to like about micro-inverters, but when might it be better to use a traditional string inverter?

1.      A string inverter is one connection point, so set up is very straight forward.

2.      When a microinverter fails, you will likely have multiple devices to replace, so this can be a hassle or an inconvenience.

3.      When you’re dealing with only one mounting plane or direction for your array, a single phase, string inverter is a very solid choice.

When to choose a micro-inverter based PV system

There are certain instances where you will definitely want to use a micro-inverter based system.

1.     The advantages of a micro-inverter set-up come into play especially when you have a system that contains multiple roof angles and possible shading as this will increase overall system output and efficiency.

2.     The second scenario is when you plan on expanding (adding panels) your system. In this case, adding extra panels and micro-inverters will be more economical because a string inverter is sized to the total system size, so can only be upgraded to a certain point before a larger or second string inverter will be required.