A micro-inverter is simply a miniature inverter built for individual solar panels. It is the counterpart to the mainstay inverter, the single, standalone, central inverter, otherwise called the 'string inverter'. Though micro-inverters are not a new invention, they first appeared in the 90s and are starting to become popular again with advancements in technology. Currently, there are more than 20 brands of micro inverters. Enphase Energy, originally founded in 2006 is regarded as the world's leading and most reputable micro-inverter manufacturer.
How Micro-inverters Work
Typically, solar panels produce DC from the sunlight which is then converted to AC by an inverter. When a solar panel is fitted with a micro-inverter, it is then able to produce AC directly. In that case, they become 'AC solar panels' rather than DC solar panels. (Some solar panels come with a factory-installed micro-inverter. These types are referred to as 'AC solar panels'.)
These micro-inverters are designed to be installed one to each solar panel. This is in contrast to the single, standalone, common (string) inverter that is usually installed away from the panels themselves and connected with solar cables. Read about solar cables and connectors here. Since micro-inverters are attached to every solar panel, each panel works independently from the rest of the solar array and the DC generated from the sunlight is converted to AC immediately on the roof.
Main Features
Because they are installed outdoors, they are built to be resistant to harsh weather conditions, UV-rays and moisture.
They have hybrid versions for battery-based systems.
Unfortunately, since they produce in the AC, they do not work with the traditional deep-cycle batteries.
They are built to protect the system from reverse polarity, short-circuiting, voltage surges, high temperatures, anti-islanding, etc.
Advantages of Micro-inverters
The main advantage of micro-inverters over string inverters is as regards the shading of the panels. Read about shading and how it affects the output of a solar panel or array here. When solar panels are connected together in a series string, shading one of them can affect the entire array and reduce the performance of the system.
Alongside shading, in an array where the condition of one panel can affect the entire system, micro-inverters have advantages for the following:
When two or more panels of different brands or even types are to be constructed together, micro-inverters remove any concerns about mismatch of panels.
When one panel in an array has aged or been damaged.
When panels are mounted at different orientations and angles. Unlike string inverters, micro-inverters are not restricted to panel placement in one or two different orientations. Et cetera.
A micro-inverter can monitor each solar panel individually. This allows the easy identification any points of failures in the system.
Micro-inverters are less redundant and more reliable than string inverters. If your series string inverter develops a fault, the entire solar array will stop producing power until it is fixed. In contrast, if a micro-inverter develops a fault, the remaining units will continue to operate, giving a more reliable system. This makes them an attraction to places where there are concerns about maximizing production. For instance, due to concerns about snowing, about 40% of the inverters installed in 2013 in America were micro-inverters.
Also, because they are independent of a centralized system, a micro-inverter system can easily be upgraded with the addition of a new panel and micro-inverter unlike a string inverter which may require the installation of new components entirely.
Micro-inverters typically have 25 year warranties while a standard inverters typically offers less than a 5-year warranty. This shows a greater level of trust by the manufacturers in their product.
Micro-inverters are also generally easier to install.
Disadvantages
While micro-inverters can help increase efficiency by almost 12%, theoretically, they have a few downsides.
They are costlier by up to 30%. But since they have a longer lifespan than string inverters, they can be more economical on the long term.
Since they are installed on the roof, maintenance is always a bit harder. And if they are installed at a great height, then there will be concerns about accidents during installation or maintenance. Regardless, manufacturers allow users to remotely monitor their inverters. In this case, the extra investment into a monitor will add to the budget.
Micro-inverters are on the roof, though placed underneath the solar panels. However, they suffer from extremes of weather including heat, cold and moisture. This means they have to be really carefully built and in many cases, use electronic components that are more robust than would otherwise be required. Nevertheless, as a general rule, extremes of temperature reduce the efficiency of electronic devices and shorten their life.
Micro-inverters have the potential to exceed string inverters in efficiency. But this makes them the inverter technology for the future.
Because micro-inverters output AC power they cannot be used with the common DC battery systems. They will require special types of AC batteries. This makes them unattractive for those who seek maximum self-consumption.
SolarKobo regards an investment in a string inverter as generally more advantageous for Nigerian users.
Read about Optimizers, a counterpart to micro-inverters here.