Handling the power of the sun: What is an inverter and how does it work

So what is an inverter? PV modules use the energy coming from the sun and turn it into direct current (DC). It can power lighting in your home and chargers for small devices, like a smartphone. But most home appliances function on alternating current (AC). This is where the power inverter for a home system comes into play: it turns direct current into alternating. The efficiency of an inverter is close to 100%, which means that almost no power loss occurs while it's working.

DC-AC converting is not its only function. Solar inverter also gives the owner an option to monitor the functionality of the whole system. Besides, it allows the produced alternating current to be fed into the commercial electrical grid. In theory it also acts as another protection device – it shuts the system down when the grid experiences abnormal conditions, says the report of PV Evolution Labs. Inverters can also act as power output maximizers as they track the voltage of panels and identify the optimum operational power for the whole array — it's the same principle of maximum power point tracking as in MPPT-controllers for batteries.

There are several types of PV inverters suitable for different budgets, energy needs and panel systems. Also it's important to understand whether you are planning to go off the grid with your system or stay connected to it.

String solar inverters are the most widespread type of inverter around the world. According to IHS Markit 2020, in 2019 they occupied more than 60% of the whole market. String inverter is grid-connected and can take care of a row of solar panels, which are considered as one string. The main disadvantage of a string inverter is its inability to cope with problematic panels: if even one panel in a row suffers from shading or is damaged and has lower efficiency as a result, it usually drags down other panels in a row to its level. However, string inverters are relatively inexpensive and reliable, which probably explains their popularity. Some models have advanced features that make interaction with the device so much easier. Take Fronius Primo 6kW – it has dual powerpoint trackers, Wi-Fi interface for seamless monitoring and a specialised online platform. If your installation is large, it is possible to use multiple string inverters.

The problem with decreased efficiency of the string inverter can be solved through addition of power optimizers. They go on top of the roof next to panels and minimize the effect of the "weak" panel on the string. They, however, don't convert DC to AC themselves. This can be a fine choice for those who aren't ready to buy more expensive microinverters, but still want to maximize the efficiency of their system.

Central inverters can be considered as solely standing type, but it is essentially still a string inverter, just a larger one, which can handle more strings. Strings aren't directly plugged into the inverter in that case, but instead go to the combiner box, and from there DC passes into the inverter. These inverters are used in large-scale solar panel systems.

Microinverters are more popular in America than anywhere else. This type of converter is installed directly on a panel, so that DC turns into AC right on the spot. It is a good choice when your panels are subjected to shading, because weak performance of one panel doesn't affect others as it is the case with string inverters. Microinverters make a system more efficient, don't occupy a lot of space, but are more expensive.

If you are using batteries as a part of your system, they might need an inverter on their own, which is called a battery inverter. They come in different shapes and sizes and perform the same function as solar inverters — take the DC from batteries and turn it into AC. If you plan to use batteries and have a power storage in case of blackout, it might be a good idea to invest in a hybrid inverter which can work both with a battery and panels at the same time. You can even go for multi-mode hybrid inverters, the latest development, which can function both on- and off-grid. If you want to know more check out our article on on-grid, off-grid and hybrid solar systems.

The size of a solar inverter is usually measured in Watts. When purchasing an inverter, you have to make sure it suits the size of your solar panel system. If your solar panel array has a combined power of 5kW then a 5000 W inverter should be just right for it. Consult with the manufacturer when in doubt and read the guidelines. Keep in mind, that if your inverter is not sized properly for your system, in case of malfunctioning you might not be able to get compensation through the warranty.

It's hard to predict how much exactly an inverter is going to cost you. Prices for the most simple models start from 500$-750$ and go up to several thousands — depending on the type, properties and functionality of the model. Inverters come with different warranties of up to 12 years. A good warranty is especially important for an inverter as it is the most fragile part of the system: inverter is a complicated device, but is often placed outside where it's subjected to different weather conditions, swings in humidity and temperature. If possible, it is best to place an inverter in a garage or in another sheltered location, where it's safe from rain, snow and direct sunlight.