Different types of inverters under the Sun

Like a human heart, a solar inverter has to work relentlessly or the whole system will stall. No doubt it is worth making some extra effort to pick the right model to ensure your system’s longevity. Read on to discover all the different types of solar inverters and learn how to make the right choice.

Solar inverters speak your home’s language

Solar inverters take direct current (DC) generated by your PV array and translate it into alternating current (AC). This procedure is an obligatory step because virtually all home appliances run on AC. Thus, a solar inverter plays an essential role – it prepares your solar harvest for consumption.

It would be wrong to state that DC to AC conversion is all that inverters do. Most modern models can also be called the brain of the system. They monitor and analyze performance of various system components, including solar panels, batteries and even EV chargers. This functionality allows users to cut costs, improve efficiency and speed up problem detection and repairs.

Solar inverter is the single most vulnerable part of your solar setup. If any other equipment fails, be it batteries, charge controller or even some of the panels, the system will most likely continue generating energy. However, should the inverter stop working for some reason, it will render the whole solar panel system unusable, even if everything else is perfectly fine. This is because technically the inverter is powering your home, not the panels.

String inverters suit any PV system

True to their name, string inverters work with strings, i.e. sets of interconnected solar modules. A residential string inverter is a rectangular box not taller than a chair. Usually it has 3-6 inputs for strings up to 12 panels each. Most devices are stackable, meaning you can use more than one in your solar setup.

Grid-tie inverters is what most people imagine when they hear the phrase ‘solar inverter’. Most residential customers embrace this solution for its affordability and simplicity. At the same time, grid-tie inverters enable Net Metering, which greatly reduces the payback time. One major disadvantage of grid-tie inverters is that they can’t function during a power outage. When there’s no power in the grid, you won’t have electricity in your house, even with solar panels on the roof and the sun in the sky.

Central inverter sometimes simply means a grid-tie string inverter. The term is also used to describe utility-scale enormous boxes that work with dozens of strings as opposed to just 3-6 in a residential unit. This solution tends to be cheaper than using multiple smaller inverters, but further centralization significantly increases risks. Shading or other technical problems will affect not only all other modules in the same string, but also a number of other strings. In case of failure hundreds of panels may stop generating, and units of this size are harder to replace.

Hybrid string inverters are a very diverse group. The word hybrid simply refers to multimodality, so you can’t expect all inverters labeled as hybrid to share the same features and functionality. The term isn’t strictly defined, which allows manufacturers to call an inverter hybrid if it has some additional function besides DC to AC conversion. It could be anything – from the ability to charge an electric vehicle to an integrated charge controller. In some cases hybrid inverters are meant for completely distinct applications, like on- and off-grid. 

Hybrid on-grid inverters are no different in appearance from grid-tie devices, but they make your PV system more flexible and truly independent. These inverters allow you to store solar power for later use, for example, during peak demand hours or in case of a blackout. 

You can often see articles comparing grid-tie, off-grid and hybrid inverters as if these were completely different categories. The truth is that most off-grid inverters are also hybrid. They can’t export the excess energy into the grid, but often can use it to charge the batteries. What makes them hybrid is an ability to run both from solar panels and batteries, while plain off-grid inverters depend on batteries only. That’s why they are also sometimes referred to as inverter-chargers.

Microinverters make your system a LEGO set

Being the latest advance in the industry, microinverters are very different from the standard solutions in shape, size and installation process. Whereas central inverters are as big as a room and standard grid-tie devices are about the size of a chair, microinverters can fit onto your palm. Unlike other types, microinverters are installed behind each panel and perform the conversion right at the spot. This makes the systems based on microinverters very scalable – a very important quality for both industrial and residential applications.

Since the output of each panel is converted individually, the performance of a particular PV module won’t affect other modules in the same string. Also there is no single central element that will drag the whole system down in case of failure. This makes a microinverter-based PV system much more reliable.

Last but not least, microinverters allow for module-level monitoring. This means access to performance and diagnostic data of each and every one of your solar panels. Such information helps to identify and fix problems that might not be otherwise noticed.

With such a lengthy list of advantages, why is anyone still using conventional string inverters? Mostly it is due to the price. Microinverters are the most expensive of available inverter types. However, if you’re dealing with shading issues you might still be better off long-term thanks to improved efficiency.

Off-grid battery inverters take solar on an adventure

Inverters of this type are often called off-grid. However, this might be a bit misleading: they can’t be used to build an off-grid system without batteries, for this you will need a hybrid or a grid-tie inverter. All these inverters do is convert DC current from the batteries into usable AC current. They can’t power your loads directly from solar panels, so it makes sense to call them battery inverters. If either the battery or a charge controller fails, the whole system will stop, even if PV modules continue to function perfectly. Despite its drawbacks, off-grid systems based on this type of inverters are simple and budget-friendly. That’s why they are an optimal choice for mobile applications, such as powering a boat or an RV.

Which is the best type of inverter for you?

If you wish to go solar while avoiding extra costs and taking advantage of net metering to help recover your money faster, traditional grid-tie inverters will be the best choice, especially if you don’t experience such issues as shading or frequent blackouts.

Microinverters are a good strategy to fight against shading and to make your system less dependent on a single central unit. They will also help you harness the power of module-level data for improved performance.

Independence and blackout protection can be compatible with the grid and Net Metering. When the grid is available, a hybrid inverter will work as a plain grid-tie device, but when it goes down, it will transition smoothly to your backup storage.

For completely off-grid solutions you may consider hybrid off-grid inverters that can power your loads using both your batteries and solar panels. Battery inverters are a less sophisticated option, but are ideal for some applications due to their price and simplicity.

Maxim Kulik

Author

Writing for electronics manufacturers like Bitmain taught Maxim to extract the important details from lengthy equipment documentation. At the same time, it made him aware of the environmental effects, and he put his talents to work for a renewable future.

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