Inverters are the second-most important component of a solar power system (you know the first one). They convert direct current (DC) coming from the solar panels into alternating current (AC), making it usable for our everyday appliances, which are designed to operate on AC power.
Therefore, they are often also compared to the human heart - and although that is an imperfect analogy, it at least outlines how crucial inverters are.
Today, there are three types of inverter setups to choose from. The first is a string inverter, which has been the default choice for many years now. It sits at the end of all solar modules and converts the accumulated DC power into AC power - straightforward.
However, string inverters really disappoint when even a part of the solar array suffers from shading, or the roof orientation is not ideal. The power drop in such cases is significant, and it begs to look for other options.
These problems are tackled by two main newer technologies:
- Inverters + power optimisers
Let’s look at each one in a bit more detail before we dive into their comparison.
What are Microinverters?
‘Micro’ stands for small, which means microinverters are - you guessed it right - small inverters. But that’s not their defining aspect. Microinverters are special in the sense that each microinverter works at the module level. Instead of a single inverter collecting power from all modules for conversion, every solar panel has its own microinverter.
An Enphase microinverter
Some solar panels come with integrated microinverters, and are even dubbed as ‘AC solar panels’. While that terminology is debatable, we can be sure that microinverters are a lot simpler affair than traditional, string inverters.
But the most important benefit of microinverters isn’t just simplicity. Unlike string inverters, systems with microinverters perform better. Partial shading of an array or panel does not lead to huge power drops.
Microinverters are also a great fit for roofs with complicated orientations. They even allow energy monitoring at the module-level.
What are Power Optimisers?
Perhaps someone felt that the idea of having dozens of tiny inverters on a system was a bit too radical (and expensive). And they came up with a middle way - a compromise between string inverters and microinverters, creating power optimisers.
Power optimisers are, as the name suggests, devices that optimize power from solar panels. They do so by continuously tracking the maximum power point and monitoring performance at the module-level. Like microinverters, they are also attached to individual solar panels.
A SolarEdge power optimizer
They do not convert DC into AC power, which means you still need a string inverter to work with them. However, the combination of inverter and optimizers provides notably better results when it comes to performance.
Now that we’ve looked at both the technologies, let us compare them.
Microinverters Vs. Power Optimisers
Let’s list down their similarities and differences of both the technologies. Before that, if you are interested in the comparison between microinverters and string inverters, check out this post.
Similarities Between Microinverters and Power Optimisers
1. Module-level operation
Both microinverters and power optimisers work at the level of individual solar panels. Owing to this, they are both classified as module-level power electronics (MLPE). Both can be attached to the mounting rack near each solar panel.
Microinverters can also come attached to the back of the solar module, sometimes known as ‘integrated microinverters’.
2. Improved performance
Microinverters improve power output from the array by eliminating partial shading effects. Power optimisers improve array performance by optimising individual modules to generate their best possible output.
Ultimately, both technologies result in an improved performance of the entire system.
3. Panel-level monitoring
A basic, string-inverter based system can be continuously monitored for performance. Any abnormal drop in the power output can be noticed. However, it is difficult to point out where the problem lies - whether it is one of the modules that is underperforming, or the entire array, or the problem lies in the inverter itself.
With microinverters and power optimisers, each module can be monitored individually. This means you can accurately know which solar panel(s) are underperforming. This helps with more accurate troubleshooting of systems.
Differences in Microinverters and Power Optimisers
1. DC to AC conversion point
While microinverters convert direct current to alternating current at the panel-level, optimisers have nothing to do with conversion. They only optimise the power while the DC-AC conversion part is handled by a string inverter.
Despite their similarities in structure and installation, a microinverter setup is much simpler than one with power optimisers. When using power optimisers, you also need a string inverter. This makes installing such a setup a bit more tedious.
Additionally, it may also lead to higher maintenance. If the string inverter fails, the power optimisers will be of no use until that is fixed. A failure with a single microinverter, however, will not lead to a downtime of the entire system.
Obviously, the cheapest option among the three setups is the traditional “string inverter only” system. If not for its low cost, this setup would have been extinct by now. On the other end of the spectrum, microinverters remain the most expensive of the three types.
Power optimisers are, as we said, a middle way, with pricing higher than inverter only systems, but lower than microinverters.
An important distinguishing factor between microinverters and the other two types of setups is the warranty. Traditional string inverters usually come with a 10, sometimes 12-year warranty.
Microinverters, on the other hand, come with longer warranties. For instance, the microinverters by Enphase (the largest microinverter brand), boast an unparalleled 25-year warranty. Despite the initial higher cost, this long life means there will be no expenditure on inverter replacement or maintenance halfway through your system’s life.
Which Inverter Setup Should You Choose?
‘All that is fine, but what is the most suitable setup for me?’, you may ask. The answer is - it depends on you, and your roof structure. If the system cost is not a concern and you want to extract maximum performance from your system, go for microinverters.
But if you want maximum value for your money, the best system will depend on what kind of roof, and house you have.
If the roof is smaller than what you’d ideally need, or if parts of it will be shaded at some point in the day, then a string inverter is not your best option. Although you will save money initially, your system may consistently underperform, leading to lower savings and a higher payback period. In such a case, it is best to go with microinverters, or at least, power optimisers.
But if you have an ideal roof, with a north-facing, perfect slope and ample space, going with a string inverter system might work best. In either case, it helps to get multiple quotes from quality installers to make sure you’re making the perfect choice.