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Solar Micro-Inverters vs. Central Inverters


The inverter is a crucial component of any photovoltaic system. Without them, we have no way of converting the direct current (DC) that flows from the solar panels into alternating current (AC) - the type of electricity that the majority of our appliances use.

Traditional central inverters (string) have dominated the market since the first solar panels started appearing on rooftops. Not only were they big and noisy, but also quite inefficient. Micro-inverters, holding the promise to eliminate the issues of the central inverts, have since been introduced on the market. Are they really better?


Image credit: Enphase Energy

How Micro-Inverters Work

Inverters have three main tasks:

  • Converting AC to DC as mentioned above.
  • Ensuring that current is switched off during repairs and blackouts
  • Optimize the solar panels that are connected to it

Usually one conventional central inverter was all you needed for a typical solar array. The central inverter optimizes every solar panel that is connected to this particular inverter. This introduces some problems, especially when it comes to efficiency.

Maximum power point tracking (MPPT)

Maximum power point tracking, an intrinsic part of modern solar inverters, is a technique that takes variables such as irradiation, temperature and total resistance into account, and optimizes for maximum power output.

Traditional central inverters optimize for the weakest link in the solar array. If one solar panel is covered by shade, dirt or anything else, chances are that the efficiency of every solar panel is going to suffer. If a solar panel stops working, the whole solar array breaks down.

Micro-inverters were made first and foremost to enable optimizing on a panel-by-panel basis. Each micro-inverter goes on the back of every solar panel in the PV-system. There is not one single point of failure as with central inverters, which enables every panel to perform at its maximum capacity. Enphase Energy, one of the top dogs in the solar inverter industry, claims that their micro-inverters will perform 5-25 % better than a typical central inverter.

Smart real time performance reports

Another key selling point of micro-inverters is that they collect data, which can be analyzed in a web-based environment, such as your computer or even your mobile phone. This enables both customers and installers to monitor performance, troubleshoot and improve efficiency.

Safety

Since micro-inverters operate on a panel-by-panel basis, DC electricity is converted into AC for each panel alone. The high voltage that we have with central inverters is not an issue.

Both micro-inverters and traditional central inverters also come with the standard advantages and disadvantages of solar power. Read more about them in solar energy pros and cons.

Comes Down to Costs

So back to the question the article started with: Are micro-inverters really better than traditional central inverters? Micro-inverters do come with helpful benefits such as the real-time performance reporting, increased scalability and safety, which certainly are nice benefits, but in my opinion, for most situations, it all comes down to costs. Are micro-inverters able to push our solar panels to deliver cheaper electricity than central-inverters?

Central inverters are less expensive

They have been on the market for a long time and have less moving parts. There is nothing beating central inverters when it comes to price - at least if we are talking about the initial costs.

Micro-inverters last longer

Enecsys, another leader in the inverter industry, says micro-inverters last at least 25 years. In other words, it needs replacement at the same time your solar panel does. In comparison, traditional inverters usually come with a 10-20 year warranty, which means that in theory this justifies a pricing of micro-inverters to be 25-250% higher.

Micro-inverters have better efficiency

Best-case scenario, central inverters can perform at 95% of the theoretical maximum, a number that seems impressive at first glans. What is not taken into account is if one or several panels are under-performing, dragging all panels connected to the same inverter down. When one solar panel is slightly shaded, performance can drop as much as 50% for the whole solar array!

A household that potentially has shading problems on their roof should definitely look into micro-inverters. These are the types of situations where micro-inverters have more pronounced benefits and a lot of money can be saved in the long run. On the other hand, if shading is not a big issue with your PV-system, you are not interested in the added safety benefits and don't care for performance reports, central inverters could be the best choice. Even though the private sector of solar power is expected to be dominated by micro-inverters in the near future, central inverters will continue to be the first choice for large industrial and utility-scale projects. These projects do not have shading issues and are carefully monitored and optimized as it is.


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