Micro inverter and Optimizer – what are they good for?

microinverter-power-optimizer

Solar micro inverters and power optimizers

Micro inverter and power optimizers both help improve output performance of a solar energy system at individual panel level. In this article, I will talk about both these devices and show you how each one works.  

Let’s start with micro inverter..

Solar micro inverter

As the name suggests, micro inverters are small in size. They are designed small enough so they can fit in the backside of each solar panel. These tiny devices convert DC current to AC current for each panel, which is why micro-inverter panels are sometimes also called AC solar panels.

Micro inverters convert DC power to AC power at each panel’s output.

enphase-microinverter
A micro inverter by enphase

Benefits of micro inverters (over string inverter)

Note: If you don’t know what string inverter is, you should read this before reading remainder of this article.

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A micro-inverter solar energy system
  • Better for shaded roof: If one micro inverter panel is shaded, it affects output of that panel only. One shaded panel in a string inverter system (without power optimizers) will bring down the output of rest of the panels in that string.
  • Scalability: Adding more micro inverter panel to your existing system is not an issue. You may have to upgrade your string inverter to bigger size if you want to add additional panels on that system.
  • No single point of failure: If a micro inverter stops working, it only affects one panel. A string inverter has single point of failure, which is the inverter itself. If this inverter stops working, every panels that are attached to this inverter stop working as well.
  • Safer roof: Micro inverter panels output 220V AC voltage, which is safer than 400V DC out of solar panels that connect to a string inverter.
  • Monitoring: If you have 20 micro inverter panels, you can monitor each panel’s output separately.

One micro inverter per panel; doesn’t require a separate string inverter.

Micro inverter solar panels have gained popularity in residential market due to the nature of the physical roof space.

If any one of the following describes your roof, micro inverter solar panels can be a better option for you than string inverter solar panel system.

  • Your roof is partially shaded.
  • You have roof space in more than one direction.
  • Your roof pitch is uneven.

If all the things about micro inverter panels sounded too good to be true for you, next I will go over some of its disadvantages.

Disadvantages of micro inverter solar panel system:

  • Outdoor: Micro inverters are attached to the backside of the solar panels which means they are left out in the roof all year round. Extreme weather conditions can damage micro inverters.
  • Poor accessibility: While string inverter is installed very conveniently inside of your house, micro inverters are on the roof. If there is a bad one, you will have to climb the roof each time to fix it.
  • Less efficient: Micro inverters are slightly less efficient in converting DC to AC. Transmission of power in low voltage AC mode from the roof into the house also results in slightly more power loss.
  • Higher Cost: Micro inverters definitely increase system performance but it also adds cost.

Power optimizers

Power-optimizers-solar

Power optimizers work just like micro inverters. Each one is placed in the backside of a panel and in case of panels mismatch, they optimize each individual panel’s output separately. However, unlike micro inverters, power optimizers don’t convert DC to AC because it is not an inverter. That is why a system with power optimizers also requires a string inverter to convert DC to AC. 

So, why do we even need power optimizers when micro inverters already do the work?

Well, if you had bunch of tree branches that suddenly shaded your string inverter solar panel system, you could retrofit power optimizers in those panels to fix the problem without cutting the trees.

That is just an example. The company, SolarEdge, that pioneered the DC optimizers has bigger motives behind them. Below are two I could come up with:

  • Power optimizers are cheaper compared to micro inverter. So, if you were building a 1 MW solar farm, choosing power optimizers instead would reduce your upfront cost while still giving the same benefit as micro inverters for performance.
  • Because the current flows at higher DC voltage (400-600V), there is less power loss along the transmission line. In large-scale installations where the cables have to travel longer distance before reaching central inverter, this can be of huge advantage.

As you can see, power optimizers can have real meaningful advantage over micro inverter only if you were doing large-scale installation.

At small-scale residential systems, the two benefits I mentioned above for power optimizer may not necessarily translate into meaningful results. 

One optimizer per panel; requires separate string inverter for DC to AC conversion.

Wrapping it up!

There you have it. Micro inverters and power optimizers in a nut-shell. If you have any questions or comments, don’t hesitate to contact me below.

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