The Solar PV market is experiencing significant growth across the world. Competition forces the continuous development of new technologies to increase system performance and return on investment (ROI) for project owners. Module-Level Power Electronics (MLPE) is a very active sector that complements solar panel developments by improving the output of each panel over time. In regions like Ohio, squeezing every ounce from the available sunshine is critical. We look at two advancements, the use of microinverters and power optimizers, and focus mostly in residential applications.
The advantages and benefits from using either microinverters or power optimizers are measured in the most important way to the owner – the PV system production over time. There are features that distinguish each design, and this gives system installers much greater flexibility to meet your economic and sustainability goals. Many suppliers offer prepacked units under the label “smart modules”. The popularity of MLPE is clear. In 2013 alone, more than half of the U.S. residential solar installations took advantage of one of these designs.
Basic System Description
The essential difference between a system with power optimizers and one with microinverters is in the approach to maximize the output of each panel installed. Microinverters are small grid-tie inverters that mount to each solar panel. Power optimizers isolate and condition the DC power of each solar panel to a string of panels fed to a central inverter. Both allow the system to monitor and “talk to” each individual panel. The software to do this, referred to as Maximum Power Point Tracking algorithms (MPPT) varies by MLPE approach and is a topic explained in more detail in a later post.
Systems using microinverters more or less operate in a way that each panel is its own power plant. The power leaving a module is compatible with the end use in the home or building. As a result, one of the most significant advantages of microinverters is the ability to add one or many modules at any time, or remove one or more modules at any time. With power optimizers, system expansion will be limited by the capacity of the central inverter. Should an owner want to expand beyond the nameplate inverter capacity, and new inverter and associated wiring will be required.
By isolating panels for monitoring and control, both MLPE technologies provide similar benefits.
System designers can place modules on different structures and at different angles.
They are no longer constrained by partial shading effects from dormers or landscaping. This opens up areas of a roof for use that would not be economical without MLPE.
Power losses from soiling and uneven aging are reduced leading to a higher performing system.
Documented results from over 6+ years show systems produce as much as 20% or 30% more power using the different versions of MLPE technology.
Both now enhance safety through remote and/or automatic shutdown capabilities.
For smaller systems typically around 20kW or less, the microinverter has become the more popular choice for a number of reasons. It is a slightly more mature product, and many believe it provides the most stable system performance when considering maintenance and service issues. Should a central inverter fail at any time, every panel with power optimizer will not produce power for you. The failure of any one microinverter is similar to that of a single power optimizer or panel failure. Only the one unit is affected.
For the Home
The balance of cost and performance is not as significant between the two MLPE approaches for most residential systems. For this reason, we prefer to design most of our installations with microinverters. This assures that each customer will get the best performance for all possible environmental conditions. And it provides some added benefits. For example, some central inverters must be installed close to the home, even in a basement. As the inverter size grows so does the need for external cooling. Both additional heat and noise from forced cooling can be unwanted by some homeowners.
Many customers also feel that using microinverters is a little safer. A microinverter limits the amount of DC current on a rooftop, converting the electricity to AC almost immediately – a situation that is potentially favorable for some types of rooftop installation. This is true particularly where wooden houses and rooftops present a greater fire risk.
For Small Business
Unlike microinverters, power optimizers handle each PV array as a unified power system rather than treating each panel as an individual energy unit. This makes solar panel power optimizers ideal for more expansive PV systems, creating a simpler setup for handling greater numbers of solar panels.
Many small business structures allow a more uniform panel layout, meaning multiple orientations, tilts, and module types are not needed. And as system size grows the need for multiple central inverters grows. Selecting power optimizers in lieu of microinverters at some point provides the better economics. But that point varies a lot depending on local conditions and customer needs.
Since there is more diversity in system requirements for small businesses, we don’t make many generalizations. We offer the best options to our business customers, and will gladly explain which MLPE approach offers the best benefits for the given circumstances. Many are surprised when microinverters can still offer the better balance and return.
For the most part, the industry is well on its way into second and third generation product development, especially for microinverters. Contrary to myths, reliability is already much higher than with first generation hardware, where unexpected failures occurred is some climates.
As of this post, a greater number of manufacturers offer microinverters, and that results in a much greater number of models and options. As a greater number of large systems using power optimizers are being installed, there will be more experience and more data. Power optimizer manufacturers of course want to build a product suitable for the broadest market. This competition will breed lower costs and higher performance across the board. And that will be a benefit for all. We keep a close eye on the industry to ensure we can deliver the best design to meet each customer’s needs.
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