However, despite the projected growth and advancements in technology, the PV industry is still experiencing a number of challenges – one of the most serious being PV shading. The most common causes of PV shading include structural objects such as trees and chimneys and intermittent debris, including falling leaves, bird droppings, dust and clouds passing overhead. These are unavoidable challenges that cannot be engineered out of an installation. In the case of structural shade, even correctly installed solar systems can be partially blocked from the sun at certain times of the day or during certain days of the year.

Two distinct approaches have emerged to address these challenges, microinverters and dc-dc solutions. Microinverters convert the optimized dc power output of each PV module directly into ac suitable for grid connection. Dc-dc solutions maximize the dc power output of each module regardless of the performance of other modules connected in the same string by compensating for module mismatch, environmental degradation, or shading, and route the optimized dc to a central inverter for dc-ac conversion.

In the microinverter approach, instead of a large single inverter, individual microinverters are attached to each solar module. With all modules being independent, there is no single point of failure, so the system will keep operating even if one or more modules go down. This fundamental approach could make it significantly easier to design, build, and monitor solar systems, particularly smaller systems for homes and businesses.

The first commercially available microinverter (designed specifically for residential and small commercial rooftops) was introduced in 2008 by Enphase Energy. In an Enphase system, each solar module is equipped with a microinverter and all of the modules are connected in parallel. In contrast to traditional PV inverters which perform maximum power point tracking (MPPT) for the entire array as a whole, each Enphase microinverter performs MPPT on the module before dc-ac conversion at near 95% efficiency. One of the advantages of this system is the lack of a single point of failure. If one microinverter fails, the balance of the PV system continues to produce power. Or if one of the solar panels loses production due to shading, debris or defect, the entire system is not affected.

An alternative approach to microinverter technology are dc dc solutions, such as National Semiconductor’s Solar Magic power optimizer. SolarMagic power optimizers operate in the dc domain, prior to the system’s inverter. They essentially do the same thing as microinverters except that they do not provide the dc-ac conversion function and are designed to be retrofitted into older, existing systems that have shade or other issues.
National Semiconductor’s SolarMagic optimizers are designed to ensure that each panel is counted individually so that one bad panel can't take down an entire string. According to the company, the problem is that the entire photovoltaic system shares an inverter to optimize output. But a single inverter isn’t capable of optimizing different conditions that panels, even in the same array, can face.

The result is either the inverter picks the highest common operating point for all the panels, which can severely decrease the output of fully functional panels, or that entire strings of panels can stop contributing to the energy harvesting, much like a string of Christmas lights that goes out because of one faulty bulb. National Semiconductor states that Solar Magic is especially suitable for areas that might have one string with partial shading or for areas that get intermittent shading from clouds on a regular basis. Unlike microinverters, Solar Magic products are only added to strings that are known to have shade.

According to the company, SolarMagic technology enables each solar panel to produce maximum energy regardless of whether other panels are under-performing due to mismatch or shading. This technology also monitors and maximizes the energy harvest of each individual solar panel and reclaims up to 57% of energy lost due to temporary or partial shading of PV panels. In addition, despite the extra step in dc conversion, the company maintains that solar Magic achieves 98.5% efficiency vs. 95.0 % efficiency for microinverters.

The problem of PV shading is expected to remain and regardless of which technology (microinverters or dc solutions) the consumer chooses over the next several years, they are certain to have an increasing number of products to choose from as a growing number of companies scramble to develop competing technologies designed to combat the effects of PV shading.

Enphase Energy Solution to PV Shading

Solar Magic Solution to PV Shading

Provided by Richard Ruiz Jr., Research Analyst, Darnell Group

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