How to Choose between Micro and String Inverters

By Gordon Algermissen
09 January 2015
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String inverters versus Micro-inverters are a common theme homeowners struggle with when going solar. One solar company will pitch micro-inverters as the best value-add ever, while others will shy away from it and even question the micro-inverters reliability. So what’s the real answer? 

The answer turns out to not be so black and white. It depends on several criteria, which this article will try and sort out for you.

First let’s cover a quick overview of the physical and functional difference between an inverter and micro-inverter. Inverters convert the Direct Current (DC) solar panels produce into an Alternating Current (AC), which provides usable electricity for your home. A standard inverter (also known as a string-inverter or central inverter) is a standalone box, slightly larger than an average home-printer, which typically is installed next to your panel box. Micro-inverters are individual units located underneath each panel on your roof and about the size of an internet router. Depending on the model, there may be only one micro-inverter unit for two panels.

Without getting too detailed, a standard inverter functions in a series circuit while a micro-inverter functions in a parallel circuit. To simply put, a standard inverter will cap the electricity production of each panel by the lowest producing panel on your roof. A micro-inverter on the other hand, will take full advantage of the production of each individual panel. Therefore the functionality of a micro-inverter does outperform a standard inverter, but is it worth the extra cost?

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That answer lies in the layout of your solar system. If a solar system is facing multiple angles, meaning some panels are facing south, some east, and some west, then micro-inverters are the way to go. Or, if you have shading issues from trees or a large chimney, again micro-inverters would be best. In these situations, the solar panels will be producing different amounts of electricity at different times of the day, but micro-inverters will ensure you harvest all of the energy, while with a standard inverter you will lose some of this production. With solar panels all facing one direction on your system, and you have marginal shading issues, then your best option is a standard inverter. You’ll get about the same production, without paying the higher cost.

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To throw more confusion in this, Optimizers are an option for standard inverters as well, which function very similarly to a micro-inverter. With an optimizer, you still have a standard inverter, but you also have optimizers for each individual panel combating production differences.

There are other aspects to consider as well. Micro-inverters typically have 25 year warranties while a standard inverters typically have 10 year warranties. The reliability of micro-inverters was in question several years ago, but the technology now has caught up with the industry and the long warranties on the micro-inverters shows the confidence the manufacturers have in their products.

 

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Micro-inverters and the add-on optimizers both offer an additional perk in system monitoring as well. With either of these devices, you have the ability to track the production of each individual panel, while with a standard inverter you only can track the production of the whole system.

If you were to expand your system in the future, micro-inverters are simple to add one at a time. However, with a standard inverter, it would be more costly to add another full unit.

To sum it all up, micro-inverters are definitely a value-add, but are only recommended if you have panels facing multiple orientations or you have shading issues. Otherwise, the less expensive standard inverter is the way to go. At Pick My Solar, we can provide you with cost and savings estimates as well as production estimates and actual bids from our installer network for solar systems with both micro and string inverters.

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