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Choosing Between a Central Inverter and a Micro Inverter

04-01-2011
Category: Solar Panels

Major components of solar energy system

When choosing a solar energy system for your home, there are three major components that you need to be most concerned about: the solar modules, solar racking and the inverters.  These are big choices and which components you choose will determine the reliability and output of your solar array for the many years that you will have the system on your home. Micro inverter

   Related article: Installing A Solar Energy System Yourself: Knowing What to Buy

For each major component, there are many choices so you need to do your homework. We have already outlined the major choices for home solar panels in other learning articles, such as whether you should buy thin film or crystalline panels.

   Related article: Solar Panels: Thin Film or Crystalline

And if you decide on crystalline panels, you can use SolarTown's compare and buy solar panels table to see the major differences among the available solar modules. There are some good options for solar mounting equipment and these options are expanding all of the time. Solar racking is easier to install with new products coming to market all the time.     

   Related article: Solar Module Comparison

But as for the solar inverters... this is where the choices must be made in the field of developing technologies. Inverters have been around as long as solar panels because they are a necessary component to convert DC energy to AC energy. A new branch of inverters has started to gain traction particularly in the residential market. The battle is on and the lines have been drawn between the idea of one central inverter (otherwise known as a string inverter) for the entire array and individual micro inverters connected to each module. So which one is more suitable for residential, commercial, and utility size projects?

Central inverters are less expensive and have fewer moving parts

The original single central inverter is still very popular among the homeowner and investors alike. Their first main benefit would be trust. They have simply been in the market longer and are believed to be efficient since they have previously proven results. These standard inverters have a maximum efficiency rate of 95%. Another benefit is economically they are less expensive than micro inverters.

Central inverters also have only central point of failure. Think of a ceiling with 10 lights versus a ceiling with one lamp.  In the past few months, there have been fast and furious claims about the reliability or unreliability of one technology over the other, but the time frame is so short that the jury is still out on whether central inverters or micro inverters are more reliable. You can guess which special interests press which claim. You can and should purchase a monitoring system to see the energy output of your entire array, but with a central inverter you cannot see the output at the panel level.

Some problems with central inverters

There are also many negatives that go along with a central inverter. One weakness is that when one module in a solar array is slightly shaded, its energy output can drop 50%. When this occurs the output from the entire array can also drop 50%--just because of one shaded module.

The whole energy output is only as strong as the weakest link. Another interesting fact is that since all the panels are linked in single converter configuration, the panels can carry 700-1600 volts of electricity-think very dangerous. Even if the inverter is turned off, the solar panels are still collecting energy. If someone is on the roof messing around with some of the conduit, they could be in for a deadly surprise.

Another weakness is that if you want to expand your solar array and add on some more panels, you may exceed the capacity of your current central inverter. You may have to shell out the big bucks for another central inverter just for these additional panels.

Micro inverters hit the market

Micro inverters gained traction in the market in the last couple of years, although micro inverters have been commercially produced since the 1990s. The micro inverter addresses many of the shortcomings of central inverters. Micro inverters minimize the issue of one module in shade affecting the entire array.  A homeowner whose roof may get some shade throughout the day has a good reason to consider micro inverters. If just one panel is partially shaded, that is the only panel loosing efficiency and will not reduce the output of the other modules that are part of the solar energy system.

Micro inverters also have 95% maximum efficiency like central inverters even though they are a newer technology. Another factor weighing in favor of the micro inverter market is that micro inverters are much safer than central inverters, since micro inverters convert the electricity to AC at the panel level. They have low individual total volt output instead of one huge dangerous voltage. Another plus many people like is that with micro inverters, a homeowner can relatively easily increase the size of his or her array. This is much more difficult on a central inverter.

The most interesting plus to micro inverters is the ability for each panel to be connected to a computer monitoring system so you can easily pinpoint which panel is experiencing lower efficiency rates. This is very helpful in discovering faulty panels or equipment.

And last but not least, with the latest technological advancements proponents of micro inverters believe the new micro inverters being developed will be able to harvest 5-20% more energy than central inverters over their lifetime. That is a lot of energy! Overall even though they are a higher initial investment, they could recoup the difference over time.

Although both central inverters and micro inverters have a place in the market, in general micro inverters are gaining ground and have become the inverter of choice for many residential installation companies throughout the country. Micro inverters are the new trend coming to market and they may make energy conversion much more efficient. Central inverters still hold great promise for large industrial and utility sized projects because solar systems designed for those projects usually do not have any shading challenges. And central inverters still are less expensive than micro inverters.

Micro inverter competition heating up

Micro inverters are gaining acceptance in the solar energy market, particularly in residential applications. The market leader is Enphase, and at this time no one is even coming close to competing with Enphase. There are a number of companies, one commentator says that as many as 20, that claim to be at various stages of developing new, better and cheaper micro inverters. Although the market is rapidly expanding, it is not large enough to absorb all of these micro inverter competitors.

Two new companies building micro inverters are Enecsys and Solarbridge. Neither has a higher peak efficiency compared to the best Enphase module. But one interesting fact that does make these other two brands more appealing is they have a higher conversion of DC to AC current. Enecsys recommends input of 360w into the module and it states its inverters output 360w of AC-that is impressive, if true. Solarbridge also has a slightly higher conversion rate of power as well. Also one thing that may interest investors in these newer companies is that the companies boast longer warranties by 5-10 years more than Enphase.  Another interesting approach from Greenray, another micro inverter company, is to integrate the solar panel and the micro inverter.

But unless these companies can show a bigger and better mouse trap, these other micro inverter companies can only hope that Enphase slips up. Until then, Enphase will continue to be synonymous with micro inverters.

   Related article: The Good, Bad and Ugly in Inverters: All the Questions You Need to Ask


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