MICRO INVERTERS

THE USE OF ELECTROLYTIC CAPACITORS IN MICRO INVERTER DESIGN

There's two simple rules for longer life when designing an inverter for use in high temperature environments when no means of active cooling are used.

1. Limit your component count.

2. Avoid the use of electrolytic capacitors in high heat applications.

Unfortunately some micro inverter designs violates both of these rules which may seriously impact your system's return on investment.


 

For every Micro Inverter that you install, you dramatically increase both your system's component count and in some of the most popular micro inverters on the market today, you'll find electrolytic capacitors.

Electrolytic capacitors have been around for decades and are used to store energy in an electric field. When used in a micro inverter application, they serve the purpose of controlling ripple voltages across the PV bus. Electrolytic capacitors utilize an aluminum or a tantalum plate and an oxide dielectric layer.

The second electrode in this type of capacitor consists of a liquid electrolyte which is connected to the circuit by a second foil plate. Electrolytic capacitors can provide very high capacitance in a small space but tend to suffer from poor tolerances, high instability and a gradual loss of capacitance, especially when they are subjected to heat that is beyond their design specifications.

Unfortunately your home's rooftop can create a high temperature environment that is hostile to the use of electrolytic capacitors, possibly causing them to burst and leak their liquid electrolyte resulting in the total loss of capacitance and premature micro inverter failure.
 

If a ground level mounted, high capacity inverter were to affected due to electrolytic capacitor failure, it's a relatively simple process to replace one or two inverters.

On the other hand, when a single micro inverter or multiple micro inverters fail due to electrolytic capacitor failures or any type of failure for that matter, in many cases it will mean the removal and replacement of several solar panels in the array in order to reach the inverter or inverters that have failed.

This can turn a what should be a low cost service call into a very expensive one when you consider that inverter failure warranties typically do not cover the labor to remove and replace inverters.

Further complicating this scenario is the fact that it would be highly unlikely for all of the electrolytic capacitors in a twenty or thirty micro inverter installation to fail at the same time. So after several years of use, you might have one or two micro inverters fail one month and maybe two or three fail two months later and so on and so on resulting in possibly a $300.00 to $500.00 service fee each time a micro inverter fails due to heat or age related electrolytic capacitor failure.    
 

It's far better to have less inverters to remove and replace at ground level than to pay an electrician to climb on to your roof and remove and replace dozens of solar panels just so he can remove and replace one or two micro inverters over the life of your system.

No matter how long of a warranty a micro inverter manufacturer offers, read your warranty documents carefully and you'll find that no inverter warranty covers the removal and replacement of a failed inverter. So the more inverters that you install the higher the risk of incurring multiple service charges as your system ages. And in the case of multiple roof mounted micro inverters, the cost per failure event will not be small.

How do we know so much about capacitors ? Well for the past 12 years, we've owned and operated one oldest factory authorized inverter repair centers in the nation and we've seen our fair share of electrolytic capacitor failures.

With a SolarEdge system there are no electrolytic capacitors that are used in their roof mounted power optimizers. Instead, they use high temperature tolerant thin film capacitors that do not use any type of liquid electrolyte. And instead of cramming the power electronics, multi point power tracking and protection circuitry all in a single small "can", SolarEdge separates the heat producing power electronics from the MPPT circuitry which reduces temperature related component stress in both their power optimizers and their inverters thus increasing life expectancy, making for more reliable products.

1.  For every 25 roof mounted inverters in a typical micro inverter installation. A SolarEdge installation only requires one inverter.

2. With a micro inverter, the multi point power tracking circuitry, the power electronics and the protection circuitry are all mounted in the same small, sealed box. Placing all of the electronics in such a small space results in higher operating temperatures which can lead to higher component stress. Especially stress to susceptible components such as electrolytic capacitors.

  Read This Informative EE Times Design Article Concerning The Problems Associated With The Use Of Electrolytic Capacitors And Opto Couplers In Micro Inverter Architecture, Written By Lesley Chisenga, Chief Architect, Enecsys Ltd
 

COMPARISON

With SolarEdge you'll not only get a bigger cash rebate in many states, but also higher energy production because SolarEdge offers the highest 240 volt single phase CEC weighted efficiency rating on the market.

And why on Earth would anyone want to connect a 280 solar panel to an inverter that's only rated to handle a maximum of 240 Watts ? And when it comes to warranties, SolarEdge's standard 25 year Power Optimizer Unit warranty says it all !