Scott Sullivan, KACO Americas
The age old argument between string and central inverters goes something like: I want a central inverter because the initial costs are lower vs. I use string inverters because all inverters fail at some time and I don’t want my entire array down while I wait for repair.
Looking back 15 years ago both of these arguments had merit, but today the discussion is more complicated. Power electronics have gotten more robust. Think back to the last inverter failure you had after commissioning. It probably was not the nuisance it was just a few years ago. Components have gotten much better while engineering, research and development have also improved. Most inverter manufacturers also now offer some sort of service system to make repair time much shorter.
We are creatures of habit. You were taught to tie your shoes a certain way and you probably have not woken up one morning thinking you need to do it differently. The same goes with learning to design solar arrays. It’s easy to stick with the same methodology through the years. So as arrays got bigger we just hung more string inverters and added combiner boxes. But then cost crept in. Labor rate and other balance of systems (BOS) costs made cents per watt really matter. Manufacturers responded by building units with long mean time to failure (MTTF) data and ensuring supply chains had parts in stock to ensure a repair time under 48 hours. These are all signs that the industry is growing up.
String Inverter
So today there are different aspects to consider when choosing between string and central inverters.
Rooftops don’t always have the structural support for a central inverter, so usually string inverters make more sense for these types of installations. String inverters also make sense if you can’t get a crane to the site do to weight or zoning restrictions.
You could use a central inverter for a rooftop solar installation if you’re able to mount the inverter on the ground and run the DC down from the roof. Central inverters also make sense for sites with high costs of labor since they take less time to wire and install.
Central Inverter
Personal preferences also play a significant role in making inverter decisions. Each project has unique needs so that neither string nor central inverters are the better solution all the time. What’s important is to find quality manufacturers that are will to invest in you and your projects with their time, engineering resources and training to allow you the most flexibility. Your customers will thank you.
By: Scott Sullivan, KACO Americas