Why Micro Inverters should be avoided

Sullivan Solar Power
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In recent weeks we have seen an increased interest among our customers in micro-inverters. Micro-inverters are similar to conventional inverters in that they turn the DC solar power produced by the solar module into AC power which can be used in the home and fed into the utility grid. However, micro inverters are different than conventional inverters in that one micro-inverter is attached to each solar module at the back of the module whereas conventional inverters, a.k.a. string inverters, are mounted at ground level, typically in the garage of a home and a single inverter will convert power for about 30 solar modules. So for a typical home that uses micro-inverters, 30 micro-inverters would be mounted at roof level under the solar array.

Many people believe micro-inverters are new, cutting-edge technology. They are not. Micro-inverter technology goes as far back as the 1980s. The manufacturers of micro-inverters consistently have gone into business and then after several years they are out of business or bought out by larger firms. The promise of micro-inverters is that since there is a single inverter per solar module, the system, as a whole will perform better. The proponents of micro-inverters argue that conditions which reduce system performance such as shading, soiling and differences in electrical characteristics amongst solar modules are mitigated or minimized because only the solar module with such a condition will be impacted and all the other modules will operate at their optimal efficiency resulting in an increase in overall energy production. Mind you, I said the “promise” of micro-inverters...Here is the reality; micro-inverters do not, based on actual real world data compiled across dozens of systems, offer a calculable increase in energy harvest over conventional string inverters. However, in rare instances, micro-inverters are a preferred option over a string-inverter such as when the roof space of the home has multiple different orientations and a single inverter's MPPT tracker will not work, or when a system is subjected to substantial shading. Otherwise, it is the opinion of this author that micro-inverters are to be avoided.

Of the several dozen systems we have installed with micro-inverters, at the request of the customer, ALL have had inverter failures. This makes sense and why we were reluctant to adopt the technology for all customers. Think about it, micro-inverters are electronic devices and they are mounted on the back of a solar module where temperatures exceed 150 degrees. Electronics and heat are not friends. Now, when a micro-inverter fails, it is not an easy fix. Technicians have to get on the roof, rip out the entire array to get to the failed inverter under the array, install the new micro-inverter (God help them) and re-install the system. Does this sound like a good idea?

It is disconcerting to see that several of our competitors have gone to offering micro-inverters standard. In about 2 years they will spend the majority of their time doing service calls to failed systems. This will likely result in their demise as businesses and we will then have to service these orphaned systems. Fine by me, but definitely not good for the local industry as a whole. If you are a homeowner looking to go solar do not get micro-inverters. You will regret it.

7/28/14 Update

I must confess, we installed a microinverter system this year. Despite having doubts about the technology, in early 2014 SMA released their version of the microinverter and we felt compelled to install a system after a customer essentially demanded it. Now, if it were not for the fact that SMA is a rock-solid company with over 400 million Euro in cash in the bank, backed by Danfoss, a 4BN euro company, and the fact that these micro inverters are manufactured in the United States, we wouldn't touch them. However, since SMA products pass Sullivan Solar Power's product selection test; 1) Manufacturer must be in business for as long as the warranty period offered, 2) Must be from a company with solid financials and financial backing, and 3) Must be a product from a socially responsible company, we decided we would give SMA's latest product a chance.

We were the first company in San Diego to install these inverters at the customer's request and, as such, we had to deal with the headaches that can be expected from a new product. The system installation was simple enough. in fact, the product's ease of installation trumps that of the other popular microinverter on the market. However, system commissioning was not simple. After multiple attempts to get the system to operate as expected, we finally got the system to work 100%.

Initially we found that 4 inverters were not checking in. We replaced two of them in accordance with directions issued by SMA's technical support. This did not solve the problem. We then replaced the multigate device. This was not the problem. After further troubleshooting we discovered the factory wiring harnesses had bad crimps. We fixed those and now the system is operating as expected.

After several months of operation it appears the SMA microinverter system is performing well. We will be watching the system closely to make sure it is ready for prime time before we release it to our customer base. It is good to know that we may finally have a microinverter system from a company that we can trust to be around to honor its warranty and therefore we may be able to offer this product once its performance is proven. However, do not misconstrue our willingness to beta-test SMA's new microinverter to mean I take back everything I said in my prior post. In fact, I stand by everything I have said (despite the hateful comments some readers have sent my way). Keep posted, let's see if SMA's engineering superiority can take a bad idea and make it work.

2/12/17 Update

It's been a while since I tended to this blog post, my apologies. So, since my last update to this post, here is the latest on the microinverter debacle.
- SMA decided to discontinue their microinverter product after it performed poorly. No surprise.
- Sunpower decided to offer microinverters integrated into the solar module in their latest convulsion, the Sunpower Equinox. Sorry this is still a bad idea, even if packaged with good solar panels.
- Enphase is currently laying people off and still has not figured out how to make money. Enphase did a round of layoffs in September 2016 and again in January 2017. Their stock price is going into the gutter and they hired McKinsey and Co. to “consult.” This may indicate, what I have long predicted, that Enphase is going to go the way of the Dodo Bird. Sorry, Enphase zealots!

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