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  • Writer's pictureAdam H. Cooke

The Great Debate Solar MicroInverter vs. Power Optimizer I

Reliability is an important factor when considering the options for a solar photovoltaic systems. Clients first inquire about the reliability of solar panels. Solar panels are extremely reliable and rarely fail in a solar energy system. Not the solar panels, but the electronics are the most common source of service problems and failures in a system.

The names of the major players will not be discussed in this article. It doesn't take long to find out who the major players in each area are. You can either leave it to me or have a discussion with me during a consultation.

Inverters in The Good Ole' Day

Inverters convert DC power into AC power, which is compatible with your utility electricity at home or in your business. Inverters were used to convert power from panels strung together. These inverters are also known as central inverters and string inverters. They were not reliable. There were some brands that were more reliable than others, while other product lines had serious issues. They were not designed to last as long as a solar energy system. Often, the replacement of the inverter was included in the investment analysis.

If a string converter fails, the whole system stops producing power.

This component can be replaced in a few minutes or it could take a lot of effort. Sometimes, a rework was necessary if a replacement was not possible. They were very heavy. Installers might need to climb onto the roof to disengage solar panels before replacing them due to poor installation techniques. Perhaps most important, some cases can be difficult to replace because of changes in the electric code.

The New Breed of Inverters


Micro-inverters were commercially viable in the 2000s. This technology combined a single solar panel and a single small-sized inverter, a microinverter. This system architecture has clear benefits and some drawbacks.

Because there is no high-voltage DC power from the roof to micro-inverters, they are safer than DC string or DC string inverters. Because each panel is connected to its inverter, it can be shade resistant. It is easy to mount the panels on the wall without a bulky, heavy box. Panel-level monitoring is revolutionary. The system is fault-tolerant, which was the main selling point. This means that even if one or two of the microinverter fails, all other inverters will continue to produce power.

Micro-inverters have a number of disadvantages, including cost and serviceability. Although microinverter can be more costly, they are still affordable when you consider how much energy they produce and other reliability factors. Opponents dislike the fact that micro-inverters can be replaced on rooftops. The likelihood of making a mistake increases because there are so many of them.

There were many reasons for early opponents to believe they were right. Microinverter failures were frequent in the early generations. Warranty replacements were easy to find and, like the plan, these owners weren't completely without power production. The technology was rewarded for those who stayed with it in the hope of further improvements. There are many generations of microinverter models, and the most recent generations have an impressive reliability record.

Along Came DC Optimizers

DC Optimizers' sales pitch is strong. In terms of cost, they are between microinverters and string inverters. They are similar in shade resistance and panel-level optimization. They have panel-level monitoring, but only DC output monitoring. DC optimizers may seem like a great compromise between the other options.

This sparked the debate on Module Level Power Electronics (or MLPE).

The DC Optimizer architecture has its downsides. These systems still have high-voltage DC wiring running through the attic via a string inverter. The voltages of these systems are usually around 400V, which can pose greater danger of injury and fire. While these systems reduce voltage to safe levels when they are turned off at ground level, the high voltage DC power issue still exists.

Another downside is that you have the worst of both possible points of failure. You need to think about the reliability of power optimizers. They are paired with one panel and a string converter. The whole system will stop production if the string inverter goes down. If power optimizers stop working, it is still necessary to replace a MLPE roof component.

A DC Optimizer system combines the serviceability concerns of microinverters and the reliability issues and single point failure of an old-school string converter.

The Debate Continues

Both sides can be fiercely loyal to one another. Many solar contractors specialize in one type of technology. This is a good thing. There are many benefits to choosing one side over the other, from a training perspective, material stocking, efficiency, and efficiency standpoint.

Both technologies are, in our opinion, good ideas. Each technology has its strengths and weaknesses, but each also has its benefits. Microinverters are the best option when weighing all options. Although it is slightly more expensive, microinverters are our preferred choice because of its safety features and AC monitoring capabilities. The string inverter is our number one influence. Why create a single point for failure? DC Optimizers need MLPE to function properly. The string of optimizers can cause the string inverter's power to stop producing power if it fails. This is something that Optimizer proponents don't often mention. This is not true for microinverters, since there is no string-inverter. Each one acts independently.

A Reason to Choose MicroInverters

I went to service for a system that I had not installed earlier today. It was a DC Optimizer system, the top-selling brand. The monitoring system could not tell me if I was checking for a string issue or a problem with the MLPE roof. This uncertainty makes it more difficult to prepare for service.

When I arrived, the system was in a state that indicated night, but was actually daytime with full sunlight. Further investigation revealed that the Optimizers mounted on the roof were producing the expected voltage given the conditions. It was the string inverter that was the problem. This meant that the entire system was not producing power for several weeks. The owner was only notified of the problem after he had to pay a large electricity bill.

The failed component is not something that a dealer would keep on the shelves. This meant that a warranty claim had to be filed and that a long wait was required for a replacement part. The client will lose over a month of energy production. We are back in the days of string inverters being the only choice. It's a step backward.

We keep spares for all models of microinverters in stock so that we can replace them as soon as possible while we wait for the warranty parts. If we don't have the right replacement, it is possible to replace only one panel that isn't producing power. The whole system is safe from any single failure point.

Bulletproof Systems are not available

In the industry, single points of failure are often referred to as multiple points of failure. All systems will experience a single point failure at the point where they interconnect. It could be a circuit breaker or fuse, but all systems are at risk. It is extremely rare, and it can be easily fixed if the interconnection point fails.

Any system that has MLPE will likely have some kind of failure during its lifetime. It is up to you to determine how severe and how easily it can be corrected. The microinverter solution is our favorite because it eliminates one major point of failure.

Conclusions of the DC Optimizer Vs. Microinverter Debate

DC Optimizer advocates often argue that microinverter promoters are just trying to make more. This is false. The advantages of microinverters are worth the slightly higher price. The cost of the two technologies is the same for most solar contractors, including ours. When we offer alternatives, we charge the cost difference. We could actually make more selling DC Optimizers but it's not in the best interests of our clients.

After selling the industry-leading brand for more than a decade, we have decided to go microinverter. We have a lot of experience in microinverter technology and design.

There will be a reason your dealer is pushing DC Optimizers. It often comes down to cost competitiveness. Long-standing solar dealers are hesitant to accept module-level AC to DC conversion. But, those who made the change to this new system architecture are getting rewarded. Client satisfaction does not lie. A good indicator is dealer success. A solar contractor's reputation is a reflection of their well-made decisions.

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