Green Light Renewable Services

Is this your year to go solar?

header photo

The Truth About String Inverters vs. Microinverters

July 7, 2016

When you choose a solar installer, you’re also choosing a specific type of inverter — string inverter or microinverter? Before we get into the differences between the two, let’s get down to basics. What exactly does an inverter do?

When you invest in a solar system, you’re purchasing two major components: the panels themselves and an inverter system. The panels absorb energy from the sun, but how does that energy turn into the electricity that keeps your home appliances running? That’s where inverters come in. Perhaps a better name would be “converters.”

The inverter is a critical part of your solar system that converts DC electricity into AC electricity. AC is what’s usable in your home and on the grid. Without an inverter, the panels on your roof or ground mount are just panels. So what’s the difference in inverters?

String Inverters

String inverters came first and are often cheaper when compared to a micro inverter system — at first. String inverters work for “perfectly installed panels” meaning they’re on a single plane and are never affected by shading or other inclement weather conditions. The older technology was introduced in 1991 by SMA Solar Tech and hasn’t changed much since.

These inverters work by “daisy chaining a ‘string’ of solar panels which produce DC electricity and wiring the final panel’s electrical leads to a device known as a central string inverter which converts DC to AC.” The reason many people choose string inverters is because they’re told it will be cheaper than a microinverter system. This is only partially true. The cost is lower (at first), but troubleshooting any problems is much more costly and time-consuming.

This chaining effect means that when one panel is producing poorly, all the panels’ production levels will drop to the lowest performing panel. The daisy chain also makes it more difficult to identify exactly where the problem is occurring. A good metaphor for understanding the ineffectiveness of string inverters is a strand of Christmas lights. When one little light goes out, so does the entire string. When the entire string is out, it’s even more difficult to find that one pesky light that’s causing the problem.

Microinverters

Enphase was the first manufacturer to introduce microinverters in 2008. Different than string inverters, a microinverter is a small, intelligent, waterproof inverter located beneath each panel. Each inverter is connected to the others by a main cable that’s wired to the customer’s home utility panel. Microinverters are engineered to be 100% “fault-tolerant” as there’s no single point of failure.

Though the microinverter technology is still at a higher price point (but not for the long…), the technology is far more sophisticated when considering your ability to monitor your solar system. When a string inverter fails, as discussed above, it’s incredibly difficult to locate exactly where the failure has occurred. The monitoring system for microinverters, and specifically Enphase microinverters, allows operators to monitor the power production of each individual panel, making it much easier to diagnose and fix a faulty panel if a failure was to occur.

What’s the biggest difference?

String Inverters

Pros:

Cons:

  • any problem with one panel is felt across the whole array’s production
  • large inverters take up space on the side of your house/garage

Microinverters

Pros:

  • utilizes ‘power point tracking’ so if one panel is shaded, the other panels are not affected at all
  • easier to troubleshoot since there’s only a single point-of-failure
  • performance issues con be identified through remote monitoring

Cons:

  • traditionally cost more per peak watt, but decreasingly so with improving technology
  • can prove more costly and complex to install because the inverters must be placed in tandem with the individual panels

String/central inverters and micro inverters are both equipped with “Maximum Power Point Tracking” (MPPT) algorithms that “calculate the optimal power output and make necessary adjustments to ensure the highest power production. Microinverters perform the task for each panel, a crucial difference that avoids the ‘Christmas lights effect’ of an array with a central inverter.” A central/string inverter is only capable of analyzing its MPPT at the system level, so your entire system production will be negatively affected if your installation is at all impacted by shading or debris. Microinverters can still operate optimally despite shading because they analyze its MPPT at the panel level. Since microinverters optimize the power output of each panel, manufacturers report a 15% increase of power per panel.

Debunking the myth: Microinverters are more expensive

Longevity is the name of the game. When a solar contractor sells you the inverter system, you’re bound to hear that string inverters are less expensive. This is true — to a point! What the installer is NOT telling you is that string inverters will likely need to be replaced twice more in their lifespan than microinverters, and the wiring must be redone once every 10-12 years. If you contractor sells you a string inverter system, he’s guaranteeing himself work in the future. A microinverter system can carry an average lifespan of 332 years.

Go Back

Comment