The inverter is the “brain” of your solar system. Solar panels make DC; your house uses AC. The inverter does precisely what the name sounds like; it inverts the current from DC to AC and sends it into your main electrical panel. The inverter also provides the monitoring data for your system to report production to you and your installer.
There are two types of inverters used in solar.
Central or String Inverters are old-fashioned technology. With this setup, all solar panels are wired in series (or strings). All the power the system makes feeds from the boards, over your roof as high voltage DC, and down through one inverter to be flipped to AC before being sent into your main electrical panel. The inverter is usually a big box (about one ′ x 2′) and is mounted on your garage wall – hopefully in the shade as they tend to fail in high heat conditions. If you have a lot of panels, you’ll likely get stuck with two or more of these clunky boxes on your wall because each inverter can only handle so much wattage. Once it hits the string size limit, you must add another inverter.
Central inverters are the weakest link in your system. Because all the panels are connected in strings, that means if the inverter has a problem or there is shade ANYWHERE on the system, the whole system stops working, or the performance of the entire string drops to whatever the least performing panel is putting out. It’s just like those old-fashioned Christmas lights when one bulb burnt out. Each solar string acts like a unit. What happens to one panel on the line happens to ALL of the panels on the series. Some companies will install a power optimizer on each module to overcome this performance loss and help the system compensate for shade, but that can’t overcome the single point of failure in the system. These systems are much more complex to design, are subject to a lot of limitations with string sizing, and are far more prone to failure as these types of inverters only have a 12-15 year lifespan on average and a pretty high failure rate. When they fail, they can take 6 hours and two people to replace, costing $1,500 to $4,000. They also produce less power over the system’s life due to the line loss from the long trip over the roof as DC.
Each panel has its inverter right on the back with a microinverter. The DC is converted to AC right at the meeting. This means the system is more efficient and produces more power over its lifetime – up to 3.1% more than the leading DC-optimized string inverter! Why? Because electricity loses strength the farther it travels before it gets flipped from DC to AC. Lower voltage AC moving across your roof is safer than high voltage DC. It also means that there is no single point of failure because the system is wired in parallel. If one panel or inverter were to fail, the rest of the system would keep making power. Robco recommends Enphase micro-inverters. They offer free lifetime monitoring with the MyEnlighten app and built-in consumption monitoring at no additional charge. Moreover, they do very well in our desert heat, with thousands of installs throughout the Las Vegas valley over the last 15 years. Microinverters have excellent reliability and a 25-year lifespan backed by a 25-year parts and labor warranty at no additional charge. If it is necessary to replace a micro inverter, the process takes less than a minute.
With a central inverter system, one shaded or dirty panel can impact the performance of your entire system. When you use advanced microinverters, each forum performs independently.
Having an inverter on every panel means each one is truly independent. If one or two panels are shaded or dirty, the rest of the system couldn’t care less and keeps making power at maximum capacity. On a central inverter system, there has to be enough light hitting the panels to create the minimum voltage on the string for the inverter to wake up from sleep. Because microinverters are independent, each meeting will wake up from sleep about 30 minutes earlier in the day and go to sleep about 30 minutes later in the evening. (Burst mode is the technical term for this.) That means you get roughly 1 hour more of production daily from a microinverter. Over 25 years, that extra hour can add up.
Mirco inverters have an expected lifespan of 25 years and are warranted (parts and labor) for all 25 years. Central inverters – even the ones with optimizers – typically last 12 to 15 years and often fail even before their expected end of life – especially if they are not installed in a shaded area. While it takes about 6 hours to do the work, it is pretty simple to replace the central inverter. That replacement does not require anyone to get up on the roof. However, they cost $3,000 or more every time they fail! If you had to replace it twice in 20 years, you just added $6,000 to the sticker price of your system and added 2-3 years to the payback time. Replacing a microinverter, on the other hand, takes less than 1 minute, and most repairs can be done with software rather than a service call. How do we know that micro inverters are more reliable? Simple. Robco has installed more than 35,000 Enphase microinverters in the last seven years and replaced only about 100.
You’ll see your system’s performance anytime with the easy-to-use Enlighten app on your phone, tablet, or desktop. Production and consumption monitoring are FREE for the life of your system. No monthly subscriptions are required.
As we’ve learned, central inverters are set up with panels wired in strings. If you want to add to a central inverter system and your inverter is already at capacity, you’ll have to add another inverter and more panels. On the other hand, micro-inverter systems will allow you to add on a single board at a time. You can perfectly size your system as your needs grow. This design flexibility also means that your install team can easily alter your panel layout in the field if needed.
This old myth has been debunked repeatedly, yet it still gets repeated. Think about it. Why would a profitable company with a sterling reputation install exclusively a product that failed in the only market they operated in? If this rumor was at all true, wouldn’t you be seeing something like “Robco installed crappy inverters that died in the heat!” over and over again in our online reviews? Microinverters failing in the heat is not mentioned in any consideration for Robco (or any company that installs microinverters in any of the hot places in the world) because this idea that they fail in the heat is just not accurate. We established several thousand microinverters in 2017 and 2018 – the two hottest years recorded in Las Vegas. In the last five years, we have installed over 35,000 microinverters. They are deployed all over Las Vegas, Henderson, Pahrump, and Mesquite. The older systems have been through multiple punishing summers. The hardware failure rate is currently .27%, less than 100 out of 25,000. The internal operating temperature on Enphase microinverters is 185 degrees. Your roof gets hot, but it’s not 185 degrees up there. Extreme heat poses no issues for microinverters.
Solar panels have no moving parts to wear out or need maintenance. On premium panels like the LG ones installed by Robco, unless there is an impact to cause physical damage, they rarely fail once installed. If a part of the system is going to die, it will be the electronics in the inverters. Central inverters, with or without optimizers, are far more heat sensitive than micros.
For more information about microinverters in the heat and comparisons against string inverters, read more below: