String Inverters or Micros?

Shopping for a solar electric system can raise a lot of questions. Here at BriteStreet we answer questions all day long about everything from financing options to panel types to “Where does the hot water come out?”. One question
we’ve been hearing more and more over the past few years is, “What type of inverter is best?”. There are two main types of inverters: string inverters and micro-inverters. The answer to the question of whether a string inverter or micro-inverters are best invariably starts with, “It depends…”

First, let’s look at the difference between a string inverter and a micro-inverter. Inverters convert the Direct Current (DC) that solar panels produce into an Alternating Current (AC), so that it becomes usable electricity for your home. A string inverter (also known as a standard inverter or central inverter) is housed in a box slightly larger than a microwave oven. It is typically installed on an exterior wall or inside a garage, most often next to your main electrical service panel or a subpanel (breaker box) inside the home. Micro-inverters are individual units located on the underside of the solar panels on your roof. They are much smaller than string inverters, about the size of a notebook instead of a microwave oven.

Without getting too technical, a string inverter functions in a series circuit (string) while a micro-inverter functions in a parallel circuit. Simply put, a string inverter will cap the electricity production of each panel by the lowest producing panel on your roof. So if one panel is shaded, the whole array of panels decreases in output to match the one shaded panel. A micro-inverter system in the same scenario would take full advantage of the production of each individual panel, and only the panel that was in the shade would decrease in production. In this case a micro-inverter outperforms a standard inverter. So why wouldn’t everybody use micro-inverters all the time? Because if your system is larger than just a few panels, it will likely end up being more expensive to use micro-inverters, and if you don’t have any shade, you could be paying more unnecessarily. But there are other scenarios where micro-inverters can help boost production. For example if you have several arrays on multiple roofs, facing different directions or at different slope angles, then micro-inverters may be recommended even if there is no shade. In these situations, the solar panels will be producing different amounts of electricity at different times of the day. Micro-inverters will ensure you harvest all of the energy, while with a string inverter you may lose some of this production. BriteStreet has system designers in house that can help you determine if micros or string inverters are best for your roof.
Optimizers are yet another option. Optimizers work in combination with string inverters. Optimizers go on each individual panel, equalizing production differences in a similar way to a micro-inverter. If you want the ultimate in power production, optimizers in combination with a high-quality string inverter such as a Fronius may be the way to go for you. There are other aspects to consider as well. Micro-inverters typically have 25-year warranties while string inverters have 10-year warranties. The reliability of micro-inverters was in question several years ago, but with the introduction of APsystems inverters like the ones we sell and install here at
BriteStreet, the technology has caught up. The long 25-year warranty shows the confidence that APsystems has in their product. We’ve yet to see one fail. Basically if you stick with a string inverter of the highest quality like the Fronius inverters we carry, or the highest-quality micro-inverters like APsystems, either one will be very reliable and very unlikely to ever need maintenance or repair. One APsystems unit actually handles two panels, lowering installation cost and overall cost compared to other micro-inverters. Fronius string inverters are the best string inverters in terms of managing shade and multiple groups of panels facing different directions, because of their advanced dual maximum power point tracking (MPPT) technology, but now we’re getting more technical than I intended with this topic. Even with MPPT, you’re better off with micros if you have shade.
Micro-inverters and optimizers both offer an additional advantage which is system monitoring. With either of these devices, you have the ability to track the production of each individual panel, while with a string inverter you can only monitor the production of the whole system. APsystems offers free monitoring for life, which is great since other micro-inverter companies offer a free trial period and then charge you for monitoring on a term basis. Fronius string inverters also come standard with Wi-Fi monitoring capabilities.
In summary, micro-inverters are definitely a value-add, but are only recommended if you have panels facing different directions, if you have shading issues, or if you desire the added granularity in monitoring or the longer warranty. Another advantage is that if you were to expand your system in the future, micro-inverters make it simple to add one panel at a time. However if you have no shade, a simple layout without multiple arrays on different roofs facing different directions, and no interest in individual panel monitoring, then a string inverter is the way to go.
BriteStreet system designers can assist in determining whether a string inverter or micro-inverters will be the most cost-effective option on your roof. If you call us to schedule a consultation at your home we can determine your cost and savings estimates on a custom designed solar electric system. Or if you prefer, our software gives us the ability to conduct a shade analysis remotely. Call us today for assistance in determining whether a string or micro inverter is right for you: