What are inverters?
Solar panels convert light to electrical direct current (DC) energy. However, the electrical power in your house is alternating current (AC). Inverters transform the energy that your solar panels collect into energy you can use in your home.
What is the difference between central or string inverters and microinverters?
Central (or string) inverters work by linking your solar panels together with “strings.” These strings are then connected to a single inverter. Conversely, microinverters pair each panel with its individual inverter. Microinverter systems are wired in parallel versus being wired in a series like string inverters.
A helpful analogy is to think of inverters like holiday string lights: central inverters are the old kind, where if one bulb goes out, the entire sequence goes out. Microinverters are like the new holiday lights: if one bulb goes out, you simply replace it.
For this and many other reasons, we at My Generation Energy strongly prefer microinverters. Read on to see why microinverters might make sense for your solar energy project, as well as things to watch out for when choosing microinverters.
Benefits of microinverters
Most roofs have shade of some sort. If it’s not trees, it could be a shadow from a chimney. Shade prevents panels from being 100% effective.
A string inverter system can only perform as well as its lowest-performing panel. So if shade or fallen leaves hinders one panel's performance, every other panel must operate at a diminished capacity.
The ability for each panel to work individually using microinverters, however, allows for greater energy production and efficiency - especially when only a few panels are in the shade or under snow. Thus, microinverters are recommended on most home solar projects, since most roofs have some sort of shading.
It’s worth noting that it’s possible to add an optimizer to some central inverters. Systems that have these D/C optimizers, however, must meet a certain voltage in order for the inverter to kick on. If half the system is shaded, it still wouldn’t be sufficient for the optimizer to do its job.
Because each panel can work on its own, microinverters offer a 5-15% increase in production for vs string inverters. This is often due to their superiority in the aforementioned shading situations, but it also applies if a solar panel (or microinverter) is damaged or dirty.
In addition, no two solar panels are identical. Normal solar energy production can vary by up to 5% between solar panels before they even leave the factory. Likewise, solar panels degrade at different rates over time. With a string inverter, solar energy production is always limited by the lowest producers. Microinverters, however, allow each solar panel to work to its highest capacity.
With individual microinverters, the conversion from DC to AC happens at the solar panel level. This ensures that the energy on your roof remains low-voltage. Conversely, with string inverters, high-voltage DC current combines and travels across your roof, increasing the risk of an electrical fire.
Monitoring, Maintenance, Warranty & Support
The lifespan of string inverters is approximately 10-15 years, but they usually only come with an 8- to 12-year warranty (unless you purchase an extended warranty). Thus, chances are good that you’ll need a swap soon after your warranty expires. Compare that with the Enphase microinverters we use, which each carry a 25-year warranty. This demonstrates the manufacturer’s confidence in its product.
Microinverters also excel when it comes to maintenance and support. Using Enphase’s monitoring, you’re able to track each one of your solar panels’ production, verify effectiveness and degradation, and identify when to have a solar panel serviced or replaced. In this way, microinverters indirectly enable you to better take advantage of your solar panel warranty. And that’s in addition to providing a better warranty themselves!
Finally, panel-by-panel monitoring reduces the need for physical on-roof inspections. It’s much easier to pinpoint issues. With a central or string inverter, however, maintenance must begin with a process of elimination. Service techs first have to find the panel in question before they can diagnose and repair it.
System up time
As noted earlier, if one inverter goes down on a central inverter, the entire system goes down. Not so with microinverter systems. One panel can be offline and the rest of your array can still churn out energy. Overall, this results in significantly greater system up time for solar arrays using microinverters.
Easier to Upgrade Your System
It’s much easier to expand a microinverter system if you want to add more panels to an existing array. Solar panels and microinverters can be added one by one. Adding to a system with string inverters, however, is more costly and complex as it requires all new panels to be routed to a separate inverter.
Flaws (but not dealbreakers) of microinverters
Possible failure rate
Simply because there are more microinverters, there is an increased risk that one of them may fail. That said, at least it’s not your entire solar PV system going down! And at least your microinverter is probably under warranty. In our experience, the failure rate is pretty low. We feel this is a minor tradeoff in exchange for having more “brains” to your system.
While comparable in price, microinverters’ up-front cost is possibly slightly higher. However, once you factor in the additional costs you’ll incur using a central or string inverter, we feel that microinverters provide significantly higher value.
First, remember, your system will be more efficient! So you’ll be generating more electricity savings.
Second, in many areas, central inverters must be in compliance with rapid shutdown requirements. Adding functionality to ensure your string inverter is rapid shutdown compliant often incurs additional costs.
Finally, as noted above, there’s a good chance you’ll need to replace your string inverter after its warranty has expired. When you factor in all of the above considerations, microinverters make the most financial sense as well.
Microinverters are best for residential solar
We’ve had over 10 years of experience installing all types of different residential and commercial systems across Cape Cod, South Shore, South Coast and Greater Boston in Massachusetts and Rhode Island. In our experience, microinverters have proven to be superior to string inverters for all of the reasons listed above.
If you have questions, please don’t hesitate to contact us. We pride ourselves on giving honest and fair advice when it comes to solar and would never push you into something that isn’t a good fit for your project.
And if you’d like a peek at the monitoring software, click here to monitor a system in real time! (Please note that if you view this early in the day or on a cloudy day, you won’t see as much production logged until the sun has been up for a while).