Microinverters vs String inverters, the pros, and cons
Inverters are one of the most important elements of any solar plant. Solar panels convert light to electrical direct current (DC) energy. However, the electrical power in your home or business is alternating current (AC). Inverters transform the energy that your solar system produces into energy you can use on your property.
Inverter technology has been steadily evolving over the past several decades to better enable properties to reach maximum efficiency from their PV systems. Both string inverters and microinverters do this job for you, but they do so in different ways.
In this blog post, we explain what string inverters and microinverters are, and how they compare to each other for use in your solar energy system.
What is a string inverter?
A string inverter, also called a “central inverter,” is a standalone box that is typically installed close to your main service panel and electricity connection point. A string inverter functions in a series circuit, with there usually being 6 to 12 (or more) individual solar panels in what is known as a “series string.
Advantages of string inverters
The main advantage of a string inverter is that you only need one (or a few) of them to convert the DC electricity coming from your solar system to AC power. This makes troubleshooting relatively easy when things go wrong.
Installing a single string inverter on a solar panel installation is cheaper than installing microinverters. Less labor is required and string inverters are more affordable than many microinverters.
Lower probability of wiring mishap
There are less connection points between solar panels and the string inverter/s. Therefore, there’s a reduced chance that a string inverter setup will be improperly cabled, compared to a microinverter system.
Disadvantages of string inverters
A string inverter system aggregates the power output of groups of solar panels in your system into “strings.” They are connected to multiple solar panels, forcing the performance to be equal to the worst performing panel. Therefore, if one panel in a string of 20 is shaded, cracked or damaged, then all panels on that string will drop to the same voltage as that shaded panel. This can pose a challenge, for instance if a section of a solar plant is shaded for part of the day.
Optimizers are able to smooth voltage and combat production differences, leading to enhanced solar power output, even in challenging, partially-shaded solar installations. Solar Edge is a leading manufacturer of power optimizers.
More complex system expansion
To reach optimal performance from a string inverter, it needs to be working near its peak capacity. Therefore, if you want to increase the size of your solar system at some point in future, those panels will need to be routed to a separate string inverter, adding in additional complexity.
String inverters are generally warrantied to last between 8 and 12 years, whereas microinverters have a 25-year warranty.
Panel-level insight is not possible with a string inverter system, since there are no components affixed to the back of each panel to do the job. While aggregate solar production is viewable, you won’t be able to see if there are individual panel performance problems which could be caused by a crack, defects, or debris.
What is a microinverter?
Microinverters perform the same basic function as string inverters, except they are installed underneath each solar panel. The big difference between microinverters and string inverters is that a solar panel installation with microinverters will typically have the same number of microinverters as there are solar panels (Note: there are microinverters that accept two or four solar panels).
While standard string inverters will cap the electricity production of each panel by the lowest producing panel in that string, microinverters don’t have this problem, since they function in a parallel circuit. A microinverter will take full advantage of the production of each individual panel. It will convert the power generated by each panel to the grid voltage. Each solar panel and microinverter combination can “do their best” and contribute as much power as they can.
Power optimizers are an option for standard string inverters, as well. They function very similarly to microinverters, though electricity is not converted into AC behind each panel. That work still gets done at the string inverter.
Advantages of microinverters
The core advantage of using microinverters is that theoretically, you can yield more solar electricity. The reason for this is that there are slight differences in currents between solar panels.
Suitability for challenging installation conditions
If a solar system is facing multiple angles, meaning some panels are facing south, some east, and some west, then microinverters are the way to go. Or, if you have shading issues from trees or a large chimney, again microinverters would be best.
In these situations, the solar panels will be producing different amounts of electricity at different times of the day, but microinverters will ensure you harvest all of the energy, while with a standard inverter you will lose some of this production.
Microinverters and the add-on optimizers have the ability to track the production of each individual panel, while with a standard inverter you only can track the production of the whole string or system.
System expansion ease
If you were to expand your system in the future, microinverters are simple to add one at a time. Each panel and microinverter pair can be easily added to your existing solar system with ease.
To sum it all up, microinverters are definitely a value-add, but are only recommended if you need to comply with rapid shutdown requirements, have panels facing multiple orientations or you have shading issues. Otherwise, the less-expensive standard inverter is usually more cost-effective and makes your system simpler to maintain.
Disadvantages of microinverters
The main disadvantage of microinverters is the price. They are typically significantly more expensive than a string inverter on a standard solar installation.
If one of your microinverters were to fail, not only would detecting which one has failed be a challenge, but once you did, servicing and replacing the component is not as easy as simply installing a new string inverter. Your solar installer would need to again get up on your roof, work with your racking system, unbolt the solar modules, and replace the microinverter to re-establish AC conversion capability.
Amount of hardware in your system
Since there’s a microinverter attached to every solar panel on your roof or land, that’s a lot of expensive metal equipment out there.
Proximity to wood
Microinverters may act as miniature lightning rods. If you’re in a storm-prone area and have a historical structure with wooden roofing materials, you might want to think twice before installing them.
Microinverters vs. string inverters: which is best?
Most microinverter manufacturers claim very low failure, many are sceptical of these claims. The most complex electronic device in a solar system is the inverter, which is generally also the most common thing to fail. Therefore, logical dictates that having less is generally wiser, except where there are shading issues.