Micro Inverters VS String Inverter (The Shading Debate is ...

Putting aside relative safety concerns with household AC v high voltage DC (it's there but not a big deal if a system is well installed), the two main benefits of micro inverters are:
i. dealing with tricky rooftops
ii. expandability

1. Tricky Rooftops or similar scenarios
There are scenarios where micros make more sense, for example when putting solar PV on a rooftop with these "modern" home designs with multi faceted roofs, multiple orientations etc with different amount of space available for panels. Such rooftops can be PITA for string sizing with string inverters, e.g. you might have space for 4 panels west, 9 south and 5 east. That's a bugger to set up with a string inverter, even with a model with 3 MPPTs the string voltages are barely going to be high enough on the smaller strings and you can't really parallel them either unless you make the strings of the same size requiring a reduction in the available production capacity.

2. Expandability.
It's generally much easier to expand a system later on with micros than with a string system. Add another panel or three? No issue. Use a different panel because the old ones are no longer available? No problem. Use a later model of micro inverter? No problem. Have a bit of space on another orientation you'd like to add panels onto? No problem. These sort of expandability options are not always so simple with a string inverter, especially if your string is already close to MPPT voltage limits, or you just can't make the string MPPT maths work.

The primary downside is the additional cost of micros per kW and being tied to that platform.

Micros are a good solution and quality units like Enphase work very well but they are more expensive. Quality string systems are also very good. It's just a matter of assessing which is more suitable for the individual application.

Installer simplicity
There are installers here which have made the call to ditch string inverters altogether. Instead of having to stock a wide range of inverters of different sizes and sales rates, they now only need to have stock of micros and panels as they can be deployed in every situation.

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Solar inverters have one core function: converting the direct current (DC) generated by the solar panels into alternating current (AC), the type of electricity used in your home.

Inverter technology has been steadily evolving over the past few decades to better allow homeowners to get the most power out of their PV systems. As a solar homeowner, both string inverters and micro inverters can do the job for you, but do the process in different ways.

What is a string inverter?

A string inverter (also called a "central inverter") is a self-contained box that is usually installed near your main service panel and electricity meter.

 

There is usually only one inverter per residential solar installation, or maybe two string inverters; it really depends on the size of the overall solar system.

 

String inverters operate in a series circuit, usually with 6 to 12 individual solar panels, called a "series string." SMA is a leading string inverter manufacturer.

Advantages of String Inverters

Easy to troubleshoot

The main advantage of string inverters is that you only need one of them to convert the DC power from the solar array to AC power. If anything goes wrong in the solar system, it's most likely the inverter - and when something goes wrong, troubleshooting is relatively easy.

 

cost

Installing a single string inverter on a solar panel installation is cheaper than installing a micro inverter. Fewer man-hours are required, and string inverters are more affordable than many micro-inverters.

 

Less chance of wiring faults

There are fewer connections between solar panels and string inverters. As a result, string inverter setups are less likely to be wired incorrectly than microinverter systems.

 

Disadvantages of string inverters

Meets fast shutdown requirements

If you live in an area that complies with rapid shutdown systems, additional labor and wiring will need to be done to bring your system into compliance.

 

A quick-close box needs to be installed near the electrical service entrance, and control wiring needs to be routed between the string inverter and the switchboard.

 

Since there is current flowing from your panel and the string inverter itself, the inverter must be disconnected at these two different places.

 

Since the cost of adding a quick shutdown requirement to your solar system is non-negligible, it's important to check your local codes and ask your installer which type of inverter system makes the most sense for you.

 

Partial Shade Efficiency

Since string inverters require solar panels in series, if the output of one solar panel is affected, the entire series of solar panels will be affected equally. This can cause major problems if parts of the solar panel array are shaded for part of the day.

 

harder system expansion

To get the best performance from a string inverter, it needs to work close to peak capacity. So if you want to increase the size of your solar panels at some point in the future, you will need to connect those panels to separate string inverters, adding additional complexity and cost.

 

shorter lifespan

String inverters are covered for 8 to 12 years, while micro inverters are covered for 25 years.

System monitoring

String inverter systems cannot gain panel-level insight because there are no fixed components on the back of each panel to do the job.

 

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While total solar production is visible, you cannot see if there are individual panel performance issues that may be caused by cracks, defects or debris.

 

What is a microinverter?

Micro inverters perform the same basic functions as string inverters, except that they are installed under each solar panel on the roof. Each of these microinverters is about the size of an internet router.

 

The biggest difference between microinverters and string inverters is that solar panel installations with microinverters usually have the same number of microinverters as there are solar panels (note: some microinverters can accepts two or four solar panels).

 

Enphase is a leading manufacturer of microinverters. Enphase microinverters have been on the market since and have become an integral part of their thriving business. Their researchers have been studying how to best apply the principle of maximum power point tracking (mppt) to their components to enhance solar photovoltaic power generation.

 

While standard string inverters will limit the amount of electricity produced per panel by the lowest producing panel on the roof, micro inverters do not have this problem because they operate in a parallel circuit.

 

Microinverters will take full advantage of the production of each individual panel. It converts the electricity produced by each panel to grid voltage. Each solar panel and micro-inverter combination can "do what it can" and provide as much power as possible.

 

A power optimizer is also an option for standard string inverters. They function much like microinverters, but the power isn't converted to AC behind each panel. This work is still done on string inverters.

 

The optimizer smooths voltages and eliminates production variances, improving solar output even in challenging, partially shaded solar installations. Solaredge is a leading manufacturer of power optimizers.

 

Advantages of Microinverters

Quick shutdown capability

New electrical codes require that solar systems be shut down quickly so first responders or firefighters are protected from high voltages when they need to work on rooftops or power lines. Microinverters meet these fast turn-off requirements and embed this functionality into each module.

 

more power

The core advantage of using microinverters is that more solar power can theoretically be generated. The reason is that the current flow is slightly different between solar panels. When solar panels are in a string, the current is reduced to that of the lowest-yielding panel in the string.

 

Suitable for challenging installation conditions

If the solar system faces multiple angles, meaning some panels face south, some east and some west, then microinverters are the way to go. Alternatively, if you have problems with shade from trees or large chimneys, microinverters are also best.

 

In these cases, the solar panels will generate different amounts of electricity at different times of the day, but the micro-inverter will ensure that you reap all the energy, whereas with a standard inverter, you will lose some of that power.

 

life

Micro inverters typically have a 25-year warranty, while standard inverters typically have an 8- to 12-year warranty. The reliability of microinverters was an issue a few years ago, but now that the technology has caught up with the industry, the long warranty of microinverters shows the confidence that manufacturers have in their products.

 

Panel level monitoring

Micro inverters and add-on optimizers are able to track the production of each individual panel, whereas with standard inverters you can only track the production of the entire system.

 

System expansion is easy

If you're expanding your system in the future, adding microinverters one at a time is simple. Each panel and micro-inverter pair can easily be added to your existing solar array without the hassle of purchasing, sited and installed additional string inverters.

 

All in all, microinverters are definitely an added value, but are only recommended if you need to meet fast shutdown requirements, face panels in multiple directions, or have shading issues.

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