String inverters are the cheapest options, but they are less efficient under shading because they reduce the power production of every panel to that of the lowest producing panel. Micro-inverters are efficient because they take full advantage of the power production of each solar panel. They also provide panel-level monitoring, but they are relatively expensive.
If you want to reduce your power bills by going solar, this discussion should interest you.
String inverters are the standard inverter set-up for solar power systems. The micro-inverters were introduced recently, but they’re fast becoming the new standard.
So, the big question is ‘which is better?’
This post will answer this question by properly examining micro-inverters and string inverters.
We’ll explain how they work, as well as their advantages and disadvantages. Lastly, we’ll tell you when each of them is best for you.
At the end of this article, you’ll have the information to help you choose the inverter set-up that’s best for your solar system.
Micro-Inverters vs String Inverters
Micro-inverters and String Inverters are technically different types of solar inverters.
Solar inverters are necessary for power conversion because solar panels produce DC (direct current), but a home relies on AC (alternating current).
So, the main job of solar inverters is to convert the DC produced by solar panels to AC that your appliances can use at home.
String inverters and micro-inverters both do this job, but differently.
What is a String Inverter
A string inverter is a stand-alone unit usually installed near your service panel to which a “string” of solar panels is connected.
A string is a group of solar panels connected in a series. So, for the string inverter, the individual solar panels are connected into a “series string”, and the string is connected to a single inverter.
In this connection, all your panels are essentially working as one big unit.
If you have a large system, instead of having all your panels wired into one series string, they can be wired into 2 series strings, which are connected to the single string inverter.
Advantages of String Inverters
You may want to go for a string inverter for your solar system because of its:
- Lower number of failure points
- Easier troubleshooting
1. String Inverters are cost-effective
For solar inverters, string inverters are the most cost-effective option.
They also require fewer labour hours for installation.
Thus, for a solar system of any size, the overall cost of having a string inverter system is lower than that of having a micro-inverter system.
2. The points of failure are reduced
Simply put, what can go wrong in a string inverter system is significantly reduced.
Unlike micro-inverter systems that require an inverter for every solar panel, string inverter systems use only one inverter no matter the number of solar panels.
Inverter failures are the leading cause of solar system failure. So, the more inverters a solar system has, the more failure points it has.
String inverter system also has less electrical wiring than micro-inverters. This also means a lower probability of wiring mishaps.
3. Troubleshooting is easier with string inverters
Because of having only one inverter, any problem with the system is easily traceable for rectification.
But before opting for a string inverter, you may want to consider some of the challenges of this PV system.
Challenges of String Inverters
- Less efficient under shading
- Expansion is more difficult
- Panel level monitoring is impossible
- Relatively shorter lifespan
1. Less efficient under shading
The biggest disadvantage of a string inverter system is that the system is only “as strong as its weakest link”.
This means that a poorly-performing panel in the system will drag down the performance of other panels to its poor level.
Consider a system that has three 250W solar panels.
If just one of the three panels is partially shaded and produces only 100W of power, every panel in the string system will produce 100W. The total production will be 300W.
This problem of string inverters comes from the connection of the panels. Because the panels are connected in series, the current produced flows in a path through them all. So, if there’s something affecting the flow of current in one panel, all the panels in the string will be affected in equal measure.
2. It’s relatively difficult to expand a string inverter system
Increasing the size of a string inverter system is relatively complex and costly.
This is because the size upgrade of such systems requires routing the new panels to a separate inverter. That is, connecting the new panels into a series string and connecting this to a new string inverter.
3. Panel-level monitoring is not possible
The string inverter will give you good data about aggregate solar production, but cannot show you data on the performance of each panel making up a string.
In a string inverter system, a group of solar panels connected to form a series string essentially functions as “one big solar panel”.
So, you can get insights on the whole. You can see the production of the “one big solar panel”. However, insights on the individual panels making the whole cannot be obtained. You cannot tell if there’re performance problems with particular panels.
4. String Inverters have relatively shorter life spans
String inverters are usually warrantied to last 8 – 12 years, whereas micro-inverters are warrantied to last 25 years.
Know that solar panels have an average lifespan of 25 years. So, when using a string inverter, you’ll have to buy a new inverter at least once in the life of your system.
What’s a Micro-inverter?
A micro-inverter is a small inverter (about the size of an A5 paper) usually installed underneath or beside a solar panel. In a micro-inverter system, every solar panel is paired with a micro-inverter to manage its DC-AC power conversion.
The number of micro-inverters used is usually equal to the number of solar panels in the system.
Benefits of Micro-inverters
Micro-inverters were developed to address the challenges of string inverters.
The benefits of micro-inverters include:
- Efficient under shading
- Suitable for challenging installation conditions
- Ease of expansion
- Panel-level monitoring
- Longer lifespan
1. Micro-inverters are efficient under shading
The biggest advantage of micro-inverters is that they contribute all the power produced by every solar panel in your PV system.
The solar panels are wired in parallel, each to its micro-inverter, so each functions independently. This means that problems in one panel do not affect other panels.
Let’s go back to our example of a system with three 250W panels.
If just one of the three panels is partially shaded and produces only 100W of power, every other panel will still produce 250W of power. The total production will be 600W (which is double the production of a string inverter system in the same situation).
2. Micro-inverters are suitable for challenging installations
Micro-inverters eliminate power losses that come from having panels facing different directions or on roofs with multiple pitches (steepness).
If panels are not facing the same direction, or are not tilted at the same angle, they’ll produce different amounts of power at each point in time.
With a standard string inverter, the power production of each panel in the system is reduced to that of the least producing panel, resulting in power losses. But micro-inverters utilise the full power produced by each panel in the system, ensuring that there are no power losses.
3. Expansion is easy with micro-inverters
Increasing the size of your system is easy. All you need is to add another “panel + micro-inverter” combo to your array one at a time.
This means that with a solar inverter system, you can start small and gradually scale up with time.
4. Panel-level monitoring is possible with micro-inverters
Because the solar panels work independently in a micro-inverter system, you can obtain information about the performance of each panel.
5. Micro-inverters have a relatively long lifespan
The micro-inverters are warrantied to last 25 years, which is as long as your solar panels will last. Whereas string inverters can only last half of that.
Downsides of Micro-inverters
Micro-inverter systems are not without their downsides.
- Relatively expensive
- More points of failure
- Troubleshooting and maintenance is relatively difficult
- Susceptible to damage by lighting
1. Micro-inverters are relatively expensive
One of the main disadvantages of micro-inverter systems is their high cost.
For the popular 5kW system, the micro-inverter option is more expensive than the string inverter option by up to $1000 or more.
2. Micro-inverter systems have more points of failure
The part of the solar system that is most likely to fail is the inverter. So, having a lot of inverters in your system is like opening the door for problems to enter.
3. Troubleshooting and maintenance is relatively complex with micro-inverters
If there’s a problem with one of the inverters, it’ll be challenging to detect.
When it’s detected, servicing or replacing it is also difficult. An installer will need to climb up your roof and lose the solar modules.
4. Micro-inverters are susceptible to damage by lightning
Micro-inverters on your roof can act as miniature lightning rods and get damaged.
This applies even to micro-inverters having built-in surge protection. A surge with sufficient energy can exceed the built-in protection and damage the equipment.
What is better, Micro-inverters or String Inverters
Choosing between micro-inverters and string inverters is not straightforward. Just as it is in many other decision-making in life, particular circumstances determine which is better.
- Cost. If you’re on a budget and want to make only a one-time investment in a solar system, the string inverter is better. This is because it is cheaper than a similarly-sized micro-inverter setup.
But if you are prepared to make further solar investments in the future, the micro-inverters may be better. This is because it allows you to start small and easily scale up.
- Shading. If shading will not be a problem, you can go for string inverters. But if your panels will frequently be shaded (even slightly), micro-inverters are better for you.
- Orientation of solar panels. If because of your rooftop, the panels will face different directions or will be tilted differently, go for micro-inverters to reduce power losses.
- Performance monitoring. If you desire a very detailed performance monitoring of your system, go for micro-inverters. This is because they provide insight into each solar panel in the system.
- Thunderstorms. If you are in an area that is prone to thunderstorms, go for a string inverter. This is because lightning will easily damage micro-inverters on your rooftops.
Are Solar Panels with Micro-Inverters better?
Considering that micro-inverters were developed to tackle power loss problems that plague standard string inverters, you can say that they are better.
Solar panels with micro-inverters are definitely better at reducing power losses due to shading and complex setups of solar panels. They are also better at providing more detailed (panel-level) performance monitoring of the solar system.
However, they are not without their downsides. As such, there are circumstances when you may be better off with standard string inverters.
Check Out Our Guides to Solar Inverters
We have a series of unique guides to solar, solar finance, batteries and more, if you are looking to do more in-depth research into solar inverters check the below:
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