The difference between micro inverter and string inverter
Solar Inverter has one core function: converting the direct current (DC) generated by solar panels into alternating current (AC), which is 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 microinverters can do the job for you, but do the process in a different way.
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 meter.
Each residential solar installation typically has only one inverter or possibly two string inverters; it really depends on the overall size of the solar power system.
String inverters operate in a series circuit, usually with 6 to 12 individual solar panels in a so-called “series string”.
Advantages of string inverters
- Easy troubleshooting
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 in a solar system can fail, it’s probably the inverter – and when something goes wrong, it’s relatively easy to troubleshoot.
Installing a single string inverter on a solar panel is cheaper than installing a microinverter. Fewer man-hours are required, and string inverters are more affordable than many microinverters.
- Lower probability of wiring accidents
There are fewer connections between solar panels and string inverters. Therefore, the possibility of incorrect wiring for string inverter setups is reduced compared to microinverter systems.
Disadvantages of string inverters
- Compliant with fast shutdown requirements
If you live in an area that complies with regulations regarding quick shutdown systems, additional labor and wiring will need to be completed to bring your system into compliance.
A quick shutdown box needs to be installed near the electrical service entrance and control lines need to be arranged between the string inverters and the switchboard.
Since there is current flowing from your panel and from inside the string inverter, the inverter must be disconnected at these two different locations.
Since the cost of adding a quick shutdown requirement to a solar system is not negligible, it is important to check local regulations and ask your installer which type of inverter system is best for you.
- Efficiency of partial shade
Since string inverters require solar panels to be connected in series, if the output of one solar panel is affected, the entire series of solar panels will be equally affected. This can cause a major problem if some parts of the solar panel series will be shaded for a portion of the day.
- More difficult system expansion
In order to get the best performance from a string inverter, it needs to operate at close to its peak capacity. Therefore, if you want to increase the size of your solar array at some point in the future, these panels will need to be connected to a separate string inverter, adding additional complexity and cost.
- Shorter life span
The warranty period for string inverters is 8 to 12 years, while the warranty period for microinverters is 25 years.
- System Monitoring
String inverter systems cannot achieve panel-level insight because there are no fixed components on the back of each panel to do the job.
While the total solar yield is visible, you will not be able to see if there are individual panel performance issues that may be caused by cracks, defects or debris.
What is a micro-inverter?
Microinverters perform the same basic functions as string inverters, except that they are mounted under each solar panel on the roof. Each of these microinverters is about the size of an Internet router.
The major difference between a microinverter and a string inverter is that a solar panel installation with a microinverter usually has the same number of microinverters as solar panels (note: some microinverters can accept two or four solar panels).
The microinverter will take full advantage of the production of each individual panel. It converts the electricity produced by each panel into grid voltage. Each combination of solar panel and microinverter contributes as much power as it “can” and as much as possible.
Power optimizers are also an option for standard string inverters. They function very similarly to microinverters, but without the conversion of electricity to AC behind each panel. This work is still done on the string inverter.
The optimizer smoothes voltages and eliminates production variances, thereby increasing solar output, even in challenging, partially shaded solar installations.
Advantages of micro-inverters
- Fast shutdown capability
New electrical codes require fast shutdown of solar systems so that first responders or firefighters are protected from high voltage if they need to be on the roof or repairing power lines. Microinverters meet these fast shutdown requirements and have this feature embedded in each module.
- More Power
The core advantage of using a microinverter is that more solar power can theoretically be generated. The reason for this is that the current varies slightly between solar panels. When solar panels are in strings, the current is reduced to that of the panel in the string that produces the least.
- Suitable for challenging installation conditions
If the solar system faces multiple angles, i.e. some panels face south, some face east, and some face west, then a microinverter is the way to go. Or, if you are having problems with shadows from trees or large chimneys, again a microinverter would be the best choice.
In these cases, the solar panels will produce different amounts of electricity at different times of the day, but the microinverter will ensure that you collect all the energy, whereas with a standard inverter you will lose some of the power generated.
Microinverters are typically warranted for 25 years, while standard inverters are typically warranted for 8 to 12 years. The reliability of microinverters was questioned several years ago, but now that the technology has caught up with the industry, the long-term warranties on microinverters show the confidence manufacturers have in their products.
- Panel-level monitoring
Microinverters and additional 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.
- Easy system expansion
If you want to expand your system in the future, you can easily add one microinverter at a time. Each panel and microinverter pair can be easily added to your existing solar array without the worry of purchasing, siting and installing additional string inverters.
In summary, microinverters are definitely a value-added product, but are only recommended if you need to meet fast shutdown requirements, if the panels face multiple directions, or if you have shading issues. Otherwise, cheaper standard inverters are often more cost effective.
Disadvantages of micro-inverter
The main drawback to microinverters is the price. They typically cost about $1,000 more than a string inverter on a standard 5kW residential solar installation.
If one of your microinverters fails, not only is it a challenge to detect which one has failed, but once it does, repairing and replacing the components is not as easy as installing a new string inverter on the side of the house.
Your solar installer will need to stand on the roof again, use your racking system, unbolt the solar modules, and replace the microinverters to re-establish AC conversion capability.
- Number of hardware on the roof
Since each solar panel on the roof is connected to a micro-inverter, there is a lot of expensive metal equipment on it.
Micro-inverters can act as miniature lightning rods. If you are in a storm-prone area and have a historic wood structure with shake roofing materials, you may want to think twice before installing them.
Foshan Sunpv Technology Co., Ltd. specializes in the manufacture of solar micro inverters, solar power optimizers and rapid shutdown. Our factory has over 10 years of experience in manufacturing precision electrical products. Our high quality solar related products are sold well in many countries around the world. We have certifications from various countries and are committed to providing our customers with the highest quality products and services! We warmly welcome new energy companies from all over the world to establish long-term cooperation with us!
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