Which Is Better? A String Inverter or a Microinverter System?
Choosing between a smart solar system with microinverters vs a string inverter solar system is one of the main decisions you will have to make when going solar. This infographic helps shows the main benefits of a micro inverter system compared to a string inverter:
What is the difference between a Microinverter System vs a String Inverter?
Let’s find out why most Solaray customers choose solar systems powered by revolutionary Enphase microinverter technology, even when they don’t have a shaded roof.
How Does A Micro Inverter System Work?
Let’s start with the basics; a solar inverter converts DC power from the solar panels to AC power that is compatible with your home. The inverter is the working part of the system, making it critical to the performance & reliability of your system as it is the component most likely to break.
With a string inverter (or central inverter), panels are connected in series. This means the string is limited to the output of the worst-performing panel. In series, the voltage of each panel is added together but not the current. It’s the inverter’s job to try and track the maximum power point, but it can only ‘see’ a string of panels, it doesn’t know how much power each panel is producing.
With an Enphase system, a small micro inverter is installed behind each panel and mounted onto the rail. The main benefit of this is that each panel outputs power independently from the rest of the array. It is this technology that has completely revolutionised the solar industry.
1. Microinverters increase output vs a string inverter, even on unshaded roofs
Solar panels are manufactured with a power tolerance. Each manufacturer is different, however, the better brands tend to have a +5W range. For example, a 405W panel from REC Solar will be anything from 405W up to 410W. The only way to take advantage of this is to have a system with panel-level output, otherwise, you will be outputting power at the rate of the worst panel in your array. At best this will be at the panels’ rating, at worst it may be much less (see the next point for more on this).
An independent study by CSIRO for Choice Magazine tested one panel from 15 of the most common solar panels available in Australia. During the test, they found that 12 out of the 15 panels performed under their claimed nominal power, some by as much as 10W. Because only one panel was used in the test, it was impossible to draw strong conclusions about certain brands, however, it certainly drew attention to the fact that there are some large inconsistencies between a manufacturer’s claimed nominal power and the real-world output. For example, a 260W panel from one of the largest manufacturers in China scored a test result of 251W. This inconsistency highlights just how critical it is to have access to panel-level monitoring (we will get to that).
The star performer in this test was LG Solar; their 300W panel produced a test result of 307W. This is in line with what we have seen from our top-of-the-range solar systems from REC Solar installed across NSW, and it emphasises the importance of buying good quality panels.
Trees are not the only thing that affects a solar system’s output
Solar panels work on light (not heat) and so the glass on the solar panels needs to be clean and free of debris for the panel to be at peak performance. Shade from trees is an immediate obstruction that obviously impacts output, but it is the build-up of dust, pollen and pollution over the course of a few months that will typically go unnoticed. This is critical because even if you monitor the output on your central inverter, how are you to know if one panel is underperforming?
Heat is also one of the main factors that affect output from a solar panel, and typically the panels in the middle of the array get much hotter than the panels on the end of each row.
– In well-controlled experiments, PVEL found that Enphase systems operated with 1.7% greater efficiency than string systems
– A DNV KEMA study found that mismatch due to degradation increases over time. Enphase systems operate with 1.45% greater efficiency over 20 years.
Yes, the rain will often wash most of the debris off most of the time, but in NSW we will often have months without rain, and in Sydney, our air is often full of dust, salt from the ocean, pollen and pollution, especially near main roads. With Enphase Micro Inverters only one panel will be affected instead of the whole string.
Small objects also have a dramatic effect on output. In a study by Lee and Raichle from Appalachian State University, they showed how a 1” x 2” wooden pole shaded only 3.2% of one panel’s surface resulted in the Enphase system producing 26% more power on average than the string inverter system, and it was worth noting that the micro inverter system was virtually unaffected by the shading. This small stick could easily be replaced by a few twigs in a real-world environment.
What this study also showed, is that the Enphase system outperformed the string system by 20% in conditions that are often found in the real world, even on an unshaded roof. For more information you can read about the study here:
Low Start-Up Voltage
The Enphase IQ7 Series Micro Inverter has a start-up voltage of only 22V. A good quality string inverter can have a start-up voltage of anywhere from 80V up to 200V or more. Because such a low amount of power is needed to turn on an Enphase system, it should typically turn on earlier and turn off later every day.
Total Increased Output with Enphase
Each of these factors adds up to a significant increase in system performance:
– Power tolerance of around 1.5%
– Baseline advantage of 1.7%
– Impact of module degradation of 1.45%
– Impact of shading from debris etc. 1%
– Impact of system availability 0.6%
The total increase in output is estimated to start at around 6%. Independent test results have shown that system performance can be increased by as much as 20% when one panel is slightly shaded and that Enphase systems recover around 50% of output lost from shade. These are impressive numbers!
2. Panel Level Monitoring Thanks To Microinverters
With a standard system with a string inverter, how do you know if a panel isn’t performing? The short answer is it can be very difficult.
With an Enphase Micro Inverter system, we install a communications gateway that connects your system to the internet. This gives Solaray as your installer access to each panel’s performance and allows us to monitor your system 24/7. We even get automated support messages if one of your panels isn’t working as it should. In the case of a warranty claim, we service a 10-year full replacement warranty from Enphase at no cost to you.
If you buy a string inverter there is no way to know if a panel is underperforming other than to physically get up on the roof and flash test each individual panel. If a panel isn’t working at all, this would be covered under warranty and until it is fixed your system will be turned off.
But what if you suspect a panel isn’t broken but is just underperforming?
Do you think an installer would come out for a service check if you called them and you said your output is 2.7kW when it should be 2.9kW? Even if they did agree to a service check, most installers will charge a fee of $200 or more, especially if they find the problem was dust rather than a technical fault. It’s a guessing game and there are very few solar installers who will play along without covering their costs.
Panels degrade over time and at different rates
As illustrated by a panel’s performance warranty, the output from a panel degrades over 25 years to around 80% of the original rated output. Typically better quality panels will degrade less, and they will also degrade more slowly, but each individual panel is different.
If you have a string inverter, the output of the system will always be at the level of the most degraded panel. At best, all panels perform as expected and your output will be as per the warranty graph. At worst, a panel seriously degrades at any stage over the life of the system and should be replaced under warranty, but again, without panel-level monitoring, you just won’t know about it.
Total system output figures may help, but a drop-off in output may be from a number of factors and finding out what’s wrong can often take time and/or money to figure out and then fix.
This is especially important if you don’t buy top of the range such as the LG NeON H module. Even mid-range panels are known to drop off in output quite significantly over time, and it is only with an Enphase system that you can keep track of each panel and make sure the array is working as promised by the manufacturer’s warranty agreement.
3. Back To Base Reporting and Updates
Each and every Microinverter is capable of transmitting its performance data back to Enphase. This means that Enphase can monitor performance and then use this information to continually improve. Enphase has been doing this for over a decade and is now manufacturing their 7th generation product.
Enphase is also able to reset and update firmware remotely, ensuring that the majority of failures are fixed without a service call required. This is a remarkable transformation in the idea of how a manufacturer is able to provide support and something that no other inverter manufacturer could hope to achieve with their product.
4. Micro Inverters are built to last much longer than a String Inverter
Considering the negative impact and the frustration of historically high inverter failure rates on installers and customers in the solar industry, Enphase knew that a successful new Micro-inverter technology must have unparalleled reliability. The result of this fixation on reliability is an inverter technology that exhibits an order of magnitude improvement in MTBF compared to existing inverter technology.
Mean Time Between Failures (MTBF) is not an indication of the actual life of a product but is rather an indication of the statistical probability that a unit will fail under specific operating and environmental conditions during the period. More information is available in the PDF below.
The Enphase M-Series Micro Inverter scored an MTBF of over 300 years, and this was confirmed by independent testing from Relex, a respected reliability engineering company that performs reliability testing for organizations such as Boeing and the U.S. Military. This is an incredible improvement on the average string inverter, which has an MTBF score of only 10-15 years.
5. Micro Inverter Systems Are Easily Expandable
Microinverter systems are expandable, limited only to your roof space. Solaray can install as many additional panels as you like, and we don’t need to match the panels to your existing array. This allows you to take advantage of any technology gains over the next few years. For example, you may find that in 3 years’ time, 300W panels are the market standard.
With a standard string inverter, you need to match the inverter size to the panel array to ensure high performance. This means that adding panels normally requires the inverter to be replaced. The other limitation is that we need to match the panels in order to add panels to a string. This limits the upgrade window to around a year or so, as trying to find old stock is close to impossible due to the fast advances in technology.
6. Micro Inverter Systems Are Much More Flexible
Using Micro Inverters allows our solar technicians to design a panel array across multiple roof areas – both across different orientations and angles. If you use most of your power in the afternoon, it can be beneficial to have panels facing both north and west to distribute the output of solar power across the day. This avoids having a big peak of solar power in the middle of the day, making it easier to use a large percentage of the solar power as it is generated, and hence increasing the value of your system.
7. Micro Inverter Systems are 100% battery ready
Enphase systems are battery ready and are the preferred option if you are considering batteries in the near future, especially because we can easily add more panels to your array when you install the battery.
The Enphase Energy Management System is unlike anything else currently available because of its compatibility. Enphase Batteries are connected directly to the meter board, where we install a control hub that manages power consumption and storage in the home. This allows the Enphase power storage system to be compatible with any existing solar system. This is in stark contrast to other battery systems that typically connect directly to an expensive hybrid solar inverter and have limited compatibility.
The system itself has been designed to be modular, expandable, easily installed and can be tailored to each customer’s usage profile. A household or business will be able to monitor their usage, solar generation and peak times, and install more battery capacity knowing that it will pay for itself in the quickest possible time. Find out more…
8. Consumption Monitoring Comes Standard With An Enphase System
Integrated, efficient and reliable, the Enphase storage solution combines solar generation, storage and load management technologies into one solution.
The Enphase communications gateway delivers solar production and energy consumption data to Enphase Enlighten monitoring software for comprehensive, remote maintenance and management of the Enphase System.
This is what so many of our customers have been asking for, and we are now able to offer it with all of our Enphase systems.
It really is exciting stuff.
With consumption monitoring, Enphase is the platform for total home energy management;
- Consumption monitoring for total energy insight
- 99.5% accuracy – miles ahead of what we have seen previously
- Bi-directional communications let the Envoy adapt to future utility requirements
- Flexible networking options with integrated Wi-Fi
- Ready for plug-play cellular networking
- Connects up to 600 microinverters
9. Micro Inverter Safety – No High Voltage Needed
Micro Inverter systems avoid the need for high voltage DC cable runs, increasing safety for the homeowner. If a string inverter system was invented today it would probably be deemed illegal due to the need for a high voltage cable run through your home. There is also power leakage on longer DC cable runs, making safe and easy AC cable runs the preferred option whenever possible.
Traditional systems have up to around 600V DC running through your home. High Voltage DC can be very dangerous and should be avoided when possible. An arc-fault can result in fire and a shock fault can result in electrocution. Do you really want to manage the risks inherent in a system with high-voltage DC for the next 20 to 30 years?
High voltage can also cause damage to your solar system:
- Damage to cells, modules, and arrays resulting from the stress of high voltage in the system
- Occurs when voltage potential and leakage current drive ions from semiconductor material to other elements such as module frame and glass, resulting in:
- Significant yield loss
- Increase in O&M cost
- Hot spots
- Irreversible electrochemical corrosion
- An increase of series resistance
- A decrease of shunt resistance
Enphase systems have a max voltage of 48V, which is isolated at the modular level. We then install a safe and easy AC cable run from the panels to your meter board, minimising fire and electrocution risks almost entirely.
The Final Word On A Micro Inverter System vs A Standard Solar Inverter
Enphase Micro Inverter Systems are the next generation of solar technology and the vast majority of Solaray Systems are now powered by Enphase. Enphase systems consistently outperform other solar systems in independent testing, and this is backed up by our portfolio of systems across NSW that on average produce 110% of the expected output. This includes both unshaded and shaded roofs in all weather conditions.
Enphase offers you control. With Enphase we monitor each panel in your system 24/7, we know when something goes wrong and we also know how responsive the support from Enphase is. The average support case is closed in 2 days, an incredible statistic made possible by back-to-base monitoring and remote access to the firmware. We can also offer a system that’s safe thanks to low voltage AC cable runs, it is truly expandable and it is battery ready.
As the largest and most experienced installer in NSW, we have the experience and expertise to make sure your system is installed to the highest standards, and if you have any questions before or after you go solar, you can call us anytime and speak with a solar expert – not a call centre.
For more information please submit a quote request below, or call 1300 525 451. We would love to hear from you.
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- No high-pressure sales, just great advice. Our experts will provide you with all the information you need to find the perfect system for your home or business.
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