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Two YouTube videos sparked a debate about micro-inverters. These videos focused on marketing claims that micro-inverters outperform string inverters when the solar panels are shaded.
Mark Cavanagh, the boss of MC Electrical, said in the video that this simplification is not very accurate: in the runoff between the micro inverter and the string inverter, the better performance depends on the shadow conditions.
We will detail Cavanagh's analysis later, but what caught my attention is that he investigated this issue first. After all, if you have a stack of solar panels that generate a considerable amount of electricity, what can attract your attention, and are you getting the expected electricity?
It turns out that the idea originally came from Eddy May, managing director of NRG Solar, who told SolarQuotes that his interest began with the Enphase kit installed in front of his warehouse in 2017.
"I noticed that when the panel is only partially obscured, Enphase's performance will drop significantly. I started to pay more attention," he said.
May passed this observation to Cavanagh, who decided to conduct a more formal test.
This veteran with 12 years of experience in the industry did "months of testing", but he told SolarQuotes that it didn't take long to see the pattern described in the video at the beginning.
"Eddy told me that this shading situation is indeed related to the micro-inverter. When I tested it, I found that he was right."
Cavanagh said that this is very out of touch with the marketing of microinverters.
"It's as simple as that. If you have a shade, you need a micro inverter. Or an optimizer. And the string inverter doesn't work in the shade, full stop.
"Sometimes it's better to have a string inverter. It doesn't make a big difference, it's pretty niche-the point is that you don't always have to pay extra money to get extra output."
What Cavanagh derives from the work recorded in his video is a simple reset that every electrician knows. This is called the "hose kinking" theory-if you have a panel that is shaded and runs at 5A, the entire string will be limited to 5A.
This is almost the premise of Enphase advertising, as shown below-this is wrong.
As Cavanagh in the video explained in detail, the problem is that the work of solar panels is not that simple. They (usually) have three bypass diodes 1-if they are in the shade, the job of the bypass diodes is to deactivate part of the panel.
This role is purely protective. Shaded cells become consumers of electricity rather than producers. If left unchecked, the battery in this state will heat up and malfunction, so the bypass diode will remove the shielded battery from the circuit.
Cavanagh believes that 20 years ago, the maximum power point tracking (MPPT) software for string inverters simply couldn't work as it does now — today, the power loss caused by partial shading is much lower than in the past.
He tested Fronius and Enphase in two types of shaded conditions—from the side and from the bottom—using Solar Analytics for data collection. The following summarizes the results of the side shadow settings. In this case, the total system loss due to Cavanagh's artificial shadows is about 15%.
He pointed out that Enphase is always better:
In the second video, he tested the inverter under bottom shading-that is, shading starts from the bottom of the solar panel, as shown below. The idea came from Dr. Johnathan Dore of Solar Analytics.
If you shade (for example) four panels, the inverter will choose whether to use four half panels or eight full panels. The string inverter has only one input, so MPPT chooses a higher current to draw.
On the other hand, Enphase microinverters can withstand the highest current that each panel can generate.
The best example is in the "extreme example", where he shaded the lower half of the entire 12 panel string. The performance of Enphase is 1% higher than the Fronius inverter. Other results:
As it happens, in the side shadow, he said,
"One shaded cell takes out the entire string" is a situation you are more likely to encounter when using a micro-inverter!
"The panels on the microinverter system only need to process a little energy [from one panel]."
This means that bypass diodes rarely work on micro-inverter panels-so a shaded battery string will reduce the power of the entire panel.
Enphase has little to say on this topic. Justin Cohen, Asia Pacific Marketing Manager, told SolarQuotes:
"As you know, there are a large number of backyard enthusiasts in the solar field, and we like that the industry has so much enthusiasm on all levels. In productive places, we invest a lot of time to keep these conversations open with the entire industry. However, The manufacturer simply does not have time to respond to each of these rabbit holes."
After completing the activity, Cavanagh has decided to hand over shading and warranty services to the solar panel manufacturer as his next task.
Manufacturers usually use the shade as an out-of-warranty card, because the shade on the bypass diode is difficult. Since it is difficult to imagine that almost any location can guarantee no shadows during the warranty period of solar panels, this is a good battle.
Richard Chirgwin is a journalist with more than 30 years of experience covering a wide range of technical topics, including electronics, telecommunications, computing, and science.
"Backyard Lovers". That cut very deep.
I have put the testing phase in my backyard. Maybe this is me. Ha ha
You must admit, this is very interesting. Will we see the reply video tag?
Mark, I have 3 strings of 8 and 8 and 7 Sunpower panels, a total of 7.5kw and Fronius inverters. Shadowing is a problem I realized, and it is recommended that when installing in 2019, I install Tigo switches on every panel I make.
After 6 months, I noticed that the production I monitored through emberpulse was not what I expected. After some time, the installer came out and found that the 6 Tigo switches on the first string were malfunctioning, and only 2 panels were working on this string. The Tigo was replaced during the warranty period.
Compared with the same month last year, my system is again far below the production level. In fact, the system dropped 54% in a few months compared to when it was first installed.
They came out again to temporarily install the Tigo monitoring system, but I know this will only confirm that the system has failed again.
Do you have any questions to ask me when I will be back. The installer is highly recommended, the system price is more than $12,000, so I did not take any cheap options. I also heard that Tigo optimizer is not suitable for Sunpower panels, but it is suitable for LG and other panels.
You have put the parallel string into one of the mppts.
Which suburb are you in? I would love to see what happened.
Queens Park, Eastern Sydney
SMA has spent a lot of blog posts detailing that there is no benefit to microinverters or DC optimizers.
My system was installed in 2013. I have 30 SolarWorld single panels (15×250 and 15×260 watts) and Enphase M215 micro-inverters, the panels are installed horizontally. My system reports to pvoutput.org. After 8 years, according to the average output (ie efficiency) of each time period per kilowatt of power installed, it ranks in the top 4%-5% of all systems at this site in the world. My system must be going well. (https://pvoutput.org/list.jsp?id=22322&sid=20215)
Yes, I did pay more for this system compared to those who chose string or DC optimizers, but the results were very good.
I think there are two different situations here. The claim for the microinverter is based on the partial shading installed, that is, some panels are in the sun and other panels are in the shade, connected in series. This video is processing partial shadows of a single panel. I think there is no reason to expect that microinverters will be better.
It is interesting to say that modern panels have bypass diodes on the panel to reduce the shadow loss of some panels. They may also contribute to the shading of some panels. It will be fun to test it out.
Has this been done for the SolarEdge optimizer/inverter?
It seems difficult to assess what is the most cost-effective in certain situations. I have a quote suggesting the use of more than 2 strings (True North and True West) of micro inverters. I can’t see how they will bring me any benefit, because I don’t have a shade problem, just a problem from the lower layer to the upper layer. The shadow transition is so late, and my output loss is not much anyway. Now using PVoutput for 3 years of monitoring, I compared my output with 3 local systems that mix similar panels and layouts and a system using micro inverters. On cloudy days, the micro-inverter system performed better than me, but I think I made the right choice, not to use it in terms of overall price/output gain. Now I am considering installing more panels with micro inverters or additional inverters on the east side, but I want to know if it is worth it. Great and interesting article.
I already have two systems, string and micro. Macro performs well in all situations.
The shadow problem is just one of at least twelve reasons why people buy micro-inverters before using batteries.
Compared with hills or buildings, it also depends on the type of shade, telephone poles or palm trees.
More than 70% of people who choose microinverters have no shadow at all, so objectively speaking, it is very important to combine this with all two product features when making an overall purchase decision.
Even so, you will never compare similar.
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1. Preferred real name-you should be happy to add your name to your comment. 2. Put down the weapon. 3. Assume positive intentions. 4. If you are in the solar industry-try to understand the truth, not to sell. 5. Please keep the theme.
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