Maintenance and runaway test for bypass diodes

[josealjim]

Dear all,

I need tour help once again. We are about to install 144 polycrystalline modules in front of the office. There will be shadow 3 months a year after noon.

- How can I check the bypass diodes before installation? multimeter?
- How can I check/avoid the runaway fault? We got a thermographic camera.

Diodes specs:

[h=3][/h]Thanks in advance

 

[jaggedben]

Checking diodes before install is not something that I've seen heard anyone place any emphasis on. Since you have a thermographic camera (I assume that's an infrared type camera), you should use that to check for problems once you put the system into operation. In doing so, you'd be way ahead of most installers. You could even partially shade each bypass section of each module one by one and take thermal pictures to insure that each diode is working adequately, but that would be awfully labor intensively.

I have no idea what you mean but runaway fault.

 

[josealjim]

Checking diodes before install is not something that I've seen heard anyone place any emphasis on. Since you have a thermographic camera (I assume that's an infrared type camera), you should use that to check for problems once you put the system into operation. In doing so, you'd be way ahead of most installers. You could even partially shade each bypass section of each module one by one and take thermal pictures to insure that each diode is working adequately, but that would be awfully labor intensively.

I have no idea what you mean but runaway fault.

With diode thermal runaway fault I mean when there is shadow and the diode gets hot and suddenly the shadow goes away and diodes start in forward mode, the temperature of the diode will make the diode leaks much more, therefore the temperature will increase blowing the diode (there some references on internet about this, sorry if I don't explain myself well)

So what u propose is to create partial shadow on each module and check is the temperature gets over 150-200 degs?

 

[josealjim]

Im doing the automation of Biogas production and biogas upgrade so i was thinking of creating alarms to detect diodes faults and replace them. I need your help for this.

- I guess the string current will the the parameter more affected when a diode fails, i suppose that by comparing the different strings currents under same conditions i would know in which string there is a fault and then by the thermographic camera i could replace the modules before having any hotspot.

What do you think about his guys? ideas for the alarm code programming code?

BR and thanks

 

[GoldDigger]

If the diode fails open, you will only see an effect when the segment it is protecting is shaded. The result will be that the voltage drops more than it would with the diode present.
If the diode fails shorted, you will see a drop in Voc and Vmp with no shade.

 

[GoldDigger]

If the diode fails open, you will only see an effect when the segment it is protecting is shaded. The result will be that the voltage drops more than it would with the diode present.
If the diode fails shorted, you will see a drop in Voc and Vmp with no shade.

PS: The voltages will change, but in the failed shorted state Imp will not change noticeably.

 

[josealjim]

Thanks for your answer.


Im working inn a Energy Research institute so we do have several plcs and microcontrollers already working on pilots plants and energy optimization systems (it would not require too much extra investment)


What about this method?:


Single strings tracking (Id do also the array strings harvesting tracking)


- from 7-10 am (no shadow along the year):


* Voltage comparison between strings ---> voltage drop higher than 12v (20 cells per diode config) --> malfunction on the string (open cell, shorted diode)---> check string with thermographic camera


* Current comparison between strings ---> current drop ---> hot cell ----> check with themographic camera


- With shadow with the same pattern on different strings:


* Current comparison between strings ---> current drop ----> bad diode/s ----> check with thermographic camera


Thanks

 

[BillK-AZ]

Decades ago I had the task of monitoring bypass diodes failing open.
We installed isolation diodes for each string, then at night when the cells were not producing any power we used a current limited power supply to energize each string with a reverse current (about 0.5A) that forward biased the bypass diodes.
The voltage of the string was measured. A relatively high voltage indicated an open bypass diode. Took only seconds per string to do manually. Could be automated these days.

 

[josealjim]

Decades ago I had the task of monitoring bypass diodes failing open.
We installed isolation diodes for each string, then at night when the cells were not producing any power we used a current limited power supply to energize each string with a reverse current (about 0.5A) that forward biased the bypass diodes.
The voltage of the string was measured. A relatively high voltage indicated an open bypass diode. Took only seconds per string to do manually. Could be automated these days.

Thanks

 

[josealjim]

Final solution for malfunction detection and maintenance

Final solution for malfunction detection and maintenance

Sorry for not giving too many details.


The 37kw on-grid pv system will be installed in front of our building as showcase.
We will use the new Leonics 3phase multistring inverters (2x15kw)



We are about to introduce in our portfolio energy optimization and management systems. It comprises many power meters distributed along the building, sending data to a micro-controller by wifi. We want to track and manage energy sources (pv system, grid, biogas generators) and loads.
The microcontroller will be linked (RS485) to the inverter as well, so once we have the system I think it would be a good idea to track the performance of the modules (field sensors plus Perez-Ineichen algorithm ) and also detect any kind of malfunction.


Following your indications, lets see if i can come up with a good solution (excuse my ignorance):


TRACKING. Worst months (November, December, January) from 10:30 to 11:30, the rest of the year from 12:00 to 13:00


-(1) Performance: Pyranometer + temperature sensors + Perez algorithm---> Error>Tolerance ---> ALARM
-(2) Strings current tracking: currents between 10-22% of each other everything OK ----> current difference bigger than 30% ----> ALARM
-(3) Array Wh harvesting: real time data from inverter ----> Array harvesting drop 50% ---> ALARM


Would it be better to track (2) and (3)? or just (3) is enough?

Once we detect a malfunction how do we find the wrong module? Thermographic camera, visual inspection and V/I measurement of each module?


MAINTENANCE:


- Cleaning modules every month
- Visual inspection, connections and corrosion every 6 months?
- Thermographic camera every 6 months or only when we detect a fault?
- Should we check open diodes by generating shadow (current near 0A) for example once a year?


Thanks for your help

 

[jaggedben]

...
TRACKING. Worst months (November, December, January) from 10:30 to 11:30, the rest of the year from 12:00 to 13:00


-(1) Performance: Pyranometer + temperature sensors + Perez algorithm---> Error>Tolerance ---> ALARM
-(2) Strings current tracking: currents between 10-22% of each other everything OK ----> current difference bigger than 30% ----> ALARM
-(3) Array Wh harvesting: real time data from inverter ----> Array harvesting drop 50% ---> ALARM

Would it be better to track (2) and (3)? or just (3) is enough?

(2) may occur just with temporary shading, so that might end up being a nuisance alarm for you. Probably a combination of (1) and (3) being best, with (3) being analyzed over a long period of time (monthly and annually) to make sure your production expectations are being met. How you analyze the data is probably more important than anything else.

Once we detect a malfunction how do we find the wrong module? Thermographic camera, visual inspection and V/I measurement of each module?

Thermographic camera will help you narrow it down and then V/I measurements will allow you to confirm.

Another option to look at is combiner products that include string level monitoring.

MAINTENANCE:

- Cleaning modules every month
- Visual inspection, connections and corrosion every 6 months?
- Thermographic camera every 6 months or only when we detect a fault?
- Should we check open diodes by generating shadow (current near 0A) for example once a year?

Most of that is probably overkill for a system this size. Cleaning is likely helpful only a couple times a year, less if it is a rainy climate, more if the panels have a low tilt (under 5deg). Compare the cost of cleaning to the cost of electricity lost due to soiling. Inspection once a year with eyes and the camera is probably a good idea for finding serious problems, including open diodes. Perhaps I'm naive, but diode failure is not known to me to be a major problem with today's modules.

 

[josealjim]

Thanks