diy solar

diy solar

Blocking Diode Question please:

I completed the testing this morning:
  • Conditions were ideal with a clear blue sky and 24°C temperature.
  • After some experimenting with positions, I ended up using an east-west facing setup as this aligned the panels best with the sun.
  • One panel was fully illuminated while the other was only receiving ambient light. No shading was present.
  • Both panels (HSL60P6-PC-1-260) are almost new, from the same batch and have no defects.
  • The panels were cleaned with a microfibre cloth prior to testing.
  • The battery had been run down prior to the test, and had approximately 150W resistive load across it to ensure the voltage didn't rise to a point where the charge controller would limit output.
  • The MPPT used during the test was an EPever Tracer 2210AN, which is a 20A, 100V unit. The tests were all within specification of the MPPT, with the second parallel power test approaching its maximum output current.

I followed the test procedure documented above and produced the following results:

ParallelSeries
VOC34.2V68.6V
MPPT Output Amps18.5A12.9A
MPPT Output Volts14.5V14.3V
Output Watts268.25W184.47W
Result: This test showed a 45.4% higher power output when the panels were wired in parallel.

The tests were then repeated in reverse to ensure no time-related factors influenced the results:
ParallelSeries
VOC34.2V68.6V
MPPT Output Amps19.7A13.5A
MPPT Output Volts14.6V14.5V
Output Watts287.62W195.75W
Result: This test showed a 46.9% higher power output when the panels were wired in parallel.

To be sure of the results I also swapped the position of the panels and repeated. The results were the same with 46% more output in parallel.

The temperature difference between the panels was substantial during the tests, with one being almost too hot to touch, while the other wasn't much above ambient temperature.
I've also attached a photo of the test setup to show that it did in fact happen ;)

To be honest I wasn't expecting such a large difference. If anyone has any feedback, suggestions or questions I'd be happy to follow up.
Exactly as expected. Thanks for the test results.
 
Yes its exactly what I expected as well.
Two series panels is probably a worst case situation for this test.
And the parallel shunting diodes across the non performing panel will not save it.
Well done Octal.
 
I completed the testing this morning:
  • Conditions were ideal with a clear blue sky and 24°C temperature.
  • After some experimenting with positions, I ended up using an east-west facing setup as this aligned the panels best with the sun.
  • One panel was fully illuminated while the other was only receiving ambient light. No shading was present.
  • Both panels (HSL60P6-PC-1-260) are almost new, from the same batch and have no defects.
  • The panels were cleaned with a microfibre cloth prior to testing.
  • The battery had been run down prior to the test, and had approximately 150W resistive load across it to ensure the voltage didn't rise to a point where the charge controller would limit output.
  • The MPPT used during the test was an EPever Tracer 2210AN, which is a 20A, 100V unit. The tests were all within specification of the MPPT, with the second parallel power test approaching its maximum output current.

I followed the test procedure documented above and produced the following results:

ParallelSeries
VOC34.2V68.6V
MPPT Output Amps18.5A12.9A
MPPT Output Volts14.5V14.3V
Output Watts268.25W184.47W
Result: This test showed a 45.4% higher power output when the panels were wired in parallel.

The tests were then repeated in reverse to ensure no time-related factors influenced the results:
ParallelSeries
VOC34.2V68.6V
MPPT Output Amps19.7A13.5A
MPPT Output Volts14.6V14.5V
Output Watts287.62W195.75W
Result: This test showed a 46.9% higher power output when the panels were wired in parallel.

To be sure of the results I also swapped the position of the panels and repeated. The results were the same with 46% more output in parallel.

The temperature difference between the panels was substantial during the tests, with one being almost too hot to touch, while the other wasn't much above ambient temperature.
I've also attached a photo of the test setup to show that it did in fact happen ;)

To be honest I wasn't expecting such a large difference. If anyone has any feedback, suggestions or questions I'd be happy to follow up.
You missed the Vmp measurement. That's the measurement at the input to the SCC. Can you measure current into SCC?
To get a better understanding, also measure a single panel, direct to sun and angled off.

What is MPPT output volts? Is that same as battery voltage? 14.5V seems extremely high battery voltage for this test.
 
At the end of the day, its what the mppt software decides to do, and we are pretty much stuck with the result.
Here is mine, due east/west Melbourne Australia, panels bolted onto a 60 degree equilateral triangular frame.
Best results by far, parallel connection of the east and west series strings, with series blocking diodes.
At solar noon, all panels contribute equally. Power output is essentiallya a flat plateau all day, from sunrise to sunset.
 

Attachments

  • 2018-01-24_0001.jpg
    2018-01-24_0001.jpg
    835.9 KB · Views: 5
I completed the testing this morning:
  • Conditions were ideal with a clear blue sky and 24°C temperature.
  • After some experimenting with positions, I ended up using an east-west facing setup as this aligned the panels best with the sun.
  • One panel was fully illuminated while the other was only receiving ambient light. No shading was present.
  • Both panels (HSL60P6-PC-1-260) are almost new, from the same batch and have no defects.
  • The panels were cleaned with a microfibre cloth prior to testing.
  • The battery had been run down prior to the test, and had approximately 150W resistive load across it to ensure the voltage didn't rise to a point where the charge controller would limit output.
  • The MPPT used during the test was an EPever Tracer 2210AN, which is a 20A, 100V unit. The tests were all within specification of the MPPT, with the second parallel power test approaching its maximum output current.

I followed the test procedure documented above and produced the following results:

ParallelSeries
VOC34.2V68.6V
MPPT Output Amps18.5A12.9A
MPPT Output Volts14.5V14.3V
Output Watts268.25W184.47W
Result: This test showed a 45.4% higher power output when the panels were wired in parallel.

The tests were then repeated in reverse to ensure no time-related factors influenced the results:
ParallelSeries
VOC34.2V68.6V
MPPT Output Amps19.7A13.5A
MPPT Output Volts14.6V14.5V
Output Watts287.62W195.75W
Result: This test showed a 46.9% higher power output when the panels were wired in parallel.

To be sure of the results I also swapped the position of the panels and repeated. The results were the same with 46% more output in parallel.

The temperature difference between the panels was substantial during the tests, with one being almost too hot to touch, while the other wasn't much above ambient temperature.
I've also attached a photo of the test setup to show that it did in fact happen ;)

To be honest I wasn't expecting such a large difference. If anyone has any feedback, suggestions or questions I'd be happy to follow up.

You should never be connecting panels in two different directions in series.

Current will be limited to panel with least illumination current.

The panel with full illumination will be driven up in loaded voltage (above its optimum Vmp) to allow some of its illumination current to be bled off down through PV cells inherent diodes to make the net series current match less illuminated panel.

This is equivalent to having two panels in series in same direction with some amount of uniform shading attenuation on half the array.

Depending on how low the illumination gets on partially shaded side, the bypass diodes will eventually kick in, increasing current but shaded side will be limited to forward conduction of bypass diodes (if 3 bypass diodes in panel it would be about -2v). The total array would then have current of the fully illuminated panel but total array voltage will be near Vmp of single illuminated panel minus the 2v of bypassed panel.

From the picture, it is unlikely the less illuminated side got low enough in illumination current to kick in its bypass diodes.
 
Last edited:
You should never be connecting panels in two different directions in series.
Current will be limited to panel with least illumination current.
You know that, and I know that, but some people here feel rather strongly that the inverse diodes fitted to the shaded panel solve that problem.
It definitely does not !
 
You missed the Vmp measurement. That's the measurement at the input to the SCC. Can you measure current into SCC?
To get a better understanding, also measure a single panel, direct to sun and angled off.

What is MPPT output volts? Is that same as battery voltage? 14.5V seems extremely high battery voltage for this test.
I did measure Vmp, however I didn't consider it relevant to the results as I'm only concerned about the amount of usable power produced by either configuration.

In any case, Vmp for parallel was 31.2v. I was surprised at the time to see that Vmp for series was lower at 28.3v. I went as far as powering down the whole system and starting again, just for it to settle back at 28.3v. This now makes sense having seen RCinFLA's response, as the voltage has to drop while passing through the panel that's not in direct sunlight.

In hindsight I should have tested just a single panel in sunlight. I suspect it would have performed better on its own than the two in series.

Regarding the battery voltage, you're right in that it was quite high. This is why I was running a load across the battery to ensure it didn't hit 14.8 volts, which is when the charge controller will go into constant voltage mode. I made sure CV mode didn't occur during any of the tests - it's quite obvious when it does, as the power output drops quite quickly.
 
Guess I missed the part where a blocking diode was involved in this test.

I thought you were going to test two-panel parallel output net power, facing east and west, with and without blocking diode in each parallel panel, to see if having the blocking diodes made any difference in net output.
 
Guess I missed the part where a blocking diode was involved in this test.

I thought you were going to test two-panel parallel output net power, facing east and west, with and without blocking diode in each parallel panel, to see if having the blocking diodes made any difference in net output.
It seemed unanimous earlier in the thread that blocking diodes are unnecessary and generally a waste of time and energy. We then moved on to series vs parallel connections for panels facing different directions.
 
Its all very interesting background information to file away.
I believe there is a lot to be gained by thinking the whole thing right through, and doing some back to back testing.
Too many old wives tales and urban myths out there.
 
Its all very interesting background information to file away.
I believe there is a lot to be gained by thinking the whole thing right through, and doing some back to back testing.
Too many old wives tales and urban myths out there.
That's for sure. There's also a big difference between theory and reality. Theory can help inform expectations, but I never assume a whole working system will exhibit the combined behavior of its isolated components, as tested in a lab.
 
I always thought it was known that an ideal system would have MPPT at each panel?

Series connected panels behave as one panel and we know what happens when a panel has a portion shaded. The bypass diodes minimize this effect but don't solve it.

My array is 3s3p and suffers severe shadowing due to site conditions. Your test has shown that I would probably benefit if I went to all parallel setup or at the very least, added my spare panel into the mix and went 2s5p.

Very nice little test. Thanks for sharing.
 
You missed the Vmp measurement. That's the measurement at the input to the SCC. Can you measure current into SCC?
To get a better understanding, also measure a single panel, direct to sun and angled off.

What is MPPT output volts? Is that same as battery voltage? 14.5V seems extremely high battery voltage for this test.

Have you tested any of this yourself? Your claim goes against well established data and what the OP investigated and found for himself.

It also doesn't make sense, even in theory.

We only series wire panels to simplify install in non-shaded/shadowed environments. It's sooo much easier to wire in series but it was never because it produced the best output.
 
I always thought it was known that an ideal system would have MPPT at each panel?

Series connected panels behave as one panel and we know what happens when a panel has a portion shaded. The bypass diodes minimize this effect but don't solve it.

My array is 3s3p and suffers severe shadowing due to site conditions. Your test has shown that I would probably benefit if I went to all parallel setup or at the very least, added my spare panel into the mix and went 2s5p.

Very nice little test. Thanks for sharing.
I think that you missed the purpose of the test.
It was to prove that panels facing different directions (east/west) should not be wired in series with each other. And confirmed that all panels in a series string should be mounted in the same plane. (Same direction and angle) while you could apply the results to shading, if the shading was permanent. (All day, every day) it wasn't about shading in general.
 
I think that you missed the purpose of the test.
It was to prove that panels facing different directions (east/west) should not be wired in series with each other. And confirmed that all panels in a series string should be mounted in the same plane. (Same direction and angle) while you could apply the results to shading, if the shading was permanent. (All day, every day) it wasn't about shading in general.

6 to 1 half a dozen to the other.

My array sees SHADOWING on individual panels within the same series string.

20220924_161528.jpg
 
Mine too.
This time of year is rough, with the sun tracking so low in the sky. I only get about 3 hours a day of unobstructed sun. The rest of the day the sun is behind trees on a hill. The only up side is that the leaves have fallen by the time the sun is this low.
 
I will admit I was wrong in thinking a east-west panel configuration in series is better than one in parallel. However I still believe a series string is better than parallel panels with partial shading. How many bypass diodes does the panel have?

For this test, battery voltage is important. The battery is 93% charged when it is at 14.3V. That's not a good place to run a test. Battery resistance increases dramatically when voltage increases above 13.5V. Charging current will be limited.

4ACharge12-18-15.jpg

The blue plot is GC2 battery voltage and the green is SOC. Charging started with battery at 50% SOC (resting battery voltage). An ideal battery voltage to run this test is 13.0 V, 70% SOC .
 
I will admit I was wrong in thinking a east-west panel configuration in series is better than one in parallel. However I still believe a series string is better than parallel panels with partial shading. How many bypass diodes does the panel have?

For this test, battery voltage is important. The battery is 93% charged when it is at 14.3V. That's not a good place to run a test. Battery resistance increases dramatically when voltage increases above 13.5V. Charging current will be limited.

View attachment 122960

The blue plot is GC2 battery voltage and the green is SOC. Charging started with battery at 50% SOC (resting battery voltage). An ideal battery voltage to run this test is 13.0 V, 70% SOC .

You're way over thinking this.

Series panels become one panel.

We know that shading one portion of a panel drops its output below that of just what we are losing due to a lower amount of sun on the panel. The shaded portion of the panel becomes a load. The bypass diodes prevent the shadowed cells from becoming too much of a load and still allow the panel to produce something. The remaining producing cells are dropped below their Vmp.

This same concept transfers to panels because they are just one big panel.

An ideal system that must operate with shadowing/shading would have all the panels in parralell.

The best system would have an MPPT controller at each panel.

The ridiculous no cost spared system would have each individual string of cells in the panel on its own controller (albeit you would need to factor in equipment switching losses)

For practical real world purposes, the best system for shade is each individual panel paralelled to the controller or micro inverters at each panel.
 
Back
Top