Do modern panels need bypass and blocking diodes added?

[blueman2]

I have a system with 6 100W Renology panels feeding into an Epever MPPT to charge a set of batteries. All purchased in the past year. I have them arranged in 2 strings of 3 panels. For clarity, each string is 3 100W panels wired in series (so about 60V total), and the 2 strings are wired in Parallel (keeping 60V but doubling their amperage). I have seen diagrams showing blocking diodes for each string (so 2 would be needed), as well as each panel also having bypass diodes added (so 6 needed). Is that necessary? Or do modern panels have these functions already built in?

[Mike90250]

Most modern panels have integral bypass diodes from the factory
Nearly every reputable charge controller has the blocking diode functionality since 1990

I would like to assume that you don't need anything more. Adding diodes causes some power loss and adds failure points. I think you should be OK, unless you have seen something specific about your models.

[blueman2]

Most modern panels have integral bypass diodes from the factory
Nearly every reputable charge controller has the blocking diode functionality since 1990

I would like to assume that you don't need anything more. Adding diodes causes some power loss and adds failure points. I think you should be OK, unless you have seen something specific about your models.

Thanks. So with modern panels, if I have 3 panels in a series string and one is shaded, does the shaded panel allow current to flow through so that the other panels can still product power?

As for the blocking diode, yes, my MPPT does have that build in so that the batteries do not back feed the panels. My concern was that I do not want one string of panels that is in the sun to back feed the other string in the shade. This occurs before it gets to the MPPT, so the MPPT blocking diode does not help in this case.

[Mike90250]

Thanks. So with modern panels, if I have 3 panels in a series string and one is shaded, does the shaded panel allow current to flow through so that the other panels can still product power?

As for the blocking diode, yes, my MPPT does have that build in so that the batteries do not back feed the panels. My concern was that I do not want one string of panels that is in the sun to back feed the other string in the shade. This occurs before it gets to the MPPT, so the MPPT blocking diode does not help in this case.

You do not want to add diodes. They will not help a bit. ( unless you buy these special ones only I sell and never ever test them )

The series fuses/breakers in each string prevent dangerous conditions.

A 3 panel array with one panel shaded, will activate the bypass diodes in that panel. Eventually, with enough time and heat, those bypass diodes burn out.

A pair of 3 panel arrays in parallel, with one panel shaded, both strings will perform at a 2 panel level. Using 2 separate charge controller$ ( one MPPT controller per string ) will improve this.
not shading the panel will improve it. What is easier for you ?

[chrisski]

I have 3 panels in series on my RV roof, 100 watts each. When I shade 2 cells on a single panel with 30+ cells per panel, total string output drops to by 25%-33%. When I shade half a single panel, my output drops by 75%. I was surprised to see this.

On the same roof, I have a different set of panels. Two panels in parallel. When I cover a panel in parallel, output drops by about 50%. No surprise there.

For blocking diodes, these are supposed to be good for the parallel panels I mentioned. Loss was actually a little more than 50%. A YouTube video I watched by Will Prowse mentioned that with parallel panels on different setups, like one set to the east and one set to the west, Blocking diodes can prevent current from backflowing through the shaded panel. So in that case, blocking diodes would work.

He did not say how much it would help. He did show how to install the blocking diodes and that each diode added probably takes away 2 watts of production.

When the parallel panel I shaded lost a little more than 50% production, maybe a blocking diode would bring this closer to 50%. Maybe the panel producing the power was not as strong because of angle to the sun, had just aged differently, or maybe it was partially shaded.

So for the three panels I said I have in series on my roof, when one gets shaded, voltage actually goes down by quite a bit. From low 60 volts DC to mid 40 volt DCs, depending on how much is shaded. I also have two of these in series—3S2P. For the measurements I mentioned, I had the second string shut down. I know throughout the day things like Air Conditioner and vents shade the different strings at different times, and I do wonder how blocking diodes would help with this.

Later this year, I’d like to add some blocking diodes to a 4P setup and see if this ales a difference. I don’t doubt there will be a measurable difference with t panels to the east and two panels to the west at sunrise, but I’m not sure this difference will add up to minutes quicker charging time or hours quicker charging time.

I also agree even if these blocking diodes work, separate charge controllers will have better results.

[bcroe]

For blocking diodes, these are supposed to be good for the parallel panels I mentioned. Loss was actually a little more than 50%. A YouTube video I watched by Will Prowse mentioned that with parallel panels on different setups, like one set to the east and one set to the west, Blocking diodes can prevent current from backflowing through the shaded panel. So in that case, blocking diodes would work.

He did show how to install the blocking diodes and that each diode added probably takes away 2 watts of production.

For an MPPT setup, I am going to suggest, blocking diodes are losers for parallel
panels, perhaps 1W for every amp being produced. Looking at the curve of a solar
panel, the voltage will rise some 25% for open circuit. For a shaded panel this
hardly changes, just the amps available are greatly reduced. I am not talking about
putting a panel in a closet.

So with parallel panels and one shaded, the unshaded will continue to produce
current at the MPPT point. The current capability of the shaded will be much reduced
(like at 10%) but open circuit voltage will be little changed. So the shaded panel
voltage will rise till it hits the MPPT voltage of the unshaded panels, and then add
its much reduced current. It will not conduct in reverse, as that would require voltage
above the open circuit. To check this you could put some 0.1 ohm 10W resistors in
series with each panel, then use your DVM across the resistors to determine the
current and direction of flow (Ohms Law).

Series panels are a different ballgame. 2 panels, even loaded, can produce a voltage
greater than the open circuit voltage of a panel. To prevent current from being forced
backwards thru a shaded panel (with big losses there), a bypass diode (s) across the
shaded section(s) to allow current to continue to flow with no help from the disabled
panel. Bruce Roe

[checkthisout]

Thanks. So with modern panels, if I have 3 panels in a series string and one is shaded, does the shaded panel allow current to flow through so that the other panels can still product power?

Yes but if you are running a series/parallel setup, the voltage of that string drops and your MPPT controller pulls the remaining strings out of their optimum MPPT. Imagine having two panels with different voltages on the same controller.

As for the blocking diode, yes, my MPPT does have that build in so that the batteries do not back feed the panels. My concern was that I do not want one string of panels that is in the sun to back feed the other string in the shade. This occurs before it gets to the MPPT, so the MPPT blocking diode does not help in this case.

Correct.

Series connect for maximum voltage up to whatever the limit is on your charge controller. Shading hurts both series and parallel setups but it's a transient condition and hard to optimize for with lots of cost involved for little gain.

Just a couple more panels to your setup if you have room to carry them and then just set them out facing the sun.

[checkthisout]

I have 3 panels in series on my RV roof, 100 watts each. When I shade 2 cells on a single panel with 30+ cells per panel, total string output drops to by 25%-33%. When I shade half a single panel, my output drops by 75%. I was surprised to see this.

Probably how the panel is constructed. Shading two two cells blocks 1 string of cells whereas blocking 1/2 the panel shades 2/3rds of the cells. Most panels are 3 strings of cells.