Blocking diodes for paralleled panels?

[KTP]

If you had a boat with four 22V open circuit 100 watt panels in series on the starboard and four 22V open circuit 100 watt panels on the port, would it be required, advantageous or disadvantageous to put a blocking diode on each series string (two diodes total) as they are paralleled into one MPPT controller (Midnite Kid marine).

One string of panels will have much more solar than the other because of shading.

[Cowpoos]

Originally Posted by KTP

If you had a boat with four 22V open circuit 100 watt panels in series on the starboard and four 22V open circuit 100 watt panels on the port, would it be required, advantageous or disadvantageous to put a blocking diode on each series string (two diodes total) as they are paralleled into one MPPT controller (Midnite Kid marine).

One string of panels will have much more solar than the other because of shading.

Get a second MPPT controller. It will work better and give you redundancy.

[KTP]

Originally Posted by Cowpoos

Get a second MPPT controller. It will work better and give you redundancy.

They are like $500 (for the Kid). I know that is only half a boat unit but still...

[CatNewBee]

Originally Posted by KTP

If you had a boat with four 22V open circuit 100 watt panels in series on the starboard and four 22V open circuit 100 watt panels on the port, would it be required, advantageous or disadvantageous to put a blocking diode on each series string (two diodes total) as they are paralleled into one MPPT controller (Midnite Kid marine).

One string of panels will have much more solar than the other because of shading.

Nope. not for 2 strings.

From 3 and more, yes. Alternative is for 3 and more strings to put a fuse per string according to the label. 100Wp panel usualy around 7.5...10A. It is for reverse current protection.

One panel alone cannot produce that amount of reverse current, so 2 strings are safe whithout diodes or fuses.

[skipgundlach]

Originally Posted by CatNewBee

Nope. not for 2 strings.

From 3 and more, yes. Alternative is for 3 and more strings to put a fuse per string according to the label. 100Wp panel usualy around 7.5...10A. It is for reverse current protection.

One panel alone cannot produce that amount of reverse current, so 2 strings are safe whithout diodes or fuses.

That's not really the issue. It's a matter of optimal production from differently shaded blocks.

From a tech discussion with Blue Sky, my controller manufacturer:

And, the other matter, of blocking diodes. As all of the manufacturers of which I'm aware have several blocking diodes, and in particular one which would prevent battery drag down at night, would those features not make it impossible for a shaded panel to 'rob' power from one which was next to it, in parallel?

Most panels utilize bypass diodes not blocking diodes. The purpose being that if a couple cells are partially shaded, the current would bypass them without causing a "dead spot" in the circuit. As far as I know, most panels do not include blocking diodes because they are not necessary for panels wired in series (bypass diodes and extra wiring would be used).

Blocking diodes do cause a very slight drop in voltage/ output, so panel manufactures might be hesitant to preemptively restrict a panels performance, leaving it up to the customer to determine the application.

couple interesting articles:

http://www.electronics-tutorials.ws/...ss-diodes.html

https://www.altestore.com/blog/2016/...-solar-panels/



If Partial shading is not an issue in your array, then they are not crucial and I would not bother. If partial shading is an issue and you are running into situations where one panel has good sun while another does not, then it may help. I'd try finding a time when all panels have sun, measure your input PV voltage then shade one panel and see if the voltage drops. Of course the output current will drop, but if the voltage does as well then blocking diodes may help as the shaded panel is robing the voltage from the sunny one.

Here is an article about combining multiple panels, although it does not mention blocking diodes in particular, notice what happens when you combine multiple panels in parallel with different voltages:

Connecting Solar Panels Together For Increased Power

[roland stockham]

I currently have 2 100w panels mounted each side of the stern arch. A lot of the time when the sun angle is lower one panel gets shaded. I wired them in series partly to reduce cable losses but also thinking that early and late in the day they will produce enough voltage to start charging sooner. (MPPT controller 43v nominal output). Still not sure this is better than either parallel wiring of 2 controllers.

For cheap controller I fitted on of these 2 years ago and it has been faultless, current price is $102US for a 20 amp unit. Eco worth site is here https://www.eco-worthy.com/catalog/w...24v-p-182.html

[john61ct]

Yes more controllers, fewer panels per controller, ideal for this purpose is 1:1.

Victrons aren't much more than $100 per.

Of course then selecting a panel best suited for the SC is ideal when starting from scratch.

[roland stockham]

Originally Posted by john61ct

Yes more controllers, fewer panels per controller, ideal for this purpose is 1:1.

Victrons aren't much more than $100 per.

Of course then selecting a panel best suited for the SC is ideal when starting from scratch.

So how do you gang 2 controller to charge 1 battery bank without the one with the higher power turning off the other one by fooling it into thinking the battery is fully charges when it sees the voltage coming from the other panel?

[travellerw]

Originally Posted by roland stockham

So how do you gang 2 controller to charge 1 battery bank without the one with the higher power turning off the other one by fooling it into thinking the battery is fully charges when it sees the voltage coming from the other panel?

Do a search, Mainsail has explained how that works.

The short version... That doesn't happen until way into the "absorbtion" phase. At that point it really doesn't matter as the one solar bank is producing enough current to finish the asborbtion phase.

I can confirm that this is exactly how it happens on our boat with 4 controllers (3 Victrons and one Chinese).

[john61ct]

All kinds of diverse charge sources can be concurrently paralleled to a bank.

No problem, but obviously similar setpoints would be ideal.

[ramblinrod]

Originally Posted by KTP

If you had a boat with four 22V open circuit 100 watt panels in series on the starboard and four 22V open circuit 100 watt panels on the port, would it be required, advantageous or disadvantageous to put a blocking diode on each series string (two diodes total) as they are paralleled into one MPPT controller (Midnite Kid marine).

One string of panels will have much more solar than the other because of shading.

Check with h to he manufacturer what diodes are included in the panel construction. Many panels do not require blocking diodes when connected in parallel. The solar cells their selves are “blocking diodes” ie the will only pass current in one direction, so “blocking” reverse current is not required.

When panels are connected in series, one may require additional bypass diodes, so that if a panel is shaded and thus cannot pass current, current is bypassed around that panel.

Larger panels may have bypass diodes built in, so partial shading affects only a portion of the panel, which is based passed.

We have 4 x 100W panels in parallel with a PWM controller. More power than we know what to do with it there is any sun at all. We’re not stupid about power consumption, because but not nazi conservative either.

[KTP]

Originally Posted by ramblinrod

We have 4 x 100W panels in parallel with a PWM controller. More power than we know what to do with it there is any sun at all. We’re not stupid about power consumption, because but not nazi conservative either.

Yeah but I need probably a lot more than you because I am going to be running eventually with a 20kWh battery bank and using a 10kW electric motor for propulsion. Harvesting 2kWh to 4kWh a day would be very nice.

[hzcruiser]

Originally Posted by KTP

Yeah but I need probably a lot more than you because I am going to be running eventually with a 20kWh battery bank and using a 10kW electric motor for propulsion. Harvesting 2kWh to 4kWh a day would be very nice.

Good on you for installing an electric motor! Using it based on solar only is going to be a huge challenge though. Let us know how you go, please.


And back to the topic, yes, you should add blocking diodes to parallel panels if the panels are not pointing in the same direction. I just did that as the panels are mounted on the lower solar arch, one on each side. The two panels on top of the arch are wired in series.

[Axel_G]

No, you do no need diodes for parallel panels.



The voltage of the shaded panel will only marginally go down, unless it is completely dark (cover it with a tarp or so). Its ability to drive current will be reduced, but that is not an issue here. So as it maintains the same voltage there will be no current flowing backward.



So basically you have a working panel, that will have an idle voltage at maybe 18V which is loaded to 16V and 6A by the MPPT tracker as this is approx. the point of the maximum power.

And you have a shaded panel which will still give 17V but maybe only 0.1A. But the voltage is still above the loaded voltage of the good panel. It will still give some 0.1A into the battery, which is the issue with shading.



Diodes will consume a lot of energy though. And the MPPT tracker already has one for the night to make sure there is no current flowing into the cells.

[ramblinrod]

Originally Posted by KTP

Yeah but I need probably a lot more than you because I am going to be running eventually with a 20kWh battery bank and using a 10kW electric motor for propulsion. Harvesting 2kWh to 4kWh a day would be very nice.

Your call, but I have yet to see electric propulsion work well on a cruising boat. It is possible to put on some form of electric propulsion fairly cheaply, but to be as effective as a small aux. diesel, is very expensive and real estate intensive. 800 W of solar (OP) will not cut the mustard. No where near it. 400 W will be good for the non energy hog leaving 400 for the electric motor. That may get you 4 miles per day at 2 knots.