Connecting Two Dissimilar current sources in series

Thread Starter

iamranjeet123

Joined Sep 22, 2021
7
I want help or insight into whether two dissimilar current sources can be connected together in series using some additional circuitry.

I am interested in connecting two solar modules in series (PV string) that have a current mismatch. Generally, we connect bypass diodes to prevent hotspots in panels, but this makes power extraction from the shaded module zero. I want to recover the power of the shaded module as well.

For example, suppose PV1 (unshaded) generates 5A and PV2 (shaded) generates 3A. Can I have additional circuitry to divert the extra 2 A from PV1 to some energy storing element and recover it at the load side.

Your thoughts please !!!!!!!
Thanks
 

crutschow

Joined Mar 14, 2008
34,679
Aren't there bypass diodes across each solar cell, so the panel keeps generating the same current, but at a reduced voltage when some cells are shaded?
 

Thread Starter

iamranjeet123

Joined Sep 22, 2021
7
Aren't there bypass diodes across each solar cell, so the panel keeps generating the same current, but at a reduced voltage when some cells are shaded?
In commercial PV modules, bypass diodes are usually connected across one-third of the total PV cells. For example if it is a 72 cell module then bypass diodes are connected across every 24 cells.

Iam interested in extracting more power from a series connected PV modules when operating under mismatch conditions. If we go with the traditional approach (bypass diode across sub-modules), it results in zero power contribution from shaded modules even when it can generate some power.

So, I want your insights on diverting the extra current in some energy-storing elements and recovering it at the load side.

In principle, I want to prevent the conduction of the bypass diode. I can only do this if I can divert the extra current from the unshaded module and recover it later. By doing this, I can prevent the shaded PV panel from getting shorted by bypass diode conduction and recover at least some energy from the shaded module.
 

Thread Starter

iamranjeet123

Joined Sep 22, 2021
7
Is there any way by which we can connect PV modules at the input in series and at the output in parallel, using some electronics in between, to avoid mismatch loss during partial shading?
 

JohnSan

Joined Sep 15, 2018
31
What MisterBill2 said. ^^^^^


On the assumption:
You are trying to recover the energy from the shaded panel(s) to improve efficiency.

Problem.
By putting a 5A source in series with a 3A source, you can only extract 3A max continuously.
That is loosing 2/5 of the energy of the 5A unit.
So that part is only ever running at 60% of its max output.

I think you need to consider another method.
 

MisterBill2

Joined Jan 23, 2018
18,934
At this point there is a problem, in that actual solar panels ONLY HAVE OUTPUTS. So are there additional interface modules of some sort??
Many solar power systems do contain additional modules to provide a constant output voltage output, either AC to mains or DC for battery charging. But we do not have any of that information yet. And without a rather complete description of what actually the system is made up of, the very best answers will be guesses based on assumptions.
So to obtain any useful suggestions we do need to know just what is actually present. And it seems that there are things that have not been mentioned yet.
 
Last edited:

Thread Starter

iamranjeet123

Joined Sep 22, 2021
7
Some interfacing mechanisms can help.

For example can I have individual DC-DC converters in between the mismatched panels and the load?

So that would mean that even if I have mismatched conditions at the input of the converters, I can parallel them to have total current generated by all panels.

On the contrary, if we go by the traditional approach (using bypass diodes), we simply short the shaded module even when it could have generated less power at least.
 
Last edited:

LvW

Joined Jun 13, 2013
1,765
I want help or insight into whether two dissimilar current sources can be connected together in series using some additional circuitry.
.....................
I am interested in connecting two solar modules in series (PV string) that have a current mismatch.
What makes you think that solar modules are current sources?
 

MisterBill2

Joined Jan 23, 2018
18,934
OK, based on no additional information, but guessing that each solar array with an interface power module, will have a DC output at some standard voltage, perhaps 24 volts, and an output that will not draw power from whatever system it is connected to, then certainly they can be connected in parallel, and each system will provide a share of the total delivered power, which might be charging batteries. THAT sort of arrangement can work quite well. If each solar power system has an inverter that will send power back into the mains, then also both can function in a similar manner.

You can have ANY NUMBER of assorted solar cell arrays, each connected to an inverter delivering a selected voltage, possibly 12 or 24 volts, each contributing some power. BUT the connection would need to be PARALLEL, not series. For a parallel arrangement it is only the voltage that must all be the same, and every array can deliver power as it is able.
 

Thread Starter

iamranjeet123

Joined Sep 22, 2021
7
OK, based on no additional information, but guessing that each solar array with an interface power module, will have a DC output at some standard voltage, perhaps 24 volts, and an output that will not draw power from whatever system it is connected to, then certainly they can be connected in parallel, and each system will provide a share of the total delivered power, which might be charging batteries. THAT sort of arrangement can work quite well. If each solar power system has an inverter that will send power back into the mains, then also both can function in a similar manner.

You can have ANY NUMBER of assorted solar cell arrays, each connected to an inverter delivering a selected voltage, possibly 12 or 24 volts, each contributing some power. BUT the connection would need to be PARALLEL, not series. For a parallel arrangement it is only the voltage that must all be the same, and every array can deliver power as it is able.
Thanks MisterBill2
 

MrAl

Joined Jun 17, 2014
11,564
Hi,

Yes you should be able to parallel two panels if they have the same characteristic voltages. If not, then you could use two buck (or boost) converters one for each panel to get to any voltage output you wanted.
 

MisterBill2

Joined Jan 23, 2018
18,934
Of course, I "made a guess" that each solar panel does have an interface module that will have an output, and I guessed that the two outputs would be the same voltage. Those are reasonable guesses but they may not be correct..
 

k1ng 1337

Joined Sep 11, 2020
984
You could use control logic circuitry to select and combine the compatible power signals.

For example, you said bypass diodes are used between cells and end up shunting useful energy.

If this is the case, sample the power output of each cell once per minute. If cells 1, 7 and 13 are shaded, use logic gates or a MCU to group these cells to a seperate output.

I imagine this working with a multiple storage batteries. If a ~12V charging voltage can be maintained at low currents, it will simply take longer to charge a secondary battery.

I've done some experimenting along these lines using supercapacitors as temporary storage with a boost converter.

Once the capacitor bank reaches the voltage threshold, the charge is dumped into a storage battery in a single pulse.

The neat about about this technique is a very low current will eventually charge the capacitor bank to the threshold voltage.
 
Top