Panel bypass with relays on a timer


#1

HI All,

Not sure if this would would work or is feasible. but as the sun goes around, I get one panel at a time go into shade. Since the whole string is degraded when this happens, I had the idea to put a dry contact of a relay across (in parallel) the panel in and output leads which is on a timer. At the right time, the contact would close, basically bypassing the panel. Then, after dark, the timers would reset the contacts open again for the next day. This could probably work well in reverse for the morning as well.

Because the panel would be in shade, I figure there’s hardly be any voltage across the panel, and it would be safe to do so without damaging panel or inverter. It’s sort of an idea to increase efficiency.

What do you guys think? Crazy idea? Or feasible?


#2

So if I understand what you’re intent is, you would bypass the first panel that becomes shaded and then at some time interval, bypass the second and then third panel and so on and then after the sun goes down, you would remove the bypass from all panels to reset for the next morning.

First issue would be voltage. Each time you bypass a panel, your string voltage is reduced which at some point will fall below your inverter minimum voltage and you’ll stop producing.

Second, you would be adding a number of moving parts to your system which reduces reliability.

Third, while there won’t be much voltage across the contact, there will be current that has to be carried. The relay contact would need to be sized to carry the maximum current a panel could produce indefinitely.

Fourth, connecting a relay to each panel would be cumbersome assuming you panels use the typical PV Connectors.

Lastly, this would void any third party certification (UL, CSA, etc) as you would be using the components in a way they were never tested.

imo…This is an idea that has too many moving parts and failure points to justify.

I do know that some manufacturers offer a panel optimizer device that can be connected to each panel that will accomplish what you’re trying to do electronically rather than with a contact. I don’t know if that’s available for your system or not.


#3

HI thanks for your reply. You could use SSRs (solid state relays) which have no moving parts, which are rated for the current, and MC4 branch connectors to easily put the contacts across in parallel.

I wouldn’t do one on every panel, but in my case there are about 3 panels (0f 12 panels) that get heavy shade. It’s a shame for the sake of that the whole array gets pulled down.

I think it would be awesome if the panel manufacturers somehow built this feature in.


#4

From my limited knowledge you already have them in the form of bypass diodes built into the panels that conduct around shaded groups of cells.

I might be corrected in this but that is my understanding.


#5

Each panel has a bypass diode which does this automatically.


#6

This is not the function of the diodes. They are there to prevent the other panels from driving power “into” the low functioning pantels. It is a protection for the panels. the the MMPT function of the PV system works to regulate the power out of a panel or string of panels to produce the maximum amount of power from a panel under any type of condition of shading. There are systems which supply MMPTs per panel which prevent one panel on a string from drastically limiting the power of the whole string. PV systems which include a MMPT per panel produces more power from a string that a single MMPT for the whole string. The benefits of the distributed MMPT function can be as much as 50% more power from a string with varying shading across the string.


#7

Since you already have the panels and inverter - DC optimisers such as from Tigo are a commercial option to achieve this…something like https://www.tigoenergy.com/products/#smart-modules-ts4-r
see https://www.solarquotes.com.au/blog/solar-panel-optimisation/

Cost is around $100 per panel - which might be a lot less than the value of your time and potential damage futzing around with a home-brew solution.


#8

This looks like just what I need. Thanks for the tip.


#9

I’m about to implement these TIGOs in the next few weeks. I’ll report back on findings :slight_smile: