Panel bypass with relays on a timer


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?


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.


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.


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.


Each panel has a bypass diode which does this automatically.


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.


Since you already have the panels and inverter - DC optimisers such as from Tigo are a commercial option to achieve this…something like

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.


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


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


OK, so I decided to go all out, and I have the TIGO optimisers installed on all my panels, plus I have the CCA cloud connect kit which allows me to individually monitor all the panels.

So far I am very impressed, and yesterday in Sydney we had an extremely cloudy day, and the system yielded about 5% “reclaimed” energy. On my filtered Live Outputs page, I’ve had the highest ranking ever.

Totally looking forward to a good sunny day soon to do some further comparisons. But so far, awesome.


Good to hear! will be very interested to hear how much it boosts your output on a sunny day, adjusting for the travelling shadow across your panels


Hmm… at the moment a bit hard to say. I can see I have jumped up a few rungs on the live outputs page, but I am not sure that the “reclaimed” energy amount shown on the tigo portal is accurate. For example, it reckons I reclaimed only 1.2kwh over the last 4 days. Seems way to low given the heavy progressive shading I have at both ends of the day. For example if one panel would drag down 13 in that string, and if bypass were truly working, I’d have to be reclaiming more than that I would have thought. Maybe not, but dunno.

The jury is out of whether there is a large effectiveness, the software and reporting is a bit buggy, nothing like the wonderful work by @bankstownbloke on this site.

Also, the power output shown for each panel is in DC watts. Which is not indicated on their portal. Only found that out via their support.

Couldn’t upload a video or animated gif here (too large). I posted one on youtube.


How are yours divided up into different strings?

I find the ‘Basic Charts’ page on their portal easier to gauge the effectiveness - here is mine from yesterday. I really only have shading on one string (and also they point in different directions), but I put Tigos on all panels including the other string to get the panel-level monitoring, just-in-case.
In my case, I get about 10%-15% improvement each day due to the optimisers (the lighter-green envelope in this pic)


I got 2 strings: 8 on one, 14 on the other. Here’s my graph from today…
I got the optimisers on all panels too…

What do you make of it?


These two examples show reclaiming 12.2% for “willisave” and 3.6% for you of the available energy for your system in these two systems. The Green area is what you should be realizing without the optimizers. You should see the greatest gains on the best sunny days and less on cloudy days. Clouds cause shading in an unpredictable way while on clear days trees and other objects cast shadows in a predictable way. The pale green areas are the reclaimed energy and most is recovered from 7:30 am to 2:30 pm or at peak production times. You should make more comparisons to get a better idea of how your optimizers are working.


Mmmm - agreed, doesn’t look like much benefit at all, surprising.
To the right of this chart, you can play with the charting - turn off the aggregate ‘Inv 1’, and click on each of the ‘String X’ headlines until you get the line-graphs of each string overlaid separately rather than the filled-in graph of the aggregate.
What do they look like?
(in mine below, ‘String B’ shows almost no benefit - these all face west, and are unshaded, so not surprising. I could have not bothered with Tigo on these. My ‘String A’ is the main benefit - they face two different directions, and have significant shading challenges)