PV String DC Voltage Limiter

[Canxane]

I think I crawl up on the roof one time when the neighbor (local utility engineer who approves the solar permits) isn't around and figure out how to rewire the strings without removing panels. Just leave one panel in each string unconnected.

 

[efficientPV]

While I do not condone such things, there have been no suitable answers on your various forums. The following is one way the array is always connected and an extra panel is added based on temperature. Only a single Y connection needs to be made. Design subject to array.

 

[Symbioquine]

That's awesome @efficientPV! I need to study your circuit in more detail later, but that's the sort of answer I was looking for on my post: https://diysolarforum.com/threads/l...ing-bypass-relay-switching.47626/#post-605672

 

[Canxane]

While I do not condone such things, there have been no suitable answers on your various forums. The following is one way the array is always connected and an extra panel is added based on temperature. Only a single Y connection needs to be made. Design subject to array.
View attachment 113507

I understand your written description - now I just need to learn to read and build the diagram. Thank you!

 

[efficientPV]

The bypass diodes are a good way to prevent large open circuit voltages when switching. Many manual switches or relays would work at this voltage. You could forget to switch, a FET or temperature control circuit could fail. In the last couple years, I have had two lightning events. I show multiple resistors in series in the power supply. Resistors have a flashover voltage. Multiple resistors provide added protection, use at least four. I am totally against shorting a panel. Theoretically you can, but there are always weak cells and that can put them under stress. Long term that could degrade them. Redundency could be built in. This is still risky. Likely there is a voltage cushion built into a good controller.

 

[Logic28]

If you can't reconfigure the array.
I think that you should buy an inverter that can handle it.

I don't agree, that is like trying to escape from the question. Even if purely for didactical reasons one should try to create an adequate limiter, this is how the world has evolved

 

[Logic28]

Need a way to limit PV string DC voltage to that allowed by a hybrid inverter.

Unique scenario. Imagine a situation where you are unable to change your panels or the string size of the panels (permits, zoning, etc) and you need to limit the DC voltage to a lower value than the string can theoretically produce. If your existing inverter strings theoretically can produce up 550V DC on a cold sunny day, and the . . . . . . Is there a way to limit the DC voltage of a PV string to protect the inverter on those few days it might be a problem?

I found your question while looking for the same thing myself. I'm sure I will find a way to construct something of the kind even if just as a protection device.
I am paranoid about the possibility of a very cold day with a strong sun irradiance risking the life of my two 250/100 Victron MPPTs

 

[DIYrich]

Zener diode to sink excess voltage?