Any way to clamp PV voltage above a certain amount?

[mvonw]

This is probably a dumb question, and I'm sure it's been asked in different contexts, but I couldn't seem to fine an answer.

I have a Sol Ark 12k and am planning my array (currently, at least) so that under summer temps would be about 485 volts on each of the two MPPT controllers (at 11amps). The issue is that in winter it gets quite cold (sometimes -30c).

Is there a way to limit the voltage coming off the solar panels so that it would never exceed the 500v/mppt limit for this inverter.

 

[DThames]

Yes. You would need to take responsibility for the design of the solution. Do you want to depend on your design to protect the inverter/chargers?

You should reduce your series panel count and if necessary combine some strings to be in parallel.

A zener, or series of zeners could be put on each panel to set a max threshold voltage. When the zener circuit has current, turn on a load to that panel that can load the panel enough to bring the voltage down. This would be a linear power type circuit and would need a power resistor to bleed off the heat. When your charger's load was enough, it would pull the panel voltage down enough that this circuit would be off, because the voltage was below the zener threshold.

 

[mvonw]

Yes. You would need to take responsibility for the design of the solution. Do you want to depend on your design to protect the inverter/chargers?

You should reduce your series panel count and if necessary combine some strings to be in parallel.

A zener, or series of zeners could be put on each panel to set a max threshold voltage. When the zener circuit has current, turn on a load to that panel that can load the panel enough to bring the voltage down. This would be a linear power type circuit and would need a power resistor to bleed off the heat. When your charger's load was enough, it would pull the panel voltage down enough that this circuit would be off, because the voltage was below the zener threshold.

Yes, I'm planning to reduce my panels to stay within a maximum possible voltage. It's just there aren't really that many days where it's cold enough to push it over the 500 volt,so the vast majority of the days, I'm not getting optimal charging, but I guess that's just how these systems are spec'd

 

[DThames]

You should select your series panel count based on "Temperature Corrected VOC", if you can find or calculate that for your panels.

 

[Sarah F]

Depending on how flexible your design is, you could seasonally drop a panel or even a series within a panel (inside the junction box). That might be the cleanest approach. Perhaps you could use a tiny solar panel that would close a SPDT relay to tap your main string at a lower voltage point when its voltage of the tiny panel exceeds some set point.

If you use zeners to clamp the voltage, you will need to use an amplified zener circuit. Be careful about too many zeners in series, because they can ring on shutoff, and a ringing series of zeners will regulate at a substantially reduced voltage. I experienced this when trying to design a simple (I thought) semiconductor clamp circuit for biasing a panel. I wasn't patient enough to figure out how to suppress all the ringing. (I went straight to a resistive design.) Potentially the worst aspect of the ringing is that you may get Voc or higher at your inverter input, so you should be careful to scope the output. of your circuit.

I wonder whether someone makes a DC:DC converter that would be easily to implement off-the-shelf.

 

[Warpspeed]

You could make the number of series panels switching, temperature dependent, and have it change the number of panels only at night which solves the arcing and welded contact problem that you will otherwise have at such a high voltage.