Inverter max VOC

[GoldDigger]

The same reason that people hate the fact that their GTI will not function during a power outage: "It seems like such a waste...."

Tapatalk!

 

[iceworm]

If the object of the crowbar is to limit the voltage from reaching Voc, ...

Nope, the voltage regulator is to draw enough current to keep the open circuit voltage under 600V.

The crowbar is to short the array if the current exceeds what the VR can handle. If the design is good, the only time the crowbar would operate is if the sun was high and inverter stopped drawing current.

... You would have better luck crowbarring one or two panels in the string until the operating voltage of the remainder of the string went low enough that adding those panels back into the string would be safe. ...

Great idea. Smaller transistors and heatsinks. Just have to sense the output voltage and switch a few panels in and out as the sun came up (or went down). I wouldn't use the term "crowbar" since that carries connotation of latching. Just be a 10A switching circuit, on or off.

... You still have the problem of what to power the crowbar circuit from. ...

If the sun is up you have power. There will be an amp or two through the module. Gin up a current source power supply - like in a 4-20ma transmitter.

For my part, this is all fluff and dung - I don't see the mfg changing for a small market. And my first order guess is maybe there is a $1000 at the retail end available.

And there is one other issue - I know very little about PV. I am mostly enjoying listening and applying some what-if's drawing from the basic physics that I do know


ice

 

[jaggedben]

- I don't see the mfg changing for a small market. And my first order guess is maybe there is a $1000 at the retail end available.

It would seem it's cheaper to use SolarEdge or other module level electronics.

 

[electrofelon]

It seems to me that the idea of having a load not controlled by the MPP itself, connected to the solar array, is a bad idea. The job of the MPP is to control the load placed on the solar array to maximize output; anything outside of the MPP is going to 'dilute' this control capability.

-Jon

Generally not a very good design, or would need to be designed very carefully for optimum efficiency, but in my case if i have an extra thousand watts that the CC cant utilize, why not? The control scheme would be such that the heating element would be cut out if the CC could take it all. This is my initial informal analysis of the MPP and the the line side series resistor: Say for a starting point of this thought experiment that the array is at MPP and power is being dissipated through the resistor. Now say the CC decides to look for more power as it will, and raises its effective input resistance. This will raise the voltage and lower the current. Now the array is not at MPP so the array power output has gone down, but also since the current went down, the power dissipated through the resistor has gone down. So what does the CC "see"? To know the effect at the CC terminals, we would need to know what went down more, the power at the array or the power at the resistor. If the power dissipated by the resistor went down more than the power went down at the array, than the CC will see a gain and will raise its effective input resistance some more and this isnt working that well. If the power dissipated by the resistor went down less than the loss in array power, than the CC will see a loss and go back to where it was. I think the latter will be the case since the current thru the series resistor wont change much and thus the CC will like where the array is at max power. This will be a good recreational math project so ill graph it up at some point and figure out exactly what will happen. Feel free to point out in flaws in my reasoning here.

ggunn

So, what's wrong with the design practice of sizing strings such that excessive/damaging/uncompliant Voc won't ever be reached?

This all started because of this exceptionally long wire run I have and the frustration of seeing the voltage at 385 instead of 550 for 96% of the operating time.

 

[jaggedben]

This will be a good recreational math project so ill graph it up at some point and figure out exactly what will happen. Feel free to point out in flaws in my reasoning here.

I admittedly know nothing of the details, but my understanding is that MPPT algorithims are proprietary, unique to the manufacturer, and sometimes quite complicated. So my wager is that your reasoning is flawed because, unless you have inside knowledge of the algorithm, you are totally gambling that the actual real behavior of the equipment will resemble the results of any recreational math project.

This all started because of this exceptionally long wire run I have and the frustration of seeing the voltage at 385 instead of 550 for 96% of the operating time.

385 seems pretty normal to me. 550 for Vmp would not within the full power MPPT range on any 600V inverter I'm familiar with. Did you mean 450? Most inverters stop at 480 or so.

 

[electrofelon]

I admittedly know nothing of the details, but my understanding is that MPPT algorithims are proprietary, unique to the manufacturer, and sometimes quite complicated. So my wager is that your reasoning is flawed because, unless you have inside knowledge of the algorithm, you are totally gambling that the actual real behavior of the equipment will resemble the results of any recreational math project.



385 seems pretty normal to me. 550 for Vmp would not within the full power MPPT range on any 600V inverter I'm familiar with. Did you mean 450? Most inverters stop at 480 or so.

You are correct, the mppt range of this one tops out at 510V. Its a schneider mppt 600.

My thinking is, and of course we could conjecture to the cows come home and never really know for sure, is this: The details of the algorithm dont matter despite how complicated they may be. The array output, resistor dissipation and voltage drop across it, power at the CC terminals are all easily calculable and definite. If the math shows that when the array is at MPP, the CC will see the most power, than thats what will happen. The only potential issue I can think of is the one that I mentioned before of the CC possibly sampling VOC and then only looking at say 75-85% of that value. Well its something I can experiment and play with and hopefully get some bonus energy from.