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Re: Tesla fires, Amphenol connector

"optimized" separately??? I guess I've been thinking the current through t he string to the inverter would pass through all the cells. But the realit y is the optimizer isolates the cells of a panel from the output current so panels in series run at the same current, but the cells of each panel run at different current from other panels?

That's what I'm having trouble wrapping my head around. If the optimizer i s duty cycling to get the input current to the MPP, the output current will be in the proportion of the duty cycle. Then the output voltage will have to be in proportion to the input voltage so the input and output power are the same. I guess this is not in opposition to the idea of the output vol tage being set externally. Then it just gets reflected back to the input v oltage by the duty cycle with the input current also being reflected to the output current since the load is current compliant.

I guess I'm hung up on the idea that in a fixed voltage output the the duty cycle is controlled to maintain the output voltage. Here that is not true . If a buck converter is operated to a fixed duty cycle a change in the ou tput load will result in varying output voltage and current as well as an i nput current variation. So that makes sense.

Ultimately the input power is being controlled and the output will adapt to whatever sort of load is attached.

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  Rick C. 

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Reply to
Rick C
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I think that's it...

The only thing an MPPT circuit is supposed to do is to load the PV module down to the voltage that puts out maximum power from that module. Whatever happens on the string side (output) has to follow along with that PV side and you get whatever you get I guess.

If a PV module that the MPPT is connected to is shaded, then it can only load it to its max power point voltage. That is, IF there is enough sun for that MPPT module to even run. At some point, there won't be enough power to run the MPPT circuit itself.

If the string that is connecting all these optimizers together does not require maximum power, then the optimizer will have to unload the solar panel and its terminal voltage will have to rise up towards open circuit Voc. Typically, Vmp is somewhere around 80% of Voc. Below Vmp, its V-I curve is mostly constant current and the voltage drops (by definition) and so does the power. It's right around that V-I knee that is the Vmp.

I can't see these modules working their best without being able to communicate with the rest of the system though.

A chainsaw will still work best for partial PV shading.... Adding optimizers can only reduce efficiency as long as the panels are fairly close to being the same type, number of cells, etc.

Reply to
boB

You know that concept is impractical in the extreme. In the afternoon some tall pine trees, about three properties away, block my roof for about 45 minutes. We have 16 panels on our garage roof, and the taller house roof blocks 1/2 to 1/3 of that, until the sun swings around to face the house. These issues cannot be solved with a chainsaw. Check it out. Click the picture, to see the shading.

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    - Win
Reply to
Winfield Hill

Of course I'm being a bit facecious about cutting down trees althouth that would fix the majority of shading issues. And chimneys are another issue. Microinverters take care of that on a per-panel basis just fine.

Also, you should be happy you don't have to add a per-module rapid shutdown system for HV strings. Turn off the power to the house and your'e all set for fire-fighting first responders.

We did a bunch of contract work for Enphase a couple of years ago that was good for profits. Would not want to have to do that again. They were very hard to work with.

boB

Reply to
boB

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