Electronics > Power/Renewable Energy/EV's

Solar panel voltage matching question

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Seekonk:

--- Quote from: cravenhaven on August 27, 2016, 02:04:28 pm ---The MPPT point for a panel will change with the irradiance

--- End quote ---

Well, indirectly.  It changes with the temperature of the panel.

Red Squirrel:

--- Quote from: cravenhaven on August 27, 2016, 02:04:28 pm ---The MPPT point for a panel will change with the irradiance, so if you have panels at different orientations paralleled into one controller then the mppt point selected by the controller will less than optimal for any of them.
As far as I have seen with solar installations you would always use separate mppt tracking regulators for each array of panels if they are significantly different from each other in either orientation or design.

--- End quote ---

That's what I was thinking too, so each array should be on it's own mppt then?  How would this work for battery charging, would I need to just set them to float, and maybe only have one that charges at a higher/variable rate?  Otherwise they'd all fight each other. Or would it just work?

mtdoc:

--- Quote from: Red Squirrel on August 27, 2016, 08:02:31 pm ---
--- Quote from: cravenhaven on August 27, 2016, 02:04:28 pm ---The MPPT point for a panel will change with the irradiance, so if you have panels at different orientations paralleled into one controller then the mppt point selected by the controller will less than optimal for any of them.
As far as I have seen with solar installations you would always use separate mppt tracking regulators for each array of panels if they are significantly different from each other in either orientation or design.

--- End quote ---

That's what I was thinking too, so each array should be on it's own mppt then?  How would this work for battery charging, would I need to just set them to float, and maybe only have one that charges at a higher/variable rate?  Otherwise they'd all fight each other. Or would it just work?

--- End quote ---

The charge controllers would each be programmed with the same bulk, absorb, and float voltages (assuming LA batteries) as recomended by the battery manufacturer. Ideally each CC will have its own temp probe at the battery bank. This will usually work just fine, with each controller transitioning from bulk to absorb to float at approximately the same time. Midnite's have a "follow me" option that allows multiple CCs to be networked via  RJ45 cables and then share one temp probe and coordinate charging stages exactly. One will act as the master and the others as slaves.

Someone:

--- Quote from: Red Squirrel on August 27, 2016, 08:02:31 pm ---
--- Quote from: cravenhaven on August 27, 2016, 02:04:28 pm ---The MPPT point for a panel will change with the irradiance, so if you have panels at different orientations paralleled into one controller then the mppt point selected by the controller will less than optimal for any of them.
As far as I have seen with solar installations you would always use separate mppt tracking regulators for each array of panels if they are significantly different from each other in either orientation or design.

--- End quote ---

That's what I was thinking too, so each array should be on it's own mppt then?  How would this work for battery charging, would I need to just set them to float, and maybe only have one that charges at a higher/variable rate?  Otherwise they'd all fight each other. Or would it just work?

--- End quote ---
Look at how much the peak power point will vary with temperature/insolation, going from a single voltage on all strings to individual MPPT on all strings will only gain a few % in increased generation. Then you can compare the costs of adding additional MPPT and cabling compared to the additional energy produced, or adding more panels to the strings.

Red Squirrel:

--- Quote from: Someone on August 27, 2016, 10:48:53 pm ---
--- Quote from: Red Squirrel on August 27, 2016, 08:02:31 pm ---
--- Quote from: cravenhaven on August 27, 2016, 02:04:28 pm ---The MPPT point for a panel will change with the irradiance, so if you have panels at different orientations paralleled into one controller then the mppt point selected by the controller will less than optimal for any of them.
As far as I have seen with solar installations you would always use separate mppt tracking regulators for each array of panels if they are significantly different from each other in either orientation or design.

--- End quote ---

That's what I was thinking too, so each array should be on it's own mppt then?  How would this work for battery charging, would I need to just set them to float, and maybe only have one that charges at a higher/variable rate?  Otherwise they'd all fight each other. Or would it just work?

--- End quote ---
Look at how much the peak power point will vary with temperature/insolation, going from a single voltage on all strings to individual MPPT on all strings will only gain a few % in increased generation. Then you can compare the costs of adding additional MPPT and cabling compared to the additional energy produced, or adding more panels to the strings.

--- End quote ---

Yeah true guess if it's not that much of a difference it may not be worth going through the trouble.  I could probably also put arrays on relays, have the relay of the less optimal one turn on when there is enough sun.   

This is more of a what if scenario anyway, chances are good I'd start with just the roof top array.    What I've been thinking about as well is I need to build a shed, I might make it use solar power for lights etc and it will make a decent solar project as a start to get an idea of what is involved.

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