Combining Strings of PV to Hawkes Bay

[ClassicCrazy]

Right now I have 3 series 3 parallel PV going to a Classic.
I have 8 series going to Hawkes Bay.
My Classic PV array gets shaded early afternoon but the Hawkes Bay gets sun into evening.
I am wondering if I can combine 8 series ( from the Classic) with the present 8 series from the Hawkes Bay ? 
Due to the shading - I don't think it would work to just series all the 16 pv into the Hawkes Bay would it ?
I am thinking  the Hawkes Bay will run cooler in the long run than the Classic , plus then I don't have to tweak two different controllers setpoints to play nicely with each other for battery charging. If the Hawkes Bay ever gets the remote sense voltage firmware update then this would be a real advantage .
Thanks for any advice .
Larry

[Vic]

Hi Larry,

Agree with you,  that running 16 S, of your PVs into the HB would not work too well ...  think that the SHADING will KILL the production of that 16 S configuration.

IMO, running 8 of the 9 PVs on the Classic,  would be OK, if the string PV Vmp, of those,  are within 10% of the existing 8 PVs that are now on the HB.

Here,  we run the Barcelona,  and the Classic 150, charging the same FLA battery bank.  We tried to get the voltage drop in each of the output conductors from each CC, to the battery, to be fairly close, when in the middle of a  typical Asorb.  This helps in each CC carrying its share of Absorb.

For the present Summer-ish WX conditions,  have set the BCLNA's Absorb to be ten minutes shorter than the Classic.  The Classic has 70% of the PVs, and the Barc has 30%.  Sometimes, the Classic would finish first (both CCs on Timed Absorb),  and then, usually, the Barc would be stuck in Bulk for the rest of the Solar day,  as it would not have enough PV power, to ever get back to Vabs, for that short bit of time to finish the last ten-ish minutes of Abs   ...

 ...  etc,  keep cool,  later, Vic

[aaapilot]

Right now I have 3 series 3 parallel PV going to a Classic.
I have 8 series going to Hawkes Bay.
My Classic PV array gets shaded early afternoon but the Hawkes Bay gets sun into evening.
I am wondering if I can combine 8 series ( from the Classic) with the present 8 series from the Hawkes Bay ? 
Due to the shading - I don't think it would work to just series all the 16 pv into the Hawkes Bay would it ?
I am thinking  the Hawkes Bay will run cooler in the long run than the Classic , plus then I don't have to tweak two different controllers setpoints to play nicely with each other for battery charging. If the Hawkes Bay ever gets the remote sense voltage firmware update then this would be a real advantage .
Thanks for any advice .
Larry

Hi Larry.  Did you ever try combining the 2 strings into HB?  I am thinking about doing the same and was curious as to your findings if you tried it.  Also, were you using the same panels on both controllers or were they different?  Thanks!

Dave

[ClassicCrazy]

Right now I have 3 series 3 parallel PV going to a Classic.
I have 8 series going to Hawkes Bay.
My Classic PV array gets shaded early afternoon but the Hawkes Bay gets sun into evening.
I am wondering if I can combine 8 series ( from the Classic) with the present 8 series from the Hawkes Bay ? 
Due to the shading - I don't think it would work to just series all the 16 pv into the Hawkes Bay would it ?
I am thinking  the Hawkes Bay will run cooler in the long run than the Classic , plus then I don't have to tweak two different controllers setpoints to play nicely with each other for battery charging. If the Hawkes Bay ever gets the remote sense voltage firmware update then this would be a real advantage .
Thanks for any advice .
Larry

Hi Larry.  Did you ever try combining the 2 strings into HB?  I am thinking about doing the same and was curious as to your findings if you tried it.  Also, were you using the same panels on both controllers or were they different?  Thanks!

Dave

No , I never did combine two strings yet.
I have the Classic set up with nine pv in 3s 3p . The Hawkes Bay is 8s . They are all Kyocera pv but the ones on the Classic are higher wattage though the voltages are close enough to combine if I ever want to. Right now due to some shading issues on the Classic array it isn't worth the effort. If the Hawkes Bay ever gets voltage sense working and some other firmware updates I might consider combining them .
Larry

[aaapilot]

Thank you for the update!  Can you tell me what voltage sensing is in regards to your comment about the HB?  I'm learning as I go with the HB and Rosie

Dave

[ClassicCrazy]

There are remote sense wires that can be attached to the Hawkes Bay. These attach to the battery posts . That way they can tell what the voltage is at the battery . If the Hawkes Bay only knows the battery voltage from the main cables to the battery , the voltage may differ from the actual battery voltage . This happens because of voltage drop on the cables that happens when there are a lot of amps flowing through the cables. So when the batteries are charging with a lot of amps , the voltage can be a little different . This can make a difference when charging lithium batteries. There is a menu in the Hawkes Bay to compensate or calibrate for this voltage difference. So for example when the batteries are charging at the highest point ( Absorb) you would tweak this setting  so both the battery posts and the Hawkes Bay are reading the same . But if you do this, then the voltage may read different when it is at a lower voltage .
So the remote voltage sense wires would eliminate this issue. But that feature has not been available yet in the Hawkes Bay firmware.
Below is example from Classic that shows what I am talking about.
The red line is the voltage the Classic is seeing. At the lower battery voltages the red line Classic voltage is below the battery voltages. As the voltage climbs you see the red line rise up to be more closely similar to the same voltage as the batteries. I have the Classic voltage offset tweaked a bit, but also have set the Classic Absorb and Float voltage setpoints set to where they will do what I want them to do for the batteries. So I can't just set the Classic to lets say 55.2v Absorb and expect it to charge the batteries to 55.2 v without doing some other stuff and monitoring it for awhile to make sure it is going to be where I want it to be. In the example it is pretty close . The Hawkes Bay is similar . For now I have both the Hawkes Bay and Classic charging the same lithium batteries but I am using the Classic to do the final absorb . The reason for that is that I can graph and remote monitor what the Classic is doing, but there is no way to do that for the Hawkes Bay until some communication protocol for the Hawkes Bay is published, or until they have a combox that will let you get the data out of .
So long answer to your question !
Larry

[aaapilot]

Very detailed answer, thank you!  I assumed this was less important with Lithium with independent BMS's that handle charging details.  I have an HB that feeds a Rosie and 6 Pytes V5 batteries.  I'm using the Rosie pick-offs for the voltage sensing wire for the system as it's 3' closer to the battery distribution posts.  Should have it running by the end of the month.  I don't know if voltage sensing is operational yet in the Rosie either, so we'll see how it goes.  Thanks again

Dave

[ClassicCrazy]

Very detailed answer, thank you!  I assumed this was less important with Lithium with independent BMS's that handle charging details.  I have an HB that feeds a Rosie and 6 Pytes V5 batteries.  I'm using the Rosie pick-offs for the voltage sensing wire for the system as it's 3' closer to the battery distribution posts.  Should have it running by the end of the month.  I don't know if voltage sensing is operational yet in the Rosie either, so we'll see how it goes.  Thanks again

Dave

The BMS really only protects the battery from under volt , over volt, temps, and over current and don't do anything for charging other than some can report to chargers. They are supposed to balance the cells though many of them only have small passive balance resistors. Some of the newer bms have much higher current active balancing. Watch Off Grid Garage because he is testing what may be the best bms so far with many new features. https://youtu.be/qqSEPzbL_i8?si=Gxe8sMZpg394CehT