Parallel strings and overpaneling or how to maximize PV production on a single inverter.

[MattiFin]

Now that is an interesting idea. Bifacials out put on both sides is the same? Have never looked into those, but this is interesting.
This was the reason for the question to begin with. A 5kw inverter for example only puts out 5kw (max power) if overpaneled some but for only maybe for an hour or 2. Before and after that it is always less and adding panels at different orientations could max the output from sunrise to sun set. But you have to know exactly what the criteria are as to how to do it.

Latest bifacials (TOPcon N-type or HJT) have only about 20% difference between the backside and front.

 

[MattiFin]

There is a way to simulate multiple arrays on JRC photovoltaic tool combined with excel but it is bit tedious:
Select "daily data" for location of interest and month, set array angles and download results in .csv
Repeat for every other array and combine all of the .csv results in excel summing up the global irradiance for each hour.

For my parents hometown in northern Finland I got 16 hours of reasonable output per day

 

[Calvin98]

Looks very interesting. You need to do careful planning. I like the look of the "total power curve," but if you inverter is already maxed out, you might be better off with another inverter that can take the am and pm sun, othwise it might do a lot of "clipping."

 

[road glide]

Parallel strings and overpaneling or how to maximize PV production on a single inverter.

In the past I was told that you could safely add 20% more panels to an inverter than the name plate rating, i.e. on a 5kw inverter, you could put 6,000 watts of PV panels. New SMA docs say you can overpanel by 60%. i.e. you can add 8,000 watts of panels to a 5,000 watt inverter. On new SMA inverters that are coming out you can supposedly overpanel by 100% i.e. 10,000 watts of panels on a 5,000 watt inverter. From what I understand the extra power is just not used (whatever that means).The most it will ever put out is 5,000 watts.

Back in the day when panels were expensive, overpaneling was not practical, but now with prices so low, overpaneling and stings of different orientations are practical.

A 5,000 watt inverter is only producing max power of a few hrs. at local noon (assuming relatively sunny (shade free) location.

The question are: How can you maximize output on 1 inverter? Can you get it to produce 5,000 watts continuously from sunrise to sunset? What do you have to keep in mind?

In general, panels are oriented due south for maximum output. That leaves the mornings and afternoons with low power outputs.

Say you already have 6,000 w of panels facing South on 2 MPPT inputs. Say you want to add 2 more arrays, both vertical to capture early morning and late afternoon sun, but 1 facing due West and the other array facing due East. That is ok as long as the min max DC voltage and amperage conditions are met?

Can you put both arrays on the same 1 string? You only have to meet the min dc voltage? They will never both produce power. Or should you put 1 array on each input? i.e. South plus East and South plus West? Can you put 3,000 watts of vertical East facing panels to the same input as the 3,000W of South facing panels?

Can strings be different sizes, i.e. 1 string of 8 panels facing West and the other 10 panels facing East? Both connected to same MPPT input as long as the min DC voltage is met?

Can you mix strings of different voltages? If yes how? Can you have a string of 3 panels at 100V be connected to a 300V string facing a different orientation?

Are microinverters maybe a good solution for some of these situations? The ones on Amazon seem to overheat and shut off, plus they seem to fail rather soon.

If there is a sunny area, but it only fits 4 panels, can those 4 panels be connected in parallel to a different string. Keeping in mind not to exceed the max current.

Lets say you have an area that gets 2 hrs of good sun, how can/should you connect that to the inverter to capture those 2 hrs of power?

Example:
Sunny Boy 5.0-US Inverter
3MPPT trackers, 1 string/MPPT tracker
Max DC Voltage 600V
Max PV Power 8,000Wp
Rated MPP voltage 220V-480V
MPPT operating Voltage 100-500V
Min DC start Voltage 100V/125V
Max operating input current per MPPT 10A

I’m guessing there is a simple rule that you can apply to all of these situations.

FYI: We have close to same system but my SB5 us 41 is AC coupled with 2 6048 SI's. We have 20 - 320w Jinko premiums 6800 configured 8-6-6 into the 3 Mppt's. So string 1 (8) is 371v, string 2 & 3 (6) is 278v each....SnapNrack all facing south. We also have the 10-240's 2400w rack of Talesuns from the DC trailer oriented east but left those wired to Midnite Classic 250 through charge controller into batteries.
Using the SMA config webpage....we had the option of running 10- 320's into Mppt 1 and the other 10 into Mppt 2. We could then run the trailer rack 2400 into MPPT . All under the 600v limit. 514-514-406. But chose not to because of additional wiring and the DC config was aready there and wired to the Charge controller.
So, the SMA inverter/panel tool was great...
Future plan is to move just the 2400 rack to another location and get another SB 40-41 (web interface) and also I have 5 extra 320w Jinko's in storage new. So I would orient those east and the 2400 rack south.

 

[Solarisium]

The 455w Solarever panels output 11 amps. The SB 5.0-41 does "derate", clip and this has happened, al biet a very small percentage of total output time, on the larger 9 panel string. With Hedges assistance, I paralleled inputs A and B for the 9 panel string. No more derating. The total string amps is now shared/split with A and B mppt's. SMA does specify that derating is normal and does not negatively impact the inverter. Just stay stay below 18amp mppt max. This may not be true for all inverters.

One thing I am unsure of, does paralleling A and B use more calculation cycles and possibly lower inverter efficiency.

Where does it say the minimum number of RSD must be 6?
That might be impacting my plan.


I have 9x455w salarever, on sb3.8 us-41 all in one string, but paralleled to A and B, and still see derating message.
I doesnt seem to have a negative impact on the inverter efficiency. But i am contemplating to split them out to two strings (4x and 5x panels).

 

[Hedges]

SMA needs 5V to wake up RSD transmitter. Tigo RSD put out 0.6V so takes quite a few in series to work. The newer SMA RSD are 1V.

SMA - Customer Community

https://assets-global.website-files.com/5fad551d7419c7a0e9e4aba4/605e5c8b77c8c1eec9c69159_Application%20Note%20-%20Tigo%20SMA%20RSS.pdf

 

[Solarisium]

SMA needs 5V to wake up RSD transmitter. Tigo RSD put out 0.6V so takes quite a few in series to work. The newer SMA RSD are 1V.

SMA - Customer Community

https://assets-global.website-files.com/5fad551d7419c7a0e9e4aba4/605e5c8b77c8c1eec9c69159_Application%20Note%20-%20Tigo%20SMA%20RSS.pdf

I use Apsmart, RSD-S-PLC output minimal voltage is 0.7V, (0.6 to 1.0 V depending on environment conditions, according to Apsmart)

https://apsmartglobal.com/wp-content/uploads/2021/04/RSD-S-PLC_Functional-Checking20200115.pdf

Thanks for saving me from a pointless hassle!

 

[Hedges]

My thought is wire one 12V or even 6V panel into MPPT "C" if unused. Or AC to DC supply feeding it.
Or connect one 12V panel of suitable amperage in series with the string, without RSD box on it.
String voltage needs to be under 30V for compliance. Otherwise would leave one ~ 40Voc panel outside RSD.
My concern is whether SB tries to hard to drain off charge, probably through FETs, and doesn't give up just at 30V. Instructions have some warning about RSD discharge function if modules not connected to RSD for shutdown, if I remember correctly.

 

[Ai4px]

SMA needs 5V to wake up RSD transmitter. Tigo RSD put out 0.6V so takes quite a few in series to work. The newer SMA RSD are 1V.

SMA - Customer Community

https://assets-global.website-files.com/5fad551d7419c7a0e9e4aba4/605e5c8b77c8c1eec9c69159_Application%20Note%20-%20Tigo%20SMA%20RSS.pdf

I ran into this problem testing the RSD modules... no setting on my Suny island would wake up the tigo modules. Later someone (maybe you??) suggested there was a min number of panels to get things kicked off. the 5v on the input makes sense now.... I would have had to put 9 panels in my test setup to have kicked off the RSD transmitter in the SB. I love it when the light bulb comes on for me.

Alas, I got ready to add 20 panels to my roof and realized I need a new roof. So I got down the rabbit hole of just creating a new ground mount system. 52 375w panels later on three parallel arrays.... and I'm ready to pull panels off the roof and decommission the old panels.