Calculating over paneling

[Bluedog225]

I’m double checking my maths before hooking up.

When I’m calculating how much I over panel my Victron 150/35, do I use the wattage of the panels divided by the voltage of the system?

E.g.: 9 panels x 275 watts = 2,475 watts

Edit-the in series; three in parallel.

2475/56 volts = 44 amps

26% over

I’ll only be running 28 amps when calculated based on the short circuit voltage times the number of parallel strings per mppt.

I think I’m in the clear right? Thanks.

 

[sunshine_eggo]

That works if you want to use your peak charge voltage, but at lower voltages, you'll be even more over-paneled.

I like to use max rated power. For that unit, it's 2000W on a 48V system.

2475/2000 = 1.24 or 24% over-paneled.

IMHO, it's more important to ensure you haven't exceeded the over-paneling limits of the controller.

Victron publishes the following these detail key to over-paneling on their datasheet:

Voc limit
Isc PV input limit.

3S3P = 116.1Voc (huge temp margin), 27.78A Isc.

Your unit has a 40A PV isc limit, so you could put ANOTHER 3S string and still not exceed the PV input Isc limit.

 

[Bluedog225]

That works if you want to use your peak charge voltage, but at lower voltages, you'll be even more over-paneled.

I like to use max rated power. For that unit, it's 2000W on a 48V system.

2475/2000 = 1.24 or 24% over-paneled.

IMHO, it's more important to ensure you haven't exceeded the over-paneling limits of the controller.

Victron publishes the following these detail key to over-paneling on their datasheet:

Voc limit
Isc PV input limit.

3S3P = 116.1Voc (huge temp margin), 27.78A Isc.

Your unit has a 40A PV isc limit, so you could put ANOTHER 3S string and still not exceed the PV input Isc limit.

I appreciate the response.

Two questions:

1. For max rated power are you using “NominalPVpower” from the data sheet?

2. Is it a bad idea to put another 3S string and get that close to the 40A PV lsc limit? A rep from a vendor was advising me against it.

I’m all for max production but have two 150/35 and don’t need to max them out or run them too hot.

Thanks for your help.

 

[robbob2112]

Great topic I haven't done a deep dive into yet, can you explain the concepts and best practices in small 1 syllable words I can lookup and understand?

Assume I have a schnieder 60 150, specs here

 

[Ampster]

When I’m calculating how much I over panel my Victron 150/35, do I use the wattage of the panels divided by the voltage of the system?

I look at voltage as the constraint. If that is not exceeded I look at DC Wattage of the panels to AC Wattage of the inverter or charge controller as a ratio of overpaneling. I have seen ratios in the area of 1.3 to 1 and as high as 1.5 to 1. The ultimate metric which I want to optimize is annual production and I try not to get distracted by ocassional clipping which can vary by season, temperature and other environmental and configuration issues. It is easy to modle PV Watts using various DC to AC ratios given the same tilt and orientation to optimize annual production. I find it interesting that many solar farms run at ratios in excess of 1.5 to 1 because optimum return is measured by annual production for them. I assume clipping is not an issue for them because market rates are lowest whe clipping is more common during mid day.

 

[Sergio95050]

SolarEdge inverters allow the ratio 2:1, BTW.

 

[sunshine_eggo]

I appreciate the response.

Two questions:

1. For max rated power are you using “NominalPVpower” from the data sheet?

Yes. That's the max power output for that system voltage.

2. Is it a bad idea to put another 3S string and get that close to the 40A PV lsc limit? A rep from a vendor was advising me against it.

Not at all. Victron is very explicit about being able to overpanel right up to the limits. The only reason the 40A limit exists is because the reverse polarity protection feature shorts the PV, and the contactor that does that is rated for 40A.

The only reason you don't want to do that is because you just don't want to be over-paneled that much.

Great topic I haven't done a deep dive into yet, can you explain the concepts and best practices in small 1 syllable words I can lookup and understand?

MPPT are output limited. In almost all cases, you can put more PV on them than they can handle.

Assume I have a schnieder 60 150, specs here

View attachment 217489

that unit has a couple of different limitations, and they don't entirely make sense. Max PV array rating of 5250W doesn't make a lot of sense because at 60A of output (60A * 58V = 3480W), there's almost no way to output that much, let alone the "oversizing up to 7200W".

I would interpret that as follows:

Voc < 150V in all conditions.
Array Isc < 60A.
Array power < 7200W.

so, if you used the same panels as @Bluedog225, you could go 3S6P yielding 4950W while not exceeding 150Voc or 60A Isc. Of course, the unit would clip anything above 3480W @ 58V.

 

[robbob2112]

Yes. That's the max power output for that system voltage.



Not at all. Victron is very explicit about being able to overpanel right up to the limits. The only reason the 40A limit exists is because the reverse polarity protection feature shorts the PV, and the contactor that does that is rated for 40A.

The only reason you don't want to do that is because you just don't want to be over-paneled that much.



MPPT are output limited. In almost all cases, you can put more PV on them than they can handle.



that unit has a couple of different limitations, and they don't entirely make sense. Max PV array rating of 5250W doesn't make a lot of sense because at 60A of output (60A * 58V = 3480W), there's almost no way to output that much, let alone the "oversizing up to 7200W".

I would interpret that as follows:

Voc < 150V in all conditions.
Array Isc < 60A.
Array power < 7200W.

so, if you used the same panels as @Bluedog225, you could go 3S6P yielding 4950W while not exceeding 150Voc or 60A Isc. Of course, the unit would clip anything above 3480W @ 58V.

Where does 58v come from?

 

[ricardocello]

Where does 58v come from?

3480W / 60A = 58V (per eggo).
That's the upper limit on power due to the 60A output current limit (assuming you can even charge up to that voltage).
Lower voltages will have less power at 60A output current.

--

Your Schneider specifications above actually say 3500W max power, 60A maximum output current, so your max voltage is 58.33V.
But no one charges their batteries at that voltage (hopefully).

So if your batteries are at 53V, you will only get 53*60A=3180W out of the solar charge controller.
Even though you can over panel to 7200W of PV.
Great for cloudy days. On the really sunny days, you are leaving solar energy on the table, normal over-paneling tradeoff.

 

[Hedges]

Reverse polarity protection is a limit on Isc, only applies if you connect the array backwards and it can provide too much current.

If your array is going to be 3s4p, leave 3 strings unconnected so it is 3s, check voltage (make sure it is no where near max allowed), then connect to MPPT.

If the device works it isn't reversed. Go ahead and connect the remaining strings.

Of course it is possible you have wires to other strings reversed, which would make them carry current into each other when connected, draw an arc when disconnected. Use DMM to check voltage before mating last MC4 in a string. Be deliberate about not touching DMM leads when other lead it in MC4 connector (would be nice to have MC4 to shrouded banana test leads.)

As for over-paneling, array STC wattage about 120% or so of MPPT wattage is needed just for NOCT or PTC wattage to reach maximum. About 150% is not unreasonable. If you parallel strings of different orientation, depending on the angle between them, overpaneling to 200% would rarely clip much.

 

[sunshine_eggo]

Where does 58v come from?

Anticipated peak charge voltage. If you're current limited (60A), your max power output will occur at peak battery voltage.

If you only charge to something more conservative like 55.2V, then you only get 60A * 55.2V = 3312W

 

[robbob2112]

I posted in a new thread what I came up wth after reading and thinking and figuring - can y'all have a peak and see if I did it all right?

Help me understand paneling and over paneling

I've read posts and the link @sunshine_eggo posted to the Victron site and I am of course still wrapping my brain around it. Question in red Hypothetical system - 6 strings of 304ah 48v LFP batteries - 87kW battery power and capable of 1200amps - obviously it won't need the wiring at that...

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