Q: MPPT

[burgerking]

I understand how MPPT works; it tracks input V vs input I and come out with the best V*I for optimum Power.
Here is my question:

Assume my Deye Inverter has dual MPPT ports, each port has Vmp 450V, Imp 13A.

Assume I have two identical PV strings. And I had observed that at max power, Voc~ 270V, Vmp ~210V, Imp ~8A for each string.

Now, If I combine these two strings, will the combined Vmp ~ 210V, Imp ~16A?
or since each MPPT can only handle 13A, will the MPPT adjust for higher Vmp and lower Imp?

I have so many times about panel oversizing, but how exactly will it work?
As you can see, this two strings has Pmax of just ~3400W and barely above Deye's PVmax of 3250W.
But obviously Deye's MPPT cannot handle 16A...

Should I instead redo this combined string into a series, and remove a few panels to reduce the Vmax?

 

[sunshine_eggo]

I understand how MPPT works; it tracks input V vs input I and come out with the best V*I for optimum Power.
Here is my question:

Assume my Deye Inverter has dual MPPT ports, each port has Vmp 450V, Imp 13A.
View attachment 104991
Assume I have two identical PV strings. And I had observed that at max power, Voc~ 270V, Vmp ~210V, Imp ~8A for each string.

Now, If I combine these two strings, will the combined Vmp ~ 210V, Imp ~16A?
or since each MPPT can only handle 13A, will the MPPT adjust for higher Vmp and lower Imp?

If you parallel the strings on the same MPPT, you'll be 3A over the 13A limit, so you will be over-paneled. This may or may not be acceptable depending on Deye's spec.

You would have a theoretical max on that MPPT of 210V * 13A = 2730W

Rather than observed, you should consider panel specs for design purposes.

 

[burgerking]

Clarification:

It is possible to Parallel multiple MPPTs together on Deye/SunSync inverters.
More accurately a single PV or Wind Turbine into multiple MPPT inputs using Diodes as shown below:

The above is a screenshot from a video released by SunSync.

www.youtube.com/watch?v=nZ6PGN2L10k&list=PLu8z4MHf_LyX_1O2U76zGuJm4S7vlYpfW&index=6

 

[sunshine_eggo]

No. Arrays hooked to multiple MPPT results in the MPPT fighting each other constantly trying to find the MPP.

Victron addresses this specifically in their MPPT documentation.

 

[burgerking]

This works for Deye/SunSync as they themselves said so.
The Blocking Diodes prevent the MPPTs from fighting each other.
They devised this both for Solar Panels and especially for Wind Turbines.

Maybe Victron cannot do it, but Deye/SunSync can.

 

[Lactophobe]

Oh my, I hope you don't get a diode fail or an imbalance due to manufacturing in a diode - that would stuff all the power the one MPPT with a good circuit.

 

[burgerking]

Oh my, I hope you don't get a diode fail or an imbalance due to manufacturing in a diode - that would stuff all the power the one MPPT with a good circuit.

Deye has logic built in circuit/logic to limit the power draw out of their MPPT.

 

[RBEL]

In this case each string will never put out more than 13A of current. If you feed it 16A worth of theoretical maximum, the 3A will be basically lost (I guess in heat), which means that you are continuously overloading the MPPT and thus potentially damaging it.

I would recommend that you do not do that.
If you really need that many panels, you can always add another inverter and put them both in parallel. Up to 8 Deye inverters can be connected in parallel.

 

[timselectric]

Solar panels don't push amps. They only make them available. An MPPT will only draw what it needs, up to its limit. (Never anything more)
Overpaneling is a great way to deal with cloudy days. Or spreading out the production over the course of a day. (With strings facing different directions)

 

[RBEL]

Solar panels don't push amps. They only make them available. An MPPT will only draw what it needs, up to its limit. (Never anything more)
Overpaneling is a great way to deal with cloudy days. Or spreading out the production over the course of a day. (With strings facing different directions)

Interesting. What happens to the extra "available" current, in case that an MPPT can take 16A instead of just 13A. Doesn't that make the system unsafe?

 

[timselectric]

Interesting. What happens to the extra "available" current

Nothing
It's just not used.
The same way you can plug in a vacuum cleaner or phone charger in the same wall outlet. They each only use what they need. They aren't forced to use all available amps.

in case that an MPPT can take 16A instead of just 13A.

Then it can take 16a, if it's available.

Voltage is pushed.
Amperage must be drawn.

 

[RCinFLA]

There are four maximum criteria, whichever of these four parameters max's out limits the output.

1) 3250 watts per MPPT input power
2) Combined two MPPT input power 6500w max.
2) 13A per MPPT input current (manual I have says 11A max for 5k model)
3) 125v-425v MPPT input voltage (since max Voc input is 500vdc and Vmp is typ 0.81 to 0.85x Voc, max Vmp is about 405 to 425 vdc)

The two MPPT controllers share a heat sink so there is a limit on amount of heat generated by the combined two MPPT controllers. It likely will not sustain 13 amps on both MPPT inputs and will cut back to about 11 amps on each.

For a single MPPT input, if you have 13A Imp, then maximum Vmp can be 3250w/13A = 250 vdc.

PV arrays less than Vmp of 250v will not be able to achieve 3250 watts from single MPPT input as it will limit input current to 13A by allowing PV array voltage to rise to reduce PV array current output.

Never feed two MPPT controller inputs from same PV array. Most MPPT algorithms allow panels to go unloaded for a moment to allow measurement of Voc then start Vmp search with an array loading to pull panel voltage down to 0.6-0.7 x Voc and creep up from there to find MPPT point.

Putting two MPPT controllers operating independently on same array will screw up this initial Voc measurement causing MPPT search to get confused and likely never find MPPT point resulting in diminished net output power. Doing this on two independent series connected AIO 120 vac HF inverters, like LV6548, can destroy inverters.

Diagram of similar arrangement on SolArk12k which is an 8 kW battery powered inverter.

 

[Derka181]

Interesting. What happens to the extra "available" current, in case that an MPPT can take 16A instead of just 13A. Doesn't that make the system unsafe?

Think the headlight (solar controller) in your car. The cars battery doesn’t push all the battery’s power to the headlight, the headlight pulls what it needs from the battery.