Panel/MPPT minimum voltage efficiency

[nezek88]

Hi,

considering I'm using an oversized Inverter/MPPT(Growatt SPF3500ES) with only x4 450w Panels (1800w), would I have efficiency problems on sunrise/set and cloudy weather?

The Panel's Max power voltage is 41V ( x4 = 164V)
The MPPT minimum voltage is 120V

While in good weather conditions the system should work normally - could I have problems hitting the MPPTS minimum voltage requirement when its cloudy?
Is it better to find an MPPT with lower voltage startup?

I'm not too sure how does the MPPT but my fear is that if the voltage is dynamic could it go under the mppt requirement and not generate any power?

Cheers,

Nezek

 

[sunshine_eggo]

I think you may be fabricating both a solution and a problem.

Light gives voltage.
Intensity of light gives amperage.

Hopefully your proposed MPPT Voc limit is 250V or higher. If so, 4S is fine.

Cloudy ALWAYS produces less power. Sunrise and Sunset ALWAYS produce less power. Why? Because there's much less energy hitting the panels. Panels are rated for 1000W/m^2 of power hitting them. If clouds cut that to 100W/m^2, then you're only going to get about 10% of output.

Talk of MPPT performing substantially better in low-light conditions are often out of context and over-hyped. Substantial improvements of very low numbers are still low.

The only meaningful way to partially compensate for cloudy is to oversize your array.

 

[nezek88]

I think you may be fabricating both a solution and a problem.

Light gives voltage.
Intensity of light gives amperage.

Hopefully your proposed MPPT Voc limit is 250V or higher. If so, 4S is fine.

I'm worried that the MPPT wont 'start' because of under voltage...
So you are saying that along as there is light the panel produces ~41V, what if I got down to 3 panels? (120-123V across 3S) should that still work too?

VOC is 450V but this is a concern with I'm trying to maximize panels in a series is it not?

 

[pollenface]

I don't think there's anything to be concerned about. 100% of solar systems have reduced output during sunrise/sunset and cloudy weather.

As above, the only practical way of yielding more during these times is to increase the size of your array.

 

[sunshine_eggo]

I'm worried that the MPPT wont 'start' because of under voltage...

Unlikely.

So you are saying that along as there is light the panel produces ~41V

No. Typically higher until they start flowing current. 41V is the maximum power voltage, I assume the Voc of the panels is 47-48V.

what if I got down to 3 panels? (120-123V across 3S) should that still work too?

If MPPT is 120V Min, I would not go below 4S

VOC is 450V but this is a concern with I'm trying to maximize panels in a series is it not?

Yep.

 

[nezek88]

I don't think there's anything to be concerned about. 100% of solar systems have reduced output during sunrise/sunset and cloudy weather.

That was never in doubt, I was worried that this MPPT wont product anything in a scenario a different MPPT would produce 10% of max array potential.

 

[sunshine_eggo]

To give you some idea:



Sunrise was 5:35am, where it's marked. So even before sunrise, my 3S 120Vmp panels saw over 100V.

 

[pollenface]

That was never in doubt, I was worried that this MPPT wont product anything in a scenario a different MPPT would produce 10% of max array potential.

I would expect it to be fine if you're within the pv specs. Your array sounds ideal as 4s.

You won't really know how efficient it is until you test it back to back with your old MPPT.

 

[sunshine_eggo]

Follow up.

Disabled charging to see what PV did without the MPPT trying to pull current:



5:21 was today's sunrise. Panels were at 113V with a peak to 138V shortly after.