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Paul Coetzee

How many 300w solar panels can I connect to a 5kva Apert invertor?

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Hi,

I currently have 10 300w solar panels connected to a 5kva Apert (Mercer) invertor.

1) What is the max 300w solar panels can I connect to a  5kva Apert invertor ?

2) Should the max be 12 panels, what advantage might I experience by doing that ?

a) batteries will be fully loaded quicker ?

(b) I will use lesser Eskom power ?

3) Will the cost of the additional 2 panels out weight the saving on my Eskom account, over a 5 year period ? 

 

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1 hour ago, Paul Coetzee said:

2) Should the max be 12 panels, what advantage might I experience by doing that ?

You can oversize the array a little bit. Up to 120% as a rule of thumb, which incidentally is exactly what you'd get if you add two more panels. The effect of that is that you'd make a bit more power in the mornings and in the afternoons, but in the middle of the day that top 20% will be "chopped off" (think of a bell curve with the top flatly sawn off) and you'll lose the extra 600W for that hour or three.

So just thumb-sucking here, the extra 600W would normally give you an extra 3kwh a day, but since it won't be doing that for 3 hours a day (12pm to 3pm), I estimate you'll get maybe an extra 2kwh a day.

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Hi 

The documentation on the Voltronic site shows 4000W for the max pv input.

This will only be for the new Axpert MKS 5K. Your documentation will show you the correct W if you have a older model.

I do not know how the panels are connected. If you have 10 300w panels they  should be connected  with 2 panels in series and 5 series panels in parallel.

This is not so good as the current is quite high >40 amps and the voltage low about 90v open circuit and working voltage about 73v.

If you oversize by adding two panels  (total 12 panels) as suggested it would be better as you will be able to have 3 panels in series and 4 series panels in parallel (open circuit voltage about 135v and about 33 amps max.). Max voltage allowed on inverter is 145v.

Higher voltage less amps is always better and more efficient.

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I agree with Plonkster that you can safely oversize the panel capacity. In addition of the inverter being able to lower the  output from the panels another reason is that because of temperature/dirt of the  panels and losses in the electrical circuit you will usually not achieve the published capacity of the panels.

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I'm of the opinion that 2 x 5 array may not be optimum, due to the low voltages that the panels give plus the voltage the Axpert needs before it "wakes" up in the morning. Don't have them on hand atm, but I'm sure you get the idea.

I run a (3 x 4) times 2 setup, thus 3600W per controller. That's a 20% over spec. This requires the number of panels to be a multiple of 3.

All I have noticed this summer, is that the controller goes up to 3000W (6000W in total), and hovers there (plus a bit over), even though there is more PV available. One just need to watch the Inverter temp, specially if you "room" gets sun in the afternoon.

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3 hours ago, Sidewinder said:

This requires the number of panels to be a multiple of 3.

Best done with 60 cell panels. Some 72 cell panels' ( in series of three)  VOC will exceed the Axpert's 145 VMax of the SCC.

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On 2/16/2018 at 1:25 PM, Sidewinder said:

I have Enersol 300W panels 3s4p. Voc max = 44.8 x 3 = 134.4V . So about 10V off Voc max. Vmax = 36.6V x 3 = 109.8V. 

Ok that sounds good is that PV Voc Max at 25°C. What is your minimum winter temperature?

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On 1/23/2018 at 11:31 AM, Fuenkli said:

I agree with Plonkster that you can safely oversize the panel capacity. In addition of the inverter being able to lower the  output from the panels another reason is that because of temperature/dirt of the  panels and losses in the electrical circuit you will usually not achieve the published capacity of the panels.

Yes you can oversize your PV array a bit, as long as the Voc of your panels don't exceed your MPPT Voc. I usually leave 20% headroom in this area. ISC can be a bit higher than the max, since the MPPT will only draw the ameperge that's needed. For safety, match you PV fuses with the MPPT's max rating + 20%

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