Start Up Voltage

[daniemare]

Hi All,

I currently have 6 (400W) Panels in Series. Under NOCT these do about 38V max, and thus 228V total

The Start Up volrage of my inverter is 125V. Now my understanding was that this voltage output must first be reached before the Inverter start using the power produced by the panels.  

The MPPT Range is 215 - 500V. This, as I understand it, is when the MPPT does its magic.

So up to now all work as intended and my system with it's 7.2kWh battery is running at a balance I like.  Yes there are still some days, especially in summer, that the panels are idle, but I cannot do another battery now.

My question however is regarding the Start Up Voltage

In the mornings, I can see that my panels start producing 60W or so as soon as the sun peaks above the mountain (and from the East, my panels are North).  I can see it is not the MPPT that is working, because within 15 minutes or so, the production jumps (and not like the typical curve for the rest of the day)

So is the panels actually procuding before it reaches the 125Vstart up voltage? (For this assume Eskom is on)

Follow up question

If I were to put 3 panels (additional) west, to extend my production during the day (and delay using the batteries).  Will this work if 114 (38V x 3) is less than the start up voltage. 

Or does start up voltage consider both strings in aggregation?

Does the MPPT voltage range of 215 - 500V also work per string or accross both strings?

 

Thanks in advance

Danie

 

[chrisc]

I have also been pondering this question.  None of the solar equipment suppliers I deal with have any idea

A slightly different take...

The inverter in question states:

Max PV open circuit voltage - 145 vdc
PV array voltage range - 60 to 115 vdc

From this I assume that the MPPT charger needs 60V to start

There are 4 x 30 volt panels, 2 each in series and the two series in parallel

Measuring the incoming PV voltage at the inverter from 09h30 to 05h30 shows 66 volts.  This is when it is connected to the inverter.  

In winter and cloudy days this gets nowhere near 60 volts. maybe 45

I could wire the two presently in series and get 132 volts

Question:  Would this harm the inverter?

Thank you
 

[wolfandy]

On 2023/01/17 at 12:26 PM, daniemare said:

So is the panels actually procuding before it reaches the 125Vstart up voltage?

Yes, I have seen on both my Sunsynk as well as my previous Victron MPPT that the MPPT often starts producing before it gets to the 'official' start-up voltage.

On 2023/01/17 at 12:26 PM, daniemare said:

If I were to put 3 panels (additional) west, to extend my production during the day (and delay using the batteries).

How many MPPTs does your inverter have? If you 2 MPPT in your inverter, then you can put panels into a different direction that your current string (if I understand correctly that is what you want to do). If you only have 1 MPPT, then I would advise against putting panels in different directions into 1 string.

On 2023/01/17 at 12:26 PM, daniemare said:

Will this work if 114 (38V x 3) is less than the start up voltage.

You might get a bit of production out of the string, but not nearly as much as the rated capacity. I would advise against this.

On 2023/01/17 at 12:26 PM, daniemare said:

Or does start up voltage consider both strings in aggregation?

If you have 2 MPPT, then the start-up voltage is for each MPPT individually

On 2023/01/17 at 12:26 PM, daniemare said:

Does the MPPT voltage range of 215 - 500V also work per string or accross both strings?

What do you mean by 'across both strings'? Do you mean paralleling 2 strings on 1 MPPT? I would only do that if you have the same voltage across both strings. Otherwise you will end up with a complete mess

On 2023/01/17 at 12:26 PM, daniemare said:

If I were to put 3 panels (additional) west, to extend my production during the day (and delay using the batteries).

On a side note here: I would advise against this. I have 3 separate strings (each in a different direction and on it's own MPPT) and the panels towards the evening sun are giving me the lowest production out of all.

If you want to add panels, I would add them in your current (I assume main) direction and beef up your string voltage. You will also get a bit more production out of it in the evenings as your MPPT will not shut down as early as it currently does (due to higher panel voltage). Not an extra hour or so, but a bit. And it will start up earlier in the mornings due to the higher voltage.

[wolfandy]

46 minutes ago, chrisc said:

I could wire the two presently in series and get 132 volts

Question:  Would this harm the inverter?

Very likely yes. I am not sure if the inverter will already go up in smoke above 115V - but I would not take the risk

I would put 3 panels in series, but not 4

[daniemare]

9 minutes ago, wolfandy said:

How many MPPTs does your inverter have?

I have 2.  Idea is to have 1 (current string) face north, and the other face west

 

10 minutes ago, wolfandy said:

If you have 2 MPPT, then the start-up voltage is for each MPPT individually

What do you mean by 'across both strings'? Do you mean paralleling 2 strings on 1 MPPT? I would only do that if you have the same voltage across both strings. Otherwise you will end up with a complete mess

Thanks.  See the spec sheet is great at stating the Current as 11 / 11 Amp (meaning 11 amp on string 1 and 11 ampt on string 2)

But the Start Up Voltage 125V and MPPT Range 215 - 500V is not stated in the same way.  So with "Accross Both strings" I mean

1 - Is this the start up voltage of each MPPT individually OR

2 - Is this the start up voltage of the system, meaning if 1 string gives you 80V and the other string 60V it is 140V and the system will start?

Conversely, if 1 String gives you 250V and the other string gives you 300V the system voltage is 550V and this outside of the MPPT range. 

But you did awnser me, those to are per string.  Just do not know why, (like for current) can't they go

Start Up Voltage 125V / 125V

MPPT Range 215 - 500V / 215 - 500V

 

So bottom line, if I want to do a west panel string, it must be a full string that meet the 125V and 215-500V requirements.

[wolfandy]

45 minutes ago, daniemare said:

I have 2.  Idea is to have 1 (current string) face north, and the other face west

Cool. Then the 2 different directions will work

48 minutes ago, daniemare said:

So bottom line, if I want to do a west panel string, it must be a full string that meet the 125V and 215-500V requirements.

Correct

But the west-facing string would not be my first priority. I am also in CPT and at one point I also added a west-facing string with the same idea as you have.

Here is my production data from yesterday. Orange is my total production across all strings, Yellow is my North string (4.5kW), and Blue is my West string (2.2kW). Each Grey horizontal line represents 1kW of production.

At 18h20 both strings were still producing around 1.4kW. At 18h45 the North string produced 0.9kW while the West was at 1.1kW. At 19h30 it was 160W vs 435W. So a bit more, but not that significantly. And in winter it is even worse because the sun is not that strong anymore that time of day...

I get much more from my East string (also 2.2kW) than from my West. East in Blue and North in Yellow (each Grey line is 0.5kW production):

 

You can see how the sun comes up over the mountain to hit my panels on the East string

So if you want to add a 2nd string, I would rather recommend East than West