Jump to content

1 string or 2 strings versus MAX Amp input


Recommended Posts

Please forgive me if this has been answered somewhere.

I have a Solis 3.6kW

It has a MAX input current of 11A +11A and 2 MPPT / 2 strings inputs (see screen grab below)

I have 12 x 320W / 8.77 Amp panels = 3962W total

All 12 panels in series in 1 string is 8.77 Amps which is well within the 11A Max

However if I want to have 6 panels in series with 2 parallel, I'm going to exceed the MAX input current by 6.54 Amps, so that is not going to work. 

Does this mean I should rather have each string of 6 panels in series connected to 1 input string each on the inverter?, i.e. string 1 to input 1 and string 2 to input 2?

Is there another way? I'm asking because I want to be able to have another string facing in another direction due to a nasty shadow on my roof and to maximise the amount of daytime sunlight, i.e. a "morning" string and a "afternoon" string (both having a midday catch)

image.thumb.png.d7c54f2fa006e66f199afdc2264d9aa6.png

Edited by Antony
Link to comment
Share on other sites

2 minutes ago, Jaco de Jongh said:

I guess the VOC of your panels is about 47.5 to 49 volts. So you will be able to connect 500 / 47.5 or 49 = 10 panels per string. 

Hi Jaco, the VOC is 46.7 if I'm reading this correctly and based even on that, it is still 10 panels per string, because of each MPPT voltage range?

image.png.08bba9b78031fe916c466bd564b4a252.png

Link to comment
Share on other sites

8 minutes ago, Antony said:

Hi Jaco, the VOC is 46.7 if I'm reading this correctly and based even on that, it is still 10 panels per string, because of each MPPT voltage range?

Sorry, Anthony, while you were typing I quickly tried to fix a mistake, thought I could snug it in before you read the response. I was wrong with the 10 per string. I only saw the 4.2kw max rating after made the post. Effectively you can use 6 panels in one string and 7 in the other and still be within all specs, but 6 and 6 is also fine to start with. 

6 x 46.7 = 280.2Volt (string one is okay)

7 x 46.7 = 326.9Volt (String two is okay)

13 x 320 4160 watts (within max array size)

 

Link to comment
Share on other sites

10 panels per string ain't bad, that would give me best possible performance with the each string facing 1 NE,  and the other NW.

OK, I just saw your update, it makes sense.

Edited by Antony
Link to comment
Share on other sites

VOC as this is the maximum voltage you could possibly have. Remember that this at STC (Standard Test Conditions) which is done at 25°C. As a panel cools so it becomes more efficient and the voltage will go up.  With 10 panels in series you will only be below  500Voc if your temperatures are above 4°C. At 4°C the Voc of each panel is 49.9V

Link to comment
Share on other sites

29 minutes ago, Chris Hobson said:

VOC as this is the maximum voltage you could possibly have. Remember that this at STC (Standard Test Conditions) which is done at 25°C. As a panel cools so it becomes more efficient and the voltage will go up.  With 10 panels in series you will only be below  500Voc if your temperatures are above 4°C. At 4°C the Voc of each panel is 49.9V

Then what amps should I look at.

My theory was Vmp x Imp to get Watts.

In this case 37.65 x 8.77 = 330.2 which is what the panel is rated at.

If I take Voc x Imp I get way more than the rating of the panel or is this not how I should look at it.

I was trying to compare different panels to get the best match and also to get as close as possible to the MAX input of the inverter

image.png.cd60dd603774c09c8cbbcca6bfb6e98d.png

Link to comment
Share on other sites

7 minutes ago, Antony said:

My theory was Vmp x Imp to get Watts.

Your theory is correct.

With Voc and Isc you not trying to confirm the productivity of the panel but checking on the maximum voltage and current  at your minimum environmental temperature (for me about minus 8) so that you do not exceed your solar charge controller's maximum voltage and current (i.e. make sure your string of panels is a good match to your SCC).

 

Link to comment
Share on other sites

On 2018/10/13 at 5:33 PM, Jaco de Jongh said:

Effectively you can use 6 panels in one string and 7 in the other and still be within all specs

Model    Solis-1P4.6K-4G
Energy source    PV
Input Side    
Max.DC Power(kw)    5.3
Max.DC input voltage(V)    600
Start-up voltage(V)    120
MPPT voltage range(V)    90-520
Max.input current(A)    11+11
MPPT number/Max input strings number    2/2


I was under the impression that it was 600v per mppt.

So ..
my 

current west facing
270 x 5 = 1350
37.9 x 5 = 189.5

I want for west facing
270 x 6 = 1620
37.9 x 6 = 227.4

Proposed for west facing

270 x 7 = 1890

37.9 x 7 = 265 .3

Current east facing
330 x 6 = 1980
45.6 x 6 = 273.6

I want for east facing 
330 x 7 = 2310
45.6 x 7 = 319.2

Proposed east facing
330 x 8 = 2640
45.6 x 8 = 364.8

Power is 1620 + 2310 = 3930

I get to voltage @ 319.2 + 227.4 = 546.6  (MPPT voltage range(V)    90-520) according to the spec sheet

which is below the 600 DC mark or is that voltage to close?

Or should I stick to six a side or 6/7 combo?

 

Link to comment
Share on other sites

26 minutes ago, flamegrilled said:

Max.DC input voltage(V)    600

To my knowledge that is 600Volt per MPPT. 

My take on this is, try to stay at a value above grid volts so that the conversion from DC to AC is more efficient. 

26 minutes ago, flamegrilled said:

Proposed for west facing

270 x 7 = 1890

37.9 x 7 = 265 .3

 

26 minutes ago, flamegrilled said:

Proposed east facing
330 x 8 = 2640
45.6 x 8 = 364.8

That sounds great. Remember you can go up to 5.3kw in total and your proposed total is only 4530 Watt, so if roof space allows and the need for more power arise, you can add another 2 panels to the west side to equals things out a bit as well as produce a bit more late afternoon. With 2 additional 270 watt panels on the west side you will have 2430 watts at 341 Volts.

Link to comment
Share on other sites

8 hours ago, Jaco de Jongh said:

My take on this is, try to stay at a value above grid volts so that the conversion from DC to AC is more efficient. 

Aaah theory time again! :-)

There are some grid tied inverters without a boost stage, so they need a really high input voltage. If you start with a high enough input voltage you don't need a boost stage to get the voltage high enough to feed it into the grid, and it does get a bit more efficient.

How high? Higher than the peak voltage of the AC side, which contrary to what you might think is not 230V, but over 325V plus some margin, so 350VDC is a good start. Because 230VAC is an RMS value, an average, it's 0.707 of the real peak.

My apologies if I just re-explained something my readers already knew :-)

Link to comment
Share on other sites

11 minutes ago, plonkster said:

so 350VDC is a good start.

 

8 hours ago, Jaco de Jongh said:

With 2 additional 270 watt panels on the west side you will have 2430 watts at 341 Volts.

 

9 hours ago, flamegrilled said:

Proposed east facing
330 x 8 = 2640
45.6 x 8 = 364.8

So in this configuration, you should be really close to Plonksters explanation. 

With my own system, under high load conditions I get 310-320V and with lower loads up to 365V. 

@plonkster, thanks for clarification, I was always aiming for minimum 300 volt under load. In the future I will rather add a panel or 2. 

 

Link to comment
Share on other sites

12 minutes ago, Jaco de Jongh said:

, thanks for clarification, I was always aiming for minimum 300 volt under load. In the future I will rather add a panel or 2. 

The less you have to boost, of course, the better. Just take a look at some "transformerless" (actually true in this case, not just marketing speak) models from SMA, look at their voltage specs, and that will give you an idea of where you need to be.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...