SB3600TL readings sound right?

[provr6]

System:

1 roof SE 8 x 195 panels (1.56kw)
1 roof SW 6 x195 panels (1.17)kw

tot sys 2.73 kw

Here are my inverter readings at 1pm today full sun on all panels no shading

Input A
1478 Watts being produced
276 V
4.7 A

Input B

1478 Watts being produced
229 V
1.0 A

the grid on both inputs reads 6.0A

Am I right in saying that the watts being produced is the total wattage of inputs A & B at all times? I was expecting the inverter to show the watts seperately as it flicked between the two inputs and for one roof to be less because of less panels.

Does the watts amount seem right given the size of the system?

Is the low reading of 1.0A on input B anything to worry about and why is so much different to the other input?

I estimate at the end of the day to have generated about 8kwh, which seems ok?, Yes/No?

 

[Somecamel]

Why did they use a SMA 3600 when you only have a 2.73kW System? Inverter is Oversized for your array or am I reading this wrong

 

[provr6]

You have read it correctly and I don't know why. I assumed it was the smallest dual inverter you could get (think the installer said something along those lines).


What sort of watts should I expect to see on the inverter at full sun on all panels?


I'm also wondering if the current reading of 1.0A is bringing the total watts down. Should it be similar to the Input A which is 4.7A ? Could this be related to an oversized inverter?

 

[yorkshiremike]

The power (upper right on display) is always total power out to the grid.
It's the sum of the DC power on each input times by the inverter efficiency (say about 97%).

So on your system, you have:

DC Power:

Input A = VxI = 1297W, Input B = VI = 229W. Sum (total) = 1526W

AC Output Power:

1526x0.97 = 1480W (should also get this if multiply the grid/AC voltage and current shown on the display)

So, input B very much less than input A (eg 6 panels but different orientation?). Also as said earlier, below 'ideal' minimum installed kWp range for the inverter (copes with 3kW - 4.2kW)

 

[provr6]

The power (upper right on display) is always total power out to the grid.
It's the sum of the DC power on each input times by the inverter efficiency (say about 97%).

So on your system, you have:

DC Power:

Input A = VxI = 1297W, Input B = VI = 229W. Sum (total) = 1526W

AC Output Power:

1526x0.97 = 1480W (should also get this if multiply the grid/AC voltage and current shown on the display)

So, input B very much less than input A (eg 6 panels but different orientation?). Also as said earlier, below 'ideal' minimum installed kWp range for the inverter (copes with 3kW - 4.2kW)

Thanks Yorkshiremike and I think I understand your calculations.

It seems to me the low current on input B is pulling it down. Should i expect 4.7A (as on input A) x 229v = 1076W. Would the different orientation effect the current that much? (its still SW)

 

[yorkshiremike]

If (big if) the illumination of the 2 arrays is similar (same relative angle to the Sun), and with each of the two arrays a single string (series connected panels), you'd expect roughly the same current in each string and the voltages in the ratio of the number of panels in each string. So that would be about 4.7A in each and if string A is 276V, then this is 276/8 V per panel (=34.5V), so you'd expect the string with 6 panels to be about the same per panel voltage (ie 207V for the string), but instead it's 229V giving a per panel voltage of about 38V.
The output of array A (about 1.3kW) is what you'd expect with full sun, whereas the output of array B 0.229kW is more what you might expect from panels in diffuse (not direct sun light). If the SW array really is in direct sunlight at 1pm, then I'd be looking for a hard shadow onto 1 or more of the panels. Without the Global Peak Optitrac switched on, you can get this effect where the MPPT trys to maintain a (too high) voltage (preventing the affected panel from bypassing) and draws too little current and power from the string.
Otherwise, if the two arrays really are orientated at 90 degrees to each other - SE and SW (and at the same pitch), then with clear skys you'd expect to get the peak from the larger 8 panel array sometime in the morning and about 3 hours later in the afternoon you should see the peak in the second array and the peak in the smaller array should be something like 6/8 (six eighths) of the larger.

 

[yellowvanman]

What panels have you got?

 

[provr6]

What panels have you got?

ET Solar M572, 195 W panels

 

[provr6]

Is there a way of checking the peak power genereated at some point in the day?

 

[yorkshiremike]

The inverter saves a lot of data, but unfortunately, it doesn't save the separate DC values, so after the event you can't recall the individual A and B values (unless you spend more money on a SMA web box). What you can recall is the AC power output produced at every 5 second interval. On the inverter display, the bar graph shows the hour by hour values, but with a PC + bluetooth and 'sunny explorer' you can view the daily graphs in more detail or even export the data to the PC to view/analyse in excel.

 

[Gavin A]

I'd hazard a guess that either your system is more like SSE & WWS or your SW facing system is suffering from some shading at that time from something like a TV aerial, soil vent pipe, chimney etc.

 

[sundown]

in the same situation as op.ie sb 3600tl 10 panels south west, 5 panels south east with chimney panels suntolight [ german] 2.5 watt.
we could check together . i live 30 miles north of london

 

[provr6]

I've had some good sun this morning and checked the outputs. The smaller array gets the sun first (this is the one with the low current reading) and the current at times matched the 4.3A reading which is good and leads me to believe it is working correctly.
Conversley, the larger array current drops earlier in the morning. This must be because the sun is not full on the panels but glances across them. This I also believe is why the current was low (1.0A) when I looked at the smaller array at 1pm in the Original post.

Hopefully in the summer both sets of panels will output full power at the same time around noon.

I haven't turned on Optitrac yet as my Bluetooth USB has not arrived. I will update when its on and report any improvements.

 

[provr6]

in the same situation as op.ie sb 3600tl 10 panels south west, 5 panels south east with chimney panels suntolight [ german] 2.5 watt.
we could check together . i live 30 miles north of london

How many Kwh are you getting on a Sunny day in March Sundown? My best is 10Kwh.

 

[sundown]

my best ever is ten kwh roof is 31 degree slope. i'd need to get in the loft to make check of the voltage ect.
i also thought the "global peak optitrac" would have been standard , sure the fitters didnt have a lap top with them. can you let me know if you have any luck with that.

 

[Glen Powell]

IMO ET Solar are one of the lowest performing panels, I may be wrong as I have not had them on my shelves, however PVsol does not give good results.

Maybe worth while looking at this to give you the answer you need without speculation from us lot on here. SUNNY DESIGN. SMA America, LLC

it is the design tool which I am assuming you will find a better inverter config regardless of panels, the inverter is as important if not more important than the panels themselves. I have to admit I have never used it so can't help in that manor.

 

[SolarCity]

I tend to agree with Glen Powell; inverter choice is possibly more important than panel selection.

Put a good panel on a bad inverter choice then you're wasting your time.

This one of the reasons why I'm not keen on kits. The characteristics of each installation are different and they all affect inverter choice.

I often wonder how many kits have been sold and installed with single MPP tracker inverters for systems with two different orientations.

 

[provr6]

I tend to agree with Glen Powell; inverter choice is possibly more important than panel selection.

Put a good panel on a bad inverter choice then you're wasting your time.

This one of the reasons why I'm not keen on kits. The characteristics of each installation are different and they all affect inverter choice.

I often wonder how many kits have been sold and installed with single MPP tracker inverters for systems with two different orientations.

When you say wasting your time, are you saying that I have completely wasted my money?

My understanding is the SMA3600 is a good inverter. From what I have researched, I can see that it is oversized. I've also read opinions that oversizing is not necessarily a bad thing but to what extent I don't know. I understand oversized inverters should run cooler, avoid nuisance tripping but not perform at their optimum efficiency (by how much? 1,2,3 kwh per day?) and cost more than you need to spend.

In reality how much is my inverter oversizing comprimising my system?

 

[Glen Powell]

I would say by Quite a bit, however, you could get it from the horses mouth, did you run the software ?? or would it be better you speak directly to SMA about it, they will be able to tell you exactly how efficiently it will or will not work. I know what they are going to say.

Oversized is OK with 10% - 15% in some climates however we are in the UK so we need to think the other way, you could put a 2kw inverter on a 2.2kw array providing all other factors are in place i.e voltage range (taking into account temperature coefficiency), amps, wattage (other 2 should take care of that).

SMA Telephone number is 01908 304850 , they may be a bit busy this week though...

 

[sundown]

got 12kwh today 19 03 12 best yet. orignal inverter was sb 300tl which has just 1 mppt. so installer changed for sb3600. with dual tracker.
my ten panels are SE. 3 months from 6th dec produced 230 kw with sb 3000