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

 

[Glen Powell]

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

Sorry unless you replied earlier that means nothing, 10 panels with sunny boy 3600, some ten panels systems have generated 16-20 kwh today as peak performances are now raising their heads again.

The inverters are called 3600, 3.6, 4400, 3000, 3.0 for a reason. this is when they work at its optimum you will see efficiency % drops as the input voltage and current are lower than the optimum.

I have been a member on this forum for a very, very short time and already I see people quizzing the people within the field and trying to big up a high efficient inverter on an overall low efficiency system.

Why did you need 2 MPPT if all on the same roof, shading? two different roof areas? or something totally different.

I am not having a go at you please understand, through this thread people have given good solid advice and I understand that people want to justify their purchase as a good one, but listen to the guys who do this for a living, there is a chance you will get you more return on your investment.

 

[provr6]

I've just used sunny designer.

Its come up with the following which I don 't fully understand.

1.The AC power of the planned single phase plant exceeds the specified unblanced load limits (3.69Kva). What does this mean? and what are the implications?
2. Inverter efficiency 92.3%. Is this good or bad?
3.Performance ratio 80.6%. Is this good or bad?

 

[Glen Powell]

I've just used sunny designer.

Its come up with the following which I don 't fully understand.

1.The AC power of the planned single phase plant exceeds the specified unblanced load limits (3.69Kva). What does this mean? and what are the implications?
2. Inverter efficiency 92.3%. Is this good or bad?
3.Performance ratio 80.6%. Is this good or bad?

I will have to do the SMA design myself to understand their software, I do not use SMA, but from what you say it is not good.

 

[Gavin A]

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...

I really don't understand what you're on about.

SMA don't make any dual MPPT inverters with a lower rating than the 3600TL, and the main other dual MPPT inverter around is the aurora 3.6 out-d / 3600.

The alternative would be 2 separate small inverters, which I've just run through sunny design, and the best I can come up with from SMA is an SB1200 and 2000HF (8 panels being too high voltage for the 1200 or 1700), and the output for the 3600TL is 2160kWh vs 2118kWh for the 2 inverter option.

so yes the 3600TL is underpowered and nowhere near as efficient as it could be with a more optimally matched system, but it's still arguably the best option SMA make for this situation.

Now, maybe micro inverters or solar edge would have been an option, but I doubt the SMA helpline is going to be recommending them.

 

[Glen Powell]

Solar edge is not a good alternative at all, if SMA cannot produce a product that is suitably matched then another product should be sourced, power one, steca, and others can cope with these ranges.

 

[Gavin A]

Why did you need 2 MPPT if all on the same roof, shading? two different roof areas? or something totally different.

from his first post on the thread he's got SW / SE arrays.

so it's not surprising that his system's not generating as much as a perfect south facing system at this time of year. Must admit though that 5 panels sounds low for the minimum voltage range of the inverter, unless they're Sanyo N series or something.

 

[provr6]

I think there is also an Aurora Power one 3.0 which was what I was originally quoted on. I assume I was given the 3600TL because of the unavailability of the former.

In hindsight this may have been a better option, albeit still oversized but not as much.

 

[Glen Powell]

Sundown didnt post the first post ?? and he quite clearly said he has 10 panels facing SE in his last one I replied to.

 

[Glen Powell]

I think there is also an Aurora Power one 3.0 which was what I was originally quoted on. I assume I was given the 3600TL because of the unavailability of the former.

In hindsight this may have been a better option, albeit still oversized but not as much.

In my opinion this would be the most suited to your needs for a single string inverter with multiple mppt.

 

[Gavin A]

Solar edge is not a good alternative at all, if SMA cannot produce a product that is suitably matched then another product should be sourced, power one, steca, and others can cope with these ranges.

tbf, the power-one 3.0 Out-d would probably have been a marginally better choice, as on checking, it does have dual MPPT, but it's probably very marginal as it has 3.3kW max AC output vs 3.68kW for the 3600TL.

I still doubt the SMA helpline would have recommended the power-one inverter though.

 

[Gavin A]

Sundown didnt post the first post ?? and he quite clearly said he has 10 panels facing SE in his last one I replied to.

yes, but he did post HIS first post on the thread.

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

 

[Glen Powell]

SMA minimum startup voltage 150v
Power one minimum start UP voltage 100v

The fact that the AC side is higher would make it more efficient

 

[Glen Powell]

And my post saying "sorry unless you replied earlier" meaning I did not go through all the posts again

 

[Glen Powell]

Before you say

voltage/temperature

yes I know voltage is not as important as current but with a small amount of panels it makes a massive difference

 

[Gavin A]

And my post saying "sorry unless you replied earlier" meaning I did not go through all the posts again

so you thought you'd just jump straight in and tell the guy his system was wrong. Interesting approach.

 

[provr6]

SMA minimum startup voltage 150v
Power one minimum start UP voltage 100v

The fact that the AC side is higher would make it more efficient

Do those min'm start up voltages matter, as surely both me and sundown easily exceed those?

 

[Glen Powell]

well if he has 5 panels SE facing then yes I would still jump in and say it is not really as good as it should be max ppt voltage on sanyo hit250 = about 175v (maximum)

 

[provr6]

well if he has 5 panels SE facing then yes I would still jump in and say it is not really as good as it should be max ppt voltage on sanyo hit250 = about 175v (maximum)

I see, but am I right in saying that the 10 panels on sundown's other roof would help meet the start up voltage? My installer said the start up voltage is based on the combined 2 roofs?

 

[Glen Powell]

I am sorry for being too eager to try and help were help is not really neaded, I dont really like SMA and was trying to get you all to change inverters for one I was trying to sell you or give others the opportunity to sell you.

Minimum voltage has no bearing on this matter
Miniimum ampage or maximum ampage are useless
Conversion factors have no relevence at all
Coil sizes and losses are just buzzwords
Transistors have no place in an inverter

I am sure the installer installed exactly what was needed for you and those bringing my posts into question

 

[Glen Powell]

I see, but am I right in saying that the 10 panels on sundown's other roof would help meet the start up voltage? My installer said the start up voltage is based on the combined 2 roofs?

2 mppt = 10 on one and 5 on the other

 

[Glen Powell]

.hmmm really

 

[provr6]

You are obviously more knowledgeable than me and I wasn't criticising your advice. I was just stating advice received from my installer and putting it out there for those in the know to verify or rebuke.

On the contrary, I am grateful for your comments and all considered comments are welcome, even if it's not good news.

 

[Gavin A]

I see, but am I right in saying that the 10 panels on sundown's other roof would help meet the start up voltage? My installer said the start up voltage is based on the combined 2 roofs?

tbf to your installer, they were right about this when they'd first installed your system as they'd wired both arrays in series to the one MPPT input.

Now it's wired to the 2 separate MPPT inputs that's not the case, the voltage on each array is independent of the other.

 

[Glen Powell]

The basics of it is this

I am the technical director of 2 companies of which 1 deployed 500 installs in February, the inverter choice for your install would not have entered my design teams heads, if the designer of your system used any design software it would have probably spat it out and said no way or it would base it on the strong MPPT and give you a very poor efficiency rating.

In one of the sticky topics I have put a spread sheet up to help measure efficiency but you do need an irradiance meter (original thread goodwilld) on page 69 of the thread.

Be fully aware this is not my investment, this is really not my concern, but if your quarterly return is less than others you will not be happy. this is why I have given links to SMA software and their phone number. you can say you are going to install a system in this way and is it acceptable, take notes, get names, etc.

I will not loose 1 snippet of sleep tonight over this, if i am right or wrong is irrelevent which is why I say speak to the manufacturers.

 

[Glen Powell]

tbf to your installer, they were right about this when they'd first installed your system as they'd wired both arrays in series to the one MPPT input.

Now it's wired to the 2 separate MPPT inputs that's not the case, the voltage on each array is independent of the other.

Doesn't matter the underperformance of one will pull the other down, 101 solar design, the weak array will create resistance for the strong array if in series, if in parallel maybe a chance but not much as there is still an adverse effect.

 

[provr6]

tbf to your installer, they were right about this when they'd first installed your system as they'd wired both arrays in series to the one MPPT input.

Now it's wired to the 2 separate MPPT inputs that's not the case, the voltage on each array is independent of the other.

Thanks for that, I didn't realise that. It does make sense now as each MPPT is like a seperate inverter.

 

[Gavin A]

Doesn't matter the underperformance of one will pull the other down, 101 solar design, the weak array will create resistance for the strong array if in series, if in parallel maybe a chance but not much as there is still an adverse effect.

you appear to think I'm defending that method of installing, I'm obviously not.

I had previously read the posters previous thread where he was asking for help because their installer had originally done this, and was merely pointing out that on the original installation as it had all been run in one string, the installer wasn't lying when he told him (presumably at that point) that both arrays combined to produce the string voltage going into the inverter.

 

[Glen Powell]

Can we please put this to bed and put a poll on it would you or any other installer put either of the inverter mentioned on this guys array based on evidence given.

We are not here to rip each other just give honest opinions, simple yes or no answers would suffice.

NO

 

[Gavin A]

Personally in this situation I'd expect I'd have strongly recommended using the Sanyo N series 240Wp panels which would have given a system that was a much better match for the 3600TL (or aurora) due both to the increased array ratings, and the string voltage being closer to optimum.

but that wasn't the point I responded to. I specifically responded to this point

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.

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

Now I have run this though the SMA software, and the 3600TL is the most efficient option available from the SMA range for this panel set up as I pointed out clearly in my first reply to you 2 hours ago.

Not that I actually needed to run it as I work with SMA kit most of the time so know what the options are pretty well, which is why I took issue with your post.

 

[yorkshiremike]

I tried to post this yesterday, but it didn't work, presumably as it had an embedded results table from PVSOL:-

"Interesting enough, if you compare simulations in PVSOl for a SE (6 ET Solar panels), SW (8 panels) into a 3600TL (based on 4000TL as PVSOl doesn't have the 3600), a 3000TL-21 (new 2 tracker version of the 3000TL) and say a Power-One 3.0 (2 tracker) then the Power-one comes out about 2.5% ahead, but the 3600TL is the same as the 3000TL-20."

The feed-in figures from PVSOL (assuming London SE/SW at 31 degress incline) are respectively (3600, 3000TL-21 and Power-One): 2305, 2304, 2369kWh

As Gavin has previously stated, SMA design 'green ticks' the 3600TL on everything (startup voltage, mppt range etc), the only thing it questions is the oversize of the inverter. And the 3000TL-21 (twin MPPT which wasn't previously available) although it is within SMAs normal +/- 20% capacity range doesn't have any greater efficiency/yield.