Discuss East - West Split - How many invertors??? in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

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ian81

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Hi, my company have sent me to do an East West split with 18 Sharp 185w panels (9 on east and 9 on west) and one Sunnyboy 3800 invertor. Ive raised my concerns over having just one invertor and i feel that i need one for each side (without working out something like 2 x SB1700). Does anyone know if its advisable to have 2 invertors or even if it will work with one invertor???? im a bit confused any help would be great!!!!
 

Energetic

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Arms
One for each side or a multistring (2 MPP trackers) inverter would do it. My understanding is the same as yours, different orientations should be seperate...
 
SB3800 is a single MPP tracker so the system is poorly designed. Certainly a much better yield from two inverters.
 
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ian81

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  • #4
Cheers for youre advice im going to go back to the office in the morning and let them know 2 invertors would be best. Weve got PvSol but i think they need some training on it!!!!! i havent yet had a chance to go on it yet maybe this is my chance to have a play with it as ive heard its one of the best around!!!!
 
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claypole

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  • #5
And even without the E/W split Sunny Design shows it won't work - unless they're NT panels, the only Sharp 185's that will produce the correct voltage range for a 3800. I received several quotes for my install based on SB3800 or 3300 that simply wouldn't work and in every case the reply was "our suppliers said it would be ok" but now we've checked it you're right, it won't work!
 
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Ramjam

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  • #6
Why east west split? It's a good idea for solar thermal where you need it to work all day but with PV you'll get more by putting it all on the west side and it's easier of inverters. The afternoon sun is generally brighter than the morning sun so west works better than east (not according to SAP calcs but in reality it does!).

If you've got a small roof and that's why you've gone east/west then try an inverter like Steca 2010 with slave 2MPPs or I would go with two SB1700 then they can both talk to one Sunnybeam display.
 
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Noshocks

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  • #7
go with the SB4000TL dual MPPT, the best inverter Fronius NEVER made
 
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claypole

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  • #8
But would that be offset slightly by increased average ambient temperature in afternoons and therefore raised cell temperatures and reduced output? Anybody running equal split E/W with some comparison figures?
Or a SB4000TL with twin MPPT inputs, maybe cheaper than 2x1700 and still able to display seperate dc input from each string, plus bluetooth inc free, plus half the cost if you choose extended warranty route, plus arguably neater install. A little oversized but near identical predicted output as 2 x 1700 on E/W.
 
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Ramjam

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  • #9
I'm almost with you but I steer clear of the TL inverters on account of the earthing and DC RCD requirements. I still haven't heard anyone explain how to wire TL inverters according to the regs and practically, the DC RCDs are apparently as rare as rocking horse manure?
 
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claypole

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  • #10
See http://download.sma.de/smaprosa/dateien/7418/RCD-UEN103120.pdf
I understand the requirement for dc breaker on transformerless inverter but there is an exemption where the unit is proven to exclude dc currents from grid and SB4000TL complies with this. There's also an excellent chart somewhere on the sma downloads showing which panels require earthing with which inverters, and again the 4000TL is fine with most, one standout exception being the Sanyo hybrid modules. I must declare I have no electrical qualification so forgive if there other UK regs affecting this.
 
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ian81

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  • #11
theres not much room on the west side for more than 9 panels due to massive shading the customer wanted the east west split. im going to go into the office this afternoon to discuss the options with them but after everyones advice im even more inclined to refuse to install the sb3800 !!!
 

Worcester

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Mentor
Arms
I just ran it through PV*SOL 2 off (1 x East, 1 x West) 9 x 185W sharp panels assuming a 40 degree roof slope and the only SMA inverter it recommedned / would allow was the SB3000TL-20 althought it has only one MPP tracker it does allow 2 strings to be connected.

The two inverter option it offered was 2 x SMA SB1700 (and it was a very good match)

It will be cheaper to purchase the single SB3000TL-20, - however see all the comments on grounding TL inverters and RCD devices

Then, if you choose two inverters the purchase cost will be higher, and then they will each need their own MCB which could be up in the loft and the connected to a single MCB on the main cosnumer unit (so only 1 cable from loft)

Whataver - by my recommemdation the SB3800 should go back to the stores .....

Pays ya money takes ya choice..
2xInverters.jpg1xInverters.jpg
 
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edexlab

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Arms
I'm not saying this is wrong ,but as the 3000tl only has one mpp tracker then how can it be suitable for a E/W split?
if it was 2 strings same no modules same tilt/azimuth etc then I can see this being ok,
but I have to say I've not read anything about this inverter as its never been a match to any of the smaller jobs we've had
 

edexlab

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Arms
See http://download.sma.de/smaprosa/dateien/7418/RCD-UEN103120.pdf
I understand the requirement for dc breaker on transformerless inverter but there is an exemption where the unit is proven to exclude dc currents from grid and SB4000TL complies with this. There's also an excellent chart somewhere on the sma downloads showing which panels require earthing with which inverters, and again the 4000TL is fine with most, one standout exception being the Sanyo hybrid modules. I must declare I have no electrical qualification so forgive if there other UK regs affecting this.
After seeing your comments on the hybrid's I had a good look through the Sma site and could'nt find any mention of this chart
could you post where this table was please
I did find the table re grounding modules but this can't be what you've found as there is no mention of Hybrids
 
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claypole

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  • #15
Edexlab, thanks for this comment because I fear I may be at error. The table I had been looking at is here http://download.sma.de/smaprosa/dateien/7418/Duennschicht-UEN093821.pdf which I'm guessing is the same table you had found. It does not of course mention Sanyo Hybrid. At the time I was looking at it I was considering the hybrids but from their data sheet I understood them to have amorphous Si(superstrate design) which would make them unsuitable for the 4000TL. I should have re-checked the table before I posted because I realise I've written the comment incorrectly as if they are mentioned by name. If you also believe this is factually wrong and that they are in fact suitable please let me know and I'll edit the post.
Interesting material here too http://download.sma.de/smaprosa/dateien/7418/Ableitstrom-UEN092510.pdf
 

Worcester

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Mentor
Arms
Thought you'ld like thise:

The Front page of the PV*Sol reports:
1 x SB3000TL-20 Output to Grid = 2042.8 kWh/a
2 x SB1700 Output to Grid = 1987.0 kWh/a

It'll proabably be down to inverter efficiencies. In theory East/West, equal strings is no different from two strings same orientation, as a shadow passes over both strings, however with only one MPP tracker ... it's not what I expected!

1xInverters_output.jpg2xInverters_output.jpg
 

SolarCity

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Arms
Goes against what I've been told also. I have correspondence from SMA where they strongly suggest dual MPP tracker inverters even in cases of shading. With east-west arrays, I am very surprised that the result comes out better for the single tracker inverter over the two seperate inverters.

In fact, aside from the inherent better efficiency from TL inverters, I can't work out why the results come out like they do.
 
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claypole

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  • #18
Intertesting. Is this partly due to the global peak mppt used in the 3000TL? Made for shade. SMA Solar Technology AG
Is it also fair to say that the E/W split problem is overplayed? If the sun's arc is 180deg and each roof roof face is pitched at 40deg that still leaves 100deg (in the best part of the day) when the sun is directly accessing both faces. And even when it's not directly accessing would the lower cell temp on the shaded side make up at least some of the ground lost by lower insolation? I'm also surprised by the figures to the extent of questioning if they can be right but now I'm nt so sure.
 
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claypole

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  • #19
Gordon, can you maybe run a 4000TL through pvsol. I realise it will show oversized but I'd expect still to see a higher output with the advantages of twin mppt and the TL higher efficiency. The start voltage is the same as the 3000TL but the mppt range is actually slightly wider. I can't see why it wouldn't give the best output, balanced of course against the extra cost, but then once you've passed the payback period surely you want the highest possible output assuming you can fund the initial spend.
 

edexlab

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Arms
Edexlab, thanks for this comment because I fear I may be at error. The table I had been looking at is here http://download.sma.de/smaprosa/dateien/7418/Duennschicht-UEN093821.pdf which I'm guessing is the same table you had found. It does not of course mention Sanyo Hybrid. At the time I was looking at it I was considering the hybrids but from their data sheet I understood them to have amorphous Si(superstrate design) which would make them unsuitable for the 4000TL. I should have re-checked the table before I posted because I realise I've written the comment incorrectly as if they are mentioned by name. If you also believe this is factually wrong and that they are in fact suitable please let me know and I'll edit the post.
Interesting material here too http://download.sma.de/smaprosa/dateien/7418/Ableitstrom-UEN092510.pdf
HIT Hybrid cells are designed to" prevent the free charge carriers recombining on the back electrode ,
this is the main cause of capacitance discharge"
they are not the same as thin film but do use some of the same materials but have different characteristics

Also Sunny design highlights modules where a -/+ ground is required
 
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claypole

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  • #21
Thank you edexlab. I can't see how to edit post so will just advise here please ignore erroneous info on post 10 ref 4000TL / Sanyo Hybrid compatibility.
 

Worcester

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Mentor
Arms
Gordon, can you maybe run a 4000TL through pvsol. I realise it will show oversized but I'd expect still to see a higher output with the advantages of twin mppt and the TL higher efficiency.
PV*SOL throughs a wobbler as it oustside the permissible sizing range - see attached (click on it to enlarge), so it won't run the economic simulations!
4000TLnverters.jpg
 

SolarCity

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Arms
Gordon, did you adjust the sizing parameters on your version of PV Sol? My version only likes 90% - 120% before it starts to panic.
 

edexlab

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Arms
Thank you edexlab. I can't see how to edit post so will just advise here please ignore erroneous info on post 10 ref 4000TL / Sanyo Hybrid compatibility.
No problem we're all here to learn I can't tell you how much this forum has helped or even just caused a bit of doubt which is no bad thing as most people will then go and check for themselves and the correct info is brought to light
I have been on other forums and there is always someone on there spouting rubbish and no one questions it .
but this is the best one I think with some really good participants
 

Worcester

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Mentor
Arms
@BiggSolar,

I always let my system choose by spec and location, here it is tweaked to allow 80% sizing, output is very similar to the SB3000TL-20, even with the twin MPP.

4000TLnverters_2.jpg4000TLnverters_2_output.jpg


My guess is that with two equally sized strings, where the primary generator is being slowly switched through the day from east to west with a balance at or around miday when both will be getting similar irradiance, is that the system is just coping.

We need someone to set this up with all three invert configurations and then measure the voltages across the strings and the current through them over a 12 hour cycle and then plot it out along with the actual Wh (not kWh) generated by the inverter at the same time..... (of course in the single tracker set up, I would expect both string voltages to be the same, though with different current flows)
 
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claypole

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  • #26
Fascinating and I fear I've made a schoolboy error in assuming that an E/W must benefit from 2 inverters or at least 2 MPPT's. If you look at a typical panel power/voltage curve the peak power voltage point is very similar across the full range of irradiation. If you then also consider that the diffrence in irradiation between E and W at any given time will never be huge (because line of sight sun is only 1 part of the overall irradiation) their max volt points will be even closer. And provided we have 2 strings in parallel the different currents will be aggregated. I think the only problem would be with 1 long series string where the sunny side roof output would be pulled down to the same level as the shady side - or am I making another schoolboy error.
I would suggest the 3000TL outperforms 2x1700 perhaps because the start voltage is slightly lower and mainly because of overall efficiency difference, (Max 97.0 v 93.5, and Euro 96.3 v 91.8), bearing in mind that from Gordon's pvsol calcs I think there is less than 3% difference.
 

SolarCity

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Arms
I've just been designing a system with an East/West split and thought I'd let you know my results so far.

Using 16no. 250w Sanyo panels, all on the east side of the roof, using an SB3800 inverter and using the climate data from Plymouth, a yield of 3,258.1 kWh is predicted.

Using 16no. 250w Sanyo panels, 8 on the east side and 8 on the west side, using two SB2000HF inverters and using the climate data from Plymouth, a yield of 3,123.6 kWh is predicted.

I've tried a few different inverer combinations but still get similar results. PVSol Expert consistently returns a better yield on an East or West facing roof rather than using a West/East split.

For comparison, if the same roof was adjusted to face due south, the same array would return 4,042.7 kWh. This means that the east facing array works at around 80% of the efficiency of the south facing array (consistent with SAP figures) and the West/East split configuration performs at around 77% of the optimum. Roof angle with all calculations was 37 degrees.

My conclusion so far is that an East/West split is useful when space is an issue, but not a good option if the goal is purely to maximise yield - not least because an East/West option is more expensive (dual MPP trackers/two inverters, extra scaffold).
 

Worcester

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Mentor
Arms
@BiggsSolar, Ireckon you're right, in a simple installation, one big East facing array would be best, if not then spilt with either dual MPP's or two inverters.

So here's the big one,

And it goes back to @Claypole's initial discussion of overpowing inverters.

How can I maximise the power I generate from my roof (for the sake of discussion assume cost irrelevant) when it faces East / West and staying within the G83 16A limit for as long as possible during the day?

The two arrays/strings have mirror image power generation profiles (morning / night), with peaks probably being very close to each other around late morning and early afternoon.

So what would be the optimum/maximimum size I should put on each side?
And which inverter(s) perform best when overpowered to clip at the combined output of 16A. I would suggest it would be a single inverter (that way 16A can't be exceeded) with two MPP's, however wether it clips or 'cuts out' is probably the most important issue, and just how big can those arrays be?
 

SolarCity

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Arms
I'd imagine that the big problem with these kind of set ups is the midday period, where both arrays would be getting lots of sunlight. I can't run this through PV Sol but I'd imagine that using a 16a limited inverter with a combined east and west array of much more than 4kWp would experience losses during this peak period as the inverter 'clips'.

In reality, this isn't really an issue because the 4kWp threshold on the FITs prevents us from installing in this way anyway.
 

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