Best Inverter Option - 1 or 2?

[Nicko1611]

Hi

I am new to the forum and would really appreciate any advice or feedback from other members.

We have recently had a 3 kW pv system installed - 12 Sanyo 250HIT panels and an SB2500 inverter. The panels are arranged in 2 arrays of 6 panels located on  2 different roof sections. Both roof sections have the same pitch (approx 40 degrees) and face the same direction SSW.

So here's our problem. One of the arrays experiences shading at this time of year due to the low sun after midday (the other array has no shading) and as a result the output drops off alarmingly from approx. 1.3 kWh to 150 Wh in a matter of minutes on a cloudless day.

I was aware that shading can have a disproportionate effect on output but this drop in performance has made me question whether our system has been configured correctly. I should point out that when the sun is higher (between Apr and Sept) no shading on either sets of panels should occur.

Our installer has acknowledge that this drop in performance could be partially solved by configuring the system differently by using 2 inverters instead of one - so that the array that does not experience any shade is not adversely effected by the array in the shade.
To be fair to our Installer they have offered as a gesture of good will to retrofit the new inverters.

However, before we accept this offer we want to make sure we have the best configuration possible. Our installer will only use SMA inverters and I have also spoken to SMA and had a play with their Sunny design tool.

The options are:

2 x SB1200 inverters
2 x SB1700 inverters
SB4000TL inverter - using 2 parallel ports and Optitrac Global Peak (I've read the marketing material that this claims to solve shading problems)

I would appreciate your thoughts on these options or if there is anything else we should consider.

Many thanks

Nick


 

[clive_allen]

Hi,

Why not try the Optitrac Global Peak settings first and see what the results are ?

[JohnS]

Optitrac Global Peak only works on certain newer inverters.  As far as I know, not on the 2500.

[Nicko1611]

You are correct the 2500 does not have Optitrac Global Peak - much to my frustration

[BruceB]

I thought I replied to this an hour or two ago but cannot see it so must have pressed the wrong button.

The SB4000TL will work but is oversized.  If you want to stick with SMA then the answer is really a SB3000TL-21, which is a 3kW dual mppt inverter.  However I have not seen one yet in this country yet and although they are meant to be here now, I suspect everyone is worrying about other things.  The standard SB3000TL-20 available here only has a single mppt.

The ideal inverter for you really is the Power-One Aurora PVI-3.0-OUTD which is 3kW, has dual mppt, has global peak optitrac equivalent and is transformerless so very efficient.  It is also hundreds of pounds cheaper than a SB4000TL.  You should ask your installer to at least consider it.

Regards
Bruce

[Nicko1611]

Hi Bruce - thank you for this advice. When I spoke to SMA UK they also mentioned the SB3000TL-21 but said it wasn't planned until Q1 next year and they couldn't be sure of this time frame.

My installer tell me that they only source inverters through their wholesalers and only use SMA inverters but I'll ask about the Power-one Aurora Inverter.

You mentioned that the SB4000TL would work but is oversized - would you mind explaining to me in layman's terms what this would actually mean relative to my set up please.

[BruceB]

An oversized inverter is fractionally less efficient.  I have not plugged some numbers in, but in the past I have seen figures of the order of 50kWh per year difference, perhaps less, so not much in monetary terms (FIT income).

An oversized inverter is more expensive.

A counter-argument is that an oversized inverter will not be stressed, so may last longer.

Take your pick.

Regards
Bruce

[Nicko1611]

Bruce - your feedback has been extremely useful thank you.

I'm leaning towards pushing for the SB4000TL - hopefully the slight loss in efficiency will be compensated by the Optitrac Global Peak (if it works). The trick now will be sourcing one in the current environment 

Much appreciated.

Nick

[Hydroteam]

Hi Nick,

We have just had installed in the last 2 weeks 14 Sanyo HIT 250 panels, a 3.5KW system, with a SMA 4000TL inverter.

We had discussions with the installer and opted for splitting the panels into 2 arrays of 7 panels each, mainly because the 4000TL inverter could take two input strings from each of the panel arrays and also because inputting all panels as a single array could mean too much voltage for the inverter. We were originally going for Sanyo HIT 240 panels and I believe this would have given a voltage of 612Vs, too much for the 4000TL inverter.

I think we rejected the 3000 inverter as this didn't have the option to input 2 strings...

One array has some slight shading over 2 panels early in the morning, but with the winter sunshine, we haven't noticed any significant difference so far.

I haven't yet activated the Optitrak shading management software in the inverter as the default is for this not to be activated. This can be activated through SMA communication software downloaded free from their website.

Hope this helps somewhat...

Roger

[akgray]

We have a 3 kw system split over two roofs like you Nick,

We took the SMA 4000tl inverter and it is working well. The back roof starts to shade the other at about 2.30 at the moment and you can see a shoulder on the output.

I would definitely split the system into 2 strings.

[AlanIOW]

Although the 4000TL may not working at its most efficient with a 3kWp system, being Transformerless it may well still be more efficient than two smaller inverters with older transformer design.

[deeyup]

I just had a play with sunny design.
Using London as the city with 12 sanyo hit 250. 2 strings of 6 panels.

Annual yield with the SB 3000tl-21 is 2637 kWh
Annual yield using thw SB 4000tl-20 is 2627 kWh.

Only 10 kWh between them according to sunny design.

using 2x SB 1700 annual yield is 2536 kWh
using 2x SB 1200 annual yield is 2523 kWh

I'm no installer, I think they all may be too busy to mess around at this time, and have no idea how accurate these figures are.
No consideration is given to angle of panels or which way they are pointing. i can only think
the software works it out using the very best of the variables??

Looks to my like the TL inverters are way ahead.

[Laurence]

Hi, I have a SMA 4000TL.  I have two arrays pointing the same way, each of which gets some shade at different times in the winter, caused by the long low shadow of a distant MASSIVE pine tree. For most of the year, the sun flies clean over the top, so it's no big deal. The tree is where it is, and isn't going away any time soon. I've decided to stop worrying about it.

Optitrack is no magic bullet. It can help make a bad situation slightly less worse in some circumstances, but it may take power away from you, while it's trying to achieve it! (the algorithm has to give up momentariliy on the MPPT it is currently tracking and wander up and down the VI curve looking for a better one, probably before going back to where it was before). It is very hard in real 'field' conditions to compare results with Optitrack on or off, but based on my limiteted trials, i can detect no difference. I have switched it back off.

The thing about an inverter like the 4000TL is that it has two MPPTs, not just two input strings (most inverters have at least that, but these two strings are simply joined at the inverter, and go into the one MPPT circuit). With two MPPT trackers you will get the optimum out of each set of panels, without one bringing the other down.

Yes, shading is a killer, but is it only going to be an issue in the shorter "dog days" of winter - when there is really naff-all energy to be had, any way? If so, it will probably have less overall impact on your system that you think.

Lots of talk about around this forum about oversized inverters. Here is my two watts' worth. Inverters like the SMA4000TL are very efficient, even down to under 1KW. The spec sheet shows this AND i have done some measurements to confirm this. It's also a newer technology - I wouldn't be at all surprised if it can actually push out more power from a 2.5KW array on a shady day than you would get from a smaller, older technology inverter on the same array!  Yes, the bigger inverter will cost a little more, but yes, it will also be less stressed, so all things being equal MAY live longer.

If you are interested in monitoring your output, a single inverter is going to be less of a headache than two inverters and two monitoring systems, and a calculator! The SB4000TL makes it about as easy as it gets to harvest all of the data you really need (unless you are a COMPLETE data junkie!). Compare that with the cost of fitting TWO sets of comms products to two smaller inverts that don't already have Bluetooth built in.

You can tell by now that i am a bit of a fan of the 4000TL, but just now, they may be getting a bit scarce like rocking horse doo-doos, and there is more than one good reason for that!

[BruceB]

I just had a play with sunny design.
.................

No consideration is given to angle of panels or which way they are pointing. i can only think
the software works it out using the very best of the variables??

The latest version of sunny design DOES allow you to enter multiple strings of any inclination and orientation.  Do NOT be fooled into thinkiing the program updates automatically, the database might, but the program you need to download regularly from SMA if you want the latest.  At least that is what I have found.  I am running program V2.11.0.R.

[deeyup]

Great, on the latest version now and can see where to put in the extra data. Ta!

Nicko, did you decide which way to go yet? If you went for the Aurora pvi 3.0 did your installer find anywhere
who has stock?

Cheers.