East - West Split - How many invertors???

[claypole]

http://download.sma.de/smaprosa/dateien/7418/TempDerating-UEN103910.pdf
The above download finally crystalised this for me, with some excellent charting to demonstrate the logic. Until reading this I was very firmly decided that there was no good reason to size the inverter smaller than array except initial cost. I'm now wholly committed to the opposite view. For my system using SB4000TL and 245 Sharps the sweet spot, in terms of kwh/kwp was something like 4.9kwp, bearing in mind the inverter max dc is 4.2 kw. I found this almost impossible to believe until I read the above download and understood the logic.
The 4kw FIt band doesn't prevent you exceeding 4kwp. It may well be that doing the sums shows that the larger array on a lower FIT rate band will still have the best rate of return, although in practice this is perhaps then governed by the DNO connection. However, from Ted's excellent DNO/G83 thread it seems most of the DNO's are swinging round to using inverter output figures, so provided they'll accept 4kw and G83 at the particular installation site that problem is removed. I also live in hope that Ofgem may at some point issue guidance that TIC may be based on inverter max dc input (albeit that's 4.2kw on the 4000TL). Personally, I've gone down the route of 3.92 array now, to extend to 4.9 after 12 months, all through 4000TL. Based purely on the maths for max rate of return.

 

[edexlab]

I have to say that although pvsol is a useful bit of software I don't really trust it as we've put designs through it and then checked them against manufacturers programs and vice,versa and found that pv sol sometimes reccommends a match which the manufacturer would say was not a good design or the opposite actually rejected a good match, a classic example of this is choosing a 3000tl one mpp tracker for a e/w split the whole concept of a multiple Mpp inverter was to overcome the necessity of having to use two inverters which is usually a more expensive option

 

[claypole]

I still wonder if E/W problem is overplayed. I WAS firm believer in 2 inverters or at least twin trackers but I'm now not certain. As stated earlier, the sun is still directly accessing both sides. Take a roof pitch of 35deg. Sun's arc is 180deg. That leaves 110 deg of the best generating part of the day when the sun is directly hitting both arrays. Given that at the lower part of those arcs will not be generating much due to adjacent buildings/terrain/diffuse light on horizon, you could be talking about 70% of the best generating time of the day when both arrays are in sun. Looking at a typical bell shaped daily production curve that's a significant amount of kwh, maybe 80/90%? And when the sun is "behind the ridge" how much difference is there in the insolation on each side? Anybody got actual figures on this from a meter? Non sun side insolation v sun side insolation at the same time. The global peak single tracker on the 3000TL will no doubt set the voltage to match peak power on the sunny side. But looking at the power/voltage curves on the panel spec sheets, this will probably only drop the power slightly below peak on the shady side, unless there is a massive insolation difference. Plus the shady cells will now also be running cooler. Given that the shady side even on 2 inverters would now be producing the least power anyway, the % drop would be an even smaller % drop measured against the total output from both arrays. If the inverter itself is more efficient than the alternative 2 inverters, then I think it's entirely feasible that the 2 factors could equal themselves out, or even that the single inverter(1 tracker) could win out. Would love to see real world figures on this. Anyone got the time and the money for a control test bed? Failing which some insolation figures would be good.

 

[claypole]

I should add that my next thought was well what's the point of a twin tracker? Well it would still overcome problems with physically different strings, eg number of panels or even different panels. Also I guess adds more versatility in design with regard to suitable string current and voltage matching. And then still offers you the benefit of cheaper and neater install over 2 inverters.

 

[claypole]

And just looking out the window now, for all the "grey" hours here in uk E/W faces will be identical to S face anyway, so again a significant portion of time where there is no difference, although to be fair these will not be high generation times.

 

[edexlab]

I've been talking today to a potential customer who's brother has an e/w split this was installed May last year in Chester, this blokes neighbour also has a system, same installer except for the inverter , on same e/w orientation
one has a 4000 tl and the other has a different make which he was'nt sure of the name but it apparently has one Mpp tracker the customer with the TL is an electrical engineer and researched Pv and told installer that was what he wanted, both have same type/ number of yingli modules
(I've asked him to get all the specifics )
He says there's no shading so it sounds like a good comparison
customer with the TL has out performed the other system by around 260 kwh to date and they were installed one after the other so there is a small difference in total run time
this has upset his neighbour and he has asked the installer to change the inverter, to the same as his mates, to which the installer has said he will do
and he also is after compensation for poor design induced losses
now without knowing which inverter he's got its not conclusive so i'll post when i know

 

[Worcester]

It'll be really good to get those answers.

He'll have great difficulty getting the compensation loss unless he can prove negligence. To do that he'll also need to get the supplier to produce the original calcs (which as he's MCS registered, will of course be on the customers file )
Also - did they pay the same price?
What was quoted according to SAP? How has it performed compared to that?

 

[claypole]

That's great, love to see those figures. I guess we could be looking at something like 5-10% depending on install dates. Even looking at it from a consumer angle I think a claim for comp is a bit harsh, hardly negligent given the early stage of the industry, and if the installer is switching inverter without cost I think that's more than fair. Unless of course there are other elements to this. Meanwhile, in selfish mode, delighted to be firing up for the first time my chosen 4000TL this am!

 

[ian81]

sorry for the delayed reply, thanks for everyones advice and help, i finally managed to convince them to get me the SB4000TL dual MPPT and everything is working fine!!!!

 

[claypole]

Bumped as this might be of interest to Stubo and also to ask if edexlab has any further info on the Chester neighbouring installs (one with twin tracker and one with single).

 

[edexlab]

Bumped as this might be of interest to Stubo and also to ask if edexlab has any further info on the Chester neighbouring installs (one with twin tracker and one with single).

one is a 4000Tl other a SB3800 same total kw, different modules, Sharp on tl
Tl was installed one week after 3800 approx 6 weeks agobut the TL over took it quite quickly and with this weather we are having is racing ahead
TL install = 407 kwh
3800 install = 366 kwh
unfortunately this is the end of the lin as the installer is changing inverter this week ,it would be interesting to see a full year however if i can get an update we'll see how the different modules fare against each other on the TL'S

 

[claypole]

Interesting.. so allowing for the extra week could be looking at something like 30% extra on the TL. No wonder his neighbour wasn't happy!
I can see one potential problem - the SB3800 start voltage is at 250v (against 150v on the TL), so if set as 2 strings might be marginal? If 1 string shouldn't be a problem although might then probably be exceeding the mpp range by some margin. Be good to know the panels involved to analyse this further otherwise I think it would be very premature to conclude this is a single v twin tracker issue. Either way seems clear design was poor (unless there is a huge variation in panel performance) but great to see the installer taking owership of the problem and attempting to resolve.

 

[edexlab]

Interesting.. so allowing for the extra week could be looking at something like 30% extra on the TL. No wonder his neighbour wasn't happy!
I can see one potential problem - the SB3800 start voltage is at 250v (against 150v on the TL), so if set as 2 strings might be marginal? If 1 string shouldn't be a problem although might then probably be exceeding the mpp range by some margin. Be good to know the panels involved to analyse this further otherwise I think it would be very premature to conclude this is a single v twin tracker issue. Either way seems clear design was poor (unless there is a huge variation in panel performance) but great to see the installer taking owership of the problem and attempting to resolve.

Agreed the TL has certain advantages but the main point is single Mpp trackers are not designed for different orientations ,this is one of the main reasons they started production of twin Mpp inverters I have this direct from SMA which we visited for their seminars for a week in Kassel ,Germany
and to be honest after going there I think they know this subject very well, as for the pvsol software it sometimes allows/and rejects configurations
which when done on manufacturers programs are the reverse , and of couse you can't argue with the manufacturer who has spent millions on research over 30 years , adding to this I've read some very good pv books and a single Mpp on dual orientations is definately not advised.

 

[claypole]

My gut is screaming that it has to be twin tracker (or 2 inverters) and I still believe that, I'm just not convinced that the differential for this reason alone is as huge as we might think. See my reply no. 33 (apologies if it's none too clear to follow). When I follow the logic and work the maths I'm left with quite a small % differential over the total generation figure. Still a difference of course, and I'd still go twin tracker as best option. But if you bring other factors into play, and particularly all the parameters of the inverters and panels in play I do still wonder if in some circs the optimal decision might be even more marginal. Have to agree fully on SMA comments, I've found their customer service to be terrific and a great range of inverters to cover all bases. Hell they're even almost attractive, or as attractive as an inverter could be.

 

[Energetic]

We are also seeing much better performance from the new HF's and TL's over the older clunkier models...