dual aspect split array with sunny boy 3800v? located in the attic????

[carolinebrett]

We are having to rush a decision on which of two quotes to give the go ahead to - both who can fit us in for install by end of november. Unfortunately our preferred installer (most reputable) couldn't fit us in.

The chap we've so far given our deposit to (with a 14 day cool -off available) has just told me that he would propose a Sunny Boy 3800v inverter for our proposed 3.44 kw system (16 x Sanyo HIT 215s). My impression from trawling the net for the last couple of days is that only the sunny boy 4000TL can handle 2 x mppts for a dual aspect system, but this chap said that wasn't true. Can anyone help me out with this? Our other possible installer was suggesting an Aurora PowerOne 3.6 which I know is supposed to be good in this sort of scenario. The first guy (the one we are currently booked to do the job with) said, 'we can go with the aurora if you want'. He seemed to be giving the impression that the Sunny boy is the 'market leader' and therefore preferable??

Our original plan was to go with a 16 x Sanyo HIT 250 system (i.e. 4 kw) but apparently it's hard to get hold of the panels now with the rush on, so unless he can get them after all we're having to compromise with the less efficient (and only slightly cheaper) system.

The other thing he suggested is to put the inverter in the attic/loft. He said that it would tolerate the max heat in there, reading the spec to me from the Sunnyboy as operating from -25 to 60 degrees. My impression is that most installers shy away from attic installations these days. He said that he could put it in the electrical cupboard 'if I wanted' but that it would be less efficient due to the long DC run (it's a 3 storey house so long drop from roof to ground floor where the consumer unit is). He also said it would be more expensive in terms of cabling etc. I seem to have gleaned the impression that long DC runs are fine so long as you overspec the cabling. Is this true? is it really that much more expensive? And should this installer/salesman have more of an idea about it?

thanks for any help with this. i'm worried we may be at the mercy of a cowboy as we've not got much time to sort things out, and by the end of the week he'll have us over a barrell in terms of installing in time before Dec cut-off for the FIT. On the other hand, perhaps he's fine and I'm just being overly worried, BECAUSE of knowing that i'm nearly overa barrel!

 

[BruceB]

There is a paper around by Fronius suggesting you can make an east west array work on a single mppt if that is what you have. But conventional wisdon is that for arrays of different orientation/inclination you MUST have dual mppt. SMA who make the Sunny Boy range definitely advise that.

A 4000TL or Aurora 3.6 both have dual mppt and would be fine.

The SB3800V although useful in some circumstances is older technology than the transformerless inverters (4000TL & Aurora) and less efficient so I would not normally choose it.

Once you have panels on the roof then the loft is much cooler and is no problem for an inverter in my opinion. Cost of ac cable run vs dc cable run is marginal in terms of cost of the installation, so do what makes sense for other reasons. Long ac runs if not done properly can cause inverters to trip out because of voltage rise problems.

Inverters need airflow for ventilation so avoid putting in cupboard unless vented top and bottom.

If you can fit x16 non-Sanyo on your roof then that should be more economical by far.

 

[carolinebrett]

Hi Bruce, thanks so much for your reply, it's great to get some advice from someone not trying to sell me something!

Regarding the Sanyo's, unfortunately our roof space is very tight and we already have a large SolarTwin solar thermal array on the ESE facing roof, so that's why the more expensive panels seem to be the best bet in terms of overall performance for our money. Unless you have another suggestion - i have to say i've not fully researched the other panel sizes as all of our quotes have suggested the Sanyos.

Good to know re: the loft issue. The cupboard i have in mind is not vented, though could be i suppose. but if the loft will be OK then it makes sense to just go with that. Although we won't know what the output is!

I'm now not sure whether to trust the guy who suggested the 3800V SMA inverter as it seems i was right and it's not the right kit for the job really. or perhaps i can just insist on the 'right' inverter, as he offered a cheaper quotation than our other possibilty who specified the Aurora 3.6.


The former guy also stated that he would override the SB 4000TL settings to keep within the 16 amp regs (or whatever it is), in the case that he can get hold of 16 Sanyo 250's. What do you think of that???
also, given that it is an ESE/WNW split array, are we better off getting the Aurora 3.6 anyway as we're unlikely ever to get up to 4kw out of the system anyway?

 

[BruceB]

If you have restricted roof space then that is a good argument for the Sanyos.

Aurora 3.6s are running out fast across the country so you/he will have to move fast to secure one.

There is no problem restricting the output of the 4000TL, it is a standard technique. It is slightly oversized for you and more expensive that the others mentioned, but I have had to offer one to a customer today in a similar situation because the shelves were getting bare at the wholesalers.

You would have to do a bit of 3D trig to prove it, but if your 2 strings are facing 180 degrees apart then I suspect the input power to the inverter would never exceed 3kW so you could even go down a size to an Aurora PVI-3.0-OUTD which also has a dual input. But that is a call for your installer who needs to understand the point and be able to do 3D trig.

You can have a remote display for any of the inverters.

Regards
Bruce