Solar/Battery Quote Questions

Alnat1

Make sure the installer is definitely intending to get the DNO approval for a larger system and get it in writing that it's included in the quote. 

bazza2000_2

Alnat1 said:

Make sure the installer is definitely intending to get the DNO approval for a larger system and get it in writing that it's included in the quote. 

Yes, will do thanks.

bazza2000_2

Martyn1981 said:

Thanks, all interesting to learn. 3.68kW export is normal, above that prior approval is needed, so best of luck, as that's a lovely big system.

Regarding the strings, I looked at the inverter data sheet and it has 2 MPPT's and 3 strings. One MPPT is designed to take twice the power of the other. So one string into the 'weaker' MPPT, and two into the stronger ..... but, you want those two strings to match as much as possible, ideally match exactly, so the same number of panels, orientation and roof pitch.

If you don't mind me asking, where about on the data sheet did you find the different MPPTs with one taking twice that of the other?

Magnitio

bazza2000_2 said:

2) I've not considered any other brands as yet, this was just the one that the installer recommended.  There is a caveat that the panel has to be all black (Not for me, but the wife has stipulated requirements ) 

If you are after an all-black panel and interested in a quality product with a lower environmental impact during manufacture, I can recommend REC Alpha Pure panels - https://www.recgroup.com/en/alpha
They also passed my wife test.

Martyn1981

bazza2000_2 said:

Martyn1981 said:

Thanks, all interesting to learn. 3.68kW export is normal, above that prior approval is needed, so best of luck, as that's a lovely big system.

Regarding the strings, I looked at the inverter data sheet and it has 2 MPPT's and 3 strings. One MPPT is designed to take twice the power of the other. So one string into the 'weaker' MPPT, and two into the stronger ..... but, you want those two strings to match as much as possible, ideally match exactly, so the same number of panels, orientation and roof pitch.

If you don't mind me asking, where about on the data sheet did you find the different MPPTs with one taking twice that of the other?

No probs, happy to help. Under the input DC section you'll see the "max input current" line gives two figures - 12.5A/25A,
also the MPPT line states "MPPT number/Max. input strings number" and gives 2/3. That translates to 2 MPPT's and 3 strings.

Put the two together and you can work out that the two string MPPT has twice the input of the single string MPPT.



Found a better source here, not a datasheet, just a description, but it all matches:

SOLIS 8.0KW 5G DUAL MPPT – SINGLE PHASE WITH DC

Please note this inverter has two MPP trackers, each with different maximum allowed DC Current!

MPP Tracker A is limited to 12.5A and should only have single string connected to it, MPP tracker B can have two strings connected to it with maximum current up to 25A.

1961Nick

What about using 2 x 4kWh inverters so you have 4 MPPTs? Would that accommodate the shading?

The DNO approval would have to be for 11.6kWh due to the battery being ac coupled.

bazza2000_2

1961Nick said:

What about using 2 x 4kWh inverters so you have 4 MPPTs? Would that accommodate the shading?

The DNO approval would have to be for 11.6kWh due to the battery being ac coupled.

Its a good idea, I can ask. I didn't realise on the DNO approval. Is that based on the lux being 3kw discharge? 

1961Nick

bazza2000_2 said:

1961Nick said:

What about using 2 x 4kWh inverters so you have 4 MPPTs? Would that accommodate the shading?

The DNO approval would have to be for 11.6kWh due to the battery being ac coupled.

Its a good idea, I can ask. I didn't realise on the DNO approval. Is that based on the lux being 3kw discharge? 

The Lux is 3.6kWh discharge.

bazza2000_2

Just wanted to update with the schematic and a query:


Should there be DC Isolators on both strings before they enter the Solis Inverter?  similarly, should there be DC isolators or fuse from the battery storage?

QrizB

bazza2000_2 said:

Just wanted to update with the schematic and a query:
...
Should there be DC Isolators on both strings before they enter the Solis Inverter?  similarly, should there be DC isolators or fuse from the battery storage?

Some inverters have integral DC isolators (my little Growatt does). Yours might, and your batteries might have built-in breakers. I'm not familar with your equipment and can't say if they do or not; hopefully someone else can say for sure.