Posted by: @makia2023

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I'm still playing with how best to set this up inverter wise. Perhaps 3x 3.6kw inverters is a better option. I'm going to look it prices again today. 

I'm not entirely sure how 3x 3.6kW inverters will play out with respect to DNO permission ... I'm guessing you'd have to use the G100 certification and promise to limit the power exported (and imported???) to some acceptable level.

As a recovering software engineer I believe that n > 1 components is (super-linearly) more complex than n == 1. The AC and DC connections need to be consistent (in terms of voltage drop) partly by making the cable lengths the same as well as ensuring consistent connections. Each inverter needs (DC and AC) circuit breakers. The interactions between inverters and their failure modes should be considered. Cable runs become more fun.

Unless I go off grid inverters thus no DNO permission required.

depending on space for installation, then i would have thought one big inverter would be better than 3 smaller ones, there would be a saving in components aswell as time spent installing?

you seem tied to Growatt .... is there a specific reason?

im really pleased with my Sunsynk 5.5kw but i was also happy with the Sofar ME3000SP - though it didnt offer any 'expansion' options, it worked perfectly for the short time i had it installed - the point i am making is that perhaps a different 'brand' might be worth considering.

@misterb Right now i'm just weighing up the pros and cons of each option, namely doing it right the first time and ensuring I get what I need out of the system.

As it stands I have a 5kw Solax system that no longer meets our needs. By going up in power output i hope to achieve 2 things:

1. Enable greater energy shedding into my 2 electric vehicles during summer months during daytime

2. Reduce requirement to use peak grid energy during winter/low solar months.

To achieve this I need sufficient output of my system to cover the following base loads:

1. Winter - ASHP, other WFH equipment (circa 1kw currently, but expected to increase to circa 1.8kw when the temps drop)

2. Summer - circa 1kw base load (air con throughout house, 7.2kw car charging).

Of course I can reduce the output power of my car charger to offset the rest but I also need to factor in peak loads for cooking/washing/dishwasher etc

So 8kw is really the minimum output I require from my batteries and Sunsynk is my preferred option for this.

Otherwise, Growatt in a 3x 5KW off grid setup would be the next go to, but does increase the cost by around £300 for the inverters (£2100 for 3 growwatt vs £1800 for 1 sunsynk) plus as you have noted around another unknown sum to make it all work. 

All that said, if I got with the @transparent plan and individually isolate each DC battery with MCCB and T-Fuse, then the additional cost to parallel the inverters is limited. Space wise I am between 2 locations - 1 is my home office/gym (old double garage within house) or my workshop (side attached). Each comes with pros and cons as follows:

1. Office - immediately next to the board but space for the batteries limited (I suppose I could place them on their "backs" so the front are pointing up to reduce footprint)

2. Workshop - loads of space but will require a long, new, difficult to access cable run for the AC at a suitable size to carry 8 or 15kw depending on choice.

Does all of that make sense?

Stew

Posted by: @chickenbig

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I'm not entirely sure how 3x 3.6kW inverters will play out with respect to DNO permission ... I'm guessing you'd have to use the G100 certification and promise to limit the power exported (and imported???) to some acceptable level.

Having the possibility of exporting more than 16A per phase requires an application to your DNO for G99FT (Fast-track).
There is no fee for this, so you can simply apply today online and let them tell you whether you would be permitted to export more.

There are lots of factors which they input to their algorithm which you don't know about:

• cable length between you and your substation
• cable current-rating and load-factor
• number of houses between you and the substation
• substation peak capacity
• how many properties on each of the phases supplied by that substation
• number of properties which already have heat-pumps and/or EV chargers installed

They won't accept a promise to keep below an export current.
You have to fit an approved current-limiting system, such as that which is embedded in SunSync's inverters.

If you don't know which grid-tied inverter you might use yet, just choose one of the SunSync models in order to complete the online form.
You can always re-apply later and change the brand & model number.

@transparent Yep. I've decided to go single Sunsync 8kw inverter. Having done a quick design on 3x 5kw growatt the circa 320amp draw potential puts the price of everything (safety devices) up too much. 

Ref DNO, all acknowledged. I have the paperwork ready from my previous application for the Solax.

@transparent what are your thoughts on standing the batterie enclosures on their backplate?

Posted by: @makia2023

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where would my excess solar go once the batteries were full and the demand from the house is low? 

Given the list of features you've described at your house, I really don't think that's going to be a problem. 🤣

But if you're stuck for ideas, may I suggest

Posted by: @makia2023

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what are your thoughts on standing the battery enclosures on their backplate?

The batteries won't mind about their orientation.
But is this a problem because you've already bought the vertical Mason boxes, and now wish to lie them down?

If you've got 'suspended flooring', you can even install a trap-door and put them beneath floor level. 🤔 
Once they're operational, why would you need to have them on view?

@transparent Ive bought the ones without wheels......that lie flat (280 non-L).

Unfortunately I dont have a suspended floor it is concrete throughout. 

Is the below image correct or am I missing anything as I will order all the bits in advance and start to position on walls.

As you'll be feeding three batteries into an 8kW inverter, you don't require the MCCB style because the current will be below 125A per battery.

Simply buy the cheaper DC MCB units which are DIN-rail mounted.