The Sunsynk hybrid inverter is a great choice, but there are other less expensive ones - for example I had a Sofar ME3000SP which you can pick up a pre used for a few hundred pounds from eBay. 

I had a Sofar but changed for a Sunsynk 5kw because I have a limited cheap rate time of use (4 hours) so needed an inverter that could charge my battery a lot faster. 

In hindsight I should have got an 8kw BUT I got it really cheap so I can always add another 5kw Sunsynk inverter if I really needed it.

Posted by: @transparent

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OK. Understood. So you will require a G98 certified inverter because it's grid-tied.
And you'll want one with a Current Transformer (CT) which is configured to prevent all export.
Whatever is stored in the battery will only get used within your house.

Have you considered a SunSynk 'Bi-directional' inverter?
They are designed to permit no export to the grid by default.
Moreover that export-limitation mechanism already has approval by the ENA (Electrical Networks Association).
So you could opt for an inverter model with greater output than 16A, and still be granted approval from your DNO (which in your case is NIEN).

You can verify this by applying online for G99F/T (Fast Track) permission, and stating a particular SunSynk model.
G99 applies to combined storage and export, and is explained more fully on that website.

You don't then have to install that model. You can change your mind and apply again.
But at least that will give you an idea of any 'issues' which the DNO thinks might apply to your particular site.

Thanks for the suggestion, it looks to be an interesting device but is probably overkill for my application. In particular I have no need for PV capability and was looking for a G98 certified unit. G99 fast track in Northern Ireland seems to only apply to multiple G98 in parallel. (See the following)

https://www.nienetworks.co.uk/connections/online-application/generation-connection-g99-ni-fast-track?formguid=4042380a-f4d8-4606-ad25-cae61ee6118f&formid=7916

I will call them next week to see if this interpretation is correct and whether a G99 certified device with export limitation is eligible for Fast Track.

Posted by: @misterb

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The Sunsynk hybrid inverter is a great choice, but there are other less expensive ones - for example I had a Sofar ME3000SP which you can pick up a pre used for a few hundred pounds from eBay. 

I had a Sofar but changed for a Sunsynk 5kw because I have a limited cheap rate time of use (4 hours) so needed an inverter that could charge my battery a lot faster. 

In hindsight I should have got an 8kw BUT I got it really cheap so I can always add another 5kw Sunsynk inverter if I really needed it.

Thanks for the suggestion, this looks like a possibility. Most of the Ebay units seem to be "refurbished", Which does raise the questions of what was wrong with these units that resulted in so many being sent back for rework. It looks a bit strange to be honest.

I haven't come across a bi-directional inverter which does not have solar input @alphonsox
That bit of the electronics isn't a substantial part of the design, and I'd be surprised if there was enough of a market for that sort of unit.

The G-standards don't exactly fit your situation for the same reason.

Any device which is incorporated into a G99 installation would be G98 certified.
G99 evaluates the overall arrangement. Not having any form of on-site generation isn't a category.
The present base assumption is that any site which has grid-tied battery storage would also have solar/wind/hydro generation, and therefore export-limitation is required.

Please don't be daunted by making such an application. It's straightforward and you'll find the engineers are very helpful.

There is also a wider benefit in your site being G99 assessed.
The calculations reveal to the DNO what constraints exist for properties supplied from the same feed and substation transformer.

Local substations aren't monitored, so there's considerable value to the DNO in checking their status over time as G99 applications arrive from the public.
Sometimes it highlights a need to upgrade/replace a feed-cable, or possibly replace the entire transformer.

A G99 application I made 3 years ago instigated an upgrade of the pole-mounted 3-phase feed along the road to my house.

The new wires are ABC (Aerial Bundled Cabling) with a higher current-rating and lower maintenance requirements.

This upgrade did not hold up the inverter installation work at my house.
Moreover the Area Manager instructed his team to run 3-phase all the way to my house because there's a chance that I might want/need it in future.
There was no charge made for that common-sense approach.

@transparent It is very refreshing to hear that common sense is employed in this way sometimes, I have no idea of the capacity of our local electrical supply; our services were I think laid in the 1930’s and though ‘patches’ are regularly being applied somewhere or other in the road every 4 to 6 months, I don’t think the capacity has been uprated since early days. My G99 application went through after some 12 weeks but no restraints or additional conditions were imposed so I suppose the capacity is adequate. My installer informed me that there are now limitations placed on my inport / export rates and the two Tesla Powerwall 2’s traffic up to 10 kW. Regards, Toodles.