DC coupled battery help on FIt system

[resybaby]

As fhe title really, im after a bit of guidance/help with adding a battery (prob a Givenergy9.5kw) onto my exisitn FIT system (3.68 SMA sunnyboy, 21x Upsolar 190 panels), obviously dont want to compromise the payments.

I would go for (and had intended originally) for an AC givenergy 13kw AIO system with 6kw generator and more panels to power that as a separate system, but having spoken to the local DNO directly he says no. He will only permit an additional 3.68kw generator to go with my existing FIT 3.68 pv panels. So the AIO is out, and this has forced me to completely rethink, bear with me im very green at this.

What im trying to do is reduce (obviously) all our demand on the grid, so wont be looking to charge at night at all, so have rethought my plans having tsken onboard the DNO chaps restrictions (inc his refusal of zero export invertor settings being an option), as well as his lack of interest in anything DC coupled, and acceptance of max 7.4kw permission (2x3.68kw)

So my current thoughts are.

1. bung another set of separate panels on my south facing roof - 5kw, connected to a 3.68invertor and increase my PV total yield.
2. Install 2 x givenergy 9.5kw DC coupled batteries, split between each system, to capture both yields. Neither of which systems can be charged from the mains, so keeping the DNO happy and within max permission of 7.4kw.

All this sounds so simple on paper (it probably is to most) but i am struggling like mad, hav8ng spent hours and hours readin up on this to pick the suitable equipment to spec to my sparky to fit. Ive found the ideal panels for me (JA solar 545w) that will visually be similar to my existing FIT panels (190w upsolars), but try as i may this electrically challenged gas fitter is baffled by the invertors to use, and how they will 'look' in a schematic of the two systems (my existing fit and my new 5kw system). Unfortuatly i like to 'see' how a system looks on paper so i can really understand it, before speccing to my MCS sparky installer.

Would appreciate any steers you guys and girls could offer me, if youd be so kind?

[nowty]

If your being allowed another 3.68kW inverter you should buy a 3.68kW hybrid inverter so you can have both panels and batteries connected to the second inverter. You make sure the second inverter does not go through the FIT generation meter and you can charge the batteries from the grid as well as the original FIT system. No need to DC couple at all.

You leave the original FIT system alone.

Guidance about adding storage to a FIT installation here.
https://www.ofgem.gov.uk/sites/default/ ... idance.pdf

Application to the DNO should be a G99 fast track one.


Example, from the guidance doc, Page 33, the inverter to the left is the original FIT system, M_G is the FIT generation meter, the inverter to the right is the new hybrid inverter and additional PV panels can be added to it as well as the storage shown.

[resybaby]

Nowty
Many thanks for your rapid reply, very much appreciated, as i say bit of a numptie with all this and may have confused myself with all the jargon, but your sketch and notes do make sense - 100% AC coupled system. Which is what i would have had if i could fit the 6kw AIO givenergy kit.
When the DNO poo poo'd that and said only 3.68 extra, he mentioned DC coupling, as he wasnt interested in anything then (i am because of FIT), so i scratched out the attached 'schematic A' based on purely DC coupling to keep DNO happy and still give me the ability to draw out 6kw (at night) from the two separate batteries in paraelle. AC coupling would only give me 3kw as in series.
I had definately misunderstood the hydrid invertor, and thought when i scribbled my 'schematic A' out that i could only have a 'dumb' invertor (dont intend to charge from grid however) but i've got that sussed out as possible now and realise i can have a hybridcharger unit, thanks to you explaining that for me.

Thinking more about the 6kw draw thats now reduced to 3kw using AC coupled and the possability of a mixture of both systems to get that back to 6kw draw with a mixture of two systems.

New one, AC coupled as your post with 3.68kw hydridcharger/3kw output givenergy,
and the FIT system modified to DC coupled storage with a similar battery/output. Im guessing that would need my original FIT dumb invertor to remain (to stay FIT and DNO compliant and not bugger up the generation meter accuracy) and so another piece of kit (a hybrid non charging invertor maybe?) would need to be installed just prior to the battery to control its PV only charging/discharging? I assume the generation readings would stay roughly the same (bar elctrical/battery losses) with the Pv generated power just being diverted to the battery initially, then going through the generation meter as used from there later.

Hopefully that makes some sense, and would appreciate your thoughts, do feel free to tell me im a plonker of im being one

Image to big to post so had to use Imgur link

Cheers
Rex

[nowty]

Regards DC coupled batteries to your existing FIT system, there are not many such devices on the market without the grid charging facilities which are against the FIT rules even if you never use the facility (expect the exception in the following paragraph). Also if you are having two battery system inverters installed, unless they are designed to work together in parallel you can get some unwanted behaviours such as one on full discharging rate and the other on full charging.

You could replace your existing FIT inverter with a single larger Hybrid inverter with batteries and more panels. Then with agreement with your FIT provider, you fit a bi-directional meter generation meter and have your FIT rate diluted with the ratio of new vs old PV capacity. But thats easier said than done.

There are different options but your trying to make things more complicated for yourself. Much easier to leave the FIT system alone if you can and have one separate storage / PV device. That keeps both the DNO and FIT provider happy.

[Countrypaul]

Sorry if this sounds a little ott, but it might help if you can distinguish between power and energy a little more. Power (in this situation) is measured in kW, where as energy is measured in kWh so 1kW for 1hr gives 1kWh. Battery storage is normally measured in kWh where as inverter output is measured in kW. When you say you want to draw 6kW overnight from your batteries, do you mean 6kW to run equipment for a shortish while, or 6kWh for example a 2kW heater for 3 hours?

One option that might serve you, is the Victron Multiplus, whereby you can have the existing FITS system used as a input to the Multiplus and also have Batteries connected, those batteries can be charged via PV panels connected directly to the Multiplus, also from the existing inverter, and if wanted from the mains (for example in winter if you have a suitable tariff). If you have more PV panels that the existing inverter and multiplus can handle then there is the option for DC charging of the batteries too.

There are a few diagrams on this site of different configurations if you wan tto look at some examples.

Unfortunately the Victron is a bit of a Rolls Royce solution with the associated price. It does seem to have a very good reputation for reliability and flexibility (read potentially complicated) though.

One thread that may help you (or confuse you more!): https://camelot-forum.co.uk/phpBB3/view ... ITS#p22846

[resybaby]

Thanks CountryPaul

In essence what my end goal is is to be able to draw as much power (6kw) to cover as best i can the usage of two separate big draws from our house, (eleccy shower and instantaneous kitchen sink heater - both draw 9.5kw). Both intermittant and not long term.

Im not going to be around much more, poss 6 months tops (cancer) so am trying to set my house up to cover as much of its bills as i can for when the wife is left behind and my salary gone. If you think im confused she's totally on a different planet

Obviously i cant cover for both/either of those devices, but they wont be used together (only 1 person here) but im trying to at least make a good dent in such peak demand, hence the inital thought of 6kw AIO the DNO wont permit, or splitting system to use additioanl DC inverter running togeather, which DNO isnt bothered about.

Will have a read up on the Victron thread you have posted and see if i can suss out how that would work (optimistic probably), am not realy to worried about the costings (to a sensible degree) i just have limited time, and lack of knowledge to learn whats best for my wife in the future.

[resybaby]

Nowty.
My FIT tarriff is with OVO and they are unbelievably woeful, so really dont want to try and get involved with them if even remotely possible. They spent a year (when they took over my FIT from SSE) emailing me to tell me my email wasnt correct and they couldnt email me! They are utterly incompetant and make me look like Einstein.
We are quite low powerusers and capture the FIT export via an Iboost currently and dump that in an oil heater in winter, it all helps on sunny days. My initial (dont laugh) barmy plumber thoughts were that i could 'capture' the excess using that device and connect a battery charger to charge batteries instead - then learnt the voltages are a tad different, so back to the dumb heater for the Iboost.
Sounds like im stuck with the FIT as it stands for the remainder of the contract then.

Thanks again for your guidance

[Lincs Robert]

Another possibly is to use Solar Kit for the new installation. It has a feature called export limitation & can be set to apply that at the site level - if that makes sense? Ok, you will have to use SE optimisers, but so what?

It’s worth investigating further I think.

[openspaceman]

In essence what my end goal is is to be able to draw as much power (6kw) to cover as best i can the usage of two separate big draws from our house, (eleccy shower and instantaneous kitchen sink heater - both draw 9.5kw). Both intermittant and not long term.

Im not going to be around much more, poss 6 months tops (cancer) so am trying to set my house up to cover as much of its bills as i can for when the wife is left behind and my salary gone. If you think im confused she's totally on a different planet

Unless you go off grid the extra cost of using the grid for this intermittent "peak lopping" is insignificant compared with the standing charges during the summer months. The main thing is to keep everything well integrated so it manages itself without need for intervention.

I went down the route of AC coupled 6.5kWh battery and 3kW inverter so as to not interfere with my FIT, then on advice from here added 1.8kW of solar pv and a battery charger added to the DC side of the battery to avoid application to DNO. It works well and the wife understands to keep loads below 3kW in darkness. Of course I want to do more, for the hell of it, but what I have is good enough.

Best wishes.

[nowty]

Bearing in mind the OPs prognosis, I cannot emphasise enough about keeping it as simple as possible, especially for SWMBO. We have had the argument about installing expensive kit to try and cover short term high power devices many times on here and it is rarely financially viable.

In the circumstances (timewise), leave the FIT system alone and no need to even contact them. Add a second hybrid 3.68kW with panels and batteries under the G99 fast track process with your DNO.

And whatever you decide, ensure your sparky is "on board" with the kit, to avoid any future maintenance issues.