Battery Charge & Export

Newbie here & not electrically minded so be kind.
We invested in solar just over a year ago, we have 14 LG 355w panels with a Solaredge SE5000HAPP inverter, unfortunately we were talked out of adding a battery at the time due to payback which we regret!
We now want to install battery storage (10-16kw) & after some investigation Givenergy seems to get a lot of good reviews.
Our solar inverter has been restricted due to the DNO to 3.68kw export to the grid. Is it possible to get a decent charge rate 5kw to the battery on cheap overnight rate & also 5kwh to supply the house from the battery during the day?

Hi Amwilt15
I'm still waiting on my Gienergy battery to be delivered, seems a little bit of a backlog to getting them currently.

Once I do have it I'm looking at the Octopus Agile Solar + Battery tariff. Ideally the best one to get would be the Octopus Go, as its only about 5p during the night for, four hours I think from memory. But Octopus changed their T&C lately to say strictly you need an EV car to go on the Go tariff.

Amwilt15 hi just be mindful that only the 8.2 kWh battery has unlimited charge cycles warranty and 100% depth of discharge. Personally I think that this is enough capacity, I’ve run calculators and too much takes too long to pay for itself. Prices have dropped dramatically so this could change, but would rather invest in a boiler for hot water as an energy store.

Amwilt15 You will need 2x AV3 and 2x 8.2kw batteries for your requirement. As for charging your solar has a max of 4.97kw and the AC3's can take 3kw each to charge the batteries. So yes you can still charge at nearly 5kw regardless of the DNO restriction. I currently have 7kw +3kw from the battery and extending that to 10 or 11kw soon and my DNO has also restricted me to 3.68kw export.

The 3.68kW constraint is on export to grid, not on PV inverter output. I have a 6kW SolarEdge PV inverter, and it will happily output 6kW until the (GivEnergy) battery is full, then it throttles back to 'consumption+3.68' kW.

steve Thanks Steve we have an EV & are with Octopus. I can't find out from anyone when the 8.2kw batteries are going to be available.

CARLMW I thought we would take the hit once as electricity use is only going up now we have an EV.

Baychattan What battery setup do you have, we are thinking to go for a larger battery & top up at cheap rate over the winter so we don't use peak rate much at all.

THALL If the 2 x 8.2kw batteries & 2 x AC3's were available (supply problems) any idea how much it would likely cost to be installed. I have been given a quote for an LG 16kw RESU Prime battery which is quite expensive.

Amwilt15 This is purely a guess, but £7500 - £8000 fully installed. £2600 per battery, £700 per AC3.

Not sure when but looks like there is a 5kW inverter and 11kWh battery coming so might be worth holding out for that.

(Givenergy replied along these lines to someone on twitter today)

judgepd This would suite my needs better than the 3kw and 8kw batt. But never mind, until this one breaks out of warranty it will do. Yes I could add another AC3 but the current setup is neat and tidy on my outside wall.

Amwilt15 I'll let you know when mine arrives.

Baychattan This is interesting. I'm new to this and wasn't aware that there was a limit you could export back to the grid. I guess they would state that to you on the DNO? What happens when battery, export and house usage are all happy, and the throttle kicks in? Does it just turn it into heat and Inverter heats up, as the energy needs to go somewhere 😄

Amwilt15 I have an AC3 and two 8.2kWh batteries. If I had known that the AC3 could be paired in parallel I would have gone for 2x (AC3 + 8.2kWh), as the 2.6kW AC3 max output gets exceeded by an electric kettle, oven, stove, etc.

(As an aside, I found that most solar/battery installers appear to be ex-double glazing / 2nd hand car salesmen, and only offer what they want to sell. It can be difficult to find out everything that is possible / desirable.)

steve The 3.68kW export 'limit' is what the DNO will accept without question. If you apply for more they may/will want to check that their network will handle it, and that takes longer. I think it is more to do with balancing loads on the 3 phases down the road (ie is there a lot more export from houses connected to one phase) rather than the wires taking the load. I suspect that installers don't like the extra work of form filling for exports of more that 3.68kW, so that's what they apply to the DNO for unless you REALLY pressure them to apply for more.

I am not sure how PV inverters control their output. I guess that they use DC voltage regulation to reduce the current from the PV panels. They certainly don't just dump excess power as heat, or they would get VERY hot!

Baychattan he AC3 can output 3000w so should be fine for single electric items like a kettle. At least it should do 3000w....

In my case there are spikes where demand exceeds what the AC 3kw inverter can supply, but it doesn't bother me as the only time this is anything other than transitory is if there's alot of cooking going on - with the oven, microwave and induction hob all running at once. Small spikes over 3kw to boil a kettle add up to not very much - I couldn't justify buying 2x inverter just to cover ( (I do have two inverters to be fair - one for PV and one for batteries**). My calculations also had to consider that I'd need more batteries per inverter - otherwise all I'm doing is just getting to 0% SoC quicker, and still importing after that.

Not saying it wouldn't be nice, but I couldn't justify the additional costs.

**During at least half the year, during the day, the solar is carrying quite a bit of the load anyway, so the house can often support say 4-5kw before grid import starts, during a sunny day at least.

GrahamRead Exactly this. A couple of months after getting my AC3 and 8.2kw batt I was determine to get a second 8.2 installed as soon as possible as the battery was sometimes empty by midday in November/December. However come the end of January the battery now lasts until my cheap rate electric kicks in. The cost of a second battery would not make financial sense for me.

@GrahamRead @THALL I think you guys have made me see sense. I'm really keen to add more solar or another battery, but the additional gains to be made just don't justify the cost. Even over winter with very little solar, charging the battery cheaply overnight represents a useful saving and as the sun gets higher each day it just gets better. The law of diminishing returns wins every time.

judgepd Just to throw a spanner in the works, I am actually adding more solar 😀 It will not pay for itself, but once my EV arrives the more I can generate myself and put into it the better. Plus more coverage will help in the winter months too, using my current battery to grab any generation I do not use. Basically the entire roof on my home will be covered by solar. Should be between 10 and 11kw plus 3kw from the battery on my 100sqm house! Got the survey being done next week just confirm how many panels will fit on the uncovered section. Plus the fact it is currently 5% VAT on renewables is the push to get this done. To me more panels make sense, a second battery....... not so much. Though in the future if I can get anotherr 8.2kw fully installed for sub £2000 then I might change my mind. Currently it would cost me £3660 (thank you EON).

@THALL Well...I'm currently trying to get quotes to add more solar too. We also have an EV due soon(ish) so it does feel like the more solar the better. Another battery would be cheaper and easier to do but I think more solar would be more useful. I suppose it doesn't always have to be about payback periods anyway.

judgepd The battery would be cheaper? I am about to add 3.3kw of solar (hopfully) and the rough quote was £3200 which is cheaper than a battery (for me at least)

I'd just made an assumption to be honest, but that gives me hope that maybe the solar is a viable option.

We'd need 2 lots of scaffolding and possibly some of the existing panels moving so I don't think it's that straightforward.

judgepd I've been quoted £350 per scaffold that goes up. But I have no idea of the cost of moving panels, if no new cables are needed that might not be too bad. That is a whole area I am not going to explore, could get expensive.

When I last asked someone (our battery installer) they said absolute minimum for scaffold was £500 per side and we would need one per side of the house so that's £1000 even before they start.

I'll see what the person coming tomorrow says as that's a different company. It would be another system with another inverter so I'm not sure how that would all connect up with the battery system and the zappi either. At least adding another battery would be an awful lot more straightforward.

judgepd Hmm scaffold can be had for cheaper, a few local companies around here respond to cash very well!

Fingers crossed. I got the feeling that the battery installers just weren't interested in the job to be honest.

Baychattan We have found it extremely difficult to find out the best possible/desirable solution for us, thank goodness for forums like this & Facebook groups.

THALL So, just had a quote for 8 x 390W panels, 4 east, 4 west and it was £4915 + VAT. Looks like I'm not adding any more solar. 😞

judgepd ouch, that including scaffolding?

Assuming that'll be a big part of that bill as it'll require 2 sides of the house?

yandards It does include scaffolding but I don't know what the breakdown is. I might keep trying to find other installers as that one seems expensive to me.

I added AC3 + 8.2battery to an exisiting solar system. The DNO required an application as potentially I could have been exporting Solar + Battery (5.8kw) to the grid on a single phase. The DNO requirement was simply a 'fast-track' application. They wanted to see a schematic of the proposed configuration (GE provide these) and an export limitation document (GA also provides this) and they were happy. No fees involved but SP Energy Networks (my DNO) took about a month to approve the 10-day fast-track! Given the backlog of battery orders at present that's no big deal.

One advantage I hadn't realised when choosing AC coupled rather than hybrid is that when the sun is shining and I use more than the panels are generating, the battery also kicks in to supply extra so my small solar system 2.82kwp with battery is capable of supplying me 5.82 kw at times when say we boil a kettle while the washing machine is running. The battery tops up again as soon as the kettle stops and the washing machine stops heating.

I'm not sure why the DNOs are so worried about battery systems. The main idea is to REDUCE export to the grid and save it for later consumption in the house. Even those who want to export at peak times for payment are taking load off power stations at peak times so it's a win-win for all concerned.

I think the DNOs should be much more worried about single pahse users on Octopus go who decide to charge their car, run the washing machine and dishwasher and take a late-night electric shower. As that scenario becomes more common I think the grid will struggle and I think the late night discount electricity will become scarce as night time car charging makes it a peak demand.

kwmc Yes, in a rare confluence of events last week, we were charging an EV, heating our hot tub and charging two 5.2 batteries and drew around 14kW as a result. Still a fair way off what our 100A mains fuse will allow, and I’m happy this was largely at Octopus Go discounted rates, but electricity prices are only going one way…

judgepd That is rather high. My quote for 8x 340w and inverter upgrade (to add to my current 8x300 panels) is £3200+ vat. Having a survey done this Thursday to see if large wattage panels could be installed. I have my eye on some 370 or 390. Looked at the 495w but the system will look like a massive Tetris piece if I do. But about £1100 per KW is about right based on friends who have panels and the 4.6kw system I had installed last year. Unless the install is more complicated, extra scaffold etc, long cable rungs etc.

It requires one full width scaffold, one half width scaffold the 8 panels and an inverter (not sure which manufacturer as it isn't even named on the quote). If I try to be very rational I think if I had more solar then other than in winter I'd have more solar generation than I could use to charge the battery and the EV so it would just be wasted.

judgepd Thats fair enough. I am maxing out my roof space as I do about 16k miles per year, so once the ev arrives the more generation I can put into it the better. Plus extra solar will help me in the winter so combining those makes more panels more valuable to me than a second battery.