Adding a second AC GivEnergy charger

Hi,

I currently have one GivEnergy 3.0 Kw AC charger connected to four 9.5 Kwh Givenrgy batteries.

I have three solar arrays, one is on Enphase microinverters and the other two are on Growatt inverters.

I plan to add another array on another Growatt inverter soon.

We are having an ASHP fitted in a couple of weeks.

We are on an Economy 7 electricity tariff with Octopus.

An electrician who cam to quote me for an ASHP said that GivEnergy were soon going to support adding a second AC charger, I understand that you can do this but it is not currently recommended?

For obvious reasons, we would like to be able to charge and discharge at 6.0 Kw rather than 3.0 Kw so that we can run entirely on solar and our E7 electricty rate even in the winter.

I can see at least one person has done this but I can't seem to find any details on how it would work and if it is now supported/recommended by GivEnergy.

We would love to be able to do it but not if it causes problems.

Thanks in advance for any advice offered.

matt-drummer An electrician who cam to quote me for an ASHP said that GivEnergy were soon going to support adding a second AC charger, I understand that you can do this but it is not currently recommended?

If you look in the GE FAQ’s it says that they don’t recommend multi-inverter “plant” setups. The problem is that each inverter doesn’t know about the other inverters and so the inverters can conflict with each other when they try to pull excess solar into the batteries and vice-versa discharge to feed the house load. You can get the batteries cross charging, one battery inverter discharges to charge the other one up. I believe the issues are worse with AC coupled than hybrid coupled inverters.

I have two hybrid 5 Gen 1 inverters (much less batteries unfortunately) and again this setup isn’t recommended. In my case and others on this forum, it does work OK. Some people find very spurious figures in the monitoring portal, not an issue I have but it happens.

To answer your question, yes GE have in development an EMS (Energy Management System) box that is supposed to connect the inverters together and resolve the issues. Having said that this product has been “in development” for absolutely ages with promised release dates just going back and back.
I saw earlier on the forum that GE have recently sent an EMS out to a customer for home trial of multi-AC inverter coupled setup; a positive sign, but how long that trial lasts, whether there will be further product enhancements required before its a proper “thing”, how easily the box can be retro-fitted to existing setups, all lots of questions with no answers yet.
Yes coming but don’t hold your breath that its next week, next month or this quarter.

I have an ASHP (in fact I have two 9kW LG ASHP’s running together in a master/slave setup) and with the house load they will pull more than 3kW some of the time. I’ve just looked at some of the data from January and typical evening load is around 2-3kW with peaks to 4kW and occasional peaks up to 5kW. The ASHP alone can pull in 20kW a day, and on really really cold days, up to 30kW. I have a 9.5kW and a 5.2kW battery which isn’t enough to run the house and ASHP in winter so I am relying on grid energy every day.

For these reasons I have decided not to go to an Economy 7 tariff as I would be paying a premium for evening electricity and not saving enough overnight from charging the batteries to make it worthwhile. I have considered adding more batteries but the payback doesn’t justify it, plus there isn’t enough time overnight on cheap rate to charge them either.

Hope this is helpful.

Geoffrey

Thank you Geoffrey.

I think I will wait for the EMS and add a second charger. If it never happens I'll work with what I have.

I will have one 9kW Daikin ASHP.

Based on my maximum daily gas usage of 100 kWh I expect my ASHP to use around 35 kWh on the coldest day (assuming my gas boiler is 90% efficient and a COP of 2.5 for the heat pump).
If my heat pump is running continuously then I will get 7/24 of it's daily consumption during the E7 period and I can heat my hot water here too. That would be around 10 kWh of my daily consumption leaving 25 kWh to be covered by the batteries and solar. Our house load is around 10 kWh a day in December as is our solar. So I am already close to being able to cover the heat pump use on the worst day from E7 charging.

I had two 9.5 kWh for a month in February and what I found was that it was very difficult to predict the next days solar generation and make a decision about how much to charge overnight.

I added more solar and two more batteries in March, the extra batteries just make it easier to manage. Strangely, I'm looking forward to the winter to see how it all works out.

We moved to this house in September 2021, it already had the Enphase system which is on FIT payments. I have now given up the deemed export and I am on Outgoing Agile at 15p per kWh, the same as my E7 overnight rate.

The idea is that my export income from Octopus will cover my imports over the winter leaving us with a net cost of zero each year.

The capital cost of the extra panels and batteries will be close to our energy costs over ten years, so although I won't be getting rich out of it, it should all pay for itself, and that was my only goal from it, to stop burning gas and effectively fix our energy costs for ten years.

In ten years, the batteries won't work so well but we'll still have the panels and the wiring. I would expect inverters to need replacing at some time but I think my plan should achieve my goal.

It would just be nicer if I could charge and discharge the batteries at a higher rate, hopefully the EMS is close to being available.

Matthew.

matt-drummer I just had a quote for a second AC3 today. £1400 :-( just under 100% increase since this time last year. Based on this I am not going to bother.

You might not get problems with dual AC3's, but you might. There are a lot of people who run multi inverters without issue, but the EMS is coming and you can have it added later.

Thank you.

I don't know what problems I could create?

I don't really understand the system well enough to make any judgement other than I don't want issues that I can't resolve.

On a really basic level, if two AC3's are connected together why do some people have issues and others don't? I would assume that the software either deals with it or it doesn't?

matt-drummer I like the thinking and logic in the way you’ve predicted your consumption with the ASHP, a COP of 2.5 is possibly slightly on the low side, but this’ll give you contingency if the COP is higher.

We had an oil boiler previously and it was the oil tank springing a leak that caused us to go for the ASHP so I don’t have similar historical usage from which to calculate the ASHP. The heat loss survey we had calculated we would require about 8,900kWh for the heat pump, whereas in year 1 we actually used 5,380kWh. We’ve tried all sorts of different approaches to running the heat pump, generally variations on a more traditional heating of having it on in the evening/night when we needed it, but setting it to come on earlier as its lower flow temperature takes longer to heat up the house. Our system was setup by the installers at 55 degrees flow temperature but we’re now running it at 50 degrees - the lower you can get the flow temp and still keep the house warm, it definitely saves money. Just before the winter ended we changed to having it on 24x7 with a 2 degrees setback overnight, and AI mode turned on. Think this will be the most efficient but have to wait to next winter to see for sure.

Yes more batteries would definitely give more flexibility and would see us through dull days we’ve had in Spring, but in winter we’d be reliant on overnight charging to fill the batteries up as our 10.4kW GE arrays weren’t generating enough to even fill the 5.2kW battery in January. I’m currently with Eon next and their E7 overnight tariff was 11.5p cheaper than the current 24x7 34p rate, so saving £1.05 each time a 9.5kW battery was filled. x5 winter months its £164 annual saving, so at £4000 for the battery it’d be 24 years payback for me! I don’t mind investing to save but this was ridiculous.

We also have an existing 4kW FIT array for which we get generation and deemed export payments. There would have been some benefits in having an AC coupled battery as I could then capture some of that generation, but when we had our 10.4kW arrays fitted we had GE hybrid inverters and batteries, which is overall more efficient and costs less as there’s less AC/DC energy conversions, but with the impact that the FIT array isn’t monitored by GE nor the energy stored. I did consider replacing the existing FIT Growatt inverter, but at £1000, its not worth it.
We get about £80-90 a year from our FIT deemed export; I’m waiting to see more annual data from the GE before deciding whether to give up on the deemed export, but it is looking favourable as we exported 500kW so far this year, which at 15p/kW would be £75. The FIT is guaranteed and index linked for 20 years so gotta consider that as well as SEG tariffs can change at any time.

My COP of 2.5 is an estimate of what it might be on the coldest day. Of course, on warmer days I would be very disappointed to not get at least 4.0. If I get a SCOP of 3.50 to 4.0 in the first year I will be happy.

I intend to run the ASHP on pure weather compensation and I think we can run with a leaving water temperature of 40c at 2c outside/20c inside. Our house is very well insulated and the heat loss is quite low, even when our conservatory is taken into account. We have good size and fairly new radiators and only need to replace one old one.

We will export at least 6 mWh in a year, at 15p we will get £900 credited to our Octopus account. I expect to have to import around 3 mWh over three months (middle of November to middle of February), about 30 kWh a day. The size of the batteries means that I can pretty much say that I will import 1,800 kWh at the night rate and 1,200 at the day rate which will work out at a cost of £930 including the standing charge, so close to my goal of £0.

We also took part in Octopus savings sessions this year and if they run them again that will add to our income , charge the batteries and heat the house.

It will be better if I could charge at a higher rate and make it easier to manage, it's only really use of the oven while the heat pump is running that is likely to cause an issue with what we can draw from the batteries.

For that reason, it is not worth risking big problems if two chargers isn't guaranteed to work.

Lots of headroom in the batteries does mean that I won't be fully charging overnight and then exporting in the morning as it is warmer and/or sunnier than I was expecting only to be importing at peak rate later on.

It's not perfect, and probably not the most financially efficient way of doing this, but it does enable me with some certainty to have fixed our energy costs, maybe too high, but then who knows how things will be in the future.

It was also a bit of a project/challenge just to see if I could make it work, we will feel good if we can be a net exporter of energy with zero costs (ignoring the capital outlay).

Ultimately it isn't always about the cost, I wanted to do this, and the large amount of generation and battery storage means that most of the time we can turn on anything we like knowing it's `free'.

geoffreycoan

My deemed export was about £120 pa, it was a no brainer to give it up.

I think you can go back onto deemed export after 12 months of being off it, so it's not permanent `mistake'

matt-drummer I think you can go back onto deemed export after 12 months of being off it, so it's not permanent `mistake'

I wasn’t aware of that. I’ll look into that because if its true it will make it much more of a simpler risk-free decision.
The 15p export tariff is very tempting but most SEG tariffs are awful and I was concerned about jumping from an index linked assumed export figure (currently around 6p/kW) to SEG rates that could well be lower in the long term

geoffreycoan The break even on 6p deemed and 15p SEG is only 80% self consumption.

geoffreycoan I’ve looked on a couple of websites including Ofgem and it covers the situation of having to give up FIT deemed export if you go onto SEG (in fact it says you have to go onto SEG when you get a smart meter, ulp, but I think the export part of mine isn’t enabled). But couldn’t find anything about going back from SEG to FIT export so I’ve sent Ofgem an email.

geoffreycoan

Received a reply back from OfGem this morning, thanks @matt-drummer you are correct, you can opt back in to FIT export from SEG in the future. This isn’t covered in the SEG guidance but OfGem confirmed its possible:

Please refer to the following extract from our Smart Export Guarantee: Guidance for generators | Ofgem

_1.25. Generators must not be in receipt of an export tariff under the Feed-in Tariff (FIT) scheme if they intend to claim SEG payments. Information about the FIT scheme is available here.

1.26. FIT payments are made in two parts:
· FIT generation payments – made for every kilowatt hour (kWh) of electricity generated by the installation; and
· FIT export payments – made for every kWh of electricity exported to the grid.

1.27. A SEG licensee is obliged to make payments under a SEG export tariff to an eligible installation (see paragraph 1.7) if that installation does not receive FIT export payments.

1.28. An installation in receipt of FIT generation payments only (ie the generator has opted out of receiving FIT export payments) can receive a SEG export tariff.

1.29. As part of the SEG application process, applicants will be asked to confirm whether they currently receive FIT export payments._

FIT generators are allowed to opt in or out of FIT Export Payments, but no more than once every 12 months. FIT licensees are required to record this change on the Central FIT Register (CFR – the database of all FIT accredited installations). Generators can change their FIT export status by contacting their FIT Licensee.

Once a FIT installation has been opted out of FIT export payments, it may be registered for the SEG, provided that the SEG eligibility criteria are met. Please note that you cannot receive both SEG and FIT payments for the same electricity – if you wish to opt back in to FIT export payments at a later date, you will first have to deregister for a SEG tariff. You should speak to your chosen SEG Licensee about how this works.

Further information on the FIT and the SEG interaction can be found in Chapter 1 of the SEG Generator guidance:

https://www.ofgem.gov.uk/system/files/docs/2020/02/seg_generator_guidance_-_final_for_publication.pdf