Retrofitting a battery to existing solar installation

Hi,

My situation is that I have a 8.64kwh solar installation with a Solis inverter which was arranged by EON. The system was installed in late August, so I've not yet seen it's full potential, but I have seen it hit around 7kwh output in one instance.

One big regret with this system is that I didn't order a battery to go with it.

In an effort to fix this, I have been researching battery solutions. I'm quite keen on getting a Givenergy system as this seems to work well with Home Assistant without needing "the cloud" to monitor performance and change settings and I do just generally like the product.

My options appear to be:

• Giv-AC 3.0 (or second generation device coming next year) - Does this system, adding to my existing solar installation, require another G99 application? I appreciate this setup is less efficient, but the hybrid inverter for my installation is significantly more expensive and I like the "separation of concerns" of a separate inverter. I don't really care for exporting to the grid using this setup; I only want it to support my own usage. Could I just set it up to have zero grid export (or somehow have it wired to prevent grid export) and then skip the G99 application?
• Giv-HY 5.0 Gen 2 (replacing the existing Solis inverter) - I assume as the power output of this is lower, I wouldn't need a fresh G99 application. Is that right? This setup would tap out at 6500w when it has 8640w of solar panels installed, unsure if that should be a concern or not?

It's worth mentioning the existing installation is being paid for via a finance arrangement, so I'm unsure if I'm even allowed to replace the existing inverter.

My question(s) is/are:
If this was your situation, what would you choose? Am I able to avoid a G99 application using either option? Any thoughts on anything I may have not thought of?

I am not an expert on any of this, and have had to self-learn, so I might be asking stupid question. Very sorry if this causes frustration.

ribs Adding capacity (ie battery storage) will need another G99 but it should be a trivial task to complete. As long as you volunteer to limit your export to whatever your existing G99 limits you to, it should go through as G99 fast track with no cost to you and should be agreed within a few days.

The existing installation is owned by you although you have finance for it, so you can do what you want.

Personally , I’d swap out the inverter for a Givenergy HY5 to reduce complexity but it adds cost. Your choice

Thank you Tim, that's very helpful.

The existing G99 "answer" (certificate?) from the DNO was never sent to me. Is there a resource online where I could download it? Getting ahold of EON is a little tricky these days.

As long as your Solis Inverter is of the Hybrid style then you should be able to easily add batteries to the system. Saves on expense and complications. You would also have to pay VAT on the new equipment - its only 0 VAT for a fully system inc PV panels

I added a AC3 and 5.2kw battery to my solar edge system in may this year. It was totally worth it.
Yes the DNO approval took an age but worth wait.
Adding the battery has allowed me to use 90% of solar production in November.

ribs You do need to get the DNO agreement letter from EON as you'll need it (and MCS certificate) for SEG and also if you ever move house. Our paperwork arrived with the handover pack, but it was a few weeks after commissioning was completed.

Tim Oh dear. Well I'll add that to the list of "you should have done this already" points to my complaint to EON as I've had nothing of the sort sent to me. We're at the brink of the Ombudsman getting involved now so that should be fun. And I use the word "fun" quite wrongly.

On the plus side your advice has been very useful. Thanks again.

dragon2905 Sadly not. It's just a regular solar inverter with no provisions for battery connections.

I'm aware of the VAT situation. It's a shame I didn't opt for the battery at install time, but as you can imagine, the situation between January when I ordered this setup and today has changed a fair bit!

Live and learn.

With that size of 8.6kw PV array you would be better off going for a separate AC Coupled system.

If you want to replace the entire Inverter and add battery(s) then GE wouldn't be the way to go due to the maximum PV DC limitation.

Personally I would look at an 8k SunSynk Hybrid Inverter but it is very likely to come down to availability of most things.

If you stick with AC you will save money and if you have an EV, be more easily able to read the excess solar for summer charging.
The main thing I would be looking at is the maximum load that the battery can cope with a Gen 1 Givenergy battery only outputs 2.6kw (2.4 with losses?) the Gen 2 stuff is much better at over 3kW.

dragon2905 @ribs The 8.6kW array does exceed the headline capability of Givenergy's hybrid inverter. However, if you know tomorrow is going to be a sunny day, simply reduce battery charge power during the shoulder PV periods and ramp up to maximum during the maximum PV period. The gen1 HY5 would push 5kW to supply house load (and export/Eddi/Zappi etc) and 2.6kW to charge the battery. If the conditions were perfect, it would result in a loss of (8.6-7.6) about 1kW to clipping. The gen2 HY5 can do 5kW to AC concurrent with 3.6kW to battery, so the issue will be to have enough battery capacity needing charge during the peak periods. This would reduce complexity although what impact it would have on cost, I can't say.

dragon2905 Yes, this was consideration for me as well.

The panels are split east/west (although the roof is very shallow) and the existing inverter is limited to 8kwh max input. Unfortunately it was installed as just the wrong time of the year to see it's full potential, but I did see it nudge 7kwh a couple of times in early September.

From what I understand the Giv-HY 5.0 Gen 2 product will tap out at 6.5kw, so it's a question of how willing I am to give up the extra potential 1.5kw during peak generation. Whilst I understand I'll lose a little with the DC to AC back to DC conversion of the stand-alone AC unit, it's not a huge deal to me. I quite like that the solar inverter will just do solar, and the battery inverter will not only charge from solar excess, but will also charge from cheap rate using something like Octopus Go or Agile. If anything, it's more about being able to charge from the grid as my lifestyle mostly allows me to push my peak electricity usage into the daytime anyway.

I don't think I'll be "unhappy" with either solution, and Tim's reassurances on the G99 aspect of it makes it into an availability and cost of equipment question rather than anything else. I think I'm giving up something either way.

As mentioned, Givenergy isn't the only game in town, but it's a front runner for me. I appreciate nothing is perfect and life is full of trade-offs but this comes with some features I quite like and seems to be a bit of a favourite for installers around my area.

I am wondering about the Gen 2 AC inverter and if anything from that would be worth the wait. I don't know if any resource exists anywhere comparing Gen 1 to Gen 2 in general. It seems that Gen 2 batteries work just fine with Gen 1 inverters with a converter cable. I don't know if anyone has a summary of feature differences between them?

IanMac Did I read somewhere that the yet to be released Gen 2 AC unit would be able to output 5kw, or did I imagine it?

ribs the gen 1 AC inverter can charge/discharge at 3kW, there's talk on here of a gen 2 that can do 3.6kW. Not worth the wait in my view as the 3kW should be more than adequate for >99% of the time.

The gen 2 battery can be used instead of/alongside gen 1 batteries, but has connectorised terminals.

ribs Giv-HY 5.0 Gen 2 product will tap out at 6.5kw

The Gen 1 HY5 is capable of 5kW PV-AC and 2.6kW PV-Battery at the same time. The Gen 2 is capable of 5kW PV-AC and 3.6kW PV-Battery also at the same time, so a total of 8.6kW. You would not be giving up any potential with the Gen 2 as long as your battery was able to sink 3.6kW PV-DC for the peak duration. BTW Givenergy's gen 2 hybrid inverters all have the same hardware; it's the firmware they run that makes them either an HY5 or HY3.6.

ribs
If your PV array output is greater than the capability of your inverter then you are risking damaging your inverter. There's a reason why they have stated capacities.

You would literally have to disconnect some of your panels to prevent permanently damaging your inverter.

Can't comment on the Gen 2 AC Inverter as haven't seen any specs on this at the moment. Assuming that it will be the same as the, comparison between the Gen 1 & Gen 2 Hybrid inverters (in that they are the same product except for firmware) , will unfortunately only lead to misinformation until the specs are actually available.

Tim 99% certain that you are mistaken.

Gen 2 HY5
Max string inputs is 2 strings with a combined 6500w DC (its typical for inverters to have built in Over Provisioning)
Gen 2 max output is 5kw
Gen 2 max battery discharge is 3.6kw
Its not a case of adding the two numbers together which means that the max combined is still 5kw just that your battery can provide upto 3.6kw of the available ac power when you are generating low amounts of PV electricity.

Gen 1 HY5
Max string inputs is 2 strings with a combined 6500w DC (its typical for inverters to have built in Over Provisioning)
Gen 1 max output is 5kw
Gen 1 max battery discharge is 2.6kw

I went AC coupled when we had our array installed. In my case it’s because I wanted integration with the ME Zappi as a hybrid system wouldn’t do it properly.

Haven’t really regretted it, I have more flexibility as I can get contributions from both solar and batteries simultaneously if require (whereas with a hybrid you’re limited to its rating (5kw or whatever it is) as a combined figure.

Only issue really is the conversion losses from DC/AC..

dragon2905 99% certain that you are mistaken

You are right, as far as the gen 2 datasheet goes, maximum input is 6500W! I must have mis-recalled something @hoggy had posted about maximum throughput. However, that means that the 6.5kW can be split anything from 5kW AC and 1.6kW battery to 3.6kW battery and 3kW AC. There is the nominal 150-550V MPPT input voltage with a maximum at 600. I don't know whether the 600V is an absolute maximum or if the inverter can to something with internal impedance to pull the voltage down. However, depending on roof orientation, (especially East/West split), the panels are unlikely (IMO) to see the full voltage of the series-connected panels on either MPPT at any time of year.

As regards maximum AC output of the gen 1 and 2 inverter, that looks to be 5kW whether from PV or PV+battery; it's just that the inverter could charge the batteries with surplus PV if the house load was the full 5kW.

@Tim Yeah so the datasheets are not correct. Dan himself (GE Lead Engineer) has stated that Gen 1 will do 3.6 + 2.6 / 5.0 + 2.6 if called upon and enough PV is screwed to them.
Never did bottom out Gen 2 stuff but seeing as there were rumours of those getting a further boost i'd assume they would pull similar tricks. The post on that is floating about somewhere.
He did say that string voltage is the limiter, so I wouldn't recommend pushing them too near that.

GE's datasheets are notoriously "fluid" - a situation that is not helpful (everyone noticed we've gone back to 80% DOD on the 5.2 & 2.6 packs yet?)

EDIT: Here is the post about it
Bonus fun fact - the 3.6 & 5 G1 Hybrids are essentially the same. They can be unlocked by GE remotely to give you a Hy5.0 out of a 3.6 if needs must.

dragon2905 Wise words. Thank you.

I used the assumption from the PC building world, where you can fit a 300w PSU or a 3000w PSU and the computer will essentially "take what it needs a leave the rest" without damage. I guess I was being a bit naive there, but as I said, I'm learning as I go with this stuff.

I would imagine a competent installer would have spotted the issue before any damage was done, but that might have ended up costing me time and money which I wouldn't have wanted to waste in any case.

Thank you.

ribs it's common design practice to have a PV array with a peak power output higher than the inverter power output to cope with typical conditions. But the open circuit string voltage at low temperature must be lower than the inverter's rated DC input voltage. Following your PSU analogy, its fine to have a higher power rating, but you wouldn't want to the PSU to put 12V on the 5V line to the motherboard.

Tim I think you are mistaking input and output capabilities.

The 5kw Hybrid is a 5kw rated inverter - it has over provisioning capability on the DC side (Solar Panels) of 6.5kw on the DC
Input side - That's a stated rate.

Ribs has an 8.64kw Solar Array and has already mentioned that he thinks he has seen 7kw recently (ie in winter). If he had connected that to a GE 5kw inverter he would have damaged it irreparably.

On the AC Side the maximum output for the inverters is 3.6 or 5kw - there is no overprovisioning feature on the AC side.

So if the Solar is producing 6.5kw then the inverter will deliver 5kw on the AC side to your house/grid.

If the Solar is producing 4kw and, assuming your requiring 5kw for your house load, then the battery will delivery the additional 1kw, total 5kw.

However the AC output from the battery, through the inverter (there is a DC to AC conversion), is rated for a maximum amount which depends on the Generation and the Size of the Inverter.

hoggy thanks for that, hadn't seen that anywhere.

I can only say that it doesn't appear to be qualified by my own data during summer 2022 - Gen 1 5.0HY + Gen 2 9.5kw Battery - maximum battery output was 2.4kw (the original number on the spec sheet) with solar of 2.6kw giving 5kw maximum.

Its possible that firmware updates have altered these numbers though.

Is it possible that what DAN meant was that if your solar is producing 6.5k and you have an 5kw inverter plus a battery that the inverter will convert 5kw DC to AC on load side and 1.5kw DC directly to the battery?

The reason I ask is that this makes sense as the GE Batteries are DC so the Hybrid inverter pushes DC straight to the battery and only converts the Solar DC or Battery DC to AC when required.

I think it's a little dangerous to base decisions on forum posts by GE staff. Installers will certainly only look at the available specs on the Data sheets.

ribs your welcome.
I think you may have an issue due to the finance and would likely have to look at an AC Coupled System in addition to your current setup.

Just realised that you didn't state what Solis Inverter you had installed by EON. It's possible that it is already a Hybrid?

Regarding the G99 Application - as long as the installation is EXPORT RESTRICTED to under 3.68kw - then the form can be submitted AFTER the installation and WON'T FAIL - it will still take upto 90 days to be approved (ours took 92days).

dragon2905 Sorry I probably didn't make that clear: It's a one way (charging) thing.
At all times AC output your stuck with 3.6 / 5kW > AC from any blended source of PV or Battery.

The 7.6kW trick can be pulled only if:
You have enough panels & they aren't too hot.
You have an empty battery
You have enough Sun

Only then you dump 5kw to AC & another 2.6kW to the battery.

Very rarely can I get mine to do it (it's often fully charged already by midday), however I've an odd setup with 6kW of panels on 2 strings & a further 2.5kW of additional battery storage I can inject on top of that into PV string 2. On some trials in summer I did get over 7kW, so it is possible - I just ran out of amps on the MPPT for that string to get the max!

The 2.6kW limit on Gen 1 is down to the busbar internally (so no magic firmware to lift it I'm afraid)
Gen 2 removes this bottleneck with some potentially hefty abilities if this exchange is genuinely correct.

dragon2905 Is it possible that what DAN meant was that if your solar is producing 6.5k and you have an 5kw inverter plus a battery that the inverter will convert 5kw DC to AC on load side and 1.5kw DC directly to the battery?

I think that's what @hoggy said and it's what I meant except that (according to Dan) the HY5 can output 5kW AC and 2.5kW (or 2.4 or 2.6, whatever figure your battery can take) DC to battery concurrently given sufficient PV. The datasheet does state a maximum PV voltage of 600V but the normal operating maximum is 550V and each string can have a maximum input current of 11A. Think that works out at (550x11x2) 12,100W which is way over the stated power rating.

Exactly how the apparently over-sized maximum input rating is reconciled with the stated rating of the inverter isn't clear to me at all. The panels I have are rated at a maximum of 11.04A and 35V (power) and 41.9V (open circuit) and with a 550V string, there could be up to 14 panels, giving a maximum open circuit voltage of 588V and at power of 490V. At those values, maximum input per string would be 5,390W. Obviously, there's a reason not to put that many panels on one string, but I don't know what it is, nor whether such an installation working at maximum output would actually damage the inverter. Perhaps it's to do with the size of busbars within the inverter?

dragon2905 GE Batteries are DC

All batteries are DC.

dragon2905 Regarding the G99 Application - as long as the installation is EXPORT RESTRICTED to under 3.68kw - then the form can be submitted AFTER the installation and WON'T FAIL - it will still take upto 90 days to be approved (ours took 92days).

A G98 can be done retrospectively. If your installation is above 3.68kW, it comes under G99 (G100 from May 2023) and must be submitted and approved before commissioning. If an installer proceeds prior to getting DNO agreement, they are working outside the regulations. They can install everything, just not connect it to the grid-connected consumer unit. Offering to limit the export to 3.68kW (or another previously agreed value) means that the G99 can be submitted as a fast track application which should be returned relatively quickly (within a few days with our DNO).

dragon2905 I think it's a little dangerous to base decisions on forum posts by GE staff.

Couldn't agree more; use the forum to improve knowledge, work out who seems to understand things and then talk to your potential supplier as a better-informed potential customer.

Hi everyone,

Just wanted to say a big thank you again for helping me so far.

One recurring question was around the existing installation being a hybrid inverter already. Sadly it seems not. I hauled my fat backside into the loft today and tried to get a good picture of underneath and the front of the inverter. Long story short: I'm fat, not very nimble, and I don't trust myself to get close enough to the inverter to not put myself through the damn ceiling.

So the closest I got was this shot of the front: https://imgur.com/LRfxHwt
And this shoot underneath (which is a terrible picture, but I don't think there is anything for batteries there): https://imgur.com/tiqUR57
Plus from what I can see online, the hybrid style have got a much larger screen, presumably to show where the electrons are flowing: https://www.itstechnologies.shop/products/3-6kw-hybrid-energy-storage-inverter-with-dc-switch-for-solar-battery-storage?_pos=10&_sid=862e11d0a&_ss=r

So I think that one is done. Sadly. Would have been a nice way around it.

So I'm back to Givenergy. Which might be better anyway as I suspect it has the features that I want and has home assistant integration. And I do kinda want the solar installation to be left alone for the most part.

I'm thinking the AC3 with 9kwh battery. I might wait for generation 2 on that one as it wouldn't necessarily be the better features, but I'd bet the newer devices will get firmware updates for longer and probably have more CPU and RAM capacity to be smarter for longer... or something. Maybe.

Silly questions, if you'd indulge me a little longer...

• If I could "source" a battery and inverter "kit" (brand new and legit, nothing dodgy from eBay or whatever), is it likely that an electrician would happily install it for me? I appreciate they would have to be givenergy trained for the warranty to be valid and I can't just get anyone. But is that a thing? I don't want to wait several months for the damn thing. I want to switch to Octopus Agile/Tracker in July when my existing fix ends so having everything up and running before than would be nice.
• What paperwork would I need beforehand? Tim said it was the "DNO agreement letter" and "MCS certificate". Anything else? Can we make do without that if we set the battery to 0 export to the grid? EON are still being unbelievably incompetent to the point where I think they've actually lost some paperwork...

Hi,
I don't know if it is possible, but if you can't get your DNO letter from EON could you try going directly to the DNO. Here is a link, showing who the DNOs are for different areas of the country. It explains a bit about what they do.
https://blog.spiritenergy.co.uk/homeowner/dno-permission

I don't think EON have their own installers they sub contract out. Their web site says
"We want to make your solar journey as smooth as possible. That's why we only work with MCS accredited solar panel installers. " Get a friend to ring them up and say they are interested in solar panels but they want to know who will be doing the installing as they would like to discuss some details with them prior to install. If you can get one , or several company names you may be able to ring round, find who did the work and get the MCS certificate from them directly. Alternatively contact MCS directly
https://mcscertified.com/consumers-communities/certificate-queries/
They won't re-issue a certificate unless the installer has gone out of business, but they should be able to tell you your MCS certificate number and the name of the installer so you could use that to find and contact them.