My first invertor. Help me choose.

[paulca]

Basic fixed requirements:  24V 220-240V off grid, pure sine.

Less fixed requirements:  Easily support at least 1kW output, without fuss or hassle.

Battery supply:  8S 1P 105Ah LiFePO4 24V pack.  Rated for 1-2C max discharge, 0.2C preferred.

I'm wrapping that in grace and taking.  1C 105A and rounding that to 100A at which I will be "breaker'ing"/fusing the battery.

So the invertor has 100A @24V MAX (at this upgrade level).  That is 2.4kW - losses.

Load side:
My aspirations on the load side are moderate multi-hour run times of ~100-250W.  And experimental short shots of 1kW.  ISLAND style.  ie.  a single 4 plug extension running off the invertor.  NEVER mixed with the grid phase. 

Earthing/Grounding:
The inverter will be terminated on the AC side in a small consumer unit.  The house wide PE ground will be attached to all metal casings, including the solar MPPT controller and thus the battery -. 
Question!!!:  I am led to believe, if you want a proper AC circuit that will for example pass a plug tester, you are required to bond the invertor Neutral to the house PE.  This will prevent the NE fault.  It will also reference the neutral and earths to the same potential as the grid mains phase neutral.  Finally it will allow the ground fault protector to function correctly on the "off grid" extension.  Is this correct?  Are there any concerns with any potentials building between the neutrals and current flowing between the two?

Future proofing:
The final deciding factor for this system is the space on the garage roof for panels.  Due to shading of the sunlight on that roof there really only is room for 3 panels portrait or maybe at a push 2x2 landscape.  That ultimately limits this system to around 1000-1500W solar.
I currently have a 40A MPPT (EPEver Tracer4210AN) which supports up to 1000W with a 50% oversizing margin up to 1500W, but limited to 1000W battery charge.
I can add more solar controllers of course.  (I have another smaller MPPT, but it's common positive and I don't want to play "that" game with floating 41V DC systems at opposite polarity sitting beside each other.)
The battery can and will obviously continue to expand.  8S 1P will take a few months to build up enough disposable for another 8 cells, but that is the plan.  Maybe (finance dependant) go up to the 280Ah cells (£1000+ for .

That is mind, a 4kW invertor sounds like a good future proof.  However.  Regardless of how big the battery really gets, I feel it only prudent to keep it's current limit to 100A.  Not least because >100A = expensive hardware.  So a load greater than 2.4kW will require the step up to 48V and 16S.  I don't see that happening with this particularly system.  Given the panel power restrictions, keeping it as a 24V, 100A system seems safe and fair.

So... if I want 2.4kW I should aim for a GOOD 3kW inverter or a mediocre 4kW.

My eyes are on one of two invertors.

Branded/warranty/certified:
A Victron Pheonix 1kW 24V:  as an interim.  £450!

Less well branded:
An EPEver IP Plus 3000W:  £400 w/ shipping.

The MPPT is EPEver, which provides that "same eco-system" appeal.

Does this sound like a plan?  Any suggestions?  Dos, don'ts?

[paulca]

The "island" load.

This is where I have concerns.  Concerns around my understanding of some of the potential pit falls. 

One plan I have is to unplug a power extension "bus" in the office and connect it to the invertor.

The office has 2 mains buses.  24/7 and switched.  It is the switched bus I want to periodically run off the invertor.  The loads it runs include:

Umpteen DC bricks supplying 19V, 12V or 5V DC to appliances like PC Monitors, desktop speakers, a bunch of LED lights and the entirety of the electronics bench.

Obviously most of that stuff is floating.  The earth referenced stuff won't matter as the "island" phase will be referenced to the same earth.  None of the appliances have dual power.

The only concern would be the signal and DC power that goes between devices.  However, all of those signals and low voltage DC items will be floating and probably galvanically (save for a few Class Ys) isolated.

How much of a concern will those "class Y cap leakages" be for a dual phase system?  I assume this is a common thing on USA split phase 120/240V  systems, so it can't be that big an issue.  Maybe my unfounded concern would be that enough leakage current coming from the "island" phase leaks to the house earth and gets seen by the ground fault protector and causes potential (pun) "nuisance trips".  Thinking about this though.  The inverter circuit provides it's own perfectly adequate and low impedence neutral and earth path so, why would ground leakage current decide to go via some other applicance and onto the other circuit when it could just go via the sub ohm route via it's own power cord.

[jonpaul]

get a stock sinewave UPS, eg APC, these use 2..4x 12 V AGM or SLA battery in series for a 24 VDC inverter ( not invertor !) bus.

A 240 V UPS does exactly the desired function

Beware the duty cycle limit

Jon

[paulca]

Yeah.  My time with lead acids is over.  50% DoC?  300 cycles?  My 100Ah Marine lead acid which I decommissioned after running 365 days a year on a 50W panel and has charge my phone etc for about 3.5 years.  You would be lucky to get 3 amps out of it before it drops below 12V and not much more than 10Ah before it's below 11V

Even after I had it in service for 6 months, taking it off a solar panel controller fully charged... it struggled to start my 2 litre petrol car.  It's a honking great boat battery!

So.  Never lead acid again for cyclic purposes.

[nctnico]

Likely you overcharged it. Lead acid doesn't like that but good lead acid chargers are rare. A traction battery (which is made for cycling) should last a long time if you don't let the charger apply too much voltage to it.

[paulca]

Likely you overcharged it. Lead acid doesn't like that but good lead acid chargers are rare. A traction battery (which is made for cycling) should last a long time if you don't let the charger apply too much voltage to it.

Why would a lead acid charger over charge a lead acid battery?  It was charged 14.40, occasionally equalised at 14.50 and floated at 13.6.  The panel charging it topped out at 2.8A

I think the issue is, I got sold a "Marine Start" battery.  Not a Marine deep cycle.  So it ended up with a surface charge memory or something.  It would recover some when it was given a full charge from 11V at high 10 amps once a year.  But I only started to do that after it became weak.

Anyway.  Compared with lithium, if you can afford lithium, lead acid are not worth considering. 

[nctnico]

Likely you overcharged it. Lead acid doesn't like that but good lead acid chargers are rare. A traction battery (which is made for cycling) should last a long time if you don't let the charger apply too much voltage to it.

Why would a lead acid charger over charge a lead acid battery?

Poor design. One of my customers does traction battery repairs (desulfation / cleaning the plates). His business exists due to crappy chargers.

[paulca]

So the inverter I choose turned out to be out of stock.

It pushes me up to a more expensive Victron Multiplus.

This lacks a few out-of-the-box features the EPEver unit had.  The one I wanted was the "prefer solar, prefer battery, last resort "shore power".  I believe the Victron Mulitplus can do that and can be configured so over the VE-Bus, I just haven't worked out how much extra victron garbage that takes me to buy first and what I can hack instead.

Anyway, without said feature the Victron, without additional config will favour "shore power".  However, if "shore power" is set to a 5 Amp limited supply and fed from a standard UK plug with a 5 Amp fuse, I can switch it myself with a smart switch.  (13Amp smart switch, so should be good for 5 Amps).

That takes care of "islanding" issues or getting any sign off as it is basically nothing more than a "Caravan setup".

[gf]

At the low-cost end, an off-grid inverter/charger like for instance this one may possibly fulfil the requirements you mentioned in the initial post. It's currently offered for ~180 GBP.

[paulca]

At the low-cost end, an off-grid inverter/charger like this one may possibly fulfil the requirements you mentioned in the initial post. It's currently offered for ~180 GBP.

I browsed around some of that end on AliExpress.  Also on YouTube.  Turns out, unsurprisingly you get what you pay for, mostly.

I went ahead and order a Victron MultiPlus 24V/800VA.  It only supports 400W constant output (700W at 25*C before it heats up and peak load 2400W which should make a motor doesn't trip it), but that's more than I need.

Turns out it was only £65 more than the EPEver and it's shipped, warrantied and supported in the UK.  Making it returnable.

[paulca]

One clunk in the workings.

A thread I had on a local builder suppliers forum produced some goods.

On regards to regulations of an off grid inverter importing for charge or backup only... fine.

Under the following stipulations. 
* If it is powering a single extension socket and the inverter is design for that purpose alone.  It will not be earthed and it will be labelled as such.
* If it is powering more than a single appliance it must be earthed and neutral bonded.
* If it shares any conductor, including neutrals and earths with the "utility/network distributor" it is subject to the islanding export regulations or at least parts of.

It's that later point.  It cannot share the PE the utility provider gives me.  It would need to be "TT".  Which has potential issues (bad pun).  Ground potential (multi ohm) issues between equipment powered from one from the other.

[gf]

I went ahead and order a Victron MultiPlus 24V/800VA.  It only supports 400W constant output (700W at 25*C before it heats up and peak load 2400W which should make a motor doesn't trip it), but that's more than I need.

Is the built-in anti-islanding of the Multiplus sufficient in your country?
[ For Germany, only the Multiplus II has the VDE-AR-N 4105 certificate. ]

[gf]

On regards to regulations of an off grid inverter importing for charge or backup only... fine.

I'm unsure whether the Multiplus can be considered a pure off-grid inverter, since it can export, and it also can "mix" utility power and inverted battery power in order to power the loads.

[paulca]

I went through the manual and there is only one reference to back feeding the grid.  It's buried in the prelim about having to select your local regulatory code you want it to comply to.  However it's like a generic statement addressing "Multiplus/Quattro".  That covers the whole range of the Multiplus, Multiplus II right up to the 8kW monsters.

There is no further mention of back feeding the grid in the manual:
https://www.victronenergy.com/upload/documents/Manual-MultiPlus-Compact-800-1200-1600-EN-NL-FR-DE-ES.pdf

Also, when you go searching for the G99 certification, you find them (the smaller MultiPlus models) not even listed.  It's only the MultiPlus 3kva and up are listed.

Also their status has been changed to "awaiting information", which actually puts their certification into a "up to the DNO" status.

I will reach out to Victron and confirm if, or if not this can be configured to export or "parallel to the grid" mode. 

[gf]

See here: https://www.victronenergy.com/media/pg/Energy_Storage_System/en/ess-introduction---features.html

EDIT: [ But I'm unsure whether the small Multiplus models support ESS. Multiplus II certainly does. ]

EDIT:

Note that ESS can only be installed on VE.Bus model Multis and Quattros which feature the 2nd generation microprocessor (26 or 27). All new VE.Bus Inverter/Chargers currently shipping have 2nd generation chips.

Feed-in is optional, and can be enabled or disabled depending on local regulations.

EDIT: The PowerAssist feature (supported by the small Multiplus models, too) also requires the inverter to run grid-tied, in order that it can mix grid power and inverter power to supply the load. So it certainly can run grid-tied, at least in particular operating modes.

[Robert Smith Eco Warrior]

Hi.
We are off grid and use two Victron 48/3000 Phoenix inverters, one of which is currently dead because I gave it too much abuse.
I would go big!
I would go for 4+ kVA if I could afford it.
The 3kVA unit works fine but I would rather it had a bit more spare capacity for when my two kids are glued to a laptop each and my wife has the washing machine on at the same time.
You can't get wiring diagrams or useful technical help from Victron. You would have to send them the unit for repair. They will not sell you boards or parts.
Beware of motor starting. My 2kW angle grinder and 2kW Dewalt saw really make the 3kVA inverter grunt and flicker the overload LED on start up. The 3kVA unit can run to 6kVA for very short durations for motor starting but I still feel it is hard on the inverter.

I use a 230v ac single phase to 230v three phase variable frequency drive for my workshop machines. That is great as it has a programable acceleration ramp so it ramps up the speed steadily and correspondingly loads the inverter in our battery shed gently. I run a 3hp metal working lathe, 3hp compressor, 2hp table saw 2hp woodturning lathe off the same variable speed drive. (one at a time).

I originally went down the APC 5kW uninteruptible power supply route. That went bang very quickly. They are not designed to be used for long periods or have power tools connected to them. That was a waste of money.

Also use ceramic fuses not the cheap plastic bodied 24v truck / car fuses. I had a 80a plastic bodied fuse on our solar input. With about 60 amps continuous for some hours it made it start to smoulder and smoke. The ceramic ones are safer in my opinion.

Also Victron units are 'parrallel connectable' to get more power by linking the two units..... What they don't tell you is the circuit board, chip and software inside the two units has to be the same. I have two 48/3000 inverters that say 'Parrallel connectable' on the front but they are not because one is a bit older than the other.

[paulca]

Can of worms.  Looks like it may be returned before it arrives.

It's looking much more likely, as this is a fixed installation within my property, that it comes under "DNO Connection" requirements.

Thankfully, it will be the lesser of the two regulation classes "G98/NI".  This only requires the connection to the grid is "Notified" by a certified engineer within 30 days of commissioning.  This is done via an online form.

However, it states bluntly that the device is required to have a test and compliance certificate for G98 (NI in my case).

Victron do not look like they care.  They have got their latest and greatest Multiplus-II and Quatro's certified, but there is a rumour that's as far as they are going to go, they will not certify their back catalog.

However they are still selling them.  Still saying they can be connected to the grid.

I'm thinking I'm lucky I bought in the UK and can return it as "not fit for purpose" and buy another one.

[paulca]

The annoying thing is the EPEver unit might have been a better option as there may have been ways to make that a "consumer device" "battery charger" with a plug on it and play ignorance.

However the Victron inverters all use the same topology, regardless of the model or what configuration it is used in.

The AC is generated from 25kHz PWM and then transformed up to line voltage.  However, the AC-In is then phase locked with the inverter and a physical relay connects the inverter directly to the AC-Input.

The ONLY thing stopping it feeding the grid is software and the output voltage of the transformers.  By keeping that lower than grid, all power is incoming.  However a DNO is not interested in that one bit.  It CAN feed the grid, it's generator output is DIRECTLY connected to the grid when in operation.  This it is classes as "Generator equipment" and must conform to G98 or for >8kW G99.

[paulca]

I could still play ignorance and put a 13 Amp plug on it and treat it like an RV power supply for my garage and if the DNO gets wind and sends me a letter I can deal with it then by unplugging it and replying, "What inverter?"

[paulca]

Oh.  Remember this is a "Solar shed" project.

The talk of 4-8kW inverters and roof solar is a different project.  I'm looking at budgetting a house roof solar system, probably straight grid-tie, bog standard 5kW East/West setup.  That WILL be a big company install.

[gf]

However, it states bluntly that the device is required to have a test and compliance certificate for G98 (NI in my case).

Victron do not look like they care.  They have got their latest and greatest Multiplus-II and Quatro's certified, but there is a rumour that's as far as they are going to go, they will not certify their back catalog.

It's not only a matter of willingness. At least for Germany, the small Multiplus models are not eligible for certification, because they have only a single relay between AC input and inverter. However, German VDE-AR-N 4105 standard for anti-islanding requires two redundant relays for safety. The newer Multiplus II models have two redundant relays now and are therefore elligible for certification. I don't know whether UK regulations require redundancy, too.

[Robert Smith Eco Warrior]

.....
The AC is generated from 25kHz PWM and then transformed up to line voltage. ........

This guy says 20kHz
https://youtu.be/UPfUn5ki7OM?t=117

[paulca]

.....
The AC is generated from 25kHz PWM and then transformed up to line voltage. ........

This guy says 20kHz
https://youtu.be/UPfUn5ki7OM?t=117

Thanks for the correction, I remembered it wrong, having watched that same video

Interesting how in it's "Eco" and search modes it can drop back to much lower switching frequencies.

I think at this stage it's up to my DNO.  I have reached out to them and regardless of the ENA requirement or not it's their choice.  They can and do approve installations which don't have the ENA cert, it's up to them.

In the meantime.  I can still run it with it's AC input disconnected.  I lose any mains backup or fall back and I can't charge the batteries from the mains, but I can still produce island power with no connection to the grid.

Just need to find a suitable 'local' earth for the island.  Cheating, darkside, just use a PE from the house.  Better use the old copper heating pipe that goes underground from the garage too the house.  Best pay a spark to put a ground rod in alone, pre-emptively for getting DNO approval or a different inverter.

I haven't dug into it enough, but there is some allowance for DIY electrical installations.  Additionally as the installation is G98 and not G99 it seems to suggest you can go ahead and do the work, even DIY, as long as the relevant engineering paperwork/application is submitted by a certified spark, after installation.  So there must be provision to pre-commission test the equipment, no?

The risk there is, something happens to the inverter in "test" mode and the DNO reply with "Denied.  Please decommission and disconnect." and Victron won't accept the used return.