Ess 24v or 48v? Multigrid or multiplus?

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apple047 asked Dec 6, '19

Ess 24v or 48v? Multigrid or multiplus?

Hi everyone!

I'm at the design stage with my installation, I have some knowledge but not much experience hence I thought it may be a good idea to ask for a second opinion from the community. At the moment I have 6 solar modules 300w Voc=45.3 and 2x 24v 250Ah lifepo batteries I want to set up an ESS with the scope to selfconsume as much energy as possible since there's no more feed in tariff in UK. I'm also planning to get another 12 solar modules in the very near future but on different array/location. We don't have any grid loss, so no generator or other sources of energy are needed. I monitored my daily consumption and it's on average 7kw daily with peaks of 3.5kw except shower which is 10kw but is not reasonable to cover it with that size inverter. Ideally I would consider 5kva,

The question now is

Would you go for a 24 or 48V set up?

What inverters work best in ESS set up? the metering/current sensor will be about 32m away from inverter.

I'm leaning more towards a 48v for efficiency but choosing inverter I find a little confusing, if any more details are needed I'll be quick to add it

Much appreciate your time

Regards George

ESS system design design

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JohnC answered · Dec 06, 2019 at 10:55 AM

Hi George.

'Second opinion'. eh? Mine mightn't rate that high, but for discussion.. Proviso - *no grid feed in*..

Go 48V. For when you're serious, also kit selection. Just easier..

5kVA seems fair for your usage. The 'Mutigrid' model was a one-off, and only 3kVA. Replaced by the Multiplus II (up to 5kVA). Also Quattro in bigger sizes. Take your pick, features, etc.

I like simple, the KISS principle. With no grid export, why do you need ESS? Your grid supply could just be looked upon as a generator alternative.

Your 32m distant 'sensor' shouldn't matter. Not needed.

You don't say much about your pv, especially whether dc- or ac-coupled. Your new array distant too? May need ac kit? Might matter.

Anyhows, just to kick your question off..

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ejrossouw answered · Dec 06, 2019 at 06:15 PM

Hi @Apple047

This is my ESS MPII 3000 48V, LG Chem RESU 10 and ET112 battery consumption chart using the Octopus GO to charge off-peak as I have not done a full solar panel install due to the ROI being pushed out well beyond the 12 years average without FIT.

You can see where the limits of the inverter are reached at 18:00 with ovens etc., but hardly an issue and typically as a result of more than one high consumer running at the same time.

I also have a full off-grid soluton with only 8 panels and only a 77Ah battery elsewhere, but even then the MPII copes with washing machines, dishwashers etc. as long as they don't start together (initial water heating can be a culprit). The MPPT works great to ramp up and supply the heavy consumers and top up as needed with battery during the day. The battery is often charged within an hour or two. My next visit to the property will see it configured to ESS grid parallel as that avoids dealing with the occasional inverter overloads.

PS - FIT will be replaced by new microgeneration scheme in Jan 2020 for which you will get paid, but at much lower rates than when FIT was introduced. Downside is suppliers will set their own rates so don't get your hopes up. With dreadful ROI, UK renewable energy sadly remains only for those with deep pockets and who want to save the planet ;)

In summary:

MP II 3000 will handle most consumers even modern ovens etc, but just not simultaneously. If grid parallel, that however poses no issues as the inverter tops it up with grid.
I am personally a fan of 48V because of lower currents easier to handle and cheaper AWG for installations. (latter benefit is likely lost due to higher 48V equipment cost)
My off-grid installation is also in the garage about 15m from the house it supplies and has absolutely no problems.
Victron kit is designed for marine, although they have branched out into many other areas, so whatever you buy, it is going to last and serve you well.
The image of my off-grid installation and consumption below show well Li and modern mono 300W panels can work. The sun is only in the right spot at about 13:00, but the panels are incredibly sensitive and the Lithium charges very fast. Pay close attention to that part of your setup. Feed-in for me is not an option, but just imagine how much energy is lost in my installation every day when the house is not in use. Another battery is on the agenda, but then they don't come cheap and again even with 8 occupants it will be a struggle to consume all the stored electricity thanks to everything from LED lights to fridges being very light consumers these days.
I keep the fridges running and alarm system too as Lithium actually likes being "self consumed".

Hope this gives you some real world insights for your design.

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apple047 commented · Dec 07, 2019 at 08:41 AM

Thanks @ejrossouw for the time taken, this gave me a lot of useful information, I'm glad multiplus II works with ET112 as I couldn't find this information anywhere. Now I'm decided, I'll go with Multiplus II 48v 5kva it's nice to have a little reserve.

Did you had to use a battery monitor? I'm thinking I may get away without one at the beginning.

Also I would like to have a display of some kind inside the house for monitoring, what's your opinion of that, what is the easiest set up to have it remote away from inverter

Very much appreciate your help

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ejrossouw apple047 commented · Dec 07, 2019 at 12:10 PM

Good choice as the 5kva was not available when I bought mine. Battery monitors are typically not necessary with Lithium as either the internal BMS of the battery or an external BMS unit will provide the most accurate readings. With smart batteries, they simplify system installations and should be the source of truth in my opinion as they typically self balance cells and also monitor each cell independently. Just make sure your battery is truly smart. (With my BlueNova the battery itself connects independently to an internet portal and I can even observe cell level detail or update the firmware remotely if so required) With DVCC enabled, the battery then tells the system what it requires and prevent over or under charging.

As for remote monitoring, I'd do it with VRM using an Octo GX connected to your local WiFi. It will then offer a direct LAN connection option as well via internet on phones, laptops etc. It also offers useful graphs for analysis (you can select widgets) and still has the remore console. I use it for everything today. The below off grid system is connected and managed via a GSM modem. Only exception for upgrades are MP II firmware has to be done via MK3 interface at the inverter.

If you just have the money to burn, a colour monitor in the house can be achieved extending the cable or you can install it in the garage. Personally I found I don't use mine unless I am at the system.

It is easy to buy all the gadgets, but today I'd think twice before buying a pricey colour GX as my experience have shown once the system runs reliably, you only become interested in things that go wrong and not sit and watch little dots entertaining you with the flow of energy in or out of the components.

Enjoy building your new system.

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Answer 1 · 2019-12-06T12:05:29Z

apple047 answered · Dec 06, 2019 at 12:05 PM

Thanks John for information,

I didn't think of the grid to be used as a "generator", fair point

The arrays are not ready yet, I'm designing and collecting materials now. Planning to have everything running for the season coming up, reason I want an ESS set up is because nobody is home during the day and the production will be lost if not stored. My inverter will be in the garage 32m away from distribution board as no closer location is viable,

I'm planning to have 2 victron mppt's from each array charging the batteries so DC coupled as this is more efficient for charging batteries.

Thanks again @JohnC for the hint I'll research a little further the Multiplus II

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JohnC ♦ commented · Dec 06, 2019 at 12:37 PM

I like your dc-coupled plans, tick from me.

But you don't need ESS to leave home. It'll all still happen.

If you're paranoid (no disrespect), maybe a Multiplus II GX with some web, and you can keep an eye on it (& control it) whilst on your next overseas holiday. Ha, don't lay down your hard-earned til you check all this stuff out. GX capability available in many forms. Recommended.

32m from inverter to loads shouldn't be an issue. You could even tweak the inverter output V to compensate transmission losses if needed.

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