question

craigeng avatar image
craigeng asked

Help with 3 phase grid tied solar system

We have a grid tied 10kw pv system... to date we have used just whatever produced power was available at the time without any storage or harvesting.

Due to the horrific jumps in energy cost we would love to harvest the energy to batteries, also we thought to take the low night rate available to boost the batteries while we sleep.

Is there an AC connected device that we could use without going to the large expense of a Powerwall or similar... I was struggling to find a device on here?

Also just to add to this.... I have a stack of little used motive batteries (lead/acid) left from a job, I know these don't compare to Li-ion but I have them so essentially they are free gratis... will any of the inverter charges be able to link to them?

Many thanks, Craig

chargerbatteryinverter rs
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8 Answers
marekp avatar image
marekp answered ·

@Craigeng

You can install 3 Multiplus-II units setup as 3 phase system.

How big MP-II you need to buy depends on your house power requirements.

The automotive lead/acid start batteries will last very short time since they are not meant to be deep discharged but you can play with them to learn the system.

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craigeng avatar image craigeng commented ·
Hi and thanks for your help.....

Just wanted to clarify the batteries I have are deep discharge motive power batteries from an electric vehicle

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marekp avatar image marekp craigeng commented ·
@Craigeng

If they are deep discharge type, than they will last longer than standard starter type but not as long as LFP.

Do not discharge them below 50% and install balancers if they are 12V size.

As for MP-II, use 48V version to minimize DC currents.

If you want your on-grid inverter to produce when grid is gone, it has to be connected to AC-out of MP-II and MP-II must be minimum 5kVA in size on each phase.

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nickdb avatar image
nickdb answered ·

I would encourage you to use victron's battery balancers with 48V banks. It will give the best use out of them.

They are poor for an ESS as depth of discharge is not great, they don't like supplying larger loads and will have a limited life.

I have an assortment of victron gel batteries in the field, at just over 2 years now, they are all wearing out and that was with a max 40% discharge.

The difference between an ESS with Lithium and one with LA is chalk and cheese.

You are more likely to decently recharge a lithium bank in your "cheap" power window than you will LA, with its long charging cycles. ESS systems are way more effective when not using old style batteries.




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craigeng avatar image
craigeng answered ·

So I guess there is no 3 phase unit?

Would I just wire the units as if I were feeding 3 separate single phase supplies?

Would there need to be three separate banks of batteries?

Thanks in advance, Craig

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marekp avatar image marekp commented ·

@Craigeng

Read the page @nickdb posted and you will know everything.

Look at the last link at that page

https://professional.victronenergy.com/online-training

You will find detail video instructions how it is done.

When you go through all, you will now if it is too difficult for you.

I build 6 MP-II 3 phase system practically by myself and the knowledge I accumulated along the way is priceless.

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craigeng avatar image
craigeng answered ·

Just wanted to Clarify the LA batteries I have are deep discharge motive power batteries taken from electric vehicle

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nickdb avatar image
nickdb answered ·

Craig, if you have not done this before, 3-phase and parallel systems are complex.

Get a professional to help you or you will have issues.

There is a lot of reading and training available.

Start here:

https://www.victronenergy.com/live/ve.bus:manual_parallel_and_three_phase_systems#parallel_split-_and_three_phase_vebus_systems

There are no 3-phase products, you configure multiple devices into a 3-phase system, with shared batteries and comms.

This community is not a substitute for qualified installers and there are many newcommers here, some who end up hopelessly out of their depth having jumped into the deep end.


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craigeng avatar image
craigeng answered ·

I was an aircraft high voltage engineer.... I do appreciate your valid concerns about newcommers, but although I am a newcommer I dont imagine I will end up out of "my depth"

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nickdb avatar image nickdb ♦ commented ·
With respect, if you don't understand the products, their integration nor features you already are. Wiring is the least interesting part of making these systems work.

There will be a pro in your area, these devices aren't cheap, get someone on the ground to assist, even if it costs a few bob.


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Kevin Windrem avatar image
Kevin Windrem answered ·

Not sure where you are located. A small number of the inverter/chargers have a UL rating but the Multiplus II and Quatro II aren't there yet last time I checked. You'd probably need UL to pass local inspections.

There really isn't a Victron solution for the US if you want to set up an ESS system and feed excess energy into the grid. Besides the UL rating, you'd also need the power company's approval for feeding energy to their grid. Other countries have different levels of approval and many have appropriate approvals for Victron units.

Tesla PowerWall might be a less expensive solution if you need to invest in a large battery bank. But in your case, salvaging the LA motive batteries may make your initial investment less using Victron inverter/chargers. Do the math to see.

Be sure to read all the documentation available on multi-phase and parallel systems. There's also training at professional.victronenergy.com. Building a multi-phase system isn't rocket science but there are critical things to insure the system is safely installed and configured.

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marekp avatar image marekp commented ·

@Kevin Windrem

Besides the UL rating, you'd also need the power company's approval for feeding energy to their grid.

He already has 10kW on-grid PV system, so feeding the grid is not an issue for him.

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craigeng avatar image
craigeng answered ·

Hi there,

Am in UK.... I find it hard to believe no one produces a dedicated 3 phase inverter charger that will accept LA or lithium????

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