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victech-power avatar image
victech-power asked

Technical explanation requested on true Power Assist vs (D)ESS power assist like capabilities

We have been installing quite some systems supporting ESS and (D) ESS.
The installation of these systems require lots of reading and proper designwork according to Victron manuals and trainings.

Lately I have come a cross collegue's in the Victron World but also websites selling or telling the story that true PowerAssist is part of the ESS Assistant and ESS Venus OS functionality.
I have also read almost "all material" there is to read and although I have seen "PowerAssist like" behavior in ESS systems, I need to know the technical/design difference.
ESS Documentation is truly telling that the PowerAssist (boost factor) setting is being ignored when enabling ESS.

ESS design and installation manual (victronenergy.com)
Page 8 : The PowerAssist setting in VEConfigure3 will be disabled and ignored when ESS is installed.

Is somebody from Victron Staff, able to explain this ?

Below some questions that I have in general that require the explanation from Victron.
F.i.: What is the technical difference or equality or is the setting ignored but the function is still there ?
Which settings does it then use if so ?
F.i If there are PA like behavior's in ESS but its not quite the same, what is the limitation or design criteria/limitations we need to "watch out for".
F.i. If you run all the loads through the Victrons via AC1 for instance, how much load is that AC1 able to cope with ? Is that the 32Ah as Auxiliary port defined in the spec sheet of the MPII 5000 ?

ESSdynamic esspowerassist
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3 Answers
Alexandra avatar image
Alexandra answered ·

@VicTech_Power

If you have implemented the ESS assistant, power assist (as an option as you know) as a base feature is no longer a user defined setting. That is all the assistant when you set it is telling you.


ESS becomes the control. It being dynamic will determine when to power assist based on the user interaction in the settings in the ESS menu on the GX device.

The amount is assists changes based on

1. the battery level allowed to be used,

2. The input current limit and

3.the availability of solar.

4. Peak shaving if it allowed

So it is now very dynamic. (This is also the reason why some of the other base features cannot be set.) And can no longer a fixed value as it would be by the boost factor x.x that would be set normally under power assist.

If you have done smaller systems you will have seen all the principles in action.

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Alexandra avatar image Alexandra ♦ commented ·
The AC 2 has a rating because it can be switched so also has a limited transfer amount.
The AC1 is not switched so really limited to the input current limit on the MP2 but ideally in system design you would only have the inverters load limited to max invert ability on only. As it will be overloading with no ability to load shed other wise.


A side note on most of the Victron range the input current limit is the inverter capability plus the limit needed to charge at full amps.

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ejrossouw avatar image
ejrossouw answered ·

Not sure what you mean by technical as the manuals very much cover it although here is my summary.

PowerAssist is used in primarily used in mobile installations when hooked up to a limited shore supply. It uses batteries to boost the shore supply e.g. you have a 10A load and the shore is only 6A, depending on the sytem, it can top up the shore with 4A from batteries.

ESS is used for domestic fixed installs with a permanent grid supply. If you have an inverter that can provide 10A to loads, anything over, will be topped up from the grid. Typically the objective is to not use the grid supply. Transfer switch ratings have to be taken into when ACOUT is used for all the loads, although many domestic install only use the ACIN.

(D) ESS is still a work in progress and looks at various things such irradiance, consumption, best tariffs etc. to manage all the available energy sources e.g. charging when electricity is cheap and there is little sun etc. A bit bit like an automated version of an enduser manually setting charging schedules based on tariffs and the next days weather forecast.

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victech-power avatar image victech-power commented ·
Thanks @ejrossouw , but this is exactly NOT the answer I am looking for.

All you write is known to me.

I need to have the question amongst other answered :
Does the "function" power assist gets disabled during the ESS implementation or does the "setting" of the function power assist gets ignored ? Which is it ?

And the response I need I would like to have it techical and not like " the manuals say it all, because they don't !"

And either way : What are the design principles ? because designing for power assist is different then designing for ESS. But is there a design principle that deploys ESS whilst supporting

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nickdb answered ·

It is ignored as per the docs, it would need to be since ESS behaviour is opposite to that of power assist and you can pretty much recreate what it does via ESS settings regardless.

While you can still enable it via veconfigure, it won't do anything as far as I am aware.

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victech-power avatar image victech-power commented ·

@nickdb , you are getting close to what I would like to read, but you I am not satisfied by a statement like "you can pretty much recreate what it does via ESS settings regardless" and I also want Victrons confirmation.

Is the way you describe it Victron's PowerAssist or is it not ?
Or is PowerAssist as a word now more or less describing a behavior and not a designed technical solution ?

Let me put it differently to put you to the test:
If a customer wants a PowerAssist solution and we deliver an ESS setup ( as you say ESS pretty much recreates just that with all the load on the AC1 OUT ) is that then a correct design ?

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nickdb avatar image nickdb ♦♦ victech-power commented ·
This isn’t a support site, if you want victons opinion, log a case with your supplier.

Arguing with people trying to help won’t get more clarity.

The docs are clear. So is the training.

Power assist and ESS are conflicting solutions for different installations, fixed vs mobile.

If you want self consumption and little to no grid usage in a domestic, fixed residence, you need an ESS.

If you are mobile and want to use shore power then you want power assist and can use the new PV priority features as well.

Don’t know what more to add than that.

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nickdb avatar image nickdb ♦♦ victech-power commented ·

Here's an example, maybe that helps.

I have an ESS, current limit set to 37A, my inverters can supply more.

The ESS tries to maintain the configured setpoint of 10W from grid, no more no less.

It will never, ever pull from grid unless there is an issue or my batteries are forced to charge.

If this wasn't an ESS and used Power Assist, it would pull from grid by default for all loads, and only cover excess load above the limit from battery.

This is typically only required by mobile installations where power supply and battery capacity/PV is severely constrained and ESS isn't supported in mobile (off grid) applications.


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victech-power avatar image victech-power nickdb ♦♦ commented ·

I don't understand why you are trying to explain the "behavior" to me.
I already know what you are explaining.

The point is that I find lots of "victron colleage's and websites" selling or telling the story that PowerAssist is working or available with an ESS system.

And I want to understand if PowerAssist like behavior in the ESS setup is to be designated and defined as "Victron PowerAssist".

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nickdb avatar image nickdb ♦♦ victech-power commented ·

You’re getting hung up on semantics.

Power assist is a feature in its own right and unrelated to ESS.

ESS has power assist like capabilities that can be configured in many ways (peak shaving etc), but they are ESS specific and operate within that far more complex framework and referred to by whatever the relevant ESS feature is called.

Maybe the simplest way of explaining it is power assist just describes a group of inverter capabilities in a specific application.

Those same capabilities are used in other applications and features, just implemented differently.

Bottom line is there are different ways to get the system to supply power above a grid limit and they are called different things because of how they are applied.


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