ESS and Multiplus Overload Questions

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bipedalprimate asked Sep 10, '22

ESS and Multiplus Overload Questions

After watching Diagnosing Inverter Overload - by Johannes Boonstra, I need some clarity on overload situations with ESS when in Grid Connected state. I suspect the YouTube is directed more at Multiplus II in Inverter only mode.

At 8:20 Johannes shows this slide:

The significant part for me is the 'rule of thumb the model spec/rated voltage is the maximal current for 30 min'. Reasoning is inverter heats up and power factor is irrelevant - it is based on Amps.

The Datasheet for Multiplus II does not mention this 30 minute limitation but that is Ok - I guess there has to be some limit but the datasheet should not say Cont. Output Power.

At 9:49 Johannes shows this slide:

Here is another mention of the 30 minutes limitation but this time associated with '30% Overload'.

Q1. What is the 30% overload base figure? Is it the 8000VA (35A) mentioned in the first slide which suggests the 30% overload value is 8000VA x 1.3 = 10,400VA (seems unlikely) or is it the other Cont. Output Power of 6400W (28A) mentioned in the datasheet which suggests the 30% overload value is 6400 x 1.3 = 8,320W (seems more likely).

Q2. If the latter, does that mean the Multiplus II 48/8000 is in an Overload state at anything above 6,400W (28A)?

Q3. In an ESS installation with Grid connected, at what point of inverter demand (28A or 35A) is the excess demand supplied from the grid? (Let's assume more than adequate battery capacity & current carrying capability.) It is possible that the answer is both and the Multiplus II adjusts based on temperature of the inverter.

Q4. With regard to Max Power (Peak Power in datasheet?) in an ESS installation with a very stable Grid connected, is the 'Output Voltage less than normal' mentioned in the second slide ever likely to eventuate? Does 'normal' is this context mean the limits that are associated with the Grid Code selected and the associated protection trip settings?

Am trying to understand how ESS works in what may appear to be extreme situations but the answers also explain normal working operation and helps with sizing an ESS system.

Multiplus-II ESS

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Answer 1 · 2022-09-15T04:52:03Z

Alexandra answered · Sep 15, 2022 at 04:52 AM

@BipedalPrimate

There is no real straight forward answer to your questions as installation conditions greatly affect an inverter system.

Q1 and Q2, the datasheets for all the inverters give their peak load capability. So always check those.

Always size an inverter for the peak loads makong sure they are in the nominal ratings. That way if there is a problem with an appliance (such as a pump) you then have the overhead to deal with the overload condition.

With regards to the 30% overload, I can't remember if the slides were talking about a particular inverter it is most likely the newer multi2s. Some like the older Quattros and multis can do a 50% 30 minute continuous overload before shutting down - usually on temperature. This in inverting conditions.

ESS is complex as there is so much customisation you can do. For the most part if you are battery cycling, you need to think of the system as inverting all the time, even though grid is connected. Hence the term self consumption.

Grid is mostly a secondary source of power unless in keep batteries charged state.

So for example your Q3 if you limit inverter power in ESS that figure pulled from grid can vary depending on the settings.

Q4 cant answer dont have stable grid in any manner where we are, so we do size for voltage derating as really the inverter is amp based equipment. Your grid settings will take care of things for you there, but then remember your peaks loads need to be able to be run in inverting mode so back to sizing as if grid does not exist.

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