question

lukas avatar image
lukas asked

Only Power Critical Loads from Battery ESS

Hi,


System Brief:

MP-II 3kW, MPPT Solar Charger (150/60) and a 225Ah 48V Battery, ET340 and ESS, system is configured without feed-in to the grid. The System is grid parallel and always connected in germany.


Is there any way with ESS to only power critical loads from the battery, aka. stop powering loads connected on the AC-IN of the MP-II and only power those at AC-1 once solar power is too low to sustain the AC-1 loads? Use case would be to use execess solar power for AC loads on the input of the multiplus but stop doing so once the system is on battery. The AC-1 loads should be always-on and powered from the MPPT and the battery.


Lukas

Multiplus-IIESS
3 comments
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Paul B avatar image Paul B commented ·

please show a diagram of what you are proposing to do, this will give everyone a clearer picture

Thanks

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lukas avatar image lukas Paul B commented ·

Noting fancy, in this setup, just a regular ESS with grid meter:



It would be great to limit the usage of battery power to critical loads only, but have the pv charger power critical loads, AC loads via the input of the MP-II and of course charge the battery. When no more solar is available (or not enough power for critical+ac loads) then the system should not power AC loads via the batteries but only the critical loads on the output of the MP-II.

Is this possible? Otherwise I will most likely switch back to the no-energy-meter configuration - the battery is sized to power the critical loads overnight but not the whole house with ac loads...

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Juha Tuomala avatar image Juha Tuomala lukas commented ·

The same issue here, I have steady 300W in critical loads output and some huge loads before the inverter. Once ESS starts discharging battery, inverter feeds also those loads between the grid and the inverter, some 1500W even my actual intended load is only 300W.


Did you find a solution for this? I think this is a bit like PowerAssist. Maybe the internal contactor should switch off once the inverter starts?

@Lukas ping

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3 Answers
Paul B avatar image
Paul B answered ·

Hi

Well I presume your critical loads are on AC1 out

I presume that the grid Tie is on AC1 out

now in the ess there is a Grid setpoint setting plus a Min SOC setting

I set my place at a SOC of 80% and a grid setpoint of 7000w


so anything upto 7000 watts will be supplied by the grid. over that comes from the battery, When grid failure happens AC1 out still has power and its drawn from the batteries if there is not enough solar to supply it, however if the mains is off for a while and the SOC drops below 80% to say 70 then a priority grid recharge is done until it reaches the 80% again, there is a charge limit setting as well but I have not used that

Excess solar is then used to charge the batteries and if grid export is allowed then its export or you can turn grid export off with the fronius

I think this is what you want ????

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lukas avatar image lukas commented ·

Amost.

Critical loads are connected to AC1 out. Grid Tie is on AC IN. There is no AC PV inverter in the system, only the dc-coupled bluesolar.

I just don't want to power any loads via AC IN, because there is a certain "grid setpoint" setup when the multi is on battery. The perfect outcome would be:

enough solar -> also power loads via AC IN and try to reach the grid setpoint, power critical loads and charge the battery

just enough solar for critical loads / battery -> slowly ignore the grid setpoint and use solar for critical loads and battery

not enough solar / battery operation -> do not feed power to loads on AC IN, only power critical loads from battery

In case of a grid failure (I'm not planning for this), critical loads should remain powered, but that's the case anyway...

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tj-botten avatar image tj-botten lukas commented ·

Hi Lukas, did you ever get a solution to this? I have the same situation and am looking for a solution.

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ccc-telecom avatar image
ccc-telecom answered ·

You want to be able to ignore AC Input on Battery low for the Parallel Loads, when in this case the input is from 1) Utility or 2) ESS, I don't think there is an ESS option for this, what you can do is use a load transfer switch or a Contactor, you have 2 options

1) Transfer to No Input on battery low - Only requires a contactor and Relay, effectively the same as the Ignore AC Input VE Bus option on AC Out2 with the loads still showing in the AC Loads box, you stop supplying power to the loads

2) Transfer to Utility - Requires ATS and Relay (Utility = Before you meter the power), what this does is pay for the load on your utility bill on a battery low condition, the load disappears from the AC Loads box, you transfer the loads from "after the meter" to "before the meter"

(I think this is what you want ??)

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bonie-wanda avatar image
bonie-wanda answered ·

6adc8473-b92c-4ddb-8d02-b34b7c9cd51d.pnga08ab071-0baa-4744-8dc7-226812807a2a.pngUnfortunately from my previous investigation , this assist feature cannot distinguish between DC-battery and DC-PV. It will use what’s available

what I’ve done was setup a battery charge cycle from

sunrise to sunset (preventing any discharge), then run my general loads (water geyser, oven,) during this period and also charge the battery.

at night my water geysers are timed off,


in the morning the water geysers can use what’s left of the battery till SOC 30% before the charge cycle starts at sunrise.

this has worked pretty well for me and dropped grid usage to 20% of total usage and most grid usage is eirher before sunrise or sunset by the water geysers . Winter might change that but Johannesburg has no extreme weathers so it won’t be by much.


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