question

furattila avatar image
furattila asked

Why is EasySolar-II discharging batteries instead of feeding PV DC to AC loads on a sunny day?

Dear Experts,

I am kindly asking for your help, because I am stuck with the following problem:


I am using an EasySolar-II with a LiFePo4 built in BMS Battery-pack. My preference is to use the whole configuration as follows:

- Working without input AC (island mode)

- Battery is used during nights

- In the morning the battery should be fully charged, after that no charge/discharge should happen

- PV should feed mainly AC loads during daytime ( there are only constant small amount of AC loads on the output, there is alway enough PV power them even during couldy daytimes)


For this purpose I configured the EasySolar-II as follows:1686938858535.png

1686938632552.png

1686938668482.png


Everything works fine except the following issue:

- in the morning after the battery is fully charged, the MPPT is not always feeding DC coupled PV power to AC loads. After some time (sometimes immediately) the battery starts to discharge and MPPT is nor charging nor providing power to the loads (0W).

When a sudden AC load appears then MPPT starts to feed in power (1000W), until the load is present. When is disconnect the huge load (1000W) and only 150W constant AC load remains than MPPT is not providing the power, the battery is used which is not accepatble during a sunny day.

When the battery is discharged by a few percentages (e.g. 5 %) then MPPT start to work and provides energy to AC loads and also charges the battery.

What am I doing wrong?

Please help me to understand what is happening, and how can I achive my goal and let the MPPT work during sunlight and skipping unnecessary battery charging/discharging.


Thank You in advance

Attila Fűr

MPPT SmartSolar
1686938632552.png (28.7 KiB)
1686938668482.png (32.9 KiB)
1686938858535.png (11.4 KiB)
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2 Answers
seb71 avatar image
seb71 answered ·

ESS should not be used without a grid connection.

When there is a big increase of the load, the grid and battery can provide the power much faster than the MPPTs.

Also, when there is a big decrease of the load and the MPPT were providing power for it, that power has to go somwhere until the MPPT throttles down. It can go either to the grid (which is not available in your case) or to the battery. The problem with the second option is that if the battery is full or close to full, it can't tace that power/current.

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furattila avatar image furattila commented ·
I understand what you say with ESS witouth grid, but I tried also the Hub-1 configuration which is dedicated for island operation but the result was the same: The battery was discharging and charging instead of MPPT power feed into AC loads, in the trivial case when there are kilowatts present for a 150w load. So somehow the MPPT doesnt resume the previous state after the battery is fully charged, until the battery is drained somewhat.


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Alexandra avatar image
Alexandra answered ·

@fur.attila

Change the re bulk offset on your mppts to 0.1v

Did you select, then edit a lifepo4 profile on them before editing for your batteries?

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furattila avatar image furattila commented ·

Dear Alexandra,


I set the lithium battery options as follows:


image.png


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I also tried to set the Re-bulk voltage offset to 0.1V, but no with no luck, nothing changed.


image.png

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after some time I restarted the system and the MPPT started to give power for a while (until the battery voltage went down from 53.1 V to 53 V see below:


image.png


image.png


After few minutes the MMPT starts to charge to battery with full power, until the battery is charged fully.

image.png

image.png

(56V is the maximum charge voltage is set in dvcc)

image.png

After reaching the 100% SOC the MMPT slowly starts to reduce the power

image.png

until it is 0W again.

After that the whole cycle starts from the beginning with draining the battery and PV is giving 0W power.


Somehow I don't realize the set Float and Absorption Voltage levels


I give you the whole cycle characteristics:

(during night times the battery is used which is correct it goes down to 85% then in the morning the battery is charged)


image.png

you can see the same thing during daytime: between 9 and 12 AM no solar power was used despite of plenty of solar power (sunny day)

What I see that inside of the EasySolar-II the The MPPT 250/100 is connected with the Multiplus Inverter via VE.Bus therefore the MPPT is under Ext.Control.

The BMS is running correctly since the charging process is done correctly, there are correct (voltage, SOC, stc) values shown in the control panel.

But somehow the MPPT doesn't resume itself after the fully charged state is reached. It is probably because it is under Ext. Control, but I dont know who is controlling the MPPT.

I suppose the Multiplus should. It is also very confusing that the Float and Absorption Voltages can be set in both (in MPPT self the Multiplus, they can be also set to different values).


I am askind kindly for you help, because i tried many different settings without any noticable difference.

Thank You!

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