question

fgingat avatar image
fgingat asked

ESS, Allow export even if batteries are not fully charged

Hello,

i have a "problem" with my installation, i have 25kWp PV production with my bluesolar mppt but 15kWp inverter (3x5kW Multiplus II), i'm allowed to export to grid without limits.

the result is at 12:00 in summer time my battery is fully charged but my solar production is capped to the power output of my inverters (15kWp instead of 25kWp)

so, i would like to allow the inverters to feed grid even if my battery is not fully charged, is this possible with 'simple' ESS or do i need to go through external control and use some magic MQTT or DBUS commands ?

Regards

Florent

ESS
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7 Answers
cacer avatar image
cacer answered ·

i use a nodered flow to set the gridsetpoint deeper in the morning, when the sunforecast in the afternoon will be high.

so battery will stay on a lower SOC till the late afternoon.


i found no other easy way to feed in earlyer.

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fgingat avatar image
fgingat answered ·

Could you please share your flow ?

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seb71 avatar image
seb71 answered ·

the result is at 12:00 in summer time my battery is fully charged but my solar production is capped to the power output of my inverters (15kWp instead of 25kWp)

Maybe I did not understood correctly, but you can't output/export to the grid at higher power than the inverters are capable. You are exporting AC power, not DC power.

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cacer avatar image cacer commented ·
this can be avoided by exporting earlyer, so that the battery can take the rest.
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fgingat avatar image fgingat cacer commented ·

Yes i know that i'm capped to the max output of my DC=>AC inverters, i want my setup to export to grid before my batteries reach 100%SOC, in this scenario i can export 15kW from DC to AC and the remaining DC goes to battery, optimisation,


in my actual setup all DC go to battery (even AC to DC,as i have a fronius connected to AC IN), when the battery is full, production is capped as the inverters cannot output more than 15kW, i want to modify this behavior to inject AND charge at the same time (of course there is no plug'nplay solution, i understand that i will need to manage/priorize by myself the charging VS inverting), so .. i lost about 10kWh/hour of production

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seb71 avatar image seb71 fgingat commented ·
Are you using a comparable amount of energy during the night? If the main purpose of your solar system is energy export to the grid, then just set a very high minimum SOC (so that the battery barely discharges unless there is a blackout).


But for a system intended mainly for export to the grid, a PV inverter is the better choice (instead of MPPTs).

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cacer avatar image
cacer answered ·

i hope it is usefull for you, because i noted everything in "german".

also the weatherforecast_node is from german dwd, with only local stations.

but perhaps you can use it to make your one easy.

also have a look in the node_red space:

https://community.victronenergy.com/articles/172211/node-red-fetch-forecasted-solar-yield.html?smartspace=node-red


my flow: (zipped it to upload - could not insert it directly. is there a better way to share?)

Gridsetpoint_nach_sonnenvorschau_regeln.zip

set-gridsetpoint.jpg



edit:

the function-node "abhängig Netzregelpunkt setzen" ( set gridsetpoint dependent from solar-power/sun forecast/SOC)

screenshot-2023-05-29-111934.jpg

here the effect:

before i used the flow, battery was full around 12:00.

now it is full in the late afternoon, dependent on my adjustments. i am finetuning these days.

screenshot-2023-05-29-112554.jpg


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fgingat avatar image
fgingat answered ·

Thanks, i will look at it tomorrow
(google translation german to french will be helpfull ^^)

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fgingat avatar image
fgingat answered ·

Your flow is really interesting, thanks again, i'm trying to adapt it to my needs but i have another "problem", i have a Fronius (managed by ESS) and another inverter (not managed) that seems to interfer with the calculation of grid outputn if i use Grid Setpoint, they are connected to AC-IN, i don't use AC-OUT.

The problem is that i didn't know how to tell to the 3x multiplus to invert at max power, i can only set Grid Set Point, and ...

if is set it to 35kW no problem, everything is exported to the grid, but if i want to finetune the grid export from the multiplus i cannot set a real value that is not related to the wattmeter monitoring grid output .. not sure if i explain well ...

I want to configure the Watts output of the multiplus ac-in directly, not using grid setpoint .. do you have an idea ?


EDIT : exemple, now it's night time, i set Grid Setpoint to 10kW but i have a load on AC-IN of 8kW, the ESS provide power to loads but is trying to achieve 10kW to the grid ...
I want to tell the multiplus to "produce" 10kW for ac-in instead of trying to export 10kW to the grid.

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cacer avatar image cacer commented ·
i would try to use a node for the "system - AC consumption" e.g. to lower the feed in while a big load is active.

but i have not done that till now.

like: if AC-consumption is more then XXX for X minutes then gridsetpoint -XXX



perhaps there are better ways.

i got only one MP2 5000 and no AC-inverters.

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andy156 avatar image
andy156 answered ·

The other thing you can do is control the limit battery charge voltage in the DVCC setting. This will mean that AC loads are serviced as normal. You are limiting the charge rate to the battery causing excess to be fed to the grid. I can' remember the numbers off the top of my head but say the battery is at 48v then limiting to 48.2v might only allow a charge rate of 1kW for example. 48.4 would be 2kW.

Work out what charge rate you want on the battery. Then monitor the battery charge rate each cycle. If it is too high then decrement voltage and if too low increment. Just do it a small amount. Its a very simple loop.

Any excess power will just be exported. I do this to force an export which is picked up by my zappie car charger.

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