Best way to set ESS "idle"

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wheeto asked Apr 29, '24

Best way to set ESS "idle"

Hello,

I have a single phase, grid-connected, system with MP-II, Cerbo, battery, and AC-coupled solar. Because of my time-of-use tariff for grid power I have thrown together a system that alters set-points etc in response to price data downloaded. I essentially want the system to be in three states:

1) Charging from grid
2) Discharging to avoid using grid
3) "Idle" where any excess solar is used to charge the batteries, but because the grid power is so cheap at these times, I don't want the system system to discharge during this time.

I've had success for the last few months, but today discovered a problem: my method of setting the system to the "idle" state is to set the charge point to a low SoC% and put the system in "charger only" mode. This worked absolutely fine until today when the grid was lost and, because the system was in "charger only" of course it didn't provide power to the rest of the installation. I was lucky enough to notice and remotely switch the system to "on" and it's now working fine while the grid is out. But.... what's the solution? How should I set the system into an "idle" mode so that excess solar is captured, but the batteries don't discharge?

Thanks,

cerbo gx grid

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Modifications Space

Node Red Space

Answer 1 · 2024-04-30T08:37:44Z

wheeto answered · Apr 30 at 08:37 AM

I wrote a lengthy answer to this, in case others had the same question, but the forum said that my attempt to post was "a CSRF attack" and lost it.

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Answer 2 · 2024-04-30T08:55:37Z

nickdb answered · Apr 30 at 08:55 AM

I would look at schedules (these can be set via node red as well) which can schedule charge and discharge levels and offer some control.

Alternatively look at DESS.

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Answer 3 · 2024-04-30T12:14:57Z

dognose answered · Apr 30 at 12:14 PM

3) "Idle" where any excess solar is used to charge the batteries, but because the grid power is so cheap at these times, I don't want the system system to discharge during this time.

To use the existing system you got: You could calculate how much power "should" be pulled from grid, most likely "Consumption - PV-Production" and then set the grid setpoint to that value, so ESS is happy with idling around while there is grid pull.

Something like

consumption = 2000 //readout
pvProduction = 1000 //readout
currentPrice = 0.10 //readout
gridPullLimit = 0.15 //fix

if (currentPrice < gridPullLimit){
  gridSetPoint = (consumption - pvProduction)
  // 1000 = 2000 - 1000
}

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Answer 4 · 2024-04-30T13:45:42Z

wheeto answered · Apr 30 at 01:45 PM

Thanks for the suggestions. I'm trying out writing 0 to

 W/<ID>/settings/0/Settings/CGwacs/MaxDischargePower

for "idle" and -1 to re-enable discharge. Won't know for sure it works until I've had excess solar, which sadly is not today!

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