question

chrisjan avatar image

What is required in order to maintain the minimum SoC and control the battery discharge at the same time?

Objectives:

1. To have electricity for as long as possible.

2. To use as much renewable energy as possible.


Challenge:

1. To have electricity for as long as possible.

- Load shedding / Unstable Grid

- Cloudy weather

Load shedding after 4am is the worst. Because State of Charge (SoC) is low and it might be cloudy or winter which means PV might only be available later. So SoC shouldn't be set too low in order to reach the first objective, but it can't be too high either in order to reach the second objective.

- High Loads during low SoC

My geyser has a 3000W element and the storage I use is a 7100W capacitor. When the geyser switches on at night then there is sometimes a voltage drop below a critical level and the system faults with a low battery alarm. Grid is then used.

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One could set the minimum SoC to 40% and have the grid supply the remaining wattage. This helps, but what happens to the 40%?


2. To use as much renewable energy as possible.

All about how the load and inverter is going to being managed.

1614168600912.png

During about my first year I was not using ESS and would only switch over to the grid if the SoC was too low, sometimes I had to go fully back onto the grid because the geyser switched on. But ESS helps, although I want to use as little from the grid as possible.

An example:

1614163331780.png

It is mid day and enough power is stored. I would rather use the stored power than the grid power to make up the balance of what PV cannot provide. .

Another example:

1614168105035.png

If somebody switches on the stove or toaster and other loads that makes the inverter want to use power from the grid then a/some/all controlled loads should be switched off so that power from the grid is used on the uncontrolled load.


Exploring solutions:

Reference to modes:

https://www.victronenergy.com/live/ess:ess_mode_2_and_3

Determine minimum SoC:

1614170475602.png

Mode 3:

Using mode 3 to control the discharge.


Question:

Grid setpoint is on 30W, but grid is being used instead of stored energy.

What is required in order to maintain the minimum SoC and control the battery discharge at the same time?

So:

Min SoC = controlled by software

Battery discharge setpoint = controlled by software

Grid Setpoint = maintains the min SoC / supplies what battery + PV can't / outside inverter spec

ESSModbus TCP
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1614168105035.png (114.4 KiB)
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2 comments
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Basically it sounds like you want to discharge the battery as much as possible, but at the same time to always keep the battery fully charged if possible.

Discharging when possible yes, but also discharging on my terms:

1614163331780.png
So I want the 651W to come from the battery.

1 Answer
gherlt avatar image
gherlt answered ·

I am not sure about your configuration:
you say
>During about my first year I was not using ESS and would only switch over to the grid if the SoC was too low, sometimes I had to go fully back onto the grid because the geyser switched on
Are you grid connected or doing manual switch over from off-grid to grind ?

1 comment
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Hi @gherlt

I use to use the system in inverter only and then manually switched over to the grid when i had to, but I've been using ESS for the past year.

Right now I am using ESS Mode 1 and controlling SoC and the grid setpoint.

Notice the 609W in the example below is power from the grid:

1615184383564.png

The 4143W load is still within the Multiplus's capability and there was still enough sunlight in the day to charge the battery. My grid setpoint is at 0W.
When i can figure out how to get +-0W from the grid in the above example and that the battery can backup the PV 100% then I will be happy.

Thank you

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