Battery is charged even if price difference (from charge price to discharge price) is nearly zero

[sushi86]

Hey =)

I tested this tool the last few days because I'm searching exactly for something like this for my victron ESS.
I recognized that the battery is very often charged even if the difference to the price when the battery is discharged is very low even though I entered 11 Cent for the battery kWh.

See here (price means Cent/kWh without taxes etc)

2025-01-01 04:00:00 +0100 CET : DISCHARGE_ALLOWED SOC: 11.906757823540842 Price: -0.001
2025-01-01 05:00:00 +0100 CET : DISCHARGE_ALLOWED SOC: 10 Price: -0.006
2025-01-01 06:00:00 +0100 CET : CHARGE_FROM_GRID SOC: 10 Price: -0.009
2025-01-01 07:00:00 +0100 CET : DISCHARGE_ALLOWED SOC: 64.64285714285715 Price: -0.001
2025-01-01 08:00:00 +0100 CET : DISCHARGE_ALLOWED SOC: 57.586179814195205 Price: -0.001
2025-01-01 09:00:00 +0100 CET : DISCHARGE_ALLOWED SOC: 52.52614577544429 Price: -0.004

So EOS is suggesting to load the battery at -0,009 Cent/kWh and then discharging it at a grid price from -0,001 Cent/kWh.
With a battery price from 11 Cent/kWh I would loose money. For me this doesn't make sense.

Even if I use 1 € / Wh for the battery EOS is suggesting to load from Grid. I

Request was:

{"ems":{"pv_prognose_wh":[0,0,0,0,0,0,0,0,0,0,469,719,847,857,753,544,315,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,454,724,1044,1471,1693,1423,890,0,0,0,0,0,0,0],"strompreis_euro_pro_wh":[0.0000216,0.000016,0,-1e-7,-1e-7,-6e-7,-9e-7,-1e-7,-1e-7,-4e-7,-3e-7,-0.000001,-5e-7,-0.000001,-0.0000101,-1e-7,-1e-7,7.000000000000001e-7,0.0000101,0.0000148,0.00001,7.000000000000001e-7,0.0001005,0.0000701,0.0000255,0.0000156,0.000034500000000000005,0.0000702,0.0001275,0.0003007,0.0006713,0.0009883,0.0012153,0.0012723,0.0012634999999999999,0.0011997,0.0011595,0.001139,0.0012220999999999998,0.0013011000000000001,0.0013859,0.0015287,0.0015294,0.0013915000000000002,0.0013,0.0011978,0.0011342,0.0008247],"einspeiseverguetung_euro_pro_wh":[0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075,0.0000777075],"preis_euro_pro_wh_akku":0.00011,"gesamtlast":[538.4006913709309,515.1285643594947,504.56656326821417,522.6620816954082,506.2200375900648,550.7818662084169,728.85808933053,839.7446021107708,602.144050611358,637.7297072883508,640.9920376286482,611.7952165808247,663.4045753113331,821.0726546635326,1272.616565570683,810.8849866760464,966.5875747164768,766.5416595200188,1302.0893613143114,913.9179484493379,1059.6693994071156,624.0590283573999,541.9028597517477,533.7397228632124,529.6875511696602,487.73427657182987,482.4310144355359,489.13503796444735,480.06154245773587,505.0503731540093,880.9688738483051,835.2617398931166,585.845560334122,663.4970215893358,496.1895681601025,507.5389538284087,777.2617304930155,577.4184466668224,728.7007405603796,764.7915424197927,656.5257970727289,773.4681770350271,928.3942710702735,738.3776700170713,768.8931931680265,739.630279429749,551.186720741159,536.6973156332999]},"pv_akku":{"kapazitaet_wh":14000,"lade_effizienz":0.85,"entlade_effizienz":0.85,"max_ladeleistung_w":9000,"start_soc_prozent":25,"min_soc_prozent":10,"max_soc_prozent":100},"eauto":{"kapazitaet_wh":80000,"lade_effizienz":0.9,"entlade_effizienz":1,"max_ladeleistung_w":11000,"start_soc_prozent":100,"min_soc_prozent":20,"max_soc_prozent":100}}

Solution:

{
    "ac_charge": [
        0.0,
        0.0,
        0.0,
        0.0,
        0.0,
        0.0,
        0.0,
        0.0,
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        0.0,
        0.0,
        0.0,
        0.0,
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        0.0
    ],
    "dc_charge": [
        1.0,
        1.0,
        1.0,
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    "discharge_allowed": [
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    ],
    "eautocharge_hours_float": null,
    "result": {
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        "EAuto_SoC_pro_Stunde": [
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        ],
        "Einnahmen_Euro_pro_Stunde": [
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        "Gesamt_Verluste": 4908.476515000594,
        "Gesamtbilanz_Euro": 0.17102516207870094,
        "Gesamteinnahmen_Euro": 0.0,
        "Gesamtkosten_Euro": 0.17102516207870094,
        "Home_appliance_wh_per_hour": [
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        "Kosten_Euro_pro_Stunde": [
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        "Netzbezug_Wh_pro_Stunde": [
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        "Netzeinspeisung_Wh_pro_Stunde": [
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        "Verluste_Pro_Stunde": [
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        "akku_soc_pro_stunde": [
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        "Electricity_price": [
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    "eauto_obj": {
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        "discharge_array": [
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        "entlade_effizienz": 1.0,
        "hours": 48,
        "kapazitaet_wh": 80000,
        "lade_effizienz": 0.9,
        "max_ladeleistung_w": 11000,
        "soc_wh": 80000.0,
        "start_soc_prozent": 100
    },
    "start_solution": [
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    "washingstart": null
}

[sushi86]

Ah, I think I got my error, I interpreted Electricity_price (in EOS response Result. Electricity_price) as Grid price...

Will take a deeper look.

[sushi86]

Ok, still this issue here, I updated the output with real grid price values, still doesnt make sense for me:

2025-01-01 17:00:00 +0100 CET : CHARGE_FROM_GRID SOC: 87.16608384763676 Price: 0
2025-01-01 18:00:00 +0100 CET : DISCHARGE_ALLOWED SOC: 100 Price: 0.1
2025-01-01 19:00:00 +0100 CET : DISCHARGE_ALLOWED SOC: 89.05807259399738 Price: 0.1
2025-01-01 20:00:00 +0100 CET : DISCHARGE_ALLOWED SOC: 81.3780898339189 Price: 0.1

Its charging at price 0 Cent/kWh and discharging at price 0.1 Cent/kWh with battery costs: 11 Cent/kWh

[drbacke]

Thanks for your support and testing.
In the First View, you forgot to Set the electricity_charges (prices are all day ahead and without fee and Taxes)
Please set battery losses both to 0.9 (discharge is set to 1)
And what do you mean with battery costs of 11cent?

• Please share the correct pdf, this would help a lot.

Which version did you test? config_overhaul is a a little buggy so far.

[sushi86]

Thanks for your support and testing. In the First View, you forgot to Set the electricity_charges (prices are all day ahead and without fee and Taxes)

electricity_charges? I will add the taxes and fees, but I doubt this will change something.

Please set battery losses both to 0.9 (discharge is set to 1)

What you mean by this? I set efficiency to 85%, see here:
"lade_effizienz":0.85,
"entlade_effizienz":0.85,

And what do you mean with battery costs of 11cent?

"preis_euro_pro_wh_akku":0.00011, means if I take 1 kWh from battery it cost me (additional) 11 Cent, am I right?

• Please share the correct pdf, this would help a lot.

Which version did you test? config_overhaul is a a little buggy so far.

I was at latest commit at this time

This should be the right one:
response.pdf

You can clearly see it in the picture, eventhough the price at the first day is more or less the same, eos is suggesting to discharge battery, in my view this would only make sense considering the efficiency and also costs for getting energy from battery (in my case 11 cent / kWh), or is my view wrong? Maybe this is wanted behaviour?

[NormannK]

preis_euro_pro_wh_akku is the value of the energy stored in the battery. In a not empty battery that energy has some value.
e.g. if you start with a 100% solar filled battery its different than 100% filled with expensive energy.
If you do not track that, I would set it to the grid energy cost in winter and change it in summer.

But looking at the rest it looks very good. We start with loading the Battery with very cheap energy, but only so long that the forecast of PV can be stored too. We never feed into the grid.
Hour 21 is super cheap again so we top up and again at 25 to get over the rest of the simulation. Later we see some soc increase bc of the PV forecast.
idk why you electric price is that low for so long but that's not the point here. I only wonder why in the Financial Balance chart we got a negative cost at the start. Could be bc the battery is not empty when we start and bc of preis_euro_pro_wh_akku but im struggling to see why.

The AC/DC Charging is complicated and i'd like drbacke comment on that as the expert.

[sushi86]

Ahh, I see, I totally missunderstood this value. But does it really make sense to discharge battery when the difference between grid energy price (from loading to current value) is nearly zero?

The prices are from first of january.

And also: I think having a variable for this (costs of getting energy from battery) makes sense.

[drbacke]

Of course it makes sense to fill your battery with 0Cent energy.
Just set the charges / fees and this will be over.

Yes it could make sense to integrate some model for battery degradation. For DIY Batteries this makes no real difference, but for commercial batteries this could make a difference. You can open an issues for that if you want to