Energy Storage should be Ah not Wh
Fabian-Schmidt opened this issue · 6 comments
Hi,
I just noticed the new device class energy storage #1698
And the text contains the following sentence:
for example the amount of electric energy currently stored in a battery or the capacity of a battery.
But all battery monitoring systems and all batteries I can purchase are measuring in Ah and not in Wh.
Can somebody please clarify? Thanks,
So I have a (pure) DC system (no AC, no Inverter) with a normal AGM battery with a Voltage between 11.5V and 14.4V and a Capacity of 95Ah and peukert factor of around 1.05.
My Victron Smart Shunt gives a very accurate consumed Ah values.
Based on your opinion how should I get the Wh for this system, so I can use the HA energy function.
I see one Option: If I multiple the current Voltage with the consumed Ah I get an incorrect value, because the Voltage various highly depending on the current load on the battery, but the actual consumed Wh not.
Multiplying by the current voltage would indeed be the way to convert between units...
My problem with using the current Voltage I can illustrate best using the following table. The measurements are taken directly at the battery. All values are taken a few second apart. I have occasional short high loads:
| current Voltage | Current | current Power | consumed Ah | consumed Wh |
|---|---|---|---|---|
| 12.68 V | -0.60 A | - 7.6 W | -5.8 Ah | - 73.54 Wh |
| 12.54 V | -9.22 A | - 115.6 W | -5.8 Ah | - 72.73 Wh |
| 12.65 V | -0.28 A | - 3.5 W | -5.8 Ah | - 73.37 Wh |
As you can see the resulting consumed Wh is jumping around very heavily, but the actual consumed Ah not. Because the short spike load has used very little power.
Ah is not an energy unit. If you don't actually care about actual energy you can make an arbitrary energy unit out of consumed Ah and battery nominal voltage 12v.
Something does not add up in your table. Is consumed Ah and consumed Wh for each "few second" or it's infinitely increasing absolute value? If latter, why consumed Wh is decreasing?
Also consumed Ah value seems to be heavily rounded. How many decimals it has? From your example, Wh seems 100x more precise, that's why it seems to be "jumping around".