I am doing battery calculations for off-grid solar panel. I don't get that why battery guides on Internet always ignore Peukert's Law for batteries of solar panel. I want to have good approximations not perfect. So, don't answer too complex please.
I want to know
- What AH battery use
- What is its charging time
- Discharging time
If I have a
1KW load and I want to have its backup for
3 hours. That makes
energy 3KWH. That means I need to generate this energy. Furthermore, 1 KW requires 4.54 current for a single phase at homes in Pakistan (220 AC at 50 Hz). This current can also be called discharging current of battery.
Id = 1000/220 Id = 4.54 A
Battery to use:
That means we require
AH = Id * Battery voltage Let's take it 12 V AH = 4.54 * 12 AH = 54.48
We should have DOD 50%, so that our battery drains only 50% and it gets the chance to charge again and doesn't go ever below 5o%. Doing so, enhances the battery life.
AH = 54.58/0.5 AH = 109.16
Is it economical to use such a huge battery for only 1 KW load?
Note that batteries come with 20 HR (hour rate). That means a battery shows its mentioned capacity if discharged in 20 hours. Otherwise so many losses occur and decreases the battery capacity. So here comes a complex pukerts formula.
where k=pukers number. But batteries don't come with pukerts no. Do they? I never ever saw written pukerts number written on any battery. Guides say that its usually between 1.1 to 1.4. But 1.1 and 1.4 makes a huge difference in calculations.
Anyway, let's choose
It tells us that when:
C=54.48 H=20 I=4.54 then t=9.78 hours and when C=109.16 AH then t=25.88 hours.
I feel like I have used extra AH battery because I dont need backup for 26 hours. I need for 3 hours only.
Charging current should be 10% of the battery capacity. Therefore,
1/10th of 109.16 is 10.916 A.
Charging current should be 10.916 A and it will take
t=109.16/10.916=10 hours to charge?
Please improve my calculations where lackings are. And correct me where I am wrong.