To know how much battery you actually need to know how much you use per day. For most of us perhaps we don’t really know how much energy we use per day. The good news is you can estimate from you monthly electricity billing and how much every KWh cost.
For example in my country every KWh cost around Rp 1.500,00. Let’s say Rp 1.400,00 every KWh so we can get higher number for safety. Then we can divide monthly electricity billing, for example: Rp 500.000,00 with how much every KWh cost: Rp 1.400,00.
It’s 357,14 KWh every month. Then we can divide this number by 30 to get energy usage per day.
From our calculation in average energy used are 11,904 let’s round it up to 12 KWh for safety. Here we get our energy usage daily. Now you know you need battery which can hold energy this much. But wait, I don’t know which battery I need and how much battery is holding 12 KWh. OK, let’s assume we are going to use Lead Acid battery. The next section we will talk about Lead Acid battery and some specification we need to know.
What is Lead Acid battery?
It’s one we use in our car to mainly start our car. Actually it’s only one variant of Lead Acid battery. LA battery come in many variant and every variant has it’s own Depth of Discharge (DoD) and
For most LA battery can only discharged to 60%. It’s means we can only get 40% out of energy stored in our battery. This means our DoD is 40%. For example we have 12V 100Ah LA Battery, means it’s nominal voltage are 12 Volt and it’s capacity is 100 Ampere Hour.
What is 100 Ampere Hour? This means if we drain this battery in 100 Amp This battery will supply as long as 1 Hour, If we drain this battery in 50 Amp this battery will supply as long as 2 Hour. Well you got it right? But wait, this battery is LA battery, which mean s we only should drain it 40% of it’s stored energy only. Which means if we drain in 100Amp we only should drain it as long as 24 minutes. OK enough talking about Ah and DoD, we still don’t tell how much KWh this battery hold? it’s easy to calculate it:
Here we get that our battery capacity is 1,2 KWh. But don’t forget about DoD we talk earlier LA battery is 40%. which means this battery only has useful capacity 
yes 0,48 KWh. Now take the number 12 KWh for our daily usage it’s easier to know how much we need battery right? it’s
Yes at least we need 25 batteries for one day operation. FYI it’s unsafe to only have one day worth of energy it’s safer to have at least two and a half day worth of energy for safety. So yes, you will need about 63 batteries.
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