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3 kW day-time plus 2 kW in night for 9 hrs

clax xiarino

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Sep 9, 2021
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I want to design a system that can run 3 kw system in day time and also charge battery bank good enough so that i can easily run my 2 kW load at night for 9 hr backup. Now my question is how much batteries do i need ? lets assume i have 12 V 200 Ah Dry Battery with 60% DOD.
According to my calculation, 16 batteries are required to cater this. 4 in series and 4 in parallel. Does it seems feasible ? if yes than how many panels do i required to charge this battery bank and also run load of 3 kW.
I also want to know if i have installed 16 batteries and want to run 2000 W load in night so how much ampere will i get? will it be 2000/220 Vac = 9 Amp or 2000/48V = 41 Amp?

PS: There is no grid.
 
2kW for 9 hours is 18kWh of usable battery capacity. At 60% you need 30kWh of batteries. A 12V 200Ah battery is 2.4kWh. 30kWh / 2.4kWh = 12.5 batteries. Since it appears you want a 48V system you need a multiple of 4. Say either 12 or 16. Since 12 isn't enough you need 16 in 4S4p. 16 12V 200Ah batteries using 60% gives you 23kWh which is more than the 18kWh needed. Your math checks out so far.

Keep in mind that this assumes your batteries are at 100% when that 9 hour period begins.

As for solar, you need enough to fully recharge the batteries from 40% (maybe closer to 50%) at the end of the 9 hour period to 100% in addition to providing the 3kW * 15 hours.

You are not going to get 15 hours of solar every day. Depending on your latitude it will vary a lot during the year. Plus there will be cloudy/rainy days. Where do you live roughly?

You may actually need two or even three times as many batteries and enough solar to charge them all in about 5 hours per day. That will be a lot. Or consider adding a generator to deal with days of poor solar.

What you really need to do first is to find a way to lower your consumption needs. Get your nighttime loads down to 1kW instead of 2. Get your daytime loads down to 1.5 or 2kW.
 
I also want to know if i have installed 16 batteries and want to run 2000 W load in night so how much ampere will i get? will it be 2000/220 Vac = 9 Amp or 2000/48V = 41 Amp?
Both are correct. If your 48V battery is providing 2000W it will be at 41A. The battery sees the 41A discharge. If the 2000W is all AC via an inverter, then the 2000W from the inverter at 220V will be 9A. The AC loads will get 9A.
 
Both are correct. If your 48V battery is providing 2000W it will be at 41A. The battery sees the 41A discharge. If the 2000W is all AC via an inverter, then the 2000W from the inverter at 220V will be 9A. The AC loads will get 9A.
What i understood from this is that in day time when PV is generating, the load will get 9 Amps (considering 2 kW load) via inverter. While in night, the same load will run on batteries through same inverter but this time current would be 41 Amps.
is that right ? if yes than i have one confusion.
If the load will run through inverter than the 48 V DC coming from battery must be converted into AC 220 V. Right? so load must consume 9 amps in night also.
 
2kW for 9 hours is 18kWh of usable battery capacity. At 60% you need 30kWh of batteries. A 12V 200Ah battery is 2.4kWh. 30kWh / 2.4kWh = 12.5 batteries. Since it appears you want a 48V system you need a multiple of 4. Say either 12 or 16. Since 12 isn't enough you need 16 in 4S4p. 16 12V 200Ah batteries using 60% gives you 23kWh which is more than the 18kWh needed. Your math checks out so far.

Keep in mind that this assumes your batteries are at 100% when that 9 hour period begins.

As for solar, you need enough to fully recharge the batteries from 40% (maybe closer to 50%) at the end of the 9 hour period to 100% in addition to providing the 3kW * 15 hours.

You are not going to get 15 hours of solar every day. Depending on your latitude it will vary a lot during the year. Plus there will be cloudy/rainy days. Where do you live roughly?

You may actually need two or even three times as many batteries and enough solar to charge them all in about 5 hours per day. That will be a lot. Or consider adding a generator to deal with days of poor solar.

What you really need to do first is to find a way to lower your consumption needs. Get your nighttime loads down to 1kW instead of 2. Get your daytime loads down to 1.5 or 2kW.
I have proposed that 14 kW is enough to run 3 kW load + charge the batteries in day time i.e. 5 hrs. I have to charge a bank of 38.4 kWh and I think 49.5 kWh ( 11kW x 4.5 hrs sun hours) is enough to charge battery bank.
Am I thinking right ?
 
What i understood from this is that in day time when PV is generating, the load will get 9 Amps (considering 2 kW load) via inverter. While in night, the same load will run on batteries through same inverter but this time current would be 41 Amps.
is that right ? if yes than i have one confusion.
If the load will run through inverter than the 48 V DC coming from battery must be converted into AC 220 V. Right? so load must consume 9 amps in night also.
Loads will always see 9A from the inverter at 220V regardless of the source or time of day. What I meant is that the battery itself will see a discharge of 41A since it is at 48V.
 
OP post #1: "will it be 2000/220 Vac = 9 Amp or 2000/48V = 41 Amp?"
It will be more than 41A due to system and inverter efficiency, typical about 85%, it will be about 49A.
 
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