How many panels needed

[jspchn]

Hi,
I am from India.
I have 40 AH 48 V VRLA deep discharge battery. I like to charge it using solar panels.
How many panels are needed. What is the charger specifications.

Thanks,
Jagadees
India

[Naptown]

you will need 2 72 cell panels is series, Total of about 40-60W and a 5A charge controller.
That is a very small battery bank for a 48V bank. I assume it is 4 12 batteries in series?

[jspchn]

Thanks for the reply.
Yes its 4 12V batteries of 40 AH in series.
You are saying, just a 60W panel is enogh?
Why it should be 72 cell panels ?
What should be the output voltage of the panels?

thanks,
Jagadees.

[Sunking]

Depends on what type of charge controller you use being PWM or MPPT to deliver a 4 amps of charge current.

If using PWM you need 270 watts of solar panels consisting of 4-12 volt battery panels of 65 watt panels, or 2 GTI 72 cell 135 watt panels with a 5 amp PWM controller.

If using a MPPT controller you need 200 watt panel consistin of 4-12 volt battery panel os 50 watts, or 2 GTI 72 cell 50 watt panel panels with a 5 amp MPPT charge controller.

[Sunking]

you will need 2 72 cell panels is series, Total of about 40-60W and a 5A charge controller.
That is a very small battery bank for a 48V bank. I assume it is 4 12 batteries in series?

Rich FWIW to get a C/10 charge current (4 Amps) using a MPPT CC = 48 volts x 4 amps = 200 watts. For PWM 4 amps x 68 volts = 270 watts

[Naptown]

Rich FWIW to get a C/10 charge current (4 Amps) using a MPPT CC = 48 volts x 4 amps = 200 watts. For PWM 4 amps x 68 volts = 270 watts

for some reason I was thinking 12V 40AH

[Sunking]

Why it should be 72 cell panels ?

For every 12 volts of battery requires 36 cells with a Vmp of 17 to 18 volts. A 12 volt battery panel is 36 cells. It takes 68 to 72 volts to charge a 48 volt battery

[inetdog]

Why it should be 72 cell panels ?
thanks,
Jagadees.

It does not need to be 72-cell panels. Since you need about 144 cells total, it seems simpler and more economical to use two high voltage panels than 4 36-cell panels. But the choice is up to you.

[Sunking]

It does not need to be 72-cell panels. Since you need about 144 cells total, it seems simpler and more economical to use two high voltage panels than 4 36-cell panels. But the choice is up to you.

Assuming a MPPT controller is used; that would be 2 less expensive GTI panels with a minimum 72 cells each right? If a PWM controller is used; more expensive 36/72 cell battery panels must be used right?

Sorry I am guilty of asking questions I know the answer too.

[inetdog]

Assuming a MPPT controller is used; that would be 2 less expensive GTI panels with a minimum 72 cells each right? If a PWM controller is used; more expensive 36/72 cell battery panels must be used right?

Sorry I am guilty of asking questions I know the answer too.

Since this is a 48 volt battery, either an MPPT or a PWM controller will need a series string of panels totaling 144 cells minimum. If the OP wants to go beyond that, he can either add more panels in series into his MPPT controller up to its input voltage limit or add more 144+ cell strings in parallel.

If using MPPT, it will be possible to add one panel or an odd number of panels at a time, while with PWM they would have to be added in 144 cell groups.

I hope that is the answer you already know, or else I have screwed up again.

[jspchn]

Thanks all for the reply.

Now I have one doubt. As per the comments I got that a 12 V battery need a panel of 36 cells.
What about the rating of the battery like AH value?

1. Is there any difference in 12V 20AH battery and 12V 40AH battery? Both can be charged with same 36 cells panel of same power?

2. Actually I have 4 - 12 V battery of 40 AH in series. If I connect them parallal then the voltage will be 12 V right? Will it can be charged with a 36 cells panel?

Thanks,
Jagadees.

[inetdog]

Thanks all for the reply.

Now I have one doubt. As per the comments I got that a 12 V battery need a panel of 36 cells.
What about the rating of the battery like AH value?

1. Is there any difference in 12V 20AH battery and 12V 40AH battery? Both can be charged with same 36 cells panel of same power?

2. Actually I have 4 - 12 V battery of 40 AH in series. If I connect them parallal then the voltage will be 12 V right? Will it can be charged with a 36 cells panel?

Thanks,
Jagadees.

One rule of thumb is that for a 12 volt system the total panel wattage should be at least as large as the Amp-Hour rating of the battery bank.

To properly charge a 40 AH battery will require twice the current and therefore twice the panel wattage as the 20 AH battery.

So it all comes down to whether you will use just one 36 cell panel, and what the wattage of that panel will be.