solar pannel nickel-iron system question!?

[BigPapaGD]

Ok, so I am a little stuck on one thing for a while now. For a nickel-iron battery bank of 24 volts, each cell is 1.2 volts and has a charging voltage of 1.65, so 33 volts is needed when for optimum charge. The 24 volt, 100Ah battery bank requires a optimal charge rate at c/4 (25 amps for a 100 Ah battery).

My question is this; If I have 3 solar panels rated at 50voc and 10isc that produce 400 watts each, and line them in a parallel circuit, I will be pushing 30 amps and 50 volts to my charge controller.

Once in my charge controller, does that 30amps and 50volts translate into enough energy to charge my battery bank in 4 hours? Or is the 30amp and 50 volts converted to watts to charge my battery bank, in which case I would be charging a 5kwh battery bank with only 1200 watts from the panels.

I would greatly appreciate clearing this up as it is hindering my further understanding of these systems.

 

[Dan]

Who are our solar gurus on here?

SolarCity ? Is it?

 

[BigPapaGD]

Oh, that forum seemed a little dead but ill post there

 

[dmxtothemax]

You need to looka at it from the KWH perspective, not just KW.
If you take , lets say 20ah out of the batterys
then you need to put that back in
How long it takes depends on the current and the time
so 2A over 10 hours = 20AH
OR
10A over two hours = 20AH

 

[BigPapaGD]

ok. Lets say my daily energy offset is 5kWh, I assume 80% efficiency and I get 5 hours perfect sunlight a day. So my KWp would be 1.25. To find out how many panels are needed would be 1250watts/400(pmax rating of single panel) = 3.12. So I would need 3 of those panels to support daily task. correct?
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You need to looka at it from the KWH perspective, not just KW.
If you take , lets say 20ah out of the batterys
then you need to put that back in
How long it takes depends on the current and the time
so 2A over 10 hours = 20AH
OR
10A over two hours = 20AH

ok. Lets say my daily energy offset is 5kWh, I assume 80% efficiency and I get 5 hours perfect sunlight a day. So my KWp would be 1.25. To find out how many panels are needed would be 1250watts/400(pmax rating of single panel) = 3.12. So I would need 3 of those panels to support 1.25KWP. i am unclear on how this translates to the amp hours

 

[BigPapaGD]

Ok I think I got it. So if I want to charge my batteries twice a day at 4hrs each charge. And the battery bank stores 5KWh every charge before being discharged. That's 3,360KWh consumed annually by the battery bank. If I divide that by 365(days in year) that's 9.2KWh needed daily. NOW I assume 80% efficiency and 5 hours perfect sunlight, and I get 2.3KWP. Now to calculate panels needed I take 2300WH/400(pmax rating of single panel) = 5.75. So I need 6 panels to put out optimal current to the bank for 2 charges day. Leaving me with 10KWH useable power a day, give or take.

 

[dmxtothemax]

For 10kw daily usage, you divide 10,000/400,
you need 25 panels
thats ignoring losses

 

[Zerax]

Ok, so I am a little stuck on one thing for a while now. For a nickel-iron battery bank of 24 volts, each cell is 1.2 volts and has a charging voltage of 1.65, so 33 volts is needed when for optimum charge. The 24 volt, 100Ah battery bank requires a optimal charge rate at c/4 (25 amps for a 100 Ah battery).

My question is this; If I have 3 solar panels rated at 50voc and 10isc that produce 400 watts each, and line them in a parallel circuit, I will be pushing 30 amps and 50 volts to my charge controller.

Once in my charge controller, does that 30amps and 50volts translate into enough energy to charge my battery bank in 4 hours? Or is the 30amp and 50 volts converted to watts to charge my battery bank, in which case I would be charging a 5kwh battery bank with only 1200 watts from the panels.

I would greatly appreciate clearing this up as it is hindering my further understanding of these systems.

There are several factors to take into account before you can arrive at a definitive answer...
Such as... how far down do you want to discharge your batteries ? 100% is never a good idea. Also, you need to work in the correct units where possible... so battery capacity is measured in Watt Hours... (Wh). Many people use Ah but that complicates matters when you have different voltages.

Your battery bank would appear to have a total capacity of 24v x 100Ah = 2.4kWh
Of this, only part of it is usable... I haven't looked that up for your battery chemistry... let's say 50% is usable.... so Usable Capacity is 50% of 2.4kWh is 1.2kWh
You have 3 solar panels that at max output give 400 Watts each... that's 1.2kWh in total (although I doubt the 400 is correct... that's a massive panel !!)
Your charge controller will convert whatever Volts and Amps it gets from the panels into the right Volts and Amps for your batteries (assuming it's setup is correct). This is not 100% efficient... lets say 90%
So... from the information you've told us... the quickest time that the usable capacity in your batteries can be replaced will be about 1 hr and 5 mins... But... the panels need to produce max output for this to happen... often clouds get in the way. You need to monitor the output over a period so that you learn what your exact location gives you.

 

[BigPapaGD]

So nickel-iron batteries have 81% useable capacity. They can be discharged to 1 volt per cell, or 18 volts per bank. So discharge would be around 20%. The idea I have in mind of having 2 charges a day is just having UP to 10kwh a day. Where if you were you to use power during the day you could use UP TO 10kwh granted the battery discharges while charging. The battery bank is actually 24 volts, 200AH (5.4KWH total, 4.3KWH usable power). The panels provide twice the amount of wattage needed to fully charge the battery once a day, so if inclement conditions arise and my panels output drops, I would have more panels capturing sunlight than needed. Now a Nickel-iron battery of 200Ah needs 50 amps at C/4, so I plan to wire 2 strings in parallel providing 60 amps and 50 volts through the charge controller.

There are several factors to take into account before you can arrive at a definitive answer...
Such as... how far down do you want to discharge your batteries ? 100% is never a good idea. Also, you need to work in the correct units where possible... so battery capacity is measured in Watt Hours... (Wh). Many people use Ah but that complicates matters when you have different voltages.

Your battery bank would appear to have a total capacity of 24v x 100Ah = 2.4kWh
Of this, only part of it is usable... I haven't looked that up for your battery chemistry... let's say 50% is usable.... so Usable Capacity is 50% of 2.4kWh is 1.2kWh
You have 3 solar panels that at max output give 400 Watts each... that's 1.2kWh in total (although I doubt the 400 is correct... that's a massive panel !!)
Your charge controller will convert whatever Volts and Amps it gets from the panels into the right Volts and Amps for your batteries (assuming it's setup is correct). This is not 100% efficient... lets say 90%
So... from the information you've told us... the quickest time that the usable capacity in your batteries can be replaced will be about 1 hr and 5 mins... But... the panels need to produce max output for this to happen... often clouds get in the way. You need to monitor the output over a period so that you learn what your exact location gives you.

So nickel-iron batteries have 81% useable capacity. They can be discharged to 1 volt per cell, or 18 volts per bank. So discharge would be around 20%. The idea I have in mind of having 2 charges a day is just having UP to 10kwh a day. Where if you were you to use power during the day you could use UP TO 10kwh granted the battery discharges while charging. The battery bank is actually 24 volts, 200AH (5.4KWH total, 4.3KWH usable power). The panels provide twice the amount of wattage needed to fully charge the battery once a day, so if inclement conditions were to arise I would have more panels capturing sunlight than needed. Now a Nickel-iron battery of 200Ah needs 50 amps at C/4, so I plan to wire 2 strings in parallel providing 60 amps and 50 volts through the charge controller. So I believe this gives me a standard of 4.3KWH with an additional 4.3KWH if the you were to use the initial 4.3KWH during the day. ​

 

[Dan]

Oh, that forum seemed a little dead but ill post there

He was a member on here too. Used to reply every now and again even after starting his forum. Be a shame to lose his knowledge.

Seems he isn't posting on his forum then too I assume? I haven't looked for a while.

I'm yet to finish of customising our solar forums. I'll take a look at his when I do that here in the coming weeks. Thanks for the heads up though!