What determines how long a bank will last...watt hours or amp hours? Or is it a combination of both?
Calculate acceptable over paneling.
- Thread starter McDubsy
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sunshine_eggo
Happy Breffast!
Ah needs voltage to be meaningful.
Wh is independent of voltage.
Your example: 500W and 10A forces system voltage to 500W/10A = 50V.
If you know something uses 100W, and you have 1000Wh of storage (regardless of voltage), you know you can run that load for 10 hours.
If you know something uses 10A @ XV, and you have a 100Ah XV battery, you know you can run that load for 10A.
X is the battery voltage.
timselectric
If I can do it, you can do it.
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Yes
timselectric
If I can do it, you can do it.
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Watt hours is the capacity.
It's determined by voltage x amperage hours.
Yes, ouch. Going to 24V and halving the needed size of the SCC reduces the cost of the SCC to less than half. Win win.
timselectric
If I can do it, you can do it.
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For $850 I can get another AIO. lol
2 chargers
2 chargers
sunshine_eggo
Happy Breffast!
Pansies!
My MPPT was over $900.... and it was the second one I bought because the first ~$700 one was too small.
My MPPT was over $900.... and it was the second one I bought because the first ~$700 one was too small.
Would you clarify that please? Do you mean a controller rated for 50 amperes output can be pushed to 100 or 150 amperes? Those are staggering increases over the rated outputs
pollenface
Solar Addict
50% over?
Panels don't push power to an SCC. The SCC pulls whatever power it needs, up to its max amperage. While I personally would not put 2 or 3 times the max usable wattage on an SCC, it should be fine with any worthwhile SCC. Again, that extra wattage is not pushed to the SCC so the extra panels are not stressing the SCC.
Let's walk through an example. Let's say we have a 12V SCC rated for up to 50A max battery charge current. If the battery can be charged at 14.4V then the SCC will take a maximum of 14.4V x 50A = 720W from the panels. Let's say you add 1500W of panels to the SCC. If it's midday and the panels could produce 1300W at the moment, the SCC will still only try to pull a max of 720W and that's if the battery is low enough and/or there is enough loads to make use of the 50A. If it's morning or evening and the panels can only possibly produce 500W at the moment then the SCC will take those 500W and convert it to 14.4V and 34.7A. That's the advantage of over paneling. If there were only 720W of panels installed then under those same conditions there would be less than 250W instead of 500W.
So over paneling helps in lower light conditions and does no harm in high solar conditions. Of course this all assumes the other important limits are respected (such as Voc).
I just read the specifications for a Victron 100-50 controller. Victron says their controller will limit the input so that the 100V input and 50 amp output current rating cannot be exceeded. Sure, I agree that over panelling does help to give the controller its designed maximum power but you will not get greater output than Victron's designed limitation.
No SCC will give you more than the max rated output current. No one has claimed any will.
Edit: use a less confusing description of the output current.
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WHAT?????????????
This started with my questioning:
''
rin67630 said:
You can exceed the max amps of the MPPT controller by factor 2 or 3 or even more, but stay well under the max voltage !
Factor 0.8 is the very maximum i would try. ''
And this has zero to do with what a battery is rated for. The discussion is about the controller
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That person meant you can over panel by 2 or 3 times in wattage. At least that is how I interpreted that statement. But the SCC will never output more than its rated amps.
I said the max amp output of an SCC is its max battery charge current. But I guess that is not the best description because that output current may not all go to the batteries. It can also go to offset loads. I didn't mean to imply that it is in any way related to the battery bank rating. I've edited my previous post to use a less confusing description.
No push back here Rmaddy. Your posts are usually rich in technicals that benefit newcomers so keep up sharing
Thanks. I certainly miss things on occasion. I have no problem correcting things when something is pointed out.
Thank you for all the terrific help and clarification. I think I have a much better handle on the situation now.
But, just to make sure, I want to run a scenario by you and see if I'm thinking correctly.
I have 8 solar panels that I want to install on my system.
They are:
-325w
-VOC 40.5v
-ISC 10.9a
The SCC is 150v/100a
And the battery bank is 12v 600ah
In order to keep the volts under the VOC of the SCC I will need to wire 2 sets 4 panels in series which would yield a string at 40.5v/43.6a
Then wire the 2 strings in parallel yielding a total of 81v/43.6a going to the SCC...which falls well below the 150v/100a limits.
Am I think that through correctly?
I apologize, I do not know how to abbreviate that wiring in a more simple way.
But, just to make sure, I want to run a scenario by you and see if I'm thinking correctly.
I have 8 solar panels that I want to install on my system.
They are:
-325w
-VOC 40.5v
-ISC 10.9a
The SCC is 150v/100a
And the battery bank is 12v 600ah
In order to keep the volts under the VOC of the SCC I will need to wire 2 sets 4 panels in series which would yield a string at 40.5v/43.6a
Then wire the 2 strings in parallel yielding a total of 81v/43.6a going to the SCC...which falls well below the 150v/100a limits.
Am I think that through correctly?
I apologize, I do not know how to abbreviate that wiring in a more simple way.
Ampster
Renewable Energy Hobbyist
i am having a DejaVu. This is how this thread began. I thought the question was answered already. Do you need the post number?
wiseacre
Solar Addict
no, you've got it backwards
You are describing a 4s2p configuration
when combining panels in series the voltage adds up while the amps remain the same
Parallel strings will add up the amps while the voltage remains the same
with a VOC of 40.5 volts a string of 4 panels will have a voltage of 162v resulting in a deep fried SCC
dropping to 3 panels in series leaves you one panel short for a balanced 3s3p configuration
with 8 panels you're looking at a 2s4p configuration
2s4p results in 81v and 43.6a
Ampster
Renewable Energy Hobbyist
I think you mean Amps. All in all that was a great description.
The only thing i would add is that the controller will never pull that many Amps because it is limited to Charging a 12 volt battery at 100 Amps which might be 1300-1400 Watts. On the panel side that would be about 17 Amps at 81 Volts.
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