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Old 02-21-2020, 11:25 AM   #1
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700 Watts of Solar with 400 AH Battery Bank - Too much?

For those knowledgeable in solar - are there any issues with this amount of solar with this battery bank? I read somewhere, don't recall where, that sometimes you can have too much solar for your battery bank.

Thanks!
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Old 02-21-2020, 11:30 AM   #2
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Originally Posted by mromberg1 View Post
For those knowledgeable in solar - are there any issues with this amount of solar with this battery bank? I read somewhere, don't recall where, that sometimes you can have too much solar for your battery bank.

Thanks!
Your panels will feed a solar controller which will look at your battery condition and only allow the power the batteries can accept. No danger of too much solar.
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Old 02-21-2020, 11:31 AM   #3
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I would say it is about right. In my experience 800 would be ideal if there is no shading and you spend winters in the South and boondock.
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Old 02-21-2020, 11:32 AM   #4
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What jcussen says. And no, 700watts is not considered large for a 400AH battery bank.
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Old 02-22-2020, 11:34 PM   #5
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As others have said, you are golden. There really is not a strong correlation or relationship to speak of between the amount of solar and the amount of battery. The amount of solar one can use is related to how much energy one uses. Ideally you'd like to collect somewhat more than one days energy use each day. More is better but if your solar can provide on the order of 1-2 days of energy use on a good sunny day, you are in good shape. By my definition, "good shape" means you won't be running a generator to charge batteries very often (less than weekly).

The battery capacity is a different calculation. You would want a bare minimum of 24 hours of battery capacity (i.e., assuming 80% discharge) but more is better. And more than that is better than that. i.e., no such thing as too much. The more battery you have the less likely you are to need to run a generator during days of inclement weather and low solar production.

I'd guess given your system that you use about 100 AH per day. Or, at least you could comfortably use about 100 AH per day and rarely need to charge from a generator. That's based on my experience .. which is about 75 AH of daily usage and a 300 AH LFP battery and 600W of solar. And exclusively fall and spring camping. I can weather four days of minimal sun without running the generator. I can do 6-12 days or more of mediocre sun. In both cases I drop behind a bit each day. In 5 months/year of camping, I used the generator twice in 2018 and once in 2019 (both on my current system). One of the times in 2019 was after 17 days of cloudy and less cloudy days. The battery charge started at 100% and wandered, losing ground most days and making up some on other days, but getting down to 20% after 17 days with no sun expected the next day ... so out came the generator.

Again, you are golden for 100 AH per day, which is a lot unless you have an electric refrigerator. In that case you will resort to the generator now and then. Now, if you run A/C from the battery, that's a whole other story.
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Old 02-22-2020, 11:44 PM   #6
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As others have said, you are golden. There really is not a strong correlation or relationship to speak of between the amount of solar and the amount of battery. The amount of solar one can use is related to how much energy one uses. Ideally you'd like to collect somewhat more than one days energy use each day. More is better but if your solar can provide on the order of 1-2 days of energy use on a good sunny day, you are in good shape.

The battery capacity is a different calculation. You would want a bare minimum of 24 hours of battery capacity (i.e., assuming 80% discharge) but more is better. And more than that is better than that. i.e., no such thing as too much. The more battery you have the less likely you are to need to run a generator during days of inclement weather and low solar production.

I'd guess given your system that you use about 100 AH per day. Or, at least you could comfortably use about 100 AH per day and rarely need to charge from a generator. That's based on my experience .. which is about 75 AH of daily usage and a 300 AH LFP battery and 600W of solar. And exclusively fall and spring camping. I can weather four days of minimal sun without running the generator. I can do 6-12 days or more of mediocre sun. In both cases I drop behind a bit each day. In 5 months/year of camping, I used the generator twice in 2018 and once in 2019. One of the times in 2019 was after 17 days of cloudy and not so cloudy days. The battery charge started at 100% and wandered, losing ground most days and making up some on other days, but getting down to 20% after 17 days with no sun expected the next day ... so out came the generator.

Again, you are golden, 100 AH per day, which is a lot unless you have an electric refrigerator. In that case you will resort to the generator now and then. Now, if you run A/C from the battery, that's a whole other story.

All of my comments above are valid only for lithium batteries. AGM would be somewhat similar but wet cells are a very different situation.
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Old 02-23-2020, 04:32 AM   #7
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No, not too much. As commented there is not really a direct correlation of solar production vs battery bank capacity. There are so many variable things impacting solar production. My sizing recommendation is to typically install as many watts as roof space allows.
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Old 02-23-2020, 07:02 PM   #8
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More solar is helpful, especially on overcast days.
Your batteries have a maximum amperage charge rate (bulk charge). The solar controller should be in charge of that, but you get what you pay for.
Check out battery university . com and your battery specs.

My 100AH AGM have a max charge rate of 30amps. You have 400AH of batteries. So I would guess that 700W (54amps at 13v) is OK.
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Old 02-24-2020, 01:56 PM   #9
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No, not too much. As commented there is not really a direct correlation of solar production vs battery bank capacity. There are so many variable things impacting solar production. My sizing recommendation is to typically install as many watts as roof space allows.

X2! I have room for two and if I push it four more 100W panels. I'm having difficulty resisting doing that. I have to keep telling myself that in 10 months of RV'ing (virtually all boondocking) I've used my generator only three times .......
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Old 02-24-2020, 02:34 PM   #10
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If the PV can generate more than the battery bank can take, set the max limit in the controller. Likely most of the time will not reach that value anyway. Average daily production will likely be higher.
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More solar is helpful, especially on overcast days.
Your batteries have a maximum amperage charge rate (bulk charge). The solar controller should be in charge of that, but you get what you pay for.
Check out battery university . com and your battery specs.

My 100AH AGM have a max charge rate of 30amps. You have 400AH of batteries. So I would guess that 700W (54amps at 13v) is OK.
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Old 02-24-2020, 02:45 PM   #11
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I have 680W of monocrystal panel's and a 40 amp mppt controller, and have never seen more than 34 amps of charging (in the best summer day in SoCal) to my four 100 amp LiFePo batteries.
I boondock a lot and wish I had bought the 1000+W system at a minimum, but everyone's needs/desires are.different.
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Old 02-25-2020, 12:47 AM   #12
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I have 680W of monocrystal panel's and a 40 amp mppt controller, and have never seen more than 34 amps of charging (in the best summer day in SoCal) to my four 100 amp LiFePo batteries.
I boondock a lot and wish I had bought the 1000+W system at a minimum, but everyone's needs/desires are.different.

That result is surprising. I'd be interested in seeing some details on the system.
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Old 02-25-2020, 01:22 AM   #13
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"I have 680W of monocrystal panel's and a 40 amp mppt controller, and have never seen more than 34 amps of charging"


Can I ask what size wire you're running from panels to controller, and from controller to batteries? And, also, (I'm nosy) did you wire your panels all parallel, or in series/parallel groups, or ???
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Old 02-25-2020, 09:08 AM   #14
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Hclarkx and Bobby F, the system I bought and installed was the GoPower AE680 (I think that what it's called), which at the time was four 170W panels (now 190W) and a single 40 amp MPPT controller.
I chose to wire the panels as to serise pairs, wired in parallel (verified acceptable by GoPower tech support). The kit comes with everything needed to wire all in series, but I bought additional connectors to support the series/parallel config.
The reason I don't get maximum theoretical charging amps, is only because my panels are fixed flat mounted and I do not try to angle or align the panels to best sun angle. That is one of the reasons I wish I'd installed at least a 1000W system so the normal average power generation was more to our usage.
The GoPower kit came with 10 gauge wire to the controller then I think 4 gauge from controller to batteries (best to look up the specific info on their website).
If I had it to do over, I'd put six 190W or larger panels, wire in 2 or 3 series pairs, down to a Victron 150/80 controller with all of the wiring sizes to meet the cable length/current requiements.
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