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Old 06-11-2018, 11:25 AM   #11
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I put the hours of use next to each item. Lets say... 3 days with no sun. Maybe another calculation with 5 days no sun. I was looking at Trojan AGM batteries.


As far as the alternator/charger, are you talking about one that converts from 12v to 24v?


Again I have no idea what any of this stuff is so without links, photos, model numbers, etc., I cannot learn anything.



Thanks
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Old 06-11-2018, 11:45 AM   #12
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I put the hours of use next to each item. Lets say... 3 days with no sun. Maybe another calculation with 5 days no sun. I was looking at Trojan AGM batteries.
8kWh times 3 days is a massive battery bank of 24kWh of usable capacity. If going lead-acid, that would be a 48kWh lead-acid bank (3,840ah). I think, if doing my math right, that would require something like 34 typical golf cart batteries (or T105's). That will weigh something around 2,100 lbs (just batteries). I'd say lithium would be a FAR better option but will cost a buck or two...

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As far as the alternator/charger, are you talking about one that converts from 12v to 24v?

Again I have no idea what any of this stuff is so without links, photos, model numbers, etc., I cannot learn anything.
Steve previously provided the following. I have no experience with this approach so can't offer much. Sorry... hopefully someone else will chime in on this.
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Originally Posted by PNW_Steve View Post
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Old 06-11-2018, 11:46 AM   #13
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What large lithium banks are available?
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Old 06-11-2018, 12:06 PM   #14
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What large lithium banks are available?
I have no idea. I only have experience with Starlight Solar (positive). Their stuff is here.
GBS 200AH Cells
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Old 06-11-2018, 12:08 PM   #15
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I have no idea. I only have experience with Starlight Solar (positive). Their stuff is here.

GBS 200AH Cells

$2,100 for 200ah?! I won't see how that is a better option than a Trojan at $300 for 300ah
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Old 06-11-2018, 04:22 PM   #16
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Deep discharge of a lead acid battery (the Trojan) causes small but irreversible damage that will shorten its lifetime. A LiFeMnPO4 battery endures deep discharge much better. The ability to discharge deeper, plus the inherently lighter weight and smaller volume of a lithium battery mean that a lithium battery will be much lighter and require much less volume as compared to a lead battery with the same usable Ah capacity. For a mobile application like an RV, size and weight become important considerations as the size of the battery bank grows.

For the 8 kWh * 3 days scenario JD wrote about a person might look at 2100 pounds of lead battery and say "no, that just isn't going to happen." The lithium option, though more expensive, could be "better" because the lead option may be impossibly heavy at that scale.


An alternative way of approaching the panel-to-battery ratio is to consider how long you're willing to wait for the battery bank to fully re-charge after it has been drawn down. To do this, a person could estimate the production from the solar array on a good day and the average (or at least the minimum) daily consumption. Feed those two figures into this equation:

[(daily production) - (average consumption)] * (days allowed to fully re-charge) / (1 - allowed depth of discharge)

The daily production minus average consumption is what's available to be stored into the battery bank. Multiply that by the number of days you want to allow for the bank to recover -- probably a fraction of a day up to a couple of days. That'll yield the "usable capacity" of the battery bank. Finally, divide by 1 minus the maximum depth of discharge you want to allow (perhaps 50% for lead batteries with reasonable life, 30% for lead batteries you're willing to replace more frequently, or 5% for lithium batteries) to account for the fact that batteries are sold by total capacity, not usable capacity.

Design of a balanced overall system (loads, storage, generation) is an iterative process: estimate the loads, calculate a storage requirement, estimate the generation, calculate whether it's adequate, adjust parameters, repeat.
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Old 06-11-2018, 10:20 PM   #17
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I am not sure that i understand your dilemma. A design is compromise. You are using 60 % of your energy on running a bunch of computers 24H a day. Why do you not take the time and turn them of when you are done with them. that would be a lot cheaper then loading your rig up with 2100lbs of lead.

I think you have to spend a lot more time reading and trying to understand what your decisions are about and what the consequences are. To just quickly ask for part numbers that others have researched for you does not lead to any understanding on your side.


Your search for vehicle generator are useless if you do not provide that length and frequency that you are running your engine and if that would be enough to even generate enough watthours to fill up you battery bank. Once you have decided or compromised on that you can go on to the next step what charger/ controller/ system to use to get those watthours actually in your battery.


Good luck.
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Old 06-13-2018, 07:31 PM   #18
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I've only read about it briefly here and there, but has anyone done or had any experience with capacitor banks??? I know it's possible, but is it sensible??
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Old 06-13-2018, 08:22 PM   #19
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Quote:
Originally Posted by family wagon View Post
Deep discharge of a lead acid battery (the Trojan) causes small but irreversible damage that will shorten its lifetime. A LiFeMnPO4 battery endures deep discharge much better. The ability to discharge deeper, plus the inherently lighter weight and smaller volume of a lithium battery mean that a lithium battery will be much lighter and require much less volume as compared to a lead battery with the same usable Ah capacity. For a mobile application like an RV, size and weight become important considerations as the size of the battery bank grows.

For the 8 kWh * 3 days scenario JD wrote about a person might look at 2100 pounds of lead battery and say "no, that just isn't going to happen." The lithium option, though more expensive, could be "better" because the lead option may be impossibly heavy at that scale.


An alternative way of approaching the panel-to-battery ratio is to consider how long you're willing to wait for the battery bank to fully re-charge after it has been drawn down. To do this, a person could estimate the production from the solar array on a good day and the average (or at least the minimum) daily consumption. Feed those two figures into this equation:

[(daily production) - (average consumption)] * (days allowed to fully re-charge) / (1 - allowed depth of discharge)

The daily production minus average consumption is what's available to be stored into the battery bank. Multiply that by the number of days you want to allow for the bank to recover -- probably a fraction of a day up to a couple of days. That'll yield the "usable capacity" of the battery bank. Finally, divide by 1 minus the maximum depth of discharge you want to allow (perhaps 50% for lead batteries with reasonable life, 30% for lead batteries you're willing to replace more frequently, or 5% for lithium batteries) to account for the fact that batteries are sold by total capacity, not usable capacity.

Design of a balanced overall system (loads, storage, generation) is an iterative process: estimate the loads, calculate a storage requirement, estimate the generation, calculate whether it's adequate, adjust parameters, repeat.


Let's not forget that this is a school bus. 2100 lbs is less than 15 kids worth of weight. In the amount of lithium batteries that it would take to store the power we are looking at, we could just buy a brand new $60,000+ motor home. I'm not worried about having to buy 10 or 15 lead acid batteries.



Quote:
Originally Posted by joeblack5 View Post
I am not sure that i understand your dilemma. A design is compromise. You are using 60 % of your energy on running a bunch of computers 24H a day. Why do you not take the time and turn them of when you are done with them. that would be a lot cheaper then loading your rig up with 2100lbs of lead.

I think you have to spend a lot more time reading and trying to understand what your decisions are about and what the consequences are. To just quickly ask for part numbers that others have researched for you does not lead to any understanding on your side.


Your search for vehicle generator are useless if you do not provide that length and frequency that you are running your engine and if that would be enough to even generate enough watthours to fill up you battery bank. Once you have decided or compromised on that you can go on to the next step what charger/ controller/ system to use to get those watthours actually in your battery.


Good luck.
later j

Please do the same with what I have taken the time to post.


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Originally Posted by jimburke77502 View Post
I've only read about it briefly here and there, but has anyone done or had any experience with capacitor banks??? I know it's possible, but is it sensible??

You can start a new thread for that. I'm sure many want to talk about it.
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Old 06-13-2018, 09:37 PM   #20
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Again I have no idea what any of this stuff is so without links, photos, model numbers, etc., I cannot learn anything.

Well then, it's time to start reading up by on it so you can make an informed decision before you take information from random internet people and invest 1000's of dollars on something you don't understand.

Start researching how different batteries work, go to the NAWS website/forum, read every thread on this site and read everything you can about power consumption, storage, and creation.

I don't think anyone here is just going to tell you what to buy because it's such a personal choice. Also, many of the people that respond here have deep knowledge of a lot of the issues here but they are not teachers. They help those who help themselves, in my experience.
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