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Old 05-22-2018, 01:28 PM   #1
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Solar Power for The Derelicte Bus

Part of me typing this is for myself, BUT another part of me wants to sanity check the hell out of this, so here we go:

I have 1.6kW of solar power. Output from 5 panels @ 24V is 65Amps. What I'm planning on doing is having an MPPT (60A) charge controller for my panels. It will feed at 12V at 130A to the battery bank.

The battery bank will be composed of 8 of these Crown Batteries and they'll be wired in parallel to deliver roughly 1600aH at 12V (800aH useable). I'll use 4/0ga wire to connect the battery bank to the Inverter and the batteries themselves. The battery bank will be monitored via this Tristar readout. There will also be a DC bus with switches/fuses/cutoffs for distribution to series lighting systems within the cabin. The Inverter will flow out to an AC bus with fuses/switches/cutoffs to the outlets that will be placed throughout the cabin.

My plan for boondocking is to not have a generator. My plan if my solar system fails is to get to an RV park and hook shore power into the inverter. I think I'll have enough solar and battery bank power to survive long enough to get to one, and worst case scenario, if the bus breaks down at the same time then I'm probably stuck anyway.

The surge on the Inverter should be enough to handle the compression stage of a 5,000btu air conditioner with residual amp usage should be well within acceptable ranges, not to mention the only other major appliance I will have is a refrigerator and a laptop.

I'm looking for constructive feedback from the forum, so any help is appreciated. Maybe I should add in another battery? I know that my 5 panels are pretty much at the upper limit of the capabilities of the TriStar MPPT charge controller (assuming they're putting out 100% power). I have read that TriStar MPPTs can be wired in parallel to feed into the battery bank. (It's just going to cost more.)

Thoughts?
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Old 05-22-2018, 01:49 PM   #2
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Good plan but how can you survive anywhere with just 5000btu's of aircon?

I know your bus is well insulated and well put together but you must handle the heat way better than myself.
Thanks,

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Old 05-22-2018, 01:55 PM   #3
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If I understand correctly, you are planning on running 5 320watt panels in parallel to feed a 60 Amp MPPT charge controller to charge 8 12v batteries in parallel.

If that is correct, I see an number of issues.

Lets start with charge controller capacity: 60 Amps. That is the maximum current that it will pass to the batteries. Configured this way you will not be able to properly charge the battery bank you spec'd. You would need to feed your batteries something close to 150 amps.

Batteries: Paralleling 8 batteries is a bad idea. Read up on parallel strings and equalizing. Also, for the capacity system you are considering you would benefit from going with a 24v or 48v battery bank.

Panels: As you will rarely, if ever, get the full rated power out of the panels your 1600watt array is undersized for this battery bank.

I am going to pause here and ask: What is your energy budget?

That is the very first question to answer in the solar design process. Figure out as best you can what your loads will be and size your system to fit.

There are a number of worksheets online that will help you list all of your loads, what their power consumption is and duty cycle. Once you have added up all of your power needs you can properly size your solar array, charge controller and battery bank.

I would suggest a bit of reading to guide your design decisions:

http://jdfinley.com/energy-audit-watt/

https://handybobsolar.wordpress.com/

https://www.solarpaneltalk.com/forum/off-grid-solar

https://www.solarpaneltalk.com/forum...your-batteries

https://www.solarpaneltalk.com/forum...tteries-part-2
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Old 05-22-2018, 02:23 PM   #4
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Originally Posted by PNW_Steve View Post
If I understand correctly, you are planning on running 5 320watt panels in parallel to feed a 60 Amp MPPT charge controller to charge 8 12v batteries in parallel.

If that is correct, I see an number of issues.

Lets start with charge controller capacity: 60 Amps. That is the maximum current that it will pass to the batteries. Configured this way you will not be able to properly charge the battery bank you spec'd. You would need to feed your batteries something close to 150 amps.

Batteries: Paralleling 8 batteries is a bad idea. Read up on parallel strings and equalizing. Also, for the capacity system you are considering you would benefit from going with a 24v or 48v battery bank.

Panels: As you will rarely, if ever, get the full rated power out of the panels your 1600watt array is undersized for this battery bank.

I am going to pause here and ask: What is your energy budget?

That is the very first question to answer in the solar design process. Figure out as best you can what your loads will be and size your system to fit.

There are a number of worksheets online that will help you list all of your loads, what their power consumption is and duty cycle. Once you have added up all of your power needs you can properly size your solar array, charge controller and battery bank.

I would suggest a bit of reading to guide your design decisions:

Energy Audit - Watt For? - JdFinley.com

https://handybobsolar.wordpress.com/

https://www.solarpaneltalk.com/forum/off-grid-solar

https://www.solarpaneltalk.com/forum...your-batteries

https://www.solarpaneltalk.com/forum...tteries-part-2
I know that handybob gets a lot of credit, but I can't stand reading his rants (which are all he writes). There's so much stuff that he references which I simply will not get because he's so deep in the industry.

I digress...

So, I was afraid that would be the case, so that means that I'd need two MPPT charge controllers.

I've got a 12V inverter, so a 24V bank is less than ideal. I have no problem downsizing the bank size to 6 (?), which would be alright in parallel then? If I'm buying less batteries, I can buy another MPPT. The panels I got for a great price, so I'm stuck with 'em.

I do, handle heat well, but more than anything 5,000 btu is perfect for my setup.
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Old 05-22-2018, 03:00 PM   #5
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Check out this sizing tool.

http://www.midnitesolar.com/sizingTool/

I have 4x350 watt panels. I'll be running 2 pairs in series parallel. I have a MPPT Midnite Classic 200 that will support this.
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Old 05-22-2018, 07:53 PM   #6
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1) Don't buy anything else until you have a proper design completed.

2) Read, study and learn.

3) Perform a thorough energy audit.

4) Design a system that will serve your needs. We will help you with this.

5) Now that you know what you need, buy the components that you need to complete the system you designed to serve your needs.

If you insist on installing 5 panels in parallel and keeping your 12v inverter you may find yourself with a system that does not meet your expectations. I'm not trying to be harsh. You kind of got ahead of yourself when you bought components for a system that you had not designed yet.
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Old 05-22-2018, 10:15 PM   #7
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The panels wonít be in parallel. The batteries would originally have been. The inverter is the limiting factor for the batteries. I could do more batteries at 6 volt wired in series/parallel. I was at roughly 13% amp output to battery capacity. My energy audit left me with a daily usage of no more than 70ah.

What would not meet my expectations as planned? The usable amp hours?
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Old 05-23-2018, 06:41 AM   #8
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To your most recent question, a long parallel string of batteries is almost guaranteed to work "poorly" due to the long string and nature of how batteries work (basically). I am a little less suspect of properly connected parallel battery installations. Read this. I am not an EE and the largest lead-acid bank I have ever worked with was four batteries so no experience with a large one. I started down the path of creating a large lead-acid battery bank (12-14 batteries) and quickly decided that lithium was an easier/better option. It does come at a price though.

Quote:
Originally Posted by Velocipedic View Post
It will feed at 12V at 130A to the battery bank.
As already noted, The Morningstar TS-MPPT-60 controller will limit its output to 60 amps (regardless of the voltage). Bumping up to a 24VDC battery bank is very helpful in this regard (twice the 'bang' from the controller).

Quote:
Originally Posted by Velocipedic View Post
The battery bank will be monitored via this Tristar readout.[/URL]
The charge controller (panel/meter) does not monitor the battery bank. It may monitor voltage but that is a poor indication of SOC. To have decent info, you need a battery monitor that watches all of the electrons flowing into/out of the bank using a shunt. We seem to mention this repeatedly - generally I mention the Victron (ok) and Trimetric (better); Steve mentions using a hydrometer (best but most inconvenient).

Quote:
Originally Posted by Velocipedic View Post
My plan for boondocking is to not have a generator. My plan if my solar system fails is to get to an RV park and hook shore power into the inverter.
It must be an inverter/charger? I don't have a generator and spend nearly all my time boondocking. The idea of living (normally) using only power from the sun is very realistic. Obviously, there are many factors that can effect this.

Quote:
Originally Posted by Velocipedic View Post
My energy audit left me with a daily usage of no more than 70ah.
70ah at 12VDC?? This sounds off a bit - especially if you have a refrigerator. This is a very small bit of power at 12VDC, obviously twice as much at 24VDC but still not a lot for the size of system that we are discussing. My refrigerator alone (it is a big one) uses nearly twice that much each day (120Ah).

Follow Steve's advice - it is rock solid!
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Old 05-23-2018, 10:01 AM   #9
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Right, so two MPPT's to feed into the bank. So I've looked for battery bank configurations and would have 12 6V's wired in series, to make 6 12V's with approximately 1200aH (maybe less?)... is this what you're suggesting?

Trimetric battery monitor. Copy.

It is an inverter/charger. Best of both worlds, but limited to 12V DC input.

I'll have a tiny mini-fridge. Most of the time I don't have stuff in my fridge anyway, so I unplug it. The A/C will only be used infrequently during the day (since I work away from home), so daytime on weekends only, with fans as needed during the night. During the winter, possibly electric blankets. TV/Electronics at a minimum, with a few LED lights. A hairdryer if/when I ever have a girlfriend.
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Old 05-23-2018, 12:09 PM   #10
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Quote:
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Right, so two MPPT's to feed into the bank.
If sticking to 12V battery bank, yes. Be sure you have the type that can be "networked" - or whatever the right manufacturer term is so they work together.

Quote:
Originally Posted by Velocipedic View Post
So I've looked for battery bank configurations and would have 12 6V's wired in series, to make 6 12V's with approximately 1200aH (maybe less?)... is this what you're suggesting?
No, I'm not suggesting that. I agree with Steve that a big lead-acid battery bank is generally a bad idea (not optimal for our typical RV style use). However; if you are going to do it, look closely at the connection information in the link I provided.
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Old 05-23-2018, 12:47 PM   #11
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No, I'm not suggesting that. I agree with Steve that a big lead-acid battery bank is generally a bad idea (not optimal for our typical RV style use). However; if you are going to do it, look closely at the connection information in the link I provided.
OK, so the way I'm seeing it, the alternative is... lithium? Or go for bigger batteries like this and max out at 6 total, 3 batteries in parallel?
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Old 05-23-2018, 05:05 PM   #12
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OK, so the way I'm seeing it, the alternative is... lithium? Or go for bigger batteries like this and max out at 6 total, 3 batteries in parallel?
Six wired series/parallel is a pretty common arrangement.

That wiring explanation is one I've seen before, and it's enormously helpful.

I'd love to go with lithium, and I understand the arguments that say it may be cheaper in the long run ... but it's very expensive upfront, and that's a factor.
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Old 05-23-2018, 05:48 PM   #13
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OK, so the way I'm seeing it, the alternative is... lithium? Or go for bigger batteries like this and max out at 6 total, 3 batteries in parallel?
Lithium is a great option, but not cheap.

I'm not saying that you should not do a large, multi-LA-battery bank. I am only saying that there are potential issues. Having never had one myself, I can't suggest one way or the other. Just read up on the potential issues, how to detect/remedy them, and go in eyes wide open.
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Old 05-23-2018, 07:34 PM   #14
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Battery to Inverter Cables

You can get 3' and 6' #2 battery cable sets from Harbor freight at a good price. With that much power flowing would recommend at least #2 cable size. They are on the shelves where they have their inverters.

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Old 06-01-2018, 08:28 AM   #15
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Ok, so this is what I'm going to use for the battery bank, 3 bricks of 2 series. I'll have two charge controllers as well and 4/0ga wires. Final thoughts before I buy?
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Old 06-01-2018, 09:29 AM   #16
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Considering what you are planning as far as the battery bank size and such... it would be better to step up in voltage. This will decrease the cost of wire and make it easier to configure a properly sized battery bank. Will also be a good bit safer.


I wouldn't go with 12v... 24-48 would be ideal.


The charge controller you have listed will do 60a charging at 48v... at 24v, your panels will produce more then that. Your voltage needs to be in spec too.


What panels are you using exactly? Have a link?


What equipment do you already own?
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Old 06-01-2018, 03:23 PM   #17
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Considering what you are planning as far as the battery bank size and such... it would be better to step up in voltage. This will decrease the cost of wire and make it easier to configure a properly sized battery bank. Will also be a good bit safer.


I wouldn't go with 12v... 24-48 would be ideal.


The charge controller you have listed will do 60a charging at 48v... at 24v, your panels will produce more then that. Your voltage needs to be in spec too.


What panels are you using exactly? Have a link?


What equipment do you already own?
The driver for the 12V is that I've got an inverter with specs that I want and it was at a great price, but at 12V. Unless a step down circuit from 24 -> 12 is worth it on the inverter.... It's an AIMS 4000W (surge to 9000).

The panels that I have output at 37V at 8.72a. They're 325W. Monocrystalline, 72 Cell panels, at about $125 each.
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Old 06-01-2018, 03:42 PM   #18
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Personally... If you are bent on using that inverter (wasn't designed to be ran off of a battery bank)... I'd get a big alternator and run it off the starting batteries and only use it with the engine running.


4kw is just too much to get reliable performance out of on a 12v based system.


With the panels you've got... that charge controller can take 150v from the array... so running the panels in series is out of the question as you'll be over that right off the bat and that doesn't take into consideration voltage rise from cool weather.


At 12v... that controller is only capable of using ~800w worth of panels (60a)... So you'd need at least 2 of them. The battery bank is going to be a pain as you would need to parallel quite a few batteries together which isn't a good idea for longevity (let alone safety as the amperage capacity will be VERY high). The cost of properly sized cables, cable ends, fuse holders, etc..etc..


I'll put it this way... I think you'll end up spending a lot of money and not being happy with the performance. If I were you, I'd use the big inverter like a generator to run bigger items while driving (or sell it)... get a smaller inverter or an inverter that can handle 24-48v for use with the solar system. Big inverters like that are meant to be powered by a big alternator on a 12v system... not a battery bank and a few solar panels.
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Old 06-01-2018, 04:11 PM   #19
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So, I might be able to find someone to buy it for roughly the same price... or eat a little bit of money and get a 24V capable inverter, but that then drives some changes... That also means that I can't run 12V DC lights direct off of the battery.

A 24V battery bank seems like it may involve more headache, but what are the benefits?

The next problem is then the battery bank configuration, since I'll then have to wire 12V batteries in series and then I'll have 3-4 sets of those. I'd rather not have two battery banks (one for AC and one for DC), but it is an option, I suppose... Really though, I don't mind spending more on wires for the battery bank or a second charge controller.
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Old 06-01-2018, 04:21 PM   #20
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You could always run 12v off the starting batteries with a low voltage shut off of some sort...


Massive inverters at 12v require LOTS of amperage. At its rated power, that inverter would be pulling almost 340 amps from the battery bank... at full surge capacity... 750 amps.


Running the same power levels at 24v cuts that in half... at 48v, you are down to ~84 amps for the same wattage. That means smaller wiring... that means a much more manageable battery bank... cheaper charge controllers.. etc.


If you want to stay at 12v... then step down the inverter size a good bit.


The most I would run would be 2kw and thats pushing it for most. 1500w would be better. If you need 4kw+ on a regular basis, get a generator or find ways to decrease your power demands.
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