Help with SOLAR electric system design...

 
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Post by Ky Speedracer » Fri. Mar. 22, 2019 11:14 am

I have recently acquired some expensive inverters, battery chargers and batteries.
My company manages a mobile mammography/cancer screening unit for a local hospital. Due to an upgrade in x-ray equipment, they had to completely upgrade the power source on the truck with larger equipment. The equipment that was removed was given to me.

I have -

2 - Xantrex Freedom SW 815-3012 inverter chargers http://www.xantrex.com/power-products/inverter-ch ... ewgen.aspx

2 - Xantrex TrueCharge2 Series battery chargers http://www.xantrex.com/power-products/battery-cha ... e-2-2.aspx

4 - 8275 series GEL Batteries from NAPA https://www.napaonline.com/en/p/NBP8275

1 - Xantrex TrueCharge2 remote panel http://www.xantrex.com/power-products/default/tru ... emote.aspx

1 - Xantrex Xanbus System control Panel http://www.xantrex.com/power-products/default/sys ... panel.aspx

and some other miscellaneous stuff like a battery disconnect, cables, fuses, etc...

I am not an electrical engineer by any stretch (nor do I play one on TV). I have a basic background in electricity and have a general knowledge of solar and how it works, and how it should be setup as a power source (probably just enough knowledge of both to be dangerous...).
I know that you use solar panels to send power to a charge controller to batteries and then the batteries send 12v, 24v, 48v DC power to an inverter to convert to AC power to run lights, appliances etc...
I know that the higher the voltage that you can use from the solar panels, the smaller the wire needed to get power from the panels to the charge controller to the batteries. I also know that the higher the DC battery voltage, the easier it is to convert to AC 120 volt.

That's basically where my expertise (or lack there of) stops.
I have read through specifications and info related to these components and it's quite honestly over my head. These components appear to be much more sophisticated than what is generally needed for a simple off-grid solar system.

I have an off-grid cabin in southern KY that I would love to have power in. My fear is, this equipment would be serious overkill for that application. I also have concern with it being remote and not used daily in the winter, there is no way to keep those batteries in a climate controlled environment. My understanding is that batteries in freezing weather is not good for them...

My next thought was to use this equipment in my primary home. Setup a grid-tie and an off-grid system. KY weather is not a great area as it relates to hours of sunlight per day. Most charts show that our area gets between 3.5 to 5.5 hours of sunlight throughout the day depending on time of year.

I know that there are several guys on this forum that are very knowledgeable with regard to solar and electric. I was hoping I could get a couple of you to take a look at what I have and give me some feedback on the equipment I have and whether there is a practical application for it in one or both of the scenarios I've described.

Thanks in advance for your time!
Steve


 
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Post by Richard S. » Fri. Mar. 22, 2019 12:21 pm

Ky Speedracer wrote:
Fri. Mar. 22, 2019 11:14 am
I also have concern with it being remote and not used daily in the winter, there is no way to keep those batteries in a climate controlled environment. My understanding is that batteries in freezing weather is not good for them...
No idea how people deal with this but my first thought would be to compartmentalize them in small insulated space and use a few light bulbs for heat. You should have plenty of electric for that, yes? Batteries would be indoors and same space could be heated with your primary heat when you are there?
My next thought was to use this equipment in my primary home. Setup a grid-tie and an off-grid system. KY weather is not a great area as it relates to hours of sunlight per day. Most charts show that our area gets between 3.5 to 5.5 hours of sunlight throughout the day depending on time of year.
There is going to be adtional expenses with net metering system and what they are depends on the utility/state, it's easily cheaper than batteries however if you have the batteries it's likely best to avoid net metering.

 
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Post by McGiever » Fri. Mar. 22, 2019 1:27 pm

Ky Speedracer wrote:
Fri. Mar. 22, 2019 11:14 am

I have recently acquired some expensive inverters, battery chargers and batteries.

I have an off-grid cabin in southern KY that I would love to have power in. My fear is, this equipment would be serious overkill for that application. I also have concern with it being remote and not used daily in the winter, there is no way to keep those batteries in a climate controlled environment. My understanding is that batteries in freezing weather is not good for them...

My next thought was to use this equipment in my primary home. Setup a grid-tie and an off-grid system. KY weather is not a great area as it relates to hours of sunlight per day. Most charts show that our area gets between 3.5 to 5.5 hours of sunlight throughout the day depending on time of year.
Where to start, hmm :annoyed:
Steve you have decent baseline understanding of solar and electric relating to it, we can launch from there. :)

Looks like you have a 12 volt system there, and that made sense for a mobile platform...not so good for fixed platform...but certainly the price was hard to be fussing over. :)

For the cabin my thought is to bury the batteries as in a "root cellar" for stable temps well above freezing. Unvented gel batteries don't off-gas hydrogen like vented flooded lead acid's do, so the otherwise critical venting is not a big issue.
The batteries, as in any location would need to be maintained with solar sourced charger float voltage during non-use periods.

As for the primary home, this set up could not inter-connect with the grid utility...best senerio would be for addition of size matched automatic transfer switch and to be used like a back-up generator during a loss of utility power. And to take it one step further to have a generator to feed the battery charger that recharges the batteries so as to not run generator often and with a light load...sorta like run it hard to full charge and then leave it off for a few hours or over night...don't forget when sunny no generator run charger would be needed.

As for Key Factors that must not be ignored:

Any 12 VDC wiring must be very, very short in length...forget getting fancy if it makes the fat wire be also long fat wires...doesn't work at this low voltage...remember voltage is the pressure.

Any solar energy received at panels goes nowhere if there no load attached drawing that energy...it is wasted without a load to consume it...batteries when becoming full will reject energy.

All except the best of the lithium batteries cannot be discharged below 50% DOD, (depth of discharge) without permanent damage done to the cells. And thank goodness protection is likely already built in to protect for this.

Any type lead acid batteries will have a lifespan and even with the best care will need replacing, is the history known for the care and upkeep of these batteries?

And an off the cuff comment/question: Might you consider selling this mobile gear and using proceeds to step up to a more appropriate 48 VDC system?
:idea: I would think someone with a large RV/Motor-Home might go gaga for your parts. :idea:

 
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Post by Ky Speedracer » Fri. Mar. 22, 2019 3:16 pm

Thanks guys!
Based on what I'm gathering from your comments, it sounds to me like the off-grid/grid-tie system for my primary residence is really not practical for this system.
With that said, I'll remove that from the equation...

I'm not opposed to selling this equipment and starting from scratch. Maybe the best option in the end...

As it relates to a remote cabin: As I understand it, the batteries should be fine for this application, correct? They can be configured in various voltage arrangements from 12 volts to 48 volts depending on the inverter setup.
As to your question McGeiver regarding the known condition of these batteries - They were put in service in June of 2018. They are less than a year old. They were maintained by this specific equipment that I have been given. This was a package unit. As I understand it, this system would automatically discharge and then recharge the batteries to different levels to maximize their life and maintain their condition. They are completely sealed. So we never did anything to them. The last set of batteries like these that were on the truck were installed in 2006. They lasted 11 years with pretty hard usage...
Regarding the cabin and solar array - I would likely place the array on the roof of the cabin to gain elevation because of trees around the property. The approximate distance to run the wire from the panels to the charge controller would be maybe 30' but to be safe, maybe figure 50'.
Regarding these specific inverters: It sounds like that, while not ideal, they can do the job to run a simple remote cabin with some lights, maybe a TV, a computer, a cellular router and a 12 volt water pump. Charging batteries for some random tools from time to time. I may have left out a couple of things, but it would all be small items.
These specific inverters appear (at least to me) to be a combination inverter and charger. So I assume that they can not only convert 12 volt DC current to 120 volt AC current, but they also can maintain battery charge too. Does that sound correct?

Let me back up and provide some insight into how this system was configured in the mobile unit (in laymans terms anyway...) - The truck had a 30KW generator on it that would run most of the coach. Lighting, HVAC, computers, appliances, etc. all ran off of the generator. The X-ray equipment was operated via the inverters and batteries. That equipment needed a pure sine wave and very stable clean power. So the inverters were setup in parallel. They were programmed to work together. One inverter provided one leg at 120 volts and the other provided the other 120 volt leg to give you 240 volts. It was essentially a UPS system.
For some reason, the configuration that was employed, did not use the built in charging system of the inverters. Instead, they had the TrueCharge 2 battery chargers setup to charge the batteries via the generator. There was 2 of them. I don't know why it was setup that way but there was obviously some job that they were doing for them to add that additional complication and cost...

So, It sounds like I can use this inverter to run my cabin by putting the batteries in series to provide 12 volts. My thinking is, essentially set it up just like the mobile truck was except replacing the generator with solar panels.
I guess the main question I have is; Do I need different "charge controller" for the 50' run of wire between the solar panels and the batteries? Maybe something that can handle a higher voltage configuration from the solar array to overcome the distance.
OR, is there a way to - Run the wire from the array to this specific inverter/charger to do the job?

I had the same though of digging a hole/root cellar to stabilize the temp of the batteries. My problem is, rock. This is on a really rocky hilltop area. I doubt I could dig a deep enough area to do any good.
However, I did see on YouTube where some dude used some simple thermostatically controlled thermal seeding mats (like a heating pad) in a heavily insulated battery box to keep his batteries warm. Seems like a viable option depending on how much energy it would use. I'd have to calculate what that looks like but with enough insulation and this large of a battery storage setup, it might be possible...

 
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Post by VigIIPeaBurner » Fri. Mar. 22, 2019 3:39 pm

That must have been quite the vehicle hauling 700+ lbs of batteries, all the equipment and instruments. The batteries would first need to be load tested to find if they're still usable as McG said. At their newest, there's 500 amps (@50% SOC) available at 12 volts from the 4 batteries. They have only so many (hundreds) of charge cycles in them.

Was there a solar array on the vehicle? I'm guessing the original set up would have been plugged into grid power daily. To keep it simple and move the decimal around, a 100W 18 volt panel yields about 5 amps/hr to the controller, IIRC. That 500 amp recharge would take a sizable array of panels. You would also need the right solar controller too. Expensive system.

Cold lead acid batteries loose efficiency at lower temperatures. Their output drops with a diminishing SOC (State Of Charge).

Something I've learned about recharging lead acid batteries is the bulk charge (higher amps charged) goes quickly and the float charge (lower) takes the longest. It's a better use of the generator's capacity to do the bulk charge and let the solar finish the float. That means you have to use the generator early in the day. Gel and AGM batteries take higher voltage quicker.

My guess is they were run as 2 banks with 2 batteries wired in parallel per charger since there's 2 of each pieces of equipment. 2 inverters/chargers and 1 control system but I'm in way over my head :lol:

Even if the batteries are short on remaining life cycles, the other equipment is amazingly powerful and RVers that would buy them. Especially if LiFePO4 batteries come down in price some. Li batteries have thousands of cycles vs hundreds for Pb which actually makes them cheaper per WHr. over the lifetime. Big bucks.

 
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Post by Ky Speedracer » Fri. Mar. 22, 2019 3:50 pm

Yes. It is a big vehicle. 50,000lb truck.
No. No solar on the vehicle. Just a 30KW generator.
These are gel batteries. According to their last report, they were never discharged less than 85%.
I’ll take them up the street and have them load tested next week. They were taken out of service in late December and fully charged before they were removed.

 
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Post by VigIIPeaBurner » Fri. Mar. 22, 2019 3:56 pm

I didn't see your post above mine before I posted! Some of it makes no difference since you explained it more.

From what you described you want to do, sell the inverter/chargers and use the $s to buy new pure sine wave inverters sized for your needs. What you described is not much different than a 4-500 W solar system in many boondocking RVs. Set you cabin's lighting system up for 12V LED lighting. There are even good 12V TVs and over the air antenna/boosters that work great. I run my small rv off a 2 batteries (90W usable) and 1 170W panel. Great in the summer but not enough panel in the fall when the sun gets low and the batteries colder.

The panes should be run in series to up the voltage, wire gauge down, and keep the loss over distance minimized. Get a higher voltage converter and keep it near the battery/inverters.

Check out this guys YouTube channel: Will Prowse Off-Grid Solar Power Channel!


 
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Post by McGiever » Fri. Mar. 22, 2019 3:58 pm

Ky Speedracer wrote:
Fri. Mar. 22, 2019 3:16 pm
I guess the main question I have is; Do I need different "charge controller" for the 50' run of wire between the solar panels and the batteries? Maybe something that can handle a higher voltage configuration from the solar array to overcome the distance.
OR, is there a way to - Run the wire from the array to this specific inverter/charger to do the job?
BTW: I'm no engineer either, just dumb ole knuckle-dragging electrician... :stfu:
Solar panels, just like batteries, can be seriesed and/or paralleled or any hybrid combination required to get best use of panel output.

So, yes, you could get a different CC to take the solar input of 150V, 200V or even 250V and regulate it out for a 12 VDC system...the 150V would do fine in your case. I'm kinda partial to the Midnite Classic line, and they make a smaller Midnite KID that may satisfy your loads at least, if you wanted a couple recommendations.

Next problem:

It will take maybe more solar panels than you may be considering to keep that entire quantity of batteries healthy.
But then again, it does depend on how deeply and how consecutively the batteries do become discharged...more deep and consecutive will be harder to keep them healthy with undersized solar output feeding them. Generator can be used for topping off batteries during occupancy of cabin and deep discharge without full solar recharge.
Last edited by McGiever on Fri. Mar. 22, 2019 4:04 pm, edited 1 time in total.

 
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Post by VigIIPeaBurner » Fri. Mar. 22, 2019 4:01 pm

From what I've read, Gel batteries are quirky. AGMs are more robust and less prone to sulfation vs gel but for free - ha! You'll have to go some to use 500 usable amps of lead acid power.

 
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Post by VigIIPeaBurner » Fri. Mar. 22, 2019 4:03 pm

BTW, gel and AGM (acid glass mat) batteries are both lead acid as well the more common flooded batteries we see more often.

 
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Post by McGiever » Fri. Mar. 22, 2019 4:09 pm

Another big factor with the gel batteries is the CC has to be able to be "tweaked settings" for using the gel battery's custom parameters...and that eliminates many CC's right off the bat.
Obviously what you have now already has this ability, although at the 12 Volt system level.
Again, look at Midnight Classic or even the Outback FM80 for 48 volt charge controllers...their usefulness would outlive us both.

 
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Post by McGiever » Fri. Mar. 22, 2019 4:25 pm

Just for the record, XANTREX is not a player in the solar industry...they are all about mobile systems.

 
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Post by VigIIPeaBurner » Fri. Mar. 22, 2019 4:33 pm

McG - what do you like for a battery monitor? I need to buy one soon, been looking at Victron w/bluetooth. Ky Speedrace sure doesn't need one with that mother load he scored!

 
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Post by McGiever » Fri. Mar. 22, 2019 6:57 pm

VigIIPeaBurner wrote:
Fri. Mar. 22, 2019 4:33 pm
McG - what do you like for a battery monitor? I need to buy one soon, been looking at Victron w/bluetooth. Ky Speedrace sure doesn't need one with that mother load he scored!
*VPB* Sorry I have no experience nor have I followed that lot..what I have is a proprietary battery monitor integrated into a single brand name product line...it is great and does way more than just to monitor, but wouldn't fit anywhere but where it's designed to fit.

You may be well aware of this already...
Battery Gauges that keep track of what comes in and what goes out of a battery are not such a refined measurement and can misrepresent what really is the given state.of a battery.
The variables are battery ambient temp, wheather charging or discharging, was it a heavy or light charge or discharge, has it been setting resting and how long has it rested, age of battery, etc...simple gauges can't know these finer details that factor in.

The made in USA Midnite Classic and Midnite Kid both use a added device called a Whizbang Jr that does a pretty good job together at counting coulombs... Check out Youtube for more info.

 
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Post by WNY » Sat. Mar. 23, 2019 7:11 am

The controllers also monitor the input/output voltages, etc... most of them can auto adjust for system voltage, 12, 24, 48 volts.
you can get the external monitors also, as stated above. As they stated, depends on how much you use/discharge system for the amount of solar panels needed. Most good MPPT controllers, will adjust over voltage for more current. I have 2 panels ( 2 x250watt) for 12 batteries (690amp/Hr bank) right now. not quite enough, but only up at the house on weekends, it works.
I have run 4 panels x 250 watts panels is about ideal for my setup. I;ve seen almost 25+ amps from 4 panel setup. I;m running an outback FM60 controller. 2 x 2500 watt Xentrex Since Inverters. whole house runs 220vac, just like a regular house. some 24 volt lighting that leftover from wind turbine for dump zones. most was already wired, but wind turbine broke and I converted to solar.

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