System spec. Question

TecateKid

Hello, I'm going to be upgrading my system and wanted to get a gut check on my components. This is for an off-grid house in Mexico. temps avg. around 75-80 degrees and the sun is quite consistent. The system is 12v and must stay that way. What I'll be using is...
1. 12 - Astronergy 285W/HV Silver Mono Solar Panel 31.8vcd
2. 2 - Outback Flexmax 80 controllers
3. 6 - L16-E AC batteries (series-parallel) (12v @ 740Ah)
4. 1 - Outback VFXR2812A Inverter
5. 1 - Outback PowerMate3S system controller

I've calculated my total consumption per day at 4,500 watt/hrs. (watts per device x hrs used) when we're there. When we're away the only thing consuming is a small fridge, an alarm system and one LED motion detector light at night.

We only use this place for weekend get-aways every other month or so and I want to make sure I keep these batteries charged above the 50% SoC. range. The system (now) is roughly 15 years old and needs to be upgraded as retirement is looming and we'll be spending more time there. 

Thoughts?
ps. I suck at math and threw the current system together. It's failed miserably.

BB.

Welcome to the forum... Sorry to hear about your system problems.

Where, roughly, is the system located (figure out hours of sun per day).

Do you have a Kill-a-Watt type meter (or other meter) to measure your Watt*Hour / kWH per day usage of 120 VAC?

How is the system "failing"?

Do you have a hydrometer and some sort of digital voltmeter?

For that large of AC inverter, you need pretty heavy/short cables for the Battery to DC inverter connections...

If you are going to be living there full time, you might want to think about a 24 or even 48 volt system for the long term (yea, new AC inverter--The MPPT charge controllers should be fine, rewiring 12 volt L16s into series 24 volt bank (assuming your existing batteries are OK for now).

If your system has been meeting your needs for 15 years--You are doing pretty good.

-Bill

Estragon

6 x 6v L16s would make for 3 strings of 2 @ 12v.  Capacity of L16s should be ~370 x 3 = 1110ah @x12v = 13.3kwh of total storage - roughly 6kwh for 50% discharge.  At 4.5kw/day, that gives you a day and a bit of autonomy.  

Instead of 3 strings of L16s, it may be worth considering lower voltage in the same size, with fewer larger 2v cells.  For example, 6 x 1100ah 2v single cell batteries would give you the same capacity, in about the same space, in a single string (no balance issues), and with 6 cells to water and check SG instead of 18.

mike95490

Estragon said:

.........
Instead of 3 strings of L16s, it may be worth considering lower voltage in the same size, with fewer larger 2v cells.  For example, 6 x 1100ah 2v single cell batteries would give you the same capacity, in about the same space, in a single string (no balance issues), and with 6 cells to water and check SG instead of 18.

Be sure you get L-16's in the 2v format, with only 1 cell cap.  One brand has 3 cells paralleled together in 1 case, with 3 caps !!

Estragon

Yeah, I still don't get the point of them doing that.  Kinda defeats a big reason to use 2v.

BB.

I always wondered why they (Trojan?) just did not "perforate" the interior cell separators and make just "one large" cell...

-Bill

Dave Angelini

I was told that Trojan just does not understand this. That is pretty stupid as they build some very large industrial batteries. I suppose Trojan had in the back of their mind that it is easier to troubleshoot. But the mind numbing work of filling 3 cells instead of one just continues to be one of those things that just does not get fixed.

All of that said, they are great batteries and you just have to do your due diligence next time.

TecateKid

Gentlemen, Thank you for your reply's. I'll do my best to answer your questions.

The system gets an easy 5-6 hrs of sun daily and it's rarely cloudy all day. The current system has been assembled with wire gages in mind and all equipment is in close proximity to each other so I see no issues there. The only "new " piece of equipment I have is one Outback 80 amp controller. Panels are old ((6) Kyocera 130w 12v 7.3A panels), Xantrex SW2512 Inverter, and 4 L16E AC's that went dead after 2 years of use. Although they would Float everyday, I wasn't checking specific gravity. I relied on my controller's numbers. (oops) I believe 2 things were happening. 1. Panels were not putting enough amperage into the batteries and 2. Being that I never checked SG, the batteries just never made it back to full charge eventually going way below 50% SoC. Hindsight being said. I should have increased Bulk and Absorption times along with checking SG. Okay so, lesson learned.

My hope is the new system/panels will supply enough power to charge the 6, L16's and keep them above the 50% SoC threshold. 

I'd be happy with (as Estragon said). ... "370 x 3 = 1110ah @x12v = 13.3kwh of total storage - roughly 6kwh for 50% discharge.  At 4.5kw/day, that gives you a day and a bit of autonomy."

The batteries have already been purchased so 2v are out of the question. 

(Side note) I did see the 2V Trojans but my internal flag went up when I saw 3 cells. .. stayed away.

Estragon

With 12 x 285w panels and 2 x 80a charge controllers, you're a bit short on controller capacity.  On 12v system, max 1000w per controller is OBs recommended, so 2000w for your 2 units.

12 x 285w = 3420w STC, likely more like 2500 in real life.  2500 ÷ 12v (~ 50% SOC) charging is just over 200a vs 160a CC capacity.  The CCs should be able to limit, but just so you're aware it could be an issue.

I'd be reluctant to leave a load like a fridge unattended for as long as an every second month visit.  A few days maybe, but IMHO there's too many things that can go wrong for longer.  I'd at least want some sort of monitoring.  

TecateKid

Thanks Estragon I'm hearing you. So since I haven't purchased the panels yet, is there something else out there that would charge the battery bank efficiently given 2 80 amp OB CC's ? 

TecateKid

OR bite the bullet and add another CC?

Estragon

Controller capacity is an issue with 12v systems.  You need 2x more capacity than a 24v system, and 4x more than a 48v system for a given wattage.  If you have to stay 12v nominal, there isn't really a good way around this.

Biting the bullet might not be such a bad idea.  All else held equal, by not running controllers at full output for long periods, they should run cooler and last longer.