Upgrading system

dhill

Since I've finished my taxes and am going to see a decent refund, I'm going to upgrade my home's solar system. I currently have 620 watts of solar panels (4-Matrix at 24v configuration) and I want to add about 400-500 more watts. Selection of the panels shouldn't be an issue, but I'm much more in need for advice about my battery bank. I'd like to double my storage capacity, and I need help in figuring out the best way to do that before I go to my battery supplier.
Currently, I'm using 8 6v exide 225ah wet cell batteries in 24v set up. Here are my questions:
1. Is 1100 watts of panels enough to charge a battery bank double my current capacity?
2. Any suggestions for type of batteries to use that will give me the double capacity would be greatly appreciated. I'd like to go AGM if possible to decrease maintanence. I've considered simply upgrading to something like the Trojan l16 because I think it's a higher amp hour battery. 8 of those instead of 8 T105s would add lots more energy to my supply.
3. Currently, I'm set up with a 24 volt panel system and a 24v battery bank. Is there any significant reason for setting my panels for 48v?

Current system is comprised of OutbackVFX3524 inverter, mx60, and panels and batteries as noted.

Thanks for any suggestions and all help.

niel

Re: Upgrading system

i don't think you want to do anything with the batteries unless you deem them old or damaged. with 4 matrix 155w pvs that will have a combined rating of 18.24amps. the battery bank currently is 450ah at 24v, if i read that right. this is a charge rate of a tad over 4%. you might get a smidge more with the mppt action of the mx60, but this won't change the general scenario much. the current pv modules are actually under the recommended min charge rate of 5%, but was doable. now even if you doubled your pvs this only puts you within the normal 5-10% basic charge rate range. seeing as how it's usually not recommended to mix old and new batteries, i say be happy you charge them up faster with more pvs. if you feel the extra battery capacity is needed then you may have a problem. idealy you would get all new batteries and this is a choice for those looking to replace all of their batteries due to age or failure. if the batteries you have are good you may wish to sell them to somebody else and still get all new batteries. the agms are a good choice as you get a better charge efficiency and little to no hydrogen when properly charged.
now if you can't swing the costs to replace all of the batteries, but were going to supplement the bank you should have these seperated from the old ones, usually with a heavy duty switch, or you'd degrade the new ones to the level of the old ones. never mix battery types like agm and standard lead acid batteries.
in my view, just add more pvs unless your batteries are old or damaged and then you'd replace all of the batteries with being able to give a minimum charge rate to the batteries of 5%.

dhill

Re: Upgrading system

Thanks, niel.
What I'm looking to do is add more to my battery capacity by doubling my battery bank. I'd like to have closer to an 800AH bank as opposed to the 450 that I have. Is 1100 Watts of solar pvs enough to charge, say 8 L16s or equivalent? My batteries are less than 2 years old so I think they are okay for longer use, but I'm actually looking to change them all out if I can go to a higher AH bank.
I've looked at lots of mfg. batteries, and I'm having a tough time deciding exactly what will work best for me. I'd like to go AGM for the maintenance factor. I could see a set up with 6- 12v agms or 8- 6v L16s, and the cost would be comparable, the AGMs a little more expensive, but probably worth it to me. The only problem with 6- 12v is that I'd have to do 3 strings for 24 volts. Is that a big no-no, or would that work ok?
Most of the time, my panels have no problem keeping my batteries full. My energy usage varies, I have a 10K gen that can boost the batteries as needed, but I'd like to have a little more oomph from my batteries. Am I expecting too much from a 1Kw system?
Thanks again.

crewzer

Re: Upgrading system

Dhill,

1)  1,100 W STC should be plenty for charging a new/larger battery bank rated at 24 V x 450 Ah. The array should be able to deliver ~32 A or more in bulk stage at mid-day in the summer. 32 A is ~7.2% of the target 450 Ah capacity, and anything over 5% is usually comfortably OK (assuming concurrent loads aren’t too high).

2)  Four size 8D batteries, each rated at 12 V x ~240 Ah, could be configured for 24 V x ~480 Ah – just what you’re looking for. East Penn (Deka and MK), Concorde, and Trojan make VRLA (AGM or gel) batteries of this size. Prices vary greatly, so check around.

Example: http://www.mkbattery.com/images/products/8A8D.jpg and http://www.mkbattery.com/images/lagm.pdf and http://www.mkbattery.com/images/8A8D-LTP.pdf

3)  A 24 V /24 V array/battery configuration can be problematic. It would be helpful for us to have more specs for your modules (i.e., Vmp, Imp) as well as an idea of where you live (environmental factors) before we can offer a credible response.

Regards,
Jim / crewzer

crewzer

Re: Upgrading system

Dhill,

I obviously misread something :oops: , so please let me try again.

1) 1,100 W STC should be adequate for a battery bank rated in the 24 V x 600 Ah - 800 Ah range. The array will deliver about 32 A at mid-day in the summer, and the charge current should be ~4% or better for an AGM battery bank. Large daytime loads will obviously interfere with recharging the batteries.

2) Six size 8D batteries, each rated at 12 V x ~240 Ah, could be configured for 24 V x ~720 Ah. East Penn (Deka and MK), Concorde, and Trojan make VRLA (AGM or gel) batteries of this size. Prices vary greatly, so check around.

Example: http://www.mkbattery.com/images/products/8A8D.jpg and http://www.mkbattery.com/images/lagm.pdf and http://www.mkbattery.com/images/8A8D-LTP.pdf

3) A 24 V /24 V array/battery configuration can be problematic. It would be helpful for us to have more specs for your modules (i.e., Vmp, Imp) as well as an idea of where you live (environmental factors) before we can offer a credible response.

Regards,
Jim / crewzer

dhill

Re: Upgrading system

Thanks, crewzer.
The info about the batteries is exactly what I'm looking for. I'm in central North Texas. Summers I get lots of sun. Usually, I can count on plenty of full sunny days in winter, too, but this year, we've had an ample supply of overcast days. My present set up of 620 W STC and 450 AH battery bank has worked admirably, but I'm wanting more production; thus, the upgrade. I've had no issues that I'm aware of running 24v panels to 24v batteries through my MX60 that I'm aware of. I have my generator set to kick on when the battery bank gets to 23.0 volts. During the summer, the gen rarely comes on. This winter when I'm running my radiant floor heat all day and through the night, I have pulled my batteries down enough for the gen to cycle.
Last summer, I ran a 500 watt A/C window unit in the bedroom throughout the night, and the generator never had to come on to bump up the batteries. I was extremely surprised and excited at that. The only significant load that is a constant run for the system is my conventional refrigerator, rated at less than 400 kwh. Other than that, I run television a couple of hours each evening with a 13 watt bulb table lamp on. That's about it.
Thanks for the response. I appreciate the knowledge you guys all impart here for noobs like me. What's even more amazing is that you guys make it all make sense even for someone with my brain density.

crewzer

Re: Upgrading system

dhill,

Glad to help. Note that charging AGM batteries wired in series (and gel too, I suspect) can cause problems since they can't be equalized in the traditional sense. You can read more about the problems a couple of us experienced, as well as our solution, at this discussion: http://www.outbackpower.com/forum/viewtopic.php?t=1750

HTH,
Jim / crewzer

niel

Re: Upgrading system

correct me if i'm wrong, but from the sound of it you are replacing your batteries altogether along with adding 3 more pvs. what jim recommended is fine for you. as you've also had a proven system that worked with a 4% charge rate then i see no problem with its continuation. sounds like you might run another air conditioner. i'd also be curious of the current or wattage rating of the air conditioner that you had used successfully.

dhill

Re: Upgrading system

Here's another question relevant to my upgrade that I could use some help with. I've looked extensively for the most convenience and value at the most affordable cost for a new battery bank. I've narrowed my choices to:

A. 6 12v 8A8D AGM 245 or 257 AH batteries. If I figured correctly, that would give me a 24v bank of 735/771 AH. The cost would be about 2400.

B. 8 L16 6v wet cell 420 9r 530 AH batteries. A 24v bank = 840/1060 AH. The cost would be about 2200, depending on the brand of battery.

C. 8 6v Discover AGM L16 390 AH batteries. 24v bank of 780 AH. Approximate cost 2500.

The AGMs offer less maintanence. The L16 offers more AH. Any suggestions as to which will give me the most bang for my buck? Thanks for the help. (I'm replacing 8 T105s.)

niel

Re: Upgrading system

that is a choice you have to weigh and make. bang for buck would look like this: cost/ah=$ for every amp of capacity. now there are other things you'd want to figure into this as agms do charge more efficiently and are much less likely to outgas, but agms are prone to overcharge where the voltage exceeds manufacturers' recommended charging voltages and cost a bit more per ah. warranty length may also influence your decision. i prefer agms myself, but we're not talking about something for me.

dhill

Re: Upgrading system

Thanks, niel. I'm leaning towards the agms because of the maintenance factor. I'm sacrificing some ah capacity for convenience, and honestly, I'm probably taking the lazy way out. Please, someone convince me that agms are more efficient so AH are more viable and they're safer or something so that I can feel completely sure of choosing that option!

niel

Re: Upgrading system

i did tell you agms are more efficient. i did a quick pro/con thing about the agms before.
"now there are other things you'd want to figure into this as agms do charge more efficiently and are much less likely to outgas, but agms are prone to overcharge where the voltage exceeds manufacturers' recommended charging voltages and cost a bit more per ah. warranty length may also influence your decision."
on the last statement you will find the agms with short warrantees compared to some standard lead acids. this is due to the overvoltage factors that they have no control over. once the battery vents, that which vented will never be recoverable/able to be put back into the battery unlike standard lead acid's ablility to be topped off. if they are properly taken care of i see no problem in them lasting every bit as long as other quality lead acid batteries. you are correct in them having less maintenance than standard lead acids. cell towers use agms.

crewzer

Re: Upgrading system

dhill,

One thing you'll want to do is search around for competitive battery prices. My AGM size 4D's were ~$220 each, and my recollection is that Brock found a great deal on his eight AGM size 8D batteries. HB Phil recently bought four AGM size 4D batteries with HD L-lugs for $243 each.

See: http://www.outbackpower.com/forum/viewtopic.php?t=848&start=45
and: http://www.wind-sun.com/smf/index.php?topic=2042.60

See Trojan Battery's "Connections Diagram" for suggestions on how to "diagonally" connect the main cables to/from your battery bank: http://www.trojanbattery.com/Tech-Support/TechnologyLibrary.aspx

HTH,
Jim / crewzer

System2

Re: Upgrading system

I got my AGM's used but in great working condition. They are Hawker 6vf11 100 AH @ the 8 hr rate. They were $42 each. These were $700 each new, have a 12 year design life, and are of the highest quality. They are used when the best units are required, like in nuclear plants etc. They are retired from the phone company in Kansas City, Missouri. They have proved to be very good, I can pick and choose which ones that I want and if any are bad, I can exchange even up and the price of a lunch for the guy's time. 800 AH @ 24 volts @ the 8 hr rate would run $672. Not too bad! I would rather go 48 volts, however, as it is half the strings. Using a copper buss bar is a good way to go also.

I use them for backup power and they rock! A new batch is in, so some shopping is in order this week!

Good Luck,

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