Upgrading my system

df_252 · January 2008

I've had 2 60 amp Unisolar modules and one Interstate 8-d type battery as my only source of electricity since 1999 (nothing to do with y2k, just tired of kerosene lights). I recently inherited a much larger system, 12 Solarex 75 watt modules, a Trace charge controller, mounting equipment, inverters, etc. I assumed that I would set the system up in a 12 volt configuration, but have seen some evidence of opinion here that 24 might be better.I would
appreciate any thoughts you might have. I also need advice on what batteries to buy, I'm leaning toward either Surrette 530s or Trojan L16HCs, but others are not out of the question. I'm building the system backward, sizing the battery bank based on the number of modules versus based on the load (my electrical needs are minimal, mostly lighting). I want to install the right number of batteries to optimize their lifespan.
Thanks for your help.

nigtomdaw · January 2008

Re: Upgrading my system

Hi with just over 1000 watts of PVs you have options, the more learned will advise you on batt capacity and higher base voltage has its plus points such as smaller guage wiring thus cost savings. Charge controllers such as the trace C series wether C35 or C60 selectable 12-24v or the C40 @ 12-24-48v Doubling the base voltage increases the PV handling capacity by a factor of 2.

Against this is the availability of more choices of direct 12 volt products vs 24 volt products and pricing. Keeping an inverter out of the loop reduces losses and boosts efficiency, Your post indicates you inherited an inverter, if you intend to use this unit then its operating voltage calls the shots !

B4 anyone can accurately give you battery capacity recomendations a breakdown of your loads and location for your solar hours would be helpful !

BB. · January 2008

Re: Upgrading my system

DF,

Your batteries are the "consumable" portion of your system... Too small, and you will not be able to ride through a few days of cloudy weather and/or you will draw them down too far and damage them.

On the other side, a large bank will last longer (assuming you have enough solar panels to charge the battery and stay ahead of your loads)... However, past certain point, you will still have to replace the batteries every ~5-10 years--so you will be "wasting money" as having excessive numbers of batteries will not last any longer (although, you will be using your generator less).

Best thing is to estimate your loads (amp*hours or Watt*hours per day/week/season), how much sun you get (in Hours per day), and if you need back up power (generator)...

You can use these two links (pdf and calculator) to see what your "hours of sun" per day is for your area (assuming you have no shadows and good weather--no marine layer).

Over all, it is really best to size your system for your load. Although, you can choose a setup based on what you have...

From the calculator link, near Charleston West Virgina, 12*75 watt panels; you will get about 3-5kWHours of solar power per day (winter-summer).

Derate that using 80% (battery charging losses), and you are down to about 2.4 to 4 kWhr per day of DC power available for your use.

Assume 10%*C battery charging factor...

900 watts of panels / 10% = 9,000 watt*hours of batteries

9,000 watt*hours / 12 volts = 750 Amp*Hours of storage batteries...

The numbers above are very rough estimates and you can move them by 1/2 or 2 times depending on your usage/needs (less cost/low amount of power usage or more storage/higher costs/less generator usage in bad weather)...

Does this help?

-Bill

df_252 · January 2008

Re: Upgrading my system

Hey guys,
Thanks for your responses. My thoughts are that I want to use 12 volt lighting as much as possible since I already have a few lights etc. I doubt that I will ever use the inverters, although I have toyed with the idea of a small microwave. I've lived without TV for so long that I can't imagine where I would get the time to sit in front of it. I do have a small radio (which is on most of my waking hours and is my alarm clock) and a cd player that I use occasionally (1-3 hours per week). The radio uses a radio shack step down transformer (12 to 6 or 8 VDC can't remember which) the cd player is 12 volt. My main goal is to add more lights. Right now I have 2 propane lights and 3 led fixtures. I want to add a few compact flourescents or some other general area lights and stop using the propane if I can.
I believe that I have plenty of PV to do a lot more than add lights. I've lived with a 225 ah battery for 7 years with the only limiting factor being sunlight, ie: I've never run out of power through usage when starting with a full battery. So, say I double my battery capacity, I'm sure that will be enough power for my needs, am I risking damage to the battery bank in any way?
A couple of other factors that may diminish the charging ability of my array:
1. The distance from the array to the battery is about 25 feet, I have enough copper #2 wire to make the run. I think that will cause about 5% line loss, but I have the wire...
2. I plan to store the batteries in an unheated cellar (6 feet by 10 feet, insulated, concrete floor, block walls). It is earth bermed and never freezes, staying about 20 to 30 degrees above outside temps in the winter. We rarely have below zero temps here, our coldest days are in the teens with 20s and 30s being typical.
3. My array is mounted about 15 degrees west of solar noon. Right now I have them tilted at 55 degrees. I know that latitude plus 15 is the standard but I read somewhere that it's not ideal and that for winter months it should be closer to 65 degrees. Any strong feelings here?
All that considered, am I better off buying the best batteries available, going with Interstates again, or something in between? Should I max out the charging capacity that I have or more or less size the batteries to my needs?
Any strong feelings on battery brand? One of the websites I visited has a chart indicating that since batteries are consumable, cheaper up front may make more sense.
I do have a generator, for occasional power tool use, which I can use to take better care of my new batteries than I did of the old. So I also need advice on a battery charger. Do I get one large enough to charge the whole battery bank at once, or just charge one battery at a time? Any words of wisdom on lighting would be welcomed too.
Thanks!
David

westbranch · January 2008

Re: Upgrading my system

HI David, have you done some (lots) of reading on these BB's? If not you will find several strings about you issue, especially around the size of array re your battery bank... and also your battery storage room.
Rule of thumb ~ 5% of batttery amps in PV capacity will keep you topped up and safe.
Regarding winter alignment, I use vertical as I can max out on reflected sun with this alignment, but you have to have lots of snow, complete ground coverage. also no (or very little) need to worry about snnow on the panel.
Lights, I use LED MR16 bulbs in track lites... just rremove the transformer ans rewire..

I am sure you will find lots of good info here.
Cheers
Eric

niel · January 2008

Re: Upgrading my system

david,
if you've been used to your old system, the new one will be like having unlimited power to you in comparison. the best thing you can do is an evaluation of your power needs. the batteries should not be allowed to be drained further than about 50% to keep their life, but only draining say 20% (bigger bank) will extend lifespan further and allow for some extra capacity for those oddball times. generally a range of 5-13% of battery ah capacity as the rate of charge for standard lead acid batteries should be used unless a manufacturer will specify a different range. the current will be the total of the operating current ratings of the pvs and the percents can be figured from that for the battery capacity range.
in the case of using 24v pvs for a 12v battery system this would require a downconverting mppt controller such as the mx60 or xw60 and i recommend a battery temperature sensor if the controller you use can accomodate one. i'm guessing you'll want to use the straight pwm controller you have inherited. (sidenote: how do you inherit this stuff when most have difficulty even buying used?:D) anyway, the wiring does need reconsidered too as you will have a higher current capacity flowing and you can use the voltage drop calculator in the general solar topics sticky.
as to the angle of the pvs you may benefit from the increased angle for winter solstice, but this necessitates being able to readjust for other time periods as that angle is far too steep for the other seasons. if you have adjustability i'd recommend not going all of the way to the solstice angle, but have it say about 5 degrees less so as to allow for bad weather making it impossible to adjust at those general times. this will still be close to the lat +15 degree point and the final decision on the best angle for you is up to you. i go with a steep winter angle for the solstice myself and use my lat +5 degrees for all other seasons. with all of this extra power coming in for you, you may not want to go with that extra effort on the angles, but then again winter is the time of least solar insolation. with the lat +15 degree being for due south you need an extra degree or 2 added anyway due to aiming 15 degrees off of due south.

df_252 · January 2008

Re: Upgrading my system

Hey again,
I inherited this system from one of the original back to the landers in this area. He happened to be my first cousin and one of the inspirations for me to return to the old home place of my ancestors in West Virginia from Chicagoland where I grew up. When he died a few years back his brothers saw fit to give his system to me.
Yesterday I picked up 4 L16H batteries from a dealer in Newcomerstown Oh. They are in place and I am,despite the 11 degree temps outside, going to start wiring them up today. I'm a little concerned that I over-bought battery capacity, but I didn't think that 420 amp would be enough. So my question is what size ac-dc battery charger do I need? I have a Homelite 3550 generator with 20 amp 120 receps and a 20 amp 240 recept. I could split the bank when I charge from the generator if necessary. From what I've read here it seem like I need 10% charging ability, does that mean an 84 amp charger (or 42 amps if I split)? Am I better off charging the batts one at a time? Does 420 Ah at the 20 hour rate mean that that is the number that I need to use in my calculations? If so then it seem like I can charge the whole bank at once with a 50 amp charger...
Sorry for being so dim witted, even though I've had a system for years, I don't really know much.
Thanks for all your help!
David

mike95490 · January 2008

Re: Upgrading my system

How are you going to wire these - series - parallel ? 12V 24V ?

niel · January 2008

Re: Upgrading my system

david,
if you are wiring for 24vdc, meaning the batteries are in series, that would be 420ah of capacity and the charge rates appropriate would be 5% (21amps) to 13% (54.6amps). if you are going with the 12 battery arrangement (2x2) this would be double the ah capacity for 840ah and would make the charging rates double of that for a 24vdc battery bank and would be 5% (42amps) to 13% (109.2amps). now trojan i believe does recommend the 10-13% range and the 10% rate for 24v is 42amps and for 12v is 84amps, but can go to the 13% rates indicated. this means a 50amp charge rate for a 24vdc battery bank is good and a 100amp charge rate is good for a 12v battery bank as many chargers would be more apt to be of those numbers than the oddball ones.
whatever your charging source it needs to be able to handle the current levels indicated for the particular voltages chosen. you have not indicated what charge controller you have, but odds are if the batteries are wired for 12vdc this controller will not suffice for the total current needed to charge the batteries. i can't say if your generator will supply all of the needed current for charging the batteries and that would need a battery charger and not a controller. good ac chargers are those that offer the multistage charge and better yet would also have the ability for temperature compensation. that is a seperate method as opposed to pvs as the source that would need and use a controller. if you could be more specific on the entire system and the components thereof, better comment may be had of it.
i do need to appoligize here and i am sorry for your loss as it never occurred to me that somebody actually had died for you to get this stuff. i am sure your brother would be happy of your interest to keep going with it rather than just sell it as many would've probably done.
i wish you luck in your connecting of the batteries with this cold weather that's here as, even though indoors, a basement floor gets real cold.

df_252 · January 2008

Re: Upgrading my system

Hi again,
I did in fact work yesterday and today and got the system charging. I wired the batteries in 2X2 (series/parallel) for 820 amps at 12 volts. We had a beautiful, sunny day today, although it did not reach 30 degrees farenheit. By about 1:00 PM I had everything on line and the charge light came on. With only a few hours of sunlight left for the day, I didn't expect much, but within a few hours the controller showed full charge. I know that had a lot to do with the fact that they are brand new batteries and were close to a full charge when I got them from the dealer, but it still made an impression on me.

The system consists of:
12 Solarex 75 watt modules mounted on Two Seas racks
Trace C60 charge controller
4 Trojan L16H batteries
I also have a couple different DC-AC inverters which I don't plan to use at this point.

My cousin bought this stuff in about 2000 from, I think, Atlantic Solar. I assume that they advised him as to the charge controller that is appropriate for the system. If, as I suspect, the C60 is only rated at 60 amps DC, what will happen if I continue to use it? He had the system on line for a few years and it didn't burn his house down or anything, and the controller seems to be working still. Maybe the effect will be that it just won't do a good job of keeping the batteries charged? Maybe I did in fact buy too much battery. Would it help to charge at 24V and then somehow convert back to 12V. I prefer ro use 12V lights etc. They seem to be more available. In fact I haven't seen any in 24V, are they out there somewhere?

Back to the AC-DC charger, I doubt that my generator will power a 100 amp charger, unless they are available in 240V models. My generator is rated at 5200 watts starting and 3550 watts continuous with 20 amps at 120V and 20 amps at 240V. The Iota 75 amp charger requires an 18 amp circuit. Will that allow me to equalize the batteries? Will it take forever? Do I need a new charge controller? I have more questions than I started with.

Niel, thanks for your words of sympathy. Don was my cousin. We were very close and I do miss him.

Thanks to all for your help. I feel like I'm learning a lot.

David

niel · January 2008

Re: Upgrading my system

david,
very good on your system components. that controller will charge the battery bank at roughly a 5% rate of charge. in my opinion it will work, but i'm no expert with the trojans. i believe that controller can use a temperature sensor and that would help track the optimal charge voltage for the batteries given the battery temperature at the time. i don't know how far away the sensor will be needed to run for you, but if you don't have one please look into getting one.
http://www.xantrex.com/web/id/105/p/1561/pt/5/product.asp
if you want to expand in the future you will find that you will need another controller to handle the current.
as to your loads try not to overload the batteries with real high current loads (>10-20%) and don't allow the batteries to drain more than 50% before giving a charge. if you run loads while charging the batteries you may find that it could lack enough current to properly charge. supplementation from the generator with an ac charger and the pvs could help this scenario. i am assuming you to be offgrid too and if i'm wrong please say so. some of the particulars from others who have these batteries may wish to chime in with some extra advice to you.

df_252 · January 2008

Re: Upgrading my system

Hi Niel,
Yes, I am off the grid and have been since summer 1991. In '99 I got the small system that I am replacing now. It served me well, but opportunity and necessity have me installing this new system. I am today looking into a battery temperature sensor and a remote battery monitor. I want more information than a flasning led can provide. As you said in an earlier post, I sill have a lot more power than I'm used to, so I doubt that over using my batteries will be a problem. I'm hoping to keep them above 80% charge at all times. I don't intend to use an inverter and I don't have any large DC loads.
Thanks,
David

niel · January 2008

Re: Upgrading my system

now as to the wire i see that it will give about a 4% vd which is better than you thought, but still isn't good as it should be under 3%. if you can't shorten the length then consider changing at least one of the polarities later on with a larger wire as it still represents a loss to your system, but is more vital with mppt controllers. i have a voltage drop calculator in a sticky at the top of general solar topics. it uses excel or any similar type program. when talking of wire runs of any length this is actually made up of 2 wires as the current goes round trip so a run like yours of 25ft will have 50ft of wire and it is that 50ft that gets entered into the calculator. figure the runs individually or it will be averaged in the calculator. 25ft of #2 with 25ft of #0 will give 3.21% vd.
25ft #2 with 25ft of #2/0 = 2.95% vd.
using all 50ft #0 = 2.48% vd.

df_252 · January 2008

Re: Upgrading my system

I do have some larger wire that I can use at some time in the future. I have more of the number 2 wire too, could I use a double run for each polarity? It's easier to handle than the big stuff (00, I think). How do you figure the cumulative capacity of two #2 wires? Actually it would be 4 wires, 2 up and 2 down. And when I tie the wires in to the controller, it will only accomodate one #2 wire. Doesn't that create a bottleneck? I'd have to use a junction lug of some kind.
I was determined to buy a battery temperature sensor today, but I also want a remote monitor. What do you think of the trimetric? I'd prefer the sensitivity of the 100 amp shunt, will that give me any problem? I doubt that my pv will ever put out the full 75 amps.
Thanks,
David

niel · January 2008

Re: Upgrading my system

the nec kind of frowns on doubling up on wires, but for the record #2s in parallel would take it to 2/0. this is not appropriate for the controller either as you already know. maybe you could run #2 and then adapt to the larger wire size to make the wire run and readapt it to the smaller #2 wire before going into the controller. i don't know if you'll find terminal blocks handling wire that big, but somebody here or an electrical supply house may have a suggestion for you on what you could use. don't let the employees at the electrical supply store talk you into using small wire because they are used to dealing with the higher 120vac that has smaller voltage drops. you don't have to rush into the wiring, but do go with the battery temperature sensor now.
the trimetric is ok. i have one, but i don't use it because i have a meter on my controller.

df_252 · February 2008

Re: Upgrading my system

Hi again,
So, I have the array on line and my batteries are showing a full charge, even after several days of no sun. I bought and installed a Trimetric monitor, haven't really learned the ins and outs of it yet...
My latest question involves the controller, Trace C60 now with BTS. The batteries are stored in an unheated, though sheltered, area. The temp lately has been about 45 degrees f. The controller seems to be equalizing every time there is any sun, charging to 15.5 volts. The controller is not showing an equalization charge, it's showing bulk charging, blinking 5 times pause, etc. I'm wondering if this has to do with the cold temperature of the batteries or if the controller is malfunctioning. I tried Xantrex's customer service (?) line, after 20 minutes the saxophone loop was driving me nuts so I gave up. I'm afraid that I'm cooking my batteries. Any ideas would be much appreciated. Also any suggestions on a new controller (other than Xantrex) if you think that's what I need.
Thanks!
David

Solar Guppy · February 2008

Re: Upgrading my system

15.5 is NOT an equailizing voltage, the controller is compensating for the battery tempature and is doing exactly what it should. ( colder tempatures require higher charge voltage )

At 77F/25C, a typical Equalize voltage would be 16 volts and as a swag, compenstated in your reported conditions would be 17.1 volts

I'm not sure what your using to determine a full charge, but if its just battery voltage, you have to adjust for the batterys being cold, sound to me as if everything is working and charging as it should

nigtomdaw · February 2008

Re: Upgrading my system

Hi,sounds like everything is going well. On the generator backup DC charging front you might be able to save buying a new charger if one of your inverters is equipped with a charger. You havent mentioned make or model if you list them here someone will be able to tell you if they are suitable for you ac to dc charging needs

HTH's

Nigel

Upgrading my system

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