A Battery Question

[WStayton]

I am in the process of spec'ing my "whole-house" alternative energy system and I have a question about batteries.

I am contemplating using a  Xantrex XW6048 inverter-charger which requires 48 volts DC on the input side.

Does it matter whether I use one string of eight each, six volt Surett S-600, or can I use three strings of US Battery US-1800
, again with eight batteries in each string, with the strings in parallel?  In the first case with the Surett's I woulod have 500 amp-hours of current available, from which I would be able to use 50%, so 250 amp=hours at 48 volts.  In the second case I would have three times 200 amp-hours for a total of 600 amp-hours at 48 volts with 300 amp-holurs at 48 volts useable.  But, do I introduce problems by having three strings in parallel in that one string could input more current and so discharge to a greater extent than one of the others, and/or, upon charging, would one string absorb more charge than the other two and thus be overcharged.  Is there some way to prevent these problems via battery isolators or something?

  Also, I am contemplating using Schott ASE145W solar panels, which are  145 watt, 33.6 Voc, 24.8 Vmpp.  Can I just wire two of these in series ( + of one to battery with its negative to another panel's + with the second panels -, again to battery, with ten  of these, double modules in parallel), to feed the battery bank of three strings of eight each, US-1800 batteries?

  I am interested in this parallel/series approach because the 24 US Battery US-1800 cost about half as much as the eight Surette S-600.  I realize that the US Batteries would be less durable than the Surette's but would I use more that two sets of the US Batteries during the life of one set of Surette's.  Surettes are warrantied for 7 years while the US Batteries are warranted for 24 months (I think!).  If it is going to require three and half sets of US Batteries to live as long as one set of Surette's, this is, obviously, a dumb idea.  At two to one it sort of makes sense - if, and only if,the other problems can be solved or are not really problems.

   So what say yee, am I bent on discovering a new way to pour money down a hole in the ground?  <smile>

Regardz,

Wayne Stayton

[LowGear]

Also, I am contemplating using Schott ASE145W solar panels, which are  145 watt, 33.6 Voc, 24.8 Vmpp.

I don't understand why you'd go for 145 Watt panels when there are 245 Watt ones available (made in the USA)?

Casey

[Tom Reed]

In general the less parallel strings the better. The fundamental problem, as you've alluded to, is unequal charge/discharge balance on the strings. Also less connections and less cells to fill are all pluses. However since this sounds like your first big investment in batteries and newbies frequently toast'em  the low cost bats may be the way to go. If they are the L-16 style you should be able to get 5-7 years out of them. Our system uses 4 -12v 1055ah Hawker PV1 bats in a single series string. I'm hoping for a 20 year life out of them.

On the panel wiring, the primary dependency is on the charge controller you select. The modern MPPT (Maximum Power Point Tracking) units will take up to around 140 vdc. Which will allow 4 panel strings with the ASE145W. This will save you on wire runs and combiner box costs. The MPPT charge controller will get you around an extra 20% more power out of the panels over the course of a year.

[mike90045]

do you have even a general idea of your AC loads ??

[WStayton]

mike90045:

  I had figured that I would need 10 kW, including starting loads, planning for one starting load at the time.  If everything started at once, I would need more like 20 kW, but I THINK (always  dangerous!) that the chances of that are fairly remote.  Since starting loads are of fairly short duration, something like 5 to 15 seconds, depending on what you're starting, I hope I'm safe in only expecting one starting load at the time.  Obviously I have to be careful and not apply power to everything at once from a dead stop - that would be BAD! <grin>

  Of course the golden rule is if something bad can happen. it WILL!

  Got any good fixes to ensure that everything doesn't start at once?

[rcavictim]

mike90045:

 
  Got any good fixes to ensure that everything doesn't start at once?

Make sure the switches for each heavy load are all in their own separate rooms and live alone.   

[LowGear]

Hi mike90045,

I have a timer on my water heater.  I guess I could do the same thing on my other "as needed" loads.  The well pump would have to rule.  But a dryer could be on a timer.  And then you could build an either-or circuit for units that would compete with the pump.  How many minutes a day can a well pump actually run?

Or did I miss the question again?

Casey

[mike90045]

Hi mike90045,
  How many minutes a day can a well pump actually run?   

My pump is on an intermatic timer, which is series'ed with a tank float and a 240V contactor.  It's set to run for 3 hours daily in summer, to keep 9,000 gallons of water tank full.  I've got an orchard which is gravity fed from that tanks which are on a hill 160' above the pond.   Generally, by noon, batteries have finished bulk, and have dropped back to absorb, and so I'm not cycling the batteries to run the pump.

--
Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV
Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 400A battery bank | 15, Evergreen ESA 205 fa3 "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT