L-16 "cycling" requirements? [RE-wrenches]

Joel Davidson joeldavidson at earthlink.net
Fri May 20 14:57:01 PDT 2005


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Hi Travis,
While filling up the kiddy pool, consider how high you fill the pool (charging), how much water is splashed out (depth of discharge) and how often you have to recharge the pool to get it to the fun splash level (charge cycle). I guess another sloppy analogy would be occasional filling to overflowinge (qualization).
Have fun.
Joel Davidson

-----Original Message-----
From: "Travis Creswell, Ozark Solar" <ozsolar at ipa.net>
Sent: May 20, 2005 2:39 PM
To: RE-wrenches at topica.com
Subject: RE: L-16 "cycling" requirements? [RE-wrenches]

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While we are talking about cycles.....

What is a cycle? 

With forklifts, floor scrubbers, and golf carts it's pretty easy to define.
Draw the battery down, often way down, then charge the heck out of it back
to 100% and do it all over again the next day.  That's a cycle that's easy
to see.

But with a RE system it's a lot more complex. Varying loads are coming and
going all the time.  At least several times a day the loads exceed the
charging system.  

Is a cycle clicked off every time state of charge changes direction?  If
that's the case some RE systems could have at least 20 or 30 cycles per day.
Even though they might just be 1% or smaller changes in state of charge
that's still a cycle, right?

Food for thought..

Have a good weekend.  I'm going to go fill up the stock tank, oops, I mean
kiddy pool and splash around with the kids. They think it's a kiddy pool and
that's what counts.

Travis Creswell
Ozark Energy Services, Inc.

-----Original Message-----
From: Todd Cory, Mt. Shasta Energy Services
[mailto:toddcory at finestplanet.com] 
Sent: Friday, May 20, 2005 1:45 PM
To: RE-wrenches at topica.com
Subject: Re: L-16 "cycling" requirements? [RE-wrenches]

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I would also like to know where this idea came from that "batteries need
exercise to stay healthy"? Trojan discounts that notion. They have also
suggested that EQing a floating battery is unnecessary... the stir the
electrolyte myth doesn't wash.

As I understand it, batteries have two "clocks working toward their end of
life.
Once clock is a chemical clock... that even floated with no cycling, they
will
only last so long. The other is a cycle clock... that counts the number of
charge / discharge cycles. Also of consideration is the length of time they
are
left discharged due to the resulting sulfation that happens to the plates.

We can talk all day about optimal bulk, float and EQ voltage settings, but
evidence suggests it is best to err on the side of slightly overcharging wet
cells rather than chronically undercharging.

I have found lead antimony wet cells are really not all that horrible in
grid
intertied applications, especially as with modern inverters like the
Outback,
float current losses are minimized. With hydrocaps watering is also
minimized
and a "cheapo" like a Trojan L-16 will typically last a good 10 to 12
years...
similar to their life expectancy in an off grid system. Plus, they are very
cost
effective. Yes, a better wet cell would be a lead calcium configuration but
for
some reason (probably manufacturing quantities?) they are horribly
expensive.

As I understand it, lead calcium's are best for shallow cycling and float
service. (Perfect for battery back up grid ties.) I suppose the reason for
the
price differential is that they are not mass produced as lead antimony cells
are. Last year I did some research about the price to replace those lead
calcium
wet cells at the hydro plant I work at since their "rated life" is nearly
up.
(Guess who gets to take them home!)
I believe the cost is going to be around $9K for 12 kW.
10 kWh of AGM's are about $1.2K
By comparison 20 kW of L-16's were about $1.3K.

Price per kWh:
Wet cell lead antimony: $65.00; life span ~10 years = $6.50/kWh/year (deep
cycle)
Wet cell lead calcium: $750.00; life span ~20 years = $37.50/kWh/year
(shallow
cycle)
AGM lead calcium: $120.00; life spam ~10 years = $12.00/kWh/year (shallow
cycle)

If labor is included in the above numbers wet cell lead calciums are more
price
competitive.


I agree that each application needs the proper battery configuration and
chemistry. Grid ties with battery backup optimally need a different battery
chemistry than off grid. The problem seems to find a cost effective approach
to
this application.

So Doug what do you use? AGM's?

This is a pertinent topic for the list, as with Outback GFX inverters, grid
intertied systems with backup power with no longer have to pay the
inefficiency
penalty we had with brand X's old SW design.

Todd

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