Why I abuse batteries was: trojan battery cycle [RE-wrenches]

[John Berdner]

Jeff:
 
I agree with your strategy of not running the generator to finish off
the absorbtion phase if possible.
The cost of fuel, maintenance, and CO2 is simply too high.
One way to mitigate this is to size the generator a bit smaller and set
it up to charge only up to the absorbtion voltage.  Ideally you can set
up the system so that it does not run the non critical loads during the
bulk phase.
Once the battery hits the absorbtion point turn on some opportunity
loads, i.e. water pumps, etc. and use the "surplus" generator power to
run these loads while the battery is absorbing.  At least this is using
more of the generator power for useful work. 
 
At the risk of being flamed I will suggest one other option that I have
found works pretty well.
Run the generator first thing in the morning up to the absorbtion point
then let the PV do the absorbtion charge to bring the battery up to a
full state of charge.
Yes, potentially you might throw away some PV energy on some days but
the overall energy cost, including battery life, should be lower in the
long run.  CO2 can also be minimized using this strategy.
 
Contact me offline and I can explain how to program a Sunny Island to
do your charging regiem or either of my scenarios.
 
Best Regards,
 
John Berdner
 
I found that I must abandon my old ways of respecting batteries and
treating them like gold and fully recharging often if not daily. True,
battery prices are going through the roof, but so is the cost of fuel
and the environmental costs of using it. I have 5 recent mega o-t-g
systems each with 28 - 36 kW of inverters and HUP batteries in the range
of 190-280 kWh, all of these 5 are solely charged by 66kW diesel
gensets. Some quick math showed that any Absrob at all is not cost
effective. I typically do a daily charge to my Absorb point (2.4 v/cell)
and shut down the genny at about an 80% SOC. Then every 2 weeks we do an
EQ. for 4 hours past 2.5 v/cell. This is giving good specific gravity
after the EQ's. As I cycle my batteries to about 50% DOD each day I also
recharge each day. To provide for a daily FULL recharge it would take an
additional 4 hours of Absrob. My genny is drinking about 3 g.p.h. at a
delivered cost of $4/gal in these remote locations. This is a daily cost
to Absorb of $48 or $17,520/year! Not to mention about double the daily
genset runtime and therefore 1/2 the years out of the genset, double the
annual oil changes and maintenance and double genset racket each day. As
it turns out at a cost of $17,520 a year in just two years the $35,000
will buy me a new set of HUP's!!
As mentioned here it is VERY hard to talk a client into a several hour
Absorb cycle, the question is - should you?? Is it wise to spend
$17,520/year to prolong a $35,000 battery beyond even 3 years, let alone
7-12 years? What about all of that CO2? When we add in other charge
sources like solar, wind and hydro the equation changes as our cost of
fuel is zero, but when it is gen/inverter/battery only I've had to force
myself to rethink battery care and charging.
I'm still playing with this and my settings as all of these systems are
just under a year old. My main goal in my work is to reduce CO2, this
means to find creative ways to reduce genset run times w/o overheating
my batteries from too aggressive charge rates. Now to get these clients
to start adding in PV, the numbers are great once one has already
invested in the rest of the BOS as PV alone is about 1/4 of the kWh cost
of diesel power.
Rethinking battery care....

-jeff o




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