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

[James Surrette]

Hi Jeff,
 
Have you considered a Low Voltage Disconnect / Auto start trigger at ~80% DOD, drive the batteries to ~80% SOC, which is relatively efficient and then EQ every 30-60 days.  Assume the HUP can handle 1500 - 2000 cycles at this depth and you would cut down on gen time / fuel / CO2, etc.
 
Regards,
 
Jamie

>>> Jeff Oldham <starpower4u at juno.com> 13/02/2008 3:10 pm >>>


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 t!
o 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


>From the Solar, Wind and Hydro powered office of Jeff Oldham/Regenerative SOLutions

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