Impact of battery efficiency on cost: Difference between revisions

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#redirect [[Impact of battery characteristics on off grid system cost]]
 
Nife batteries are relatively inefficient.  To decide on how important an impact this has on cost let's do some reckoning:
 
The Efficiency compensated equivalent cost needs to be estimated calculated for various batteries, I define this as the effective cost per Wh of battery in a solar power system:
 
Basically we need to know how much energy the battery wastes, and the find the cost of that and add that to the sticker price of the battery.
 
 
It's the total energy that needs to be withdrawn from the socket by the user plus the energy wasted by the battery, which is the total energy the array needs to supply, divided by the array cost per unit energy, minus what the cost woudl be if the battery was 100% efficient.
 
Es=Wh that must be delivered/day to socket
Ea= Wh delivered per day by the solar array/watt of array
EFb= Efficiency of battery charge/discharge overall
Cc=cost of collector, in $/watt.
Fsib=fraction of the energy that gets to the socket that had to be stored in the battery
 
 
Cb= cost of battery per Wh of storage
 
ECc=efficiency compensated cost per Wh of battery
Cabbi=Total cost added by battery inefficiency
 
 
Cabbi=((Es+(((Fsib*Es)/EFb)-Fsib*Es))*Cc/Ea)-Cc*Es/Ea
 
 
then
(Cabbi/(Fsib*Es))+Cb=ECc
 
Cost added per Wh of battery storage needed by the system, plus cost of battery per Wh.
 
So if
Es=1000Wh
Ea= 5Wh/watt
EFb= 0.65
Cc= $2/watt
Fsib= 0.5
 
 
Cb= $0.2
 
 
Cabbi=((1000+(((0.5*1000)/0.65)-0.5*1000))*2/5)-2*1000/5
 
Cabbi=507.69-400 =107.69
 
(107.69/0.5*1000)+0.2= 0.415
 
It more than doubles the effective cost of the battery for Nife.  Lithium iron phosphate batteries are already available at $0.4 per watt, but only 80-90 percent efficiency they are only just inferior according to wikipedia (might be higher, remember hearing it was, should check battery handbook) search ebay for "thundersky lithium". And they have cycle durability in the same range as nife :http://evolveelectrics.com/Thunder%20Sky%20Lithium%20Batteries.html
 
But if the cost of the nife batteries was $0.1 per Wh then we'd be ahead of the game even with the low efficiency.  Plus the cost of collectors is going to go down, probably a lot faster than the cost of batteries.  Indeed the cost of batteries may well increase substantially, especially lithium batteries, due to market fluctuations or the cost of materials, especially lithium which is coming into huge demand.  With zinc bromide we might get the best of both worlds, producing an exceptionally cheap system.

Latest revision as of 07:59, 28 January 2012

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