Battery pack design, and actual energy

Hi All,

I hardly started to find some battery (only a couple so far :s ) but still it's a start ^^
So I'm thinking about my dream pack, how should I design it, to start from somewhere, and that can grow bigger and bigger.

So first question/thought :
My first usage will be to cover my idling power consumption which is around 200W 24/7. So no big Current draw.
200w during 12hours (I assume, the 14 other hours of the day, the solar panel won't draw anything from my batterie) : it's 2.4kWh
So if I depending the DOD, my ideal pack would need to be between 2.4kWh and 5kWh or even more.
What would be an acceptable DOD rate ? 50% ?


second question :
lets say, I start with a 7s40p which will give me around 2kWh of power with lets assume 280 cells. (please correct me if I'm wrong)
then I could just to 48V and double the cap without too much redesign.
So what about using the sell holder that you all use, but making let say 20 cell row, that would give me 2 full row, leaving the 3 other empty for future use ?
What do you think ?
Also, Cells with 10A of max current discharge is enough ? or I should aim for larger ?

Last but not least :
thinking about buying cell, I found the NCR18650PF which are 3.7*2.9Ah = 10.7Wh for 2.25
let say I get 2000 cycles at 50% DOD rate, the battery will provide : 10.7 kWh which brings the cost of the kWh from the battery at 0.2/kWh ? today I pay 0.14/kWh so buying the battery cell is not so interesting right ? Or am I wrong somewhere in the way I think ?

Thanks guy for the help

1. I think you need to count higher. Do you really have sun 12 hours a day that will produce atleast 200W? Note that you ALSO need to produce enough to charge up the pack during the day = 2x the capacity atleast.
What about bad weather days?
LiIon can take alot more than 50% DOD but if you want to preserver them a long time 50% is good choice.

2. 7x40 = 280 cells. With 2.9Ah cells that would give you: 2,9*3,7*280 = 3kWh total energy. With 50% thats 1,5kWh useable energy.

No its not cheap to buy and store battereis. Dont forget all losses transforming the energy back and forth as well.

daromer said:

1. I think you need to count higher. Do you really have sun 12 hours a day that will produce atleast 200W? Note that you ALSO need to produce enough to charge up the pack during the day = 2x the capacity atleast.
What about bad weather days?
LiIon can take alot more than 50% DOD but if you want to preserver them a long time 50% is good choice.

2. 7x40 = 280 cells. With 2.9Ah cells that would give you: 2,9*3,7*280 = 3kWh total energy. With 50% thats 1,5kWh useable energy.

No its not cheap to buy and store battereis. Dont forget all losses transforming the energy back and forth as well.
=> got an offer for 36 Thoshiba battery 8 cells, 4400mha 150 brand new. thats 0.5 a each. Decent price ? or

Click to expand...

1. =>You are right, but I'll use a MPP off grid inverter, that will be connected to grid for back up. I need to start low, because otherwise I won't start at all

2. ok cool, I'll go for 50% DOD then

3. => got an offer for 36 Thoshiba battery 8 cells, 4400mha and 6 cells battery for 100 brand new. thats 0.4 a cell. Decent price ? or