18650's suitable for off grid bank?

[RiverRat]

Hey I have a friend who needs to get an off grid bank together and need some advice as well as for my own interest in upgrading my existing battery bank.

I have a lead acid bank right now. using the cheapest batteries I could get and achieved a 4kwh capacity @ 20% discharge for around 3500$ US. I run a few basic things with it like keeping food cold running computers etc.. It's was simple enough to build and maintenance is pretty easy. The solar charger is an Outback Flexi max 80 which can charge at 12v 24v or 48v. Atm is charging at 13.7 v to the 12v bank but the amp rate varies depending on how sunny it is.

Seems to me that 1850's stack up now in terms of dollars to usable storage capacity but there must be something I'm missing or there'd be more people using them for this purpose.

Are there any deal breakers to put this idea to rest?

IS the shelf life just to short in comparison to lead acid?

Which 18650 given you'd be buying them by the 100's would make the most financial sense?

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[Nobuo]

Lithium-ion NCA chemistry is what I would use, or LiFePo4 because that applications are continuously charging and discharging.

using the cheapest batteries I could get and achieved a 4kwh capacity @ 20% discharge for around 3500$ US.

Are You talking about 18650 cells?. Today 1KWh ~= $350 of high quality 18650 cells. So 4KWh ~= $1400

The solar charger is an Outback Flexi max 80 which can charge at 12v 24v or 48v. Atm is charging at 13.7 v to the 12v bank but the amp rate varies depending on how sunny it is.

What are the nominal output Voltage of the solar cells at average sunlight and at raw(before it reaches charger controller)? I would charge at that Voltage, or highest possible to maximize efficiency.
Also it would count what Voltage is the destination uses. If you will use an 125V/240V DC-AC inverter for Home applications, I would also build/buy the highest Voltage battery that could charge the controller.

Are there any deal breakers to put this idea to rest?

IS the shelf life just to short in comparison to lead acid?

Which 18650 given you'd be buying them by the 100's would make the most financial sense?

Elon Musk next hit, is just that

SLA life is not far at the level of most lithium technology, but in terms of efficiency at charging or discharging is just the worst chemistry from the used today.

18650 it's really perfect in terms of Energy / price ratio, but it implies the hardest job of building it (spot welding, attaching, etc.)

It depends from where you buy to choose the right 18650 cell, but I would only look for the most density ones. In that applications discharge rates are not important. (Assuming that grid banks for Home Solar installations must be Huge, and weight or space is not the worst issue.)

 

[okashira]

Model S modules will be perfect for this application.
> 4000 cycles if you use 10% - 70% DOD. Better calendar life then LiFePO4 or Lead Acid.
Not to mention both smaller, lighter, and cheaper for the same capacity and power and better lifetime. They are win/win/win
We are working on inverter and BMS solutions.

 

[circuit]

Hi okashira. Can you tell us more about what you are working on?