Cost of ownership is important (for most people) who are exploring the installation of Off-Grid alternative energy. The battery bank can be one of the more expensive aspects to an overall Off-Grid design.
Lithium Iron Phosphate batteries are a fairly recent technological advancement and they are being used in Off-Grid and battery backup installations due to a number of advantages. These include a much smaller footprint, much less weight, a very high depth-of-discharge (DOD), and a lower cost of ownership over its comparative cycle life.
I put together some data which compares three different depth of discharge values (50%, 80%, and 100%) along with each of their associated cycle life values for the Lithium Iron Phosphate batteries listed below.
Note that if you discharged lead-acid batteries at these depths, it wouldn’t be long and they would become bricks or boat anchors, so to speak.
I’ve also included:
- Maximum daily consumption values (kWh – kilowatt hours) for while drawing off the battery bank.
- Cost per kWh for each of several different Lithium Iron Phosphate batteries available from “Iron Edison” based on their listed prices as of this original post date.
Why Iron Edison? Because they are a leader in this battery type system for Off-Grid energy storage, and their latest battery has some great looking specs.
Battery ‘End of Life’
The industry standard definition of “end of life” for a battery is when the capacity has degraded to 70% of nameplate value. They will continue functioning well beyond this point, just at a diminished capacity.
The following values are based on the ‘end of life’ definition as written above. Though even after that, the batteries will continue to hold capacity! So really, in my view, they’re not ‘dead’ (yet)…
Lithium Iron Phosphate Battery Cycle Life
The following specifications reflect those of the ‘4LiFe’ Lithium Iron Phosphate batteries from Iron Edison:
48v – 100Ah – 5.1 kWh
48v – 200Ah – 10.2 kWh
48v – 300Ah – 15.4 kWh
48v – 400Ah – 20.4 kWh
48v – 600Ah – 30.8 kWh
48v – 800Ah – 40.8 kWh
48v – 900Ah – 46.2 kWh
48v – 1200Ah – 61.6 kWh
The sweet spot for optimizing capacity versus cycle life and cost appears to be 80% DOD (depth of discharge) for these Lithium Iron Phosphate batteries.
The amazing thing compared to lead acid is the DOD with no apparent detriment to the battery. A lead acid battery DOD ‘rule of thumb’ might be 30% – and maybe you’ll get 3,500 cycles with good care? (variable depending on battery model).
The intriguing observations from their technical specifications which stand out for me are:
- very long cycle life
- deep depth of discharge capability
- lower operating cost over its cycle life
IronEdison.com does advertise on our site. I endorse their products without reservation. They are located in Denver, Colorado. If you’re serious about a long-term battery bank for Off-Grid, I encourage you to at least contact them with any of your questions. They offer free system design!
Other articles on MSB about Iron Edison: