Please find below a little document i have put together from 2 long time users of Li-Ion and LifePO4.
Both these guys have actual experiences, you may find their comments useful.
NEW BATTERY TECHNOLGIES FOR OFF GRID, 2021.
This is the present situation from Off Grid folk and installers from around the World. The 2 responses are from folk that actually have working systems of many years duration.
QUESTION asked ……
Hi all,
I am trying to get a better understanding of energy storage system design with lithium ion batteries. I work in developing countries where lithium ion batteries are still very uncommon outside of plug-and-play PV systems, but are likely to become more prevalent in the coming years. I only have experience with BMZ and Sonnen from years ago in the states. A few questions that I hope might lead to an interesting discussion:
1. It seems like LiFePo is the preferred chemistry for off-grid applications. It seems like Discover and SimpliPhi are popular and produce a good product. Are there other recommended brands? Any thoughts for what would be the most appropriate for smaller, very remote installations in the developing world?
2. Is anyone using NMC batteries here? If so, what brand?
3. Are there any other lithium-based chemistries that are currently commonly used for off-grid applications or will be in the future? Any that might be particularly interesting for developing country applications?
4. Is it possible to develop design general guidelines for energy storage system sizing with lithium ion batteries like has been done with lead acid batteries? Lead acid batteries definitely vary in their parameters by manufacturer, but there are some guidelines (DoD/cycles and charging/discharging current) that seem to hold reasonably consistent for AGM/Gel/FLA that can be used for design purposes.
Could this be done with the major lithium chemistries or do you see them as varying too much between manufacturer? For example:
LiFePo:
• SimpliPhi recommends a maximum C/2 charge and discharge rate. Claims a useable DoD of 100%. Recommend an 80% DoD for best cycle life. Claims around 98% roundtrip efficiency.
• Discover recommends a maximum C/1 charge and discharge rate. Claims a useable DoD of 90%. Claims around 98% roundtrip efficiency.
• Blue Planet Energy recommends a maximum C/2 discharge rate. Claims a useable DoD of 100%. Claims around 98% roundtrip efficiency.
Would it work to use general sizing parameters for LiFePo like:
• Maximum charge/discharge of C/2. (Is this reasonably consistent?)
• Recommended DoD 80% (Would provide a storage buffer. Does this tend to provide best LCOE?)
• Roundtrip efficiency 98% (Should this be more conservative?)
• Minimum charging temperature 0C.
Any/all thoughts welcome!
RESPONSE No1,,,,,,,,,
1) Lead acid batteries are forgiving, and generally "die" gracefully
2) Li batteries are unforgiving. 1 overcharge or 1 deep discharge, and they are toast. Might get a few more cycles out of them before they die, but either condition damages the battery.
3) LFP / LiFePo / LP4 (all the same battery, just different abbreviations) are the "safer" batteries that tend to just fail, or swell up and stink. Any of the other Li chemistry mixes, involve failure with fire or going bang.
4) Some Mfg's include the top and bottom 10% safety margins internal their BMS systems.
Some don't and you have to program that into your loads and chargers. Your Mileage May Vary. Some rate the full capacity, but only deliver 70% of capacity.
Lead acid batteries like 50% -100%, so same protocols will NOT work for each.
RESPONSE No 2………….
Each lithium type has its advantages and disadvantages, mostly related to energy density, specific power, life expectancy, performance, cost and safety. LiFePo4 is more of a compromise, it isn't the lightest nor can it deliver the current some others can however they are one of the safest, which is why they are a popular choice. The pre-assembled batteries or battery systems are roughly double the price of building a bank using prysmatic cells, some system can be integrated with other equipment, inverters etcetera, able to communicate information from the BMS regarding state of charge.
2. There are some I believe who are using NMC in the form of Nissan leaf batteries
3. Generally, a battery is chosen for a specific application, LIPO for example is extremely light with high performance capabilities, which is why they are the choice for drones, they are however dangerous, since weight is not as important but safety is makes LiFePo4 an ideal choice for off grid. There are variations even within that LFP made to enhance certain aspects of performance, according to some articles I've read. Not sure there is anything specifically available for developing countries but one thing is known, lithium batteries do not perform in temperatures below 0°C.
4. There are some manufacturers of drop in replacement type LFP who advertise that their battery can be discharged to 100% of the listed capacity, but in fact the actual capacity is greater, the BMS cuts the load when ~20% to protect against damage. Simpliphi has different warranty periods for differing charge /discharge levels, it is good practice when building a DIY bank to keep within certain parameters, commonly 90% and 20% of capacity. This extends the cycle count expectancy, programmable BMS's are available which can be set to whatever value is desired, but manufacturers will be cautious to preserve their reputation, one would hope.
My grateful thanks to these 2 contributors who have kindly allowed me to use their responses.
Note, I believe there is merit in these new technologies, but getting actual empirical evidence from working systems for long-term reliability is another matter.