Hi David,
Yes, I am happy with lead acid management.
But the new tech stuff is just that, it seems every type and every manufacturer do there own thing.
LIFEPO4 seem to better understood.
I did a paper of recent tech batteries, it runs to about 5 pages of A4. I am constantly asked so it works as a hand out.
Heres a bit below...........
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.
Comment from Jim, “Swell up and fail is a 'true' statement. Most LiFePO4s are made in China. They do not advertise that the battery needs to be caged and compressed. But, when push come to shove, they will admit this. All of their test data on prismatic cells are in a test cage with 12 psi applied the sides of the cell. Without a cage and compression, the cell will swell. The swelling causes internal cell damage and drastically shortens cell life. The cage and compression is a 'pain in the neck'. Once you assemble a bank, you don't move them easily”.
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.
Comments from Jim, “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.
LiFePO4 batteries operate from 2.5 volts to 3.65 volts. Lead acid battery protocols will not work for LIFePO4 batteries. Totally different chemistry. Totally different characteristics. These cells have proven to deliver 100%+ of their rated capacity between these two voltages. My research and experience shows that they have a very flat charge/discharge curve at 3.2 volts over most of there capacity. When you approach the end of discharge, the voltage drops off quickly from 3.2 volts to 2.5 volts. The same on the charge side. The voltage slowly rises from 3.2 volts to 3.4 volts. Then the last 5% of the charge cycle, the voltage rapidly rises to 3.65 volts. If you limit the operating voltage zone of the battery from 3.0 volts to 3.4 volts, you will get 90% of the rated capacity every cycle AND you will avoid the over charging and over discharging associated with early cell death. These are programmed into the LiFePO4 chargers and BMS. The BMS is the safety device to protect the battery and ensure long life. I also program these charge parameters into my solar charger and inverter.
I am still fairly new to LiFePO4 batteries (24 months). So far they are performing well.
I will keep you posted as time goes by. I am not afraid to admit I was wrong, if and when they fail. Keeping my fingers crossed.
Hopes this helps to understand the LiFePO4 prismatic batteries better. Just a note. The cage and compression does not apply to the round cylinder cells. Only the rectangular prismatic cells.”
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. Note, A forum member in Norway re-repairs and re-uses Nissan Leaf battery packs very successful, its sort of unofficial but he still gets them from Nissan Norway and re-cycles the packs.
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 Thanks to the FORUM, ‘Northern Arizona Wind & Sun’, especially to the Moderator ‘Bill’……. Thanks also to Jim from the ‘Fieldlines’ Forum Online Community for Discussing Solar Power, Wind Power, And Other Forms Of Renewable And Alternative Energy.
From the Fieldlines forum
JimOK
Re: battery information
« Reply #17 on: May 21, 2021, 06:10:00 PM »
1) Lead acid batteries are forgiving, and generally "die" gracefully.
Unless you accidentally run them dead one time, then they lose capacity and start dying pretty quick.
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.
Same as lead acid. Many expensive L16s have been run dead by accident. Their 15 year expectancy dropped to 1 or 2 years. That's why I stuck with the 6 volt golf cart batteries. Just in case I screwed up. Been known to happen.
3) LFP / LiFePo / LP4 are the "safer" batteries that tend to just fail, or swell up and stink.
Swell up and fail is a 'true' statement. Most LiFePO4s are made in China. They do not advertise that the battery needs to be caged and compressed. But, when push come to shove, they will admit this. All of their test data on prismatic cells are in a test cage with 12 psi applied the sides of the cell. Without a cage and compression, the cell will swell. The swelling causes internal cell damage and drastically shortens cell life. The cage and compression is a 'pain in the neck'. Once you assemble a bank, you don't move them easily.
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.
LiFePO4 batteries operate from 2.5 volts to 3.65 volts. Lead acid battery protocols will not work for LIFePO4 batteries. Totally different chemistry. Totally different characteristics. These cells have proven to deliver 100%+ of their rated capacity between these two voltages. My research and experience shows that they have a very flat charge/discharge curve at 3.2 volts over most of there capacity. When you approach the end of discharge, the voltage drops off quickly from 3.2 volts to 2.5 volts. The same on the charge side. The voltage slowly rises from 3.2 volts to 3.4 volts. Then the last 5% of the charge cycle, the voltage rapidly rises to 3.65 volts. If you limit the operating voltage zone of the battery from 3.0 volts to 3.4 volts, you will get 90% of the rated capacity every cycle AND you will avoid the over charging and over discharging associated with early cell death. These are programmed into the LiFePO4 chargers and BMS. The BMS is the safety device to protect the battery and ensure long life. I also program these charge parameters into my solar charger and inverter.
I am still fairly new to LiFePO4 batteries (15 months). I have done a lot of research. So far they are performing well.
I will keep you posted as time goes by. I am not afraid to admit I was wrong, if and when they fail. Keeping my fingers crossed.
Hopes this helps to understand the LiFePO4 prismatic batteries better. Just a note. The cage and compression does not apply to the round cylinder cells. Only the rectangular prismatic cells.