I have an older (circa 2000) grid tied system using PVs, a Trace SW4024, and ~20KWHs of AGM batteries. The batteries are beginning to show their age and so I have begun investigating which batteries would be a good replacement for them. This system will be attached to a working grid almost all the time, and so the batts will be in float most of the time. Once or twice a year the grid does go down, and the batts will be called upon to keep the core functions of the house running. Battery box is in a temp controlled space which rarely get above 80F or below 40F. The problem I am running into is different experts have very different suggestions. Here is what I have been able to figure out so far (feel free to correct if any of this is in error):
LiFePO4 seems to be the battery of choice for off-grid systems. Certainly seems that when you are cycling them daily they will deliver more storage and cycles than any of the other chemistries for the lowest cost in the long run, but more expensive up front. They have a greater percent of their storage available for use. Seems that for a grid tied, where cycling will be minimal, they may not be ideal since you will not be utilizing their cycling ability, and they would be kept near fully charged (depending you your set points) which is not good for them.
FLA is the cheapest up front, handles being kept in float well. Disadvantages are they require venting while charging and watering on a regular basis. If not well maintained or overdrawn they have a drastically reduced life.
AGM-LA are more expensive than FLA up front. They are not supposed to handle being kept in float as well as FLA, but do not require watering nor venting. Typically it seems they have a lower lifespan than well maintained FLAs, but longer than FLAs which are neglected.
So that is what I have found so far. Not necessarily a clear winner that I can see. Any factors that I've missed or gotten wrong? What do folks think?
LiFePO4 seems to be the battery of choice for off-grid systems. Certainly seems that when you are cycling them daily they will deliver more storage and cycles than any of the other chemistries for the lowest cost in the long run, but more expensive up front. They have a greater percent of their storage available for use. Seems that for a grid tied, where cycling will be minimal, they may not be ideal since you will not be utilizing their cycling ability, and they would be kept near fully charged (depending you your set points) which is not good for them.
FLA is the cheapest up front, handles being kept in float well. Disadvantages are they require venting while charging and watering on a regular basis. If not well maintained or overdrawn they have a drastically reduced life.
AGM-LA are more expensive than FLA up front. They are not supposed to handle being kept in float as well as FLA, but do not require watering nor venting. Typically it seems they have a lower lifespan than well maintained FLAs, but longer than FLAs which are neglected.
So that is what I have found so far. Not necessarily a clear winner that I can see. Any factors that I've missed or gotten wrong? What do folks think?