To all of you who are hesitating to invest into a Lithium Ferro Phosphate, I would like to take some of the uncertainty out of the decision making.
Let’s start with the sizing of a battery bank.
AGM or flooded lead acid batteries are a proven technology. The LIFEPO batteries are a much newer technology and as with so many new developments people hesitate to adopt new.
A lead acid battery bank should not be discharger below 50% if it’s capacity to prolong the life span of the batteries. So a 50 kW/hr battery bank is considered 25 kW/hr of usable capacity. Lead acid based batteries are also not taking nicely do prolonged under or deficit charging. So the charge current, in most cases should be between 5 % and 20 % of the A/hr rating. If your batteries have a rating of 500 A/hr your charge current should be between 25 A to 100A maximum. Under charging will cause sulphation, batteries loose capacity, and over charging will deteriorate the plates and cause a lot of maintenance and also shorten the life expectancy. A mistake made often times is adding new batteries to an aging battery bank in hopes to prolong the life. Bad idea, as the new batteries will age much faster compared to a total replacement with new. A simple way to extend the battery life on an AGM battery is to only use the top twenty five percent of the storage before re-charging. (Working on my own experiment here myself and nine years into the game my AGM energy storage is showing no noticeable sign of aging.)
In my experience most cottage or full time “Off Gridders” are expecting to replace their lead acid batteries every ten years, often times limping the last two years with very limited electricity storage.
Let’s take look at a good quality LIFEPO battery in comparison. A LIFEPO battery with a built in BMS (Battery-Management -System) has surprising charge and discharge performance. Let’s say the manufacturer guarantees 6500 deep discharge to 20 % capacity and still have 80% of usable energy storage after, that would amount to nearly eighteen years. There are actually products with 10 year warranties and up to 10,000 dep discharges available. To deep-discharge a well-designed battery bank every day for eighteen years is very unrealistic. In case of the 10,000 times deep discharge that wold amount to over twenty seven years. Running your home on a thirty Kw/Hr of storage, and use twenty four of that every day, is nowhere happening in the cottage world or full time living off grid world.
So in my opinion, the LIFEPO option is the absolute winner in the energy storage competition.