While lead acid battery chargers typically have a three state charger with limited voltage ranges, a good Li-ion charging system should have the ability to maintain a single charging voltage conventional lead acid battery charger.
Please note: battery safety and maintenance is a separate topic, thoroughly research all applicable international and local safety standards and practices, and always follow the manufactures recommendations and guidelines before installing batteries.
Adding Energy Storage to an Existing PV/solar system
Many people with grid-tied only PV systems regret not having grid-interactive power conversion with energy storage—especially after life-changing events such as super storms. Other benefits of energy storage included using the renewable energy 24/7 for managing utility surcharges, increased self-consumption, plus having power during emergencies and outages. With AC-coupling technology grid-tied PV owners can now upgrade to grid-interactive with integrated storage after-the-fact.
There are complete system packages available from the leading grid-interactive inverter brands and other resellers with many variations and options, but it gets down to essentially adding a second, storage based inverter/charger connected to a battery bank. The original grid-tied inverter still performs its normal function of selling excess PV production back to the grid, while the new storage based inverter “sees” both the grid and the PV system connected to the grid-tie inverter and passes the PV generation on the grid when the grid is present, but when the grid is not present, or the system owner wants to switch to self-consumption, the storage based inverter takes over and manages energy requirement accordingly, such as using PV to charge batteries, drawing on battery power, starting a generator, etc.
Adding AC-coupling to a grid-tied system is relatively economical, usually no more than an additional 15-20% of the cost of a grid-interactive hybrid system to begin with, and because it makes use of the PV/solar system already in place, it is a less intensive installation, usually requiring a second electrical panel for back-up load distribution. System guidelines include making sure that daily critical loads do not exceed 80% of the battery bank’s depth of discharge, and selecting an additional grid-interactive inverter that has 125% the power capacity of the original grid-tied one—so a 5kW grid-tied inverter would be connected with a 6.2kW or larger grid-interactive inverter/charger in an AC-coupled system.
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