Electrical batteries consist of one or more electrochemical cells that convert stored chemical energy into electrical energy. Rechargeable batteries or secondary cells can be recharged by applying electric current, which reverses the chemical reactions that occur during its use. Phaesun offer different types of rechargeable batteries as essential parts for Off-Grid power systems. The main types are:
(Flooded) Sealed lead-acid batteries
This is the oldest and most established form of rechargeable batteries. It contains an acid liquid in an unsealed container. Therefore the battery must be kept upright and well ventilated to ensure safe dispersal of the hydrogen gas produced by these batteries during charging. The lead–acid battery is very heavy. Despite this, its low manufacturing cost and its high surge current levels make it perfectly fitting where a large capacity (over approximately 10 Ah) is required or where the weight and ease of handling are not concerns.
Gel batteries contain a semi-solid gelified electrolyte. The sulfuric acid is mixed with silica fume, which makes the resulting mass gel-like and immobile. Therefore these batteries do not need to be kept upright. Gel batteries reduce the electrolyte evaporation, spillage, and boast greater resistance to extreme temperatures, shock, and vibration.
Absorbent Glass Mat (AGM) batteries
AGM batteries absorb the electrolyte in a special fiberglass matting. Very thin glass fibers are woven into a mat to increase surface area enough to hold sufficient electrolyte on the cells for their lifetime. The fibers that compose the fine glass mat do not absorb nor are affected by the acidic electrolyte they reside in. The plates in an AGM battery are of different shape. Some are flat, others are bent or rolled.
Lithium-ion (Li-ion) batteries
In contrast to the above mentioned battery technologies Li-ion batteries are dry-cell batteries. A dry cell has the electrolyte immobilized as a paste, with only enough moisture in it to allow current to flow. Li-ion batteries use a technology in which lithium ions move from the negative electrode to the positive electrode during discharge, and back when charging. Lithium-ion batteries are common in consumer electronics. They are one of the most popular types of rechargeable battery for portable electronics, with one of the best energy densities, no memory effect, and only a slow loss of charge when not in use. Due to technological innovations and price reductions Li-ion batteries get more and more popular for PV Off-Grid systems.
The following technologies are suitable for PV Off-Grid systems:
- Lithium Iron Phosphate (LiFePO4)
Li-phosphate offers good electrochemical performance with low resistance. This is thanks to nano-scale phosphate cathode material. The key benefits are excellent thermal stability, tolerant to abuse, high current rating and long cycle life.
- Lithium Cobalt Oxide (LiCoO2)
Li-cobalt is characterized by a high specific energy but moderate safety, life span and specific power.
- Lithium Manganese Oxide (LiMn2 O4 )
Lithium manganese oxide improves ion flow on the electrodes. It is characterized by a good current handling and solid thermal stability with a low internal resistance.
The NMC uses nickel, manganese and cobalt as cathode material. Nickel is known for its high specific energy but low stability, and manganese forms a spinel structure for low internal resistance but offers limited specific energy. NMC offers good overall performance with high specific energy, low internal resistance and a moderate price.