How does a lithium-ion battery work? What advantages does it have over a lead-acid battery? When does a lithium-ion battery storage pay off?
A lithium-ion battery (short: lithiumion battery or Li-ion battery) is the generic term for accumulators based on lithium compounds in all three phases, in the negative electrode, in the positive electrode as well as in the electrolyte, the electrochemical cell. Lithium-ion battery have high specific energy compared to other types of batteries, but require electronic protection circuits in most applications, as they react adversely to both deep discharge and overcharge.
Lithium ion solar batteries are charged with electricity from the photovoltaic system and discharged again as required. For a long time, lead batteries were considered the ideal solar power solution for this purpose. However,based on lithium-ion batteries have decisive advantages, although the purchase is still associated with additional costs, which are, however, recouped through targeted use.
Technical Structure and Energy Storage Behavior of Lithium-ion Batteries
Lithium-ion batteries do not differ fundamentally from lead-acid batteries in their general structure. Only the charge carrier is different: When the battery is charged, lithium ions "migrate" from the positive electrode to the negative electrode of the battery and remain "stored" there until the battery is discharged again. High-quality graphite conductors are usually used as electrodes. However, there are also variants with iron conductors or cobalt conductors.
Depending on the conductors used, the lithium-ion batteries will have different voltages. The electrolyte itself must be water-free in a lithium-ion battery since lithium and water trigger a violent reaction. In contrast to their lead-acid predecessors, modern lithium-ion batteries have (almost) no memory effects or self-discharges, and lithium-ion batteries retain their full power for a long time.
Lithium-ion power storage batteries usually consist of the chemical elements manganese, nickel and cobalt. Cobalt (chemical term: cobalt) is a rare element and therefore makes the production of Li storage batteries more expensive. In addition, cobalt is harmful to the environment. Therefore, there are multiple research efforts to produce the cathode material for lithium-ion high-voltage batteries without cobalt.
Advantages of Lithium-ion Batteries Over Lead-acid Batteries
◎ The use of modern lithium-ion batteries brings with it a number of advantages that simple lead-acid batteries cannot deliver.
◎ For one thing, they have a much longer service life than lead-acid batteries. A lithium-ion battery is capable of storing solar power for a period of nearly 20 years.
◎ The number of charging cycles and the depth of discharge is also many times greater than with lead batteries.
◎ Due to the different materials used in production, lithium-ion batteries are also much lighter than lead batteries and more compact. They, therefore, take up less space during installation.
◎ Lithium-ion batteries also have better storage properties in terms of self-discharge.
◎ In addition, one must not forget the environmental aspect: Because lead batteries are not particularly environmentally friendly in their production due to the lead used.
Technical Key Figures of Lithium-ion Batteries
On the other hand, it must also be mentioned that, due to the long period of use of lead batteries, there are much more meaningful long-term studies than for the still very new lithium-ion batteries, so that their use and associated costs can also be calculated better and more reliably. In addition, the safety system of modern lead batteries is in part even better than that of lithium-ion batteries.
In principle, the concern about dangerous defects in li ion cells is also not unfounded: For example, dendrites, i.e. pointed lithium deposits, can form on the anode. The probability that these then trigger short circuits, and thus ultimately also cause a thermal runaway (an exothermic reaction with strong, self-accelerating heat generation), is particularly given in lithium cells that contain low-quality cell components. In the worst case, propagation of this fault to neighboring cells can lead to a chain reaction and a fire in the battery.
However, as more and more customers use lithium-ion batteries as solar batteries, the learning effects of the manufacturers with larger production quantities also lead to further technical improvements of the storage performance and higher operational safety of lithium-ion batteries and also further cost reductions. The current technical development status of Li-ion batteries can be summarized in the following technical key figures:
|Applications||Home Energy Storage, Telecom, UPS, Microgrid|
|Application Areas||Maximum PV Self-Consumption, Peak Load Shifting, Peak Valley Mode, Off-grid|
|Efficiency||90% to 95%|
|Storage Capacity||1 kW to several MW|
|Energy density||100 to 200 Wh/kg|
|Discharge time||1 hour to several days|
|Self-discharge rate||~ 5% per year|
|Time of cycles||3000 to 10000 (at 80% discharge)|
|Investment cost||1,000 to 1,500 per kWh|
Storage Capacity and Costs of Lithium-ion Solar Batteries
The cost of a lithium-ion solar battery is generally higher than that of a lead-acid battery. For example, lead batteries with a capacity of 5 kWh currently cost an average of 800 dollars per kilowatt hour of nominal capacity.
Comparable lithium systems, on the other hand, cost 1,700 dollars per kilowatt hour. However, the spread between the cheapest and most expensive systems is significantly higher than for lead systems. For example, lithium batteries with 5 kWh are also available for as little as 1,200 dollars per kWh.
Despite the generally higher purchase costs, however, the cost of a lithium-ion solar battery system per stored kilowatt hour is more favorable calculated over the entire service life, since lithium-ion batteries provide power for longer than lead-acid batteries, which have to be replaced after a certain period of time.
Therefore, when buying a residenitial battery storage system, one must not be frightened by higher purchase costs, but must always relate the economic efficiency of a lithium-ion battery to the entire service life and number of stored kilowatt hours.
The following formulas can be used to calculate all the key figures of a lithium-ion battery storage system for PV systems:
1) Nominal capacity * charge cycles = Theoretical storage capacity.
2) Theoretical storage capacity * Efficiency * Depth of discharge = Usable storage capacity
3) Purchase cost / Usable storage capacity = Cost per stored kWh
|Lead-acid Batteries||Lithium ion Battery|
|Nominal capacity||5 kWh||5 kWh|
|Theoretical storage capacity||16.500 kWh||29.000 kWh|
|Depth of discharge||65%||90%|
|Usable storage capacity||8.795 kWh||24.795 kWh|
|Acquisition costs||4.000 dollars||8.500 dollars|
|Storage costs per kWh||$0,45 / kWh||$0,34 / kWh|
BSLBATT: Manufacturer of Lithium-ion Solar batteries
There are currently many manufacturers and suppliers of lithium-ion batteries. BSLBATT lithium-ion solar batteries use A-grade LiFePo4 cells from BYD, Nintec, and CATL, combine them, and provide them with a charge control system (battery management system) adapted to photovoltaic power storage to ensure the proper and trouble-free operation of each individual storage cell as well as the entire system.