The battery pack for stationary use can be optimized for two main uses: cyclical and in buffer.
Use in buffer, stand-by, is that typical of UPS for home or professional use. Lead batteries are widely used and represent a good and economical solution.
The introduction of lithium technology can increase both the efficiency of the system, thanks to their lower self-discharge, and the operational life.
In particular, it has advantages than lead in all applications where storage is used with frequent and deep charge-discharge cycles.
A limitation of lead technology optimized for use in buffer is to withstand badly frequent charge-discharge cycles reducing the useful life of the battery. An example is the car battery that well supports strong discharge currents for starting, but if it is discharged in depth it deteriorates quickly after only a few cycles.
Cyclic use is fundamental to support wind and photovoltaic plants and in other similar cases with 300-350 cycles/year.
In cyclic use, an important parameter is the DOD (Deep Of Discharge), a parameter that indicates the amount of energy that we take from the total/nominal value. Essentially for all the electrochemical batteries this parameter has a heavy impact on the operating life of the battery itself.
For lead batteries between a 100% DOD cycle and a 30% DOD cycle, the service life can be reduced up to eight times, from 150 to over 1000 cycles (see Table 3). This directly impacts both on the cost of the plant, having to oversize it, and on the maintenance cost with frequent substitutions.
Lithium batteries may instead have far better performance reaching and exceeding 5,000 cycles with Li-titanate, but there are industrial proposals that exceed 15,000 (see).
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