# Ranking of Electricity Accumulation Possibilities: Multicriteria Analysis
## 4 Results and Discussion  
After performing a multi-criteria decision analysis using the TOPSIS method and setting an equal weighted weight of 0.111, the obtained results for alternative batteries are visible in Figure 2.  
It was determined that among the four analysed types of batteries, lithium-ion batteries are the closest to the ideal option, with a proximity coefficient of 0.67. Although the investment in a lithium-ion battery (EUR/kWh) is the highest among the compared batteries, this parameter was outweighed by its high-power density, which is about twice as high as the other alternatives, as well as the significantly high efficiency and number of charge/discharge cycles, which are considered primary aspects for achieving such results. It is important to note that the social factor and technological readiness of lithium-ion batteries were also rated the highest. Therefore, lithium-ion batteries are considered the most potential solution for energy storage. Next, with a proximity coefficient of 0.55, flow batteries are ranked. The main advantages of these batteries are their long lifespans and high number of charge/discharge cycles, providing high power density while maintaining relatively low investment costs. Accordingly, lead-acid (0.48) and sodium-sulphur (0.36) batteries have received lower evaluations. Such results are mainly influenced by their relatively low power density and operational lifespan. However, it should be taken into account that the capacity of batteries decreases with increasing charging and discharging time [42; 43], and a more in-depth study taking into account the factors of battery degradation is needed to gain insight into its impact on the overall results. In terms of the environmental impact assessment (kgCO\({}_{2}\)eq/kg) and comparison, both lithium-ion and flow batteries demonstrated lower impact ratios when compared to lead-acid and sodium-sulphur batteries. However, even the battery types with lower overall ratings are not considered uncompetitive in the energy storage technology market. Under specific parameters, which may differ primarily depending on technological needs and individual views, flow batteries, lead-acid batteries, and sodium-sulphur batteries, by further developing their innovation potential, can provide effective energy storage, promoting a global transition to the use of renewable resources. Similarly, after performing a multicriteria decision analysis using the TOPSIS method and setting an equal weighted value of 0.125, the results obtained for the alternatives of energy storage systems are visible in Figure 3.  
Figure 2: Battery TOPSIS MCDA analysis results. Among the compared six energy storage systems, it was found that the hydroelectric pumped storage station is the closest solution to the ideal renewable energy storage technology, reaching a proximity coefficient of 0.60. This result was mainly obtained because it is the most matured storage system among those considered, as electricity storage is also possible in hydroelectric reservoirs, so large capital expenditures are not necessary. The operational lifetime is also significantly longer, reaching up to 80 years, and the efficiency is the highest at 77.5%. The hydrogen energy (0.54) and green ammonia (0.51) storage technologies are ranked lower. According to the literature analysis, these two technologies for energy storage were also evaluated as the most promising and with a higher added value outside the energy sector. However, capital expenditures for these storage systems are significantly higher, and the technological solutions are still in the innovation development process. With a proximity coefficient of 0.45, the electric thermal energy storage technology is ranked lower because, although the capital expenditures EUR/KWh are the lowest among the compared storage systems, technological readiness is still at the demonstration level, hence the social factor is evaluated the lowest.