# Supercapacitor-Based Energy Storage in Elevators to Improve Energy Efficiency of Buildings
## 6 Discussion  
The simulation results showed that significant energy savings can be achieved with EESS. During the reference cycle, which is the elevator trip with high possible energy savings, energy savings of up to 52% were achieved, with a 43% reduction in the peak power of the grid. When real traffic data from on-site measurements were used as input to the simulation model, the simulation results showed energy savings of 35% and a reduction in the peak power of the grid by 22%. The energy savings are highly dependent on elevator traffic, which is inherently stochastic. The energy stored in the SC bank depends on the frequency of elevator trips, the type of trips (regenerative or motor), the duration, and the arrangement of regenerative and motor trips. The energy savings achieved also depend on the control algorithms. Higher energy savings can be achieved if the dispatch algorithm  
Figure 16: Simulation results for real traffic data. (**a**) DC bus voltage. (**b**) SC bank power and braking resistor power. (**c**) Voltage and current of the SC bank.  
maximises stored energy. Higher peak power reduction can also be achieved by a different control approach, where the EESS provides energy mainly during the acceleration time of the elevator.  
The simulation results during the two consecutive regenerative trips have shown that it is impossible to achieve the same nominal power for each SC bank voltage due to the voltage fluctuations of the SC bank and the maximum output current of the DC/DC converter. For this reason, even though the SC bank was not fully charged and was designed for two regenerative trips with maximum energy, power dissipation occurred at the braking resistor during two consecutive regenerative trips. By increasing the output current capacity of the DC/DC converter, it would be possible to store all the regenerative energy in the SC bank, which could increase the overall efficiency of the elevator system, but also increase the cost.  
Simulation results also confirmed the effectiveness of the proposed EESS. Most of the regenerative energy was stored in the SC bank and effectively used during the motor mode. Due to the current limitation of the DC/DC converter, power dissipation at the braking resistor occurred when the voltage of the SC bank was lower or the SC bank was fully charged.  
The elevator system with the EESS can achieve significant energy savings in a building and provide additional functionality because the energy storage can be used to supply other equipment. Integrating the elevator system with the EESS into the building management system (BMS) could provide a quick and controllable energy source and storage, further improving the energy efficiency of the building. Renewable energy sources, such as solar panels, can also be connected to the energy storage system, creating an elevator with a positive energy balance.  
Future work will focus on exploring potential energy savings in a group of elevators where higher energy savings may be possible and on exploring control algorithms that could further improve energy savings. In addition, the prototype of the proposed EESS will be validated through experimental testing.