tailieunhanh - Renewable Energy Part 3

Tham khảo tài liệu 'renewable energy part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 64 Renewable Energy The methodology used along this chapter begins with the description of the power unbalance between generation and demand issue and the solutions for its mitigation. After that the available energy storage technologies are presented as well as the energy storage system design process. Following a brief discussion on the different perspectives for the location of embedded energy storage system in the power grid is presented. Finally the results for Portuguese power system case study are presented analysed and discussed. 2. Balancing Power Demand and Generation Traditionally the power system operation is based on the principle that at each moment in time the power demanded by the load is generated at that moment by the set of power plants in the system. For that reason if either the demand or the generation experience a sudden and sharp increase or decrease power unbalances would occur resulting in power system instability. As in general the power demand is not controlled by the power system operator its action is focused on the power generation dispatching. Power generation dispatch is also known as the unit commitment and it consists of defining which power units should be operating at a specific moment and the power generated by each unit dispatch in order to satisfy the power demand. Power demand varies along time and according to different drivers such as seasonality weather condition geographical location and the society economic activity. Extreme weather temperatures usually induce a higher power demand. On the other hand there is a reduction on the power demand during the night and during the weekends as a result of lower industrial activity and people s specific daily routine. Figure 1 presents different time cycles variations imposed by each one of the causes referred above. Fig. 1. Power demand variation along different time cycles REN 2008 In the past from the power system operator perspective the uncertainly was mainly on the .