No abstract

No abstract

Keywords:Compressed air energy storage Round trip cycle Axial turbine Off-design analysis Energy efficiency analysis a b s t r a c t Compressed air energy storage (CAES) system is an "electricity to electricity" device. To reveal the energy conversion process and understand the energy loss principle are critical to improve the energy conversion efficiency. In this paper, the charge/discharge process analysis of an axial turbine based CAES with constant volume is executed in constant turbine inlet pressure mode and variable turbine inlet pressure mode. Firstly, the energy efficiency analysis of a whole round trip cycle of CAES system under design condition is carried out. The second law efficiencies of the operation mode 1 and the operation mode 2 are 44.56% and 45.16%, respectively. It also can be found that the throttling loss in operation mode 1 can be offset by the benefits of higher isentropic efficiency of turbines. Then, the off-design analysis of these two operation modes is implemented by considering the different power levels and speed levels. The mass flow rates of working fluids across the expansion train both increase with the increased load rate or the decreased speed. The load rate or speed both have the positive effect on the exergy efficiency and the energy generated per unit volume of storage, but have the negative effect on the heat rate.

No abstract

No abstract

No abstract

a b s t r a c tHigh wind power penetration in power system leads to a significant challenge in balancing power production and consumption due to the intermittence of wind. Introducing energy storage system in wind energy system can help offset the negative effects, and make the wind power controllable. However, the power spectrum density of wind power outputs shows that the fluctuations of wind energy include various components with different frequencies and amplitudes. This implies that the hybrid energy storage system is more suitable for smoothing out the wind power fluctuations effectively rather than the independent energy storage system. In this paper, we proposed a preliminary scheme for capacity allocation of hybrid energy storage system for power system peak shaving by using spectral analysis method. The unbalance power generated from load dispatch plan and wind power outputs is decomposed into four components, which are outer-day, intra-day, short-term and very short-term components, by using Discrete Fourier Transform (DFT) and spectral decomposition method. The capacity allocation can be quantified according to the information in these components. The simulation results show that the power rating and energy rating of hybrid energy storage system in partial smoothing mode decrease significantly in comparison with those in fully smoothing mode.

No abstract