Extensible Modeling of Compressed Air Energy Storage Systems

Abstract

There is a growing number of renewable energy sources that can supply power to the electrical grid. These renewable sources of energy are intermittent in nature and therefore the transition from using fossil fuels to green renewables requires the use of energy storage technologies to maintain and regulate a reliable supply of electricity. Energy storage technologies play a key role in allowing energy providers to provide a steady supply of electricity by balancing the fluctuations caused by sources of renewable energy. Compressed Air Energy Storage (CAES) is a promising utility scale energy storage technology that is suitable for long-duration energy storage and can be used to integrate renewable energy (such as Wind energy) to the electrical grid. CAES technologies can be broadly classified into 3 types: Diabatic-CAES (D-CAES), Adiabatic-CAES (A-CAES) and Isothermal-CAES (I-CAES).

The author first performs a review on the different types of energy storage available today and a literature review on of CAES system level models, Turbomachinery models, and cavern models. After the gaps in literature are identified, the author then develops a flexible and extensible model of an A-CAES system, which can be used a CAES plant designer to obtain a first order thermodynamic evaluation of a particular plant configuration. The developed model is scalable, modular and can be connected to a control strategy. The model is able to capture time dependent losses and part load behavior of turbomachinery. The modeling methodology is focused around keeping the model extensible, i.e. components and their fidelity can be easily altered for the model’s future growth. The components modeled are the compressor, the turbine, the induction motor, the generator, and a thermal energy storage device to the make the CAES plant adiabatic. The model is created using the Matlab/Simulink® software, which is commonly used tool for modeling.

The A-CAES plant model was simulated for 23.3 hours comprising of 12.47 hours of charging using a mass flow rate of 107.5 kg/s, 8 hours of storage and 2.83 hours of discharge using a mass flow rate of 400 kg/s. The maximum and minimum cavern pressures were 72 bar and 42 bar respectively. The obtained round trip efficiency is 76.24%. Additionally, the turbine start-up time was found to be 760 seconds. The compressor train average efficiency was calculated as 70%, the expansion train average efficiency was calculated as 81% and the TES efficiency was calculated as 91%. The models simulated the behavior of an A-CAES plant accurately with the compressor and turbine showing a close resemblance to their performance maps. The results indicate that Adiabatic-CAES is a promising and emerging technology. However, further research and development is required beyond this thesis; specifically, in the area of thermal energy storage and management. Finally, the author makes recommendations on how to further improve upon the achieved objectives in this work.