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In power systems, load is continuously fluctuating and is difficult for slow generating units, such as coal-fired, nuclear and hydro power plants, to follow. Therefore, fast but expensive generation units like open cycle gas turbine (OCGT) are widely used to provide frequency regulation, maintaining system frequency within its specified limit. Owing to energy storage system (ESS)'s zero-net energy and fast response nature, one of the applications of ESS in power system is to provide frequency regulation. This paper proposes a method of sizing OCGTs and advanced lead-acid batteries to provide frequency regulation under different types of load following patterns. The rain-flow counting algorithm is used for battery lifetime modelling. The cost and savings from displacing OCGTs with ESS are calculated and discussed. It was concluded that the system load following ability is the key factor when considering whether ESS is cost effective when providing frequency regulation in a control area. The method of battery and OCGT rating presented in this paper is applicable to the situation when regulation load requirement is known or can be estimated.

In this paper, multi-carrier energy system (MCES) optimization problem is solved by using Similar Decoupled Form (SDF) energy hub modeling. Compared with the traditional energy hub modeling method, the Similar Decoupled Form modelling method improves flexibility and automation of the energy hub system. More importantly, energy hub does not need to be linear when using this method. In other words, the limitations of SDF are greatly reduced and it can be used in a more general energy system with energy storage equipment. This method can be used to analyze power flow from both sides of the energy hub (input side and output side) and the stability of the energy hub system. Finally, SDF shows the dynamic change of the energy hub system rather than only the result of mathematical optimization.

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