Transient Energy Sources to Support Renewable Energy Conversion Systems

  • Yiheng Hu

Student thesis: Doctoral Thesis


Electrical supply industries world-wide are facing major challenges in moving towards net zero CO2 generation scenarios. This thesis reviews the supply of electrical energy in the UK and projections made in 2009 towards mid-century. It then compares these predictions with actual data from UK governmental statistics for the ten years from 2009 to 2019. Industry energy projections from 2019 to 2050 for four case study scenarios are then presented, the last case being related to a 60% market penetration of electric vehicles (EVs) by 2050. These studies are further projected to consider the case for 100% EV penetration by 2050. Finally, the role of electrical energy storage is discussed, and energy estimates proposed for both the 60 and 100% EV scenarios.
The connection of renewable energy sources to local low-voltage networks is becoming more accepted as electrical power networks progress to higher renewable penetration. Renewable energy resources, for example, wind and solar are highly dynamic and intermittent compared with more traditional generation sources, which imposes increasing challenges to the electrical network operator in terms of effectively managing the resource to maximise energy transfer and maintaining system stability. Therefore, transient energy storage systems (TESSs), for example, electrochemical batteries with fast charging and discharging capabilities are potential candidates to improve the availability and reliability of connected renewable systems. Due to their high power and energy density, lithium-ion (Li-ion) batteries are the default choice to date. However, energy-intensive production of Li-ion batteries is associated with high environmental impacts. Therefore, future electric applications may well be powered by a state-of-the-art lithium-free battery, such as sodium batteries. Sodium–nickel Chloride (NaNiCl2) battery electrical and thermal models are developed in this thesis. Therefore, in this study, two potential TESS technologies are presented and evaluated, the Li-ion and NaNiCl2 battery, and their feasibility to improve power systems in terms of power delivery and frequency fluctuations are compared. Experimentally validated battery models are presented and used to investigate the TESS performance in terms of state-of-charge (SoC), terminal voltage variation, peak current, iv power, energy, and efficiency. The models and general design procedure may be applied to systems of different ratings and duty variations.
Maintaining the electrical power system frequency is becoming a severe challenge due to the increasing penetration of RES schemes, which are highly dynamic and intermittent and result in the reduction of electrical network system inertia. System operators are investigating ways of solving these problems. A suitably controlled battery TESS is presented for system frequency, investigating the feasibility of published frequency control strategies and assessing their impact on TESS design. Additional to the TESS battery, the power electronic and transformer forming the TESS powertrain are studied and specification ratings discussed to reduce system plant
Date of Award9 Nov 2023
Original languageEnglish
SupervisorNigel Schofield (Main Supervisor)

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