An assessment of flywheel storage for efficient provision of reliable power for residential premises in islanded operation

Energy storage systems (ESS) are key devices for improving power quality, electrical system stability and system efficiency by contributing to the balance of supply and demand. They can enhance the flexibility of electrical systems by mitigating supply intermittency, which has recently become problematic due to the increased penetration of renewable generation. The subject of this thesis is flywheel energy storage system (FESS), a technology that is gathering great interest due to benefits offered over alternative energy storage solutions, including high cycle life, long calendar life, high round‐trip efficiency, high power density, operation at high ambient temperatures and low negative environmental impact. This thesis describes the modelling and assessment of small scale energy system incorporating FESS with solar photovoltaic (PV) and a diesel generator for use in islanded residential premises with highly intermittent or non‐existent grid infrastructure. In this application, incorporation of FESS is shown to be beneficial in comparison to a system without storage or one with the alternative storage technology, Li‐Ion batteries. The thesis begins with a description of flywheel storage systems configured for electrical storage which comprises of a mechanical part; flywheel rotor, bearings and containment, and an electric drive part; motor‐generator and associated power electronics. Each of these components is described in the thesis along with the equations and modelling, itself carried out in the MATLAB/Simulink environment. Finally, the flywheel model is combined with a model of an islanded residential power system incorporating a solar PV system with a diesel generator. Such a system would be particularly useful for offgrid applications or those with weak grids as occurs in developing countries

Assessment of the Carbon and Cost Savings of a Combined Diesel Generator, Solar Photovoltaic, and Flywheel Energy Storage Islanded Grid System

The use of diesel generators to provide power for islanded grids has been the technology of choice but they generate substantial carbon emissions unless the part or all the fuel comes from a renewable source. Notwithstanding this, the engine must be sized to meet maximum demand and will operate inefficiently at part load most of the time, which is particularly bad for a synchronous constant speed engine. Given the availability of low cost solar photovoltaic (PV) systems, it is very enticing to fit a diesel generator and allow the engine to be turned off during PV generation. However, this combination will not work without some form of energy storage since it takes time for the engine to start, leading to gaps in supply and instability of the system. Lithium-ion batteries are typically considered to be the best solution to this problem because they have a high response rate, costs are lower, and they are available as products. However, they will suffer from the limited cycle and calendar life due to high cycling requirements in the application described. It is, therefore, proposed that a flywheel system could offer a lower lifetime cost alternative since only short duration bridging power storage is needed and flywheels of appropriate design can offer lower power cost than Lithium-ion battery systems. Flywheels are particularly attractive since they have a very high calendar with almost an infinite cycle life and are fully recyclable at the end of life. This research, therefore, presents an assessment of the flywheel energy storage system (FESS) as an alternative to electrochemical batteries to supplement solar PV systems backed up by diesel generators. The model of an islanded PV system combined with a diesel generator and a FESS supplying power to a residential load is implemented in MATLAB/Simulink. The results of the analysis for the cases with and without storage based on a number of different charge-discharge strategies provide evidence to support this hypothesis

Hybrid PV System with High Speed Flywheel Energy Storage for Remote Residential Loads

Due to low system inertia in microgrids, frequencies may vary rapidly from the nominal value, leading to the complete blackout of the system unless there is an adequate spinning reserve available for balancing the supply with the demand load. This issue of instability in microgrids under islanded operation has attracted particular attention recently. A diesel generator is considered to be an ideal spinning reserve to provide back-up power to the load along with the renewable energy source in islanded system. However, the high maintenance cost and CO2 emissions of diesel generator are detrimental factors which have inspired searches for more cost effective and cleaner technologies. The integration of an energy storage system (ESS) in islanded system along with generator not only reduces generator maintenance costs but also reduces the CO2 emissions by limiting its operating hours. This paper proposes an islanded PV hybrid microgrid system (PVHMS) utilizing flywheel energy storage systems (FESS) as an alternative to battery technology to support the PV system and meet the peak demand of a small residential town with 100 dwellings. The diesel generator is used in the islanded system as a spinning reserve to maintain the stability of the islanded system when the PV system and flywheel storage cannot meet the load demand. Results of analysis of such a system demonstrate that flywheel energy storage technology of appropriate size offers a viable solution to support the operation of the standalone PV system. Furthermore, the reduction in CO2 emissions and fuel consumption has been quantified as compared with the case with flywheel energy storage systems which means the diesel generator but always be operating