Concluding remarks

This thesis investigates the effects of different types prime movers (i.e. ICE and MGT) when integrated into hybridised systems with PV modules and satisfying highly dynamic electric, heating, and cooling demand in a stand-alone community. The study analyses the impact of incremental increases to simulation complexity and different hardware components on the optimised systems. The meteorological data used in GA part of this work is from a remote location of Western Australia (Broome: 17˚56’S latitude and 122˚14’E longitude) and load profiles from a stand-alone application are incorporated. The load profiles are scaled and post-processed to allow different overall scales to be investigated. The research has been largely focused on using MATLAB-based single- and multi- objective Genetic Algorithms (GA) to address the research questions presented in Chapter 1. The optimisation results of stand-alone hybridised power, CHP, and CCHP systems are reported with several key performance indicators under the specific set of constraints tested. The findings reported in this thesis are summarized as follows:

• Cost of Energy: The Cost of Energy is comparable when hybridised systems are sized between a single large capacity and multiple prime movers operating in tandem meeting an electric demand. The other factors such as start-up thresholds, temporal resolution and transient time have insignificant effects on COE when the hybridised system is optimised using single objective optimisation. However, the PV/Batt/ICE-based hybrid system is more cost effective than the PV/Batt/MGT-based system because of higher capital cost of MGT than ICE. When the hybridised system is sized meeting electric and heating loads, the load following strategies have marginal effects on COE. The COE is comparable between PV/Batt/ICE and PV/Batt/MGT regardless of optimisation techniques used. With changing the relative magnitude of electric and heating loads, the COE is comparable for PV/Batt/ICE-based system whereas the COE is higher in larger heating demand for PV/Batt/MGT-based system. The COE for hybridised CHP system is slightly lower compared to the stand-alone CCHP system because of the additional hardware component (absorption chiller) in CCHP. The FEL/FTL type PMS leads to better economic benefits compared to FEL strategy for all system configurations. Additionally, COE is comparable for PV/Batt/ICE system while changing the magnitude of heating and cooling loads. The COE however increases considerably for PV/Batt/MGT-based hybrid CCHP system at the higher thermal load compared to the cooling load. Whilst the system (PV/Batt/MGT) is sized meeting electric, heating, and cooling loads, the COE for power only system is lower than the CHP and the CCHP system configurations. However, the COE is comparable with changing the magnitude of heating and cooling loads. The COE and NPC for

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a lead acid battery (PV/ICE) based stand-alone hybridised system meeting power demand only are comparable with the Li-ion based system and lower than a vanadium redox flow based system while the system is optimised using HOMER. The similar trend is appeared when system is sized while changing the scalability of load demand. However, the availability and the lower capital cost of lead acid battery attributed to the extensive use in the hybridised system applications.

• Overall system efficiency: The Power Management Strategies strongly affect the system overall efficiency for both PV/Batt/ICE- and PV/Batt/MGT-based hybridised CHP systems using single or multi-objective optimisation techniques. Higher heating loads lead to greater overall CHP efficiency for all hybridised CHP systems. The overall system efficiency is also hardware specific because of their operating characteristics. The stand-alone hybridised CHP system achieves lower cost at the expense of overall system efficiency. The overall system efficiency (CHP/CCHP) is noticeably higher in FEL/FTL type PMS than FEL for both PV/Batt/ICE and PV/Batt/MGT-based hybrid CHP/CCHP systems. However, the system efficiency is not affected by the magnitude of heating and cooling loads. Although a stand-alone CCHP system (PV/Batt/MGT) has higher overall system efficiency than power only and CHP systems, the overall exergy efficiency is lower than the CHP system and comparable with power only system. However, changing the relative magnitude of heating and cooling loads has insignificant effects on overall system energy efficiency; however, these changes affect the overall system exergy efficiency.

• Consequential performance: Higher Renewable Penetration in a single larger capacity engine- based hybridised system leads to lower Life Cycle Emissions as well as operational emissions than multiple engine-based hybrid system. However, the waste heat generation is considerable higher in the systems with multiple engine than a single engine. Waste heat generation and emissions are also larger with the lower minimum starting threshold. It is also evident that finer temporal resolution attributed to better environmental benefits. The use of hybrid PMS in CHP system sizing leads to lower LCE compared to FEL type PMS. The system with higher heating load has environmental benefits in single optimisation sizing. Although no significant improvements can be achieved in terms of COE and overall efficiency between single- and multi-objective optimisations, the biggest merits of multi-objective functions are to meeting higher heating demand through recovered waste heat. Higher renewable penetration in CHP system leads to lower operational emissions than CCHP system when operating in FEL/FTL strategy. PV/Batt/MGT-based hybrid CHP/CCHP systems produce lower operational emissions compared to PV/Batt/ICE. Power Management Strategies have significant effects on operational emissions. Additionally, the systems with relatively higher heating demand generate smaller amount of emissions than larger cooling loads. A stand-alone hybridised PV/Batt/MGT power system has higher DF at the expense of operational emissions than a CHP

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and a CCHP systems when the systems operating on FEL/FTL type PMS. Lower operational emissions and higher renewable penetration are achieved in a hybridised CCHP system with a higher heating load than a cooling load at the cost of DF. In HOMER optimisation, the PV/ICE/LAB-based system has lower operational emissions and higher renewable penetration than the PV/ICE/Li-ion and the PV/ICE/VRF-based hybridised systems. Both Li-ion and VRF batteries require lower capacity to meet the load demand as they can discharge down to zero and have lower annual depletion rate than a lead acid battery.