Energy has been linked to economic growth and will play a vital role in the recovery of the global economy in this post-COVID era. The world’s population has risen to about eight billion, and is driving the mounting demand for energy. This is an issue of great concern that is worsening the energy trilemma of affordability, sustainability, and reliability. To this end, several ingenious attempts are being made to advance the technologies for energy generation some of which have been tested and deployed across the globe. Among these technologies, decentralised energy systems (DES) are becoming popular due to their prospects for minimising energy wastage and ability to utilise local available clean fuels to drive the energy conversion processes in the system.
In this PhD thesis, three new configurations of DES are modelled, optimised, simulated, and analysed. The global aim is to enhance the efficiency and reliability as well as minimise the cost and pollutant emissions of contemporary DES, by shifting from the heavy reliance on fossil fuel to clean energy based solutions. First, a multi-carrier DES that comprises a combined cycle Stirling engine (ST) and organic Rankine cycle (ORC) prime mover, biomass drier and combustor, single effect absorption chiller and waste heat boiler has been proposed and will be powered by woodchips. The proposed DES can produce cooling, heating, electric power and dry woodchips, simultaneously. A comprehensive thermal model of the ST prime mover has been developed to predict accurate results of the engine’s performance at its operational speeds. The enhanced model predicts the thermal efficiency and brake power of the prototype engine with relative errors of +0.3% and -4.02%, respectively. Based on the developed model, overall primary energy savings and carbon emissions reductions of the multi-carrier DES have been examined and are 51% and 40%, respectively compared to a fossil fuel based separate cooling, heating, and power system. This is an improvement of 42.2% and 9.45%, respectively, compared to a multi-carrier system utilising sole ST prime mover.
Further, another DES solution has been proposed to overcome the challenge of heavy dependence on diesel generators (DG) to augment the reliability of renewable energy systems. The proposed DES concept consists of wind turbine, solar photovoltaic, and battery storage and will deploy wood chips biomass powered split ST or combined ST and ORC as the back-up to fulfill the electricity demand. The optimal number and types of the components of the energy system that simultaneously minimises the loss of power supply probability (LPSP), levelised cost of energy (LCOE) and dumped power have been found using the genetic algorithm. Obtained results show that the deployment of combined ST+ORC back-up in load following mode yields 60.70% and 33.71% reductions in the LCOE and CO2 emissions, respectively compared to the DG back-up system but with slightly higher LPSP. While 61.4%, 33% and 24.47% reductions in the LCOE, CO2 emissions and LPSP have been observed with the deployment of split ST in circuit charging mode.
The final DES proposed integrates the multi-carrier DES and the hybrid system and deploys the ST+ORC as back-up and prime mover in the system. Some modified rule-based energy management strategies (EMS) are proposed to effectively coordinate the simultaneous generation of energy vectors, while the optimal number of system components and the best control strategy are found by deploying a bi-level optimisation. Results indicate the best control strategy and system configuration achieve slight reductions in dumped power and CO2 emissions but increases the number of start-ups of the back-up by 36%. However, it demonstrates additional capabilities in handling complex systems by doubling the generation of heating and increasing the rate of cooling generation.
The results obtained highlight the capabilities of decentralised multi-carrier energy systems in reducing primary energy consumption, energy cost and pollutant emissions as well as in improving system reliability. Increasing cases of flooding and other environmental issues linked to global warming and the mounting energy costs are compelling arguments that favour their deployment, particularly in the remote locations of developing countries.
