Benefits of multi-energy system integration for decarbonizing energy sectors
Creators: name: Zhang, Xi
Publisher: name: Imperial College London
Year: 2018

description: Heat accounts for approximately half of the total energy consumption and is responsible for over 25% of carbon emissions in the U.K. Therefore, decarbonization of the heat sector is one of the key challenges in achieving the 80% carbon reduction target by 2050. The utilisation of various low-carbon heating technologies to replace gas boilers, which currently dominate the UK heating sector, is crucial in facilitating the transition to a low-carbon future energy system. Additionally, the building thermal characteristics can also provide us an alternative perspective to realise the carbon target while alleviating the burden of new investment at the end-side. This thesis first proposes a District Heating Network (DHN) investment model by using a fractal-image-based algorithm. Through this model, the investment cost of DHNs driven by different user penetrations in different representative areas can be quantified and the DHN investment cost functions can be incorporated into the whole system investment model to optimize the penetration of DHNs. This thesis also investigates the value of pre-heating through inherent building thermal storage. By comparing the operational costs between the case where pre-heating is enabled and the case where additional TES is installed, the economic value of pre-heating can be evaluated while the capability of the inherent storage of buildings under given thermal parameters of buildings can be quantified. We then propose a novel whole-system integrated electricity and heat system model in which, for the first time, operation and investment timescales are considered while covering both the local district and national level infrastructures. The modelling of DHN investment and pre-heating are also integrated into this whole-system model. A series of case studies are then carried out to investigate the benefits of different heating technologies. Electric HPs, hybrid heating technology and DHN are the main low-carbon heating technologies that can deliver the ambitious carbon reduction target in the UK. The optimal design of the heating system on a national scale to maximize the economic benefits regarding both investment cost and operation cost while satisfying the carbon target remains an open question. This thesis compares the economic advantages as well as the associated impacts on the electricity system under the full deployments of ASHP, hybrid HP-Bs (ASHP and gas boilers), DHNs and hydrogen boilers by using the whole-system integrated electricity and heat system model. The optimized strategy for heat sector decarbonisation is also demonstrated, providing an outline of the optimal deployment for different heating technologies in terms of their penetrations and deployed areas. The UK case study suggests the significant economic advantage of the hybrid HP-B over the other three heating technologies, while DHN may play an important role in urban areas under the optimized heat decarbonisation strategy. The results also clearly demonstrate the changes in the electricity side driven by the different decarbonisation strategies in the heating system. Additionally, the benefits through considering the interaction between electricity and heat systems at the planning stage are investigated, as the system integration will play an important role in facilitating the cost effective transition to a low carbon energy system with high penetration of renewable generation. The whole-system integrated electricity and heat system model is applied to optimize decarbonization strategies of the UK integrated electricity and heat system, while quantifying the benefits of the interactions across the whole multi-energy system, and revealing the trade-offs between portfolios of (a) low carbon generation technologies (renewable energy, nuclear, CCS) and (b) district heating systems based on heat networks and distributed heating based on end-use heating technologies. Overall, the proposed modeling demonstrates that the integration of the heat and electricity system (when compared with the decoupled approach) can bring significant benefits by increasing the investment in the heating infrastructure in order to enhance the system flexibility that in turn can deliver larger cost savings in the electricity system, thus meeting the carbon target at a lower whole-system cost. Last but not least, a cost-oriented representative-day-selection approach that can significantly reduce the computational burden of the whole-system integrated electricity and heat system model is proposed. Through a series of case studies, we demonstrated the superior performance of the proposed cost-oriented representative-day-selection approach against the widely used input-based approach.