https://www.mdu.se/

Production planning of an energy system is dependent on parameters such as energy demand and energy conversion technologies, which are influential in making decisions on operation strategy and optimal performance of the system. In accordance with the European Union energy policy, the share of renewable resources in the energy supply is growing. Improvement in energy technology is considered to be a pathway to achieve the target of 100% renewable power supply in Sweden by 2040. Increased utilization of renewable resources in energy systems and transportation sectors as well as improved energy conversion technologies would add complexity to the systems. Development of such complex systems depends on several key parameters, including availability of local resources, changes in daily energy use behavior, market price and weather conditions. Therefore, optimization and long-term production planning of such systems will be crucial considering the alternating nature of renewable resources.  

The aim of this thesis is to develop an optimization model for a regional energy system to provide advanced knowledge for production planning for combined heat and power (CHP) plants. The energy system in the county of Västmanland in central Sweden is used as the case for study. The regional system consists of CHP plants, heat only boilers and renewable resources. Two different optimization cases are developed for the analysis, one with increased energy supply from local renewables, and the other with integrated transport fuels production in a polygeneration system. The model includes the whole chain from availability of resources to the final energy use. 

The effect of different parameters relating to trends in energy demand and supply on operational strategy of the studied system is investigated by developing different scenarios. The potential solar power production from grid-connected solar cells installed on the rooftops of buildings in the region is added to the system in the base scenario. Then, the first scenario analyzes the increased application of heat pumps to replace the district heating in some of the buildings in the region. The influence of electrification of the transportation system as a result of increased penetration of electric vehicles is investigated in the second scenario. Two further scenarios evaluate the effects of integration of bioethanol production with existing CHP plants and increased application of bioethanol cars and hybrid vehicles in the regional transportation system. 

The study demonstrates the importance of production planning of the energy system at the regional scale in relation to resource availability and energy imports. The main conclusion of this thesis is that the polygeneration and increased use of heat pumps could influence the production planning of the system in terms of fuel use, plants operation, fossil-based emissions, and energy demand and import. However, increased use of hybrid vehicles represents the optimal case for the mentioned parameters.

The global energy system is undergoing a transformative change towards renewable energies. The share of Renewable Energy Sources (RES) and bioenergy in the world’s primary energy use has increased in the recent years. Based on the EU Roadmap 2050 energy plan, the share of renewables in final energy use in Europe will reach at least 55%, a 45% increase from its share today.

Due to the intermittent energy supply from renewables, their high penetration in energy systems can jeopardize the system flexibility, in terms of the balance between energy demand and supply. Lack of system flexibility could cause energy curtailments, increase system costs, or make renewables unreliable sources of energy. Moreover, the expansion of the renewable energy supply could influence the operational strategy of existing energy systems like Combined Heat and Power (CHP) plants. Therefore, the current study focuses on increasing system flexibility of a CHP-dominated regional energy system with increased renewable power supply. Two flexibility options, including a polygeneration strategy and large-scale energy storage using power-to-gas technology, were modelled. The system is then optimized using a Mixed Integer Linear Programming (MILP) method to investigate the production planning of CHP plants in a renewable-based energy system with higher level of flexibility. Different technical and market factors could influence the results of the optimization model, and thereby system flexibility. Thus, the study is carried out under various scenarios for better understanding of the future challenges regarding energy supply, market prices, and climate change.

The investigation provides an increased knowledge of production planning for the existing CHP plants with increased interaction with renewables. Based on the overall observations of this thesis, the proposed power storage system contributes to the increased system flexibility. However, the study suggests polygeneration and integration strategy as the optimal pathway to increase RES penetration and to support system flexibility, considering future energy developments and changes in energy demand and supply.