Decentralization in energy systems - Low-carbon technologies and sector coupling on the household, community and city scales

Doktorsavhandling, 2021

The number of installations of distributed energy technologies, such as solar photovoltaic (PV) and battery systems, has increased dramatically in recent decades. The required transition towards a decarbonized energy system entails electrification of the different sectors. Both these developments provide new opportunities for energy autonomy and sector coupling in decentralized systems, and allow local actors to contribute to reducing their climate impact.

The aim of this thesis is to study the utilization of local energy technologies and the potential for system flexibility in three decentralized energy systems: prosumer households, prosumer communities, and city energy systems. In addition, the thesis investigates the interactions of decentralized systems with the surrounding regional energy system.

In this work, four techno-economic energy system optimization models are used. In the first model, PV-battery systems in prosumer households are analyzed within the North European electricity system dispatch. In the second model, they are examined as part of prosumer communities. In the third, city-scale model the investment and dispatch in the electricity and district heating sectors are optimized, while considering flexible and inflexible charging of electric cars and buses. The fourth model combines the city and regional scales, to study the operation, design and interaction of both systems, while considering different connection capacities for electricity exchange between the systems.

The results show that the economic incentives for electricity self-consumption in prosumer households promote a way of utilizing household battery systems that is not in line with the least‑cost dispatch of the electricity system. Consequently, prosumer households are, within the current tariff structure, unlikely to provide flexibility that would assist the balancing of intermittency in the regional electricity system. In prosumer communities, where prosumer households have the possibility to share electricity, a financial benefit accrues to the participating households primarily when there is a reduced connection capacity for electricity exchange to the energy provider.

For city energy systems, it is shown that power-to-heat technologies in combination with thermal storage systems and flexibility with regards to the charging of battery electric vehicles facilitate the uptake of local solar PV. The city electric car fleet provides the potential to postpone up to 85% of the demand for charging, which leads to more than twice the share of solar PV in the electricity mix for charging, as compared with inflexible charging. A 50% connection capacity between the city-scale and regional-scale energy systems implies only 3% higher costs for the installation and operation of energy technologies on both scales, as compared with a system that has 100% connection capacity.

This thesis outlines the potential for increased decentralization of the energy supply and highlights the need for strategies to integrate decentralized and centralized energy systems.