Seasonal thermal energy storage of solar heat: Its role in the clean heating transition in China
Authors:   , Yang Tianrun 
Published: January 2024

Since the adoption of the Paris Agreement, countries and regions have been submitting their climate action plans, aiming to achieve carbon neutrality in the coming decades to combat climate change. Since fossil fuels are fundamentally storable and renewables almost invariably less so, the seasonality of heat demand in the built environment provides a real challenge for the decarbonization of this sector. Seasonal thermal energy storage (STES) can harvest and store solar thermal energy in summer and use it for heating in winter, and could thereby be an enabler for the transition to fossil fuel-free heat supply.
This thesis aims to conduct an in-depth analysis and optimization of STES technologies employing solar heat from technical, economic, environmental, and implementation feasibility perspectives to identify their overall attractiveness in the heating market and to assess their benefits in the clean heating transition and renewable power integration. The analysis in this thesis focuses on the heat transition in the built environment in China.

We first conduct a comprehensive techno-economic review analysis of STES technologies based on previous research and projects worldwide to provide a general overview of the development status, barriers, and economic competitiveness of STES technologies in the current heating market.

Second, we study STES technologies at four locations in China to assess how the local context impacts the optimal configuration planning, techno-economic-environmental performance, and feasibility of STES applications. The results show that the prospects for STES of solar heat vary across China. STES implementation is attractive in locations with rich solar resources, high heating loads, and current coal-based heating systems. Appropriately reducing the borehole number for the STES system in cold climates and increasing the solar collector area in warm climates is conducive to achieving a lower CO2 avoidance cost.

Third, we zoom in on the most promising regions for STES to compare the technical, economic, and environmental performance of STES with other sustainable heating technologies and their implementation feasibility at the local level. It is found that STES of solar heat is attractive with competitive levelized cost of heat and CO2 avoidance cost compared to natural gas boiler, biomass boiler, electric boiler, and solar-assisted ground source heat pump. It is a promising technology with a decreasing levelized cost of heat and increasing CO2 emission reduction ability.

Finally, we study STES in the context of the regional energy system. We specifically evaluate the impact of replacing (coal-based) district heating systems with STES on the regional power and heat supply and the effects that the introduction of STES has on renewable power integration. We conclude that replacing fossil fuel-based district heating systems with STES technologies can reduce fossil fuel consumption and CO2 emissions across the combined heat and power systems at an affordable cost. STES in fact facilitates the integration of wind and solar power into power grids by reducing curtailment. STES of solar heat offers an attractive option for realizing a sustainable heating transition in line with the carbon-neutral target.