Feasibility, optimization and economic analysis of solar district heating systems in China

Abstract

Solar thermal contributes little to space heating in China. In 2014, although China shared 75.8% of the total solar collector installations in the world, only less than 0.3% of the solar collectors were used for space heating. The Chinese solar thermal market status was reviewed and a market transition trend based on a prediction model and extensive market survey was proposed. The status and prospect of solar heat for industrial processes in China was discussed. Lessons from experiences on the mandatory installation of solar water heating systems in China in terms of technology application and policy implementation were summarized. To promote solar district heating (SDH) in China, based on Danish experiences and Chinese clean heating transformation practices, an extensive survey and on-site investigation were carried out to identify the applicability of SDH in China. The potentiality and feasibility of SDH in China were explored. To find optimal economic solutions for SDH and compare the economics of SDH with household solar heating in China, two evaluation models based on the levelized cost of heat (LCoH) were proposed. A Python program was developed based on the two evaluation models to calculate the LCoH of SDH systems and household solar heating systems using the quasi-dynamic test (QDT) method. The calculation results were discussed. To explore the economic rationality and regional adaptability of solar heating technologies in different cities in China, the methods in the research on economics were used to calculate the LCoH values for nine cities in China. The LCoH curves for the target cities show that the calculation models can not only be used to judge economics of different technology combinations in a city but also can be used to judge economics of one technology combination in different cities. To fully understand the operating performance and potential optimizations of a demonstration SDH system built on the outskirts of Beijing, a TRNSYS model of the solar assisted ground source heat pump system (SAGSHP) was established and validated by the measured operating data. The climatic conditions of the site, the inlet and outlet temperatures of the borehole heat exchangers, the inlet and outlet temperatures of the solar collector field and the electricity consumption of various components were measured. Through the simulation analysis of the model, an optimized solution was proposed. The process of modelling and analysing in details were described. Through extensive investigations and research on demonstration projects, the study considers that SDH has a broad application prospect in China with abundant solar resources and favourable policies. Rural villages and small towns with better infrastructure are the best target market for SDH in the next five years. Particular areas with low population density, scarce resources, and strict environmental requirements, e.g., Tibet, should be given high priority for SDH. The solar-heated area can achieve 756 million m2 with an assumption of 3% coverage of the total heat demand of buildings. The solar thermal plus heat pump heating system shows strong climate adaptability and gives the lowest LCoH in most cities. Seasonal heat storage can maximize the advantages of solar thermal when gas boilers are used as an auxiliary heat source. The solar thermal system can achieve higher cost reductions in larger SDH systems. A solar-assisted GSHP system is a reliable solution as a form of SDH. An auxiliary solar collector field can be added to those GSHP systems that do not recharge enough heat in the soil to improve the system efficiency and to reduce operating costs. Maintain the heat balance of the soil is the key to the sustainable operation of a solar assisted GSHP system. The research findings of the thesis are helpful for policymakers to fully understand the development trend of China's solar thermal market, and on this basis, profoundly understand the prospects, technical routes, economics and regional adaptability of SDH in China. The dynamic calculation method on LCoH proposed in this study can be used not only as a useful planning tool but also to optimize technical combinations for engineering companies and to improve production efficiency for manufacturing companies.