Thermal performance attenuation characteristics of solar collector field in solar district heating system

n centralized solar district heating systems, the optical performance attenuation of the solar collector field significantly impacts the system’s heating efficiency and economics. However, accurate lifecycle models for the optical performance attenuation of solar collector fields are still needed. In this paper, the attenuation patterns of transmittance, absorption, and emissivity are systematically established through accelerated attenuation tests and calculation models. Based on this, a lifecycle model for optical performance attenuation was developed using TRNSYS and applied to a centralized solar heating system in Langkazi, XiZang. The results indicate that low inlet temperatures and high flow rates reduce optical performance attenuation, with ultraviolet damage of the glass cover being the main cause of performance attenuation, accounting for 74.5 % of heat loss. A 15-year lifecycle analysis shows that performance attenuation in the solar collector field results in a 16.7 % reduction in effective heat collection, a decrease in the solar fraction from 66.1 % to 55.1 %, and a 32.4 % increase in auxiliary heat supply. Increasing the heating area or thermal storage to collection area ratio helps mitigate optical attenuation. Based on this, from the perspective of mitigating the attenuation of collection efficiency, the thermal storage to collection area ratio should exceed 0.2 m3/m2, and the solar fraction is recommended to be kept below 0.7. Additionally, considering optical attenuation, the levelized cost of heat increases by over 0.03 CNY/kWh when the thermal storage to collection area ratio exceeds 0.2 m3/m2. The results provide a methodological basis for more accurate design of the solar heating system.