Design of non-tracking solar concentrating systems based on acceptance angle constraints and optimization of tilt angle adjustment strategies

Addressing the issues of complex structure and high cost in traditional tracking systems, this paper proposes a design method for a non-tracking solar concentrator system (NTSCS) based on acceptance angle (θ) constraints. The method establishes a relationship model between the concentration ratio (CR) and θ using non-imaging optical theory. Therefore, the corresponding θ can be determined from a target CR, providing a quantitative basis for the structural optimization design of the NTSCS. This paper designs an NTSCS with a CR of 5.2 (θ = 14°). The ray-tracing results demonstrate that the NTSCS maintains an optical efficiency (ηo) of 93.1% when αin is within θ/2 (−7° to 7°), but ηo decreases sharply when |αin| > 7°. Therefore, an tilt angle (β) optimization strategy with solar altitude variation (Δh) is proposed to mitigate optical loss caused by fixed installation. When the |αin| ≤ 7° within a given period, this period can be regarded as a β adjustment interval (over 10 days). When |αin| > 7°, the β is adjusted for once every 10 to 12 days to ensure that most incident rays remain within the θ range. This results in the annual average ηo of the NTSCS reaching 91.48% when adjusting β based on Δh, which is only 0.28% lower than adjustments made once a day. Additionally, under outdoor operation conditions, the average ηo of NTSCS reaches 88.4%, which is only 4.7% below the theoretical value. And NTSCS achieves an thermal efficiency of 49.8%−50.3%, with a maximum outlet temperature reaching 110.8 °C.