Long-term performance data from grid-connected photovoltaic plants operating in harsh desert environments are critical for establishing economic feasibility and guiding energy policy. This research provides a complete fiveyear (2018-2022) assessment of a 6 MWp solar power plant in the Algerian Sahara, analyzing its technical performance, degradation rate, and financial feasibility using real operational data. In accordance with the IEC 61724 standards the performance parameters include an annual energy output of 54,672.10 MWh, with a final yield of 5.05 kWh/kWp/day, a performance ratio of 71.74 %, a capacity factor of 20.79 %, and an overall system efficiency of 10.73 %. We present a novel Weighted Degradation Rate (WDR) that is based on four statistical models in order to accurately measure performance degradation. This novel method yields a robust degradation rate of -1.70 %/year, which reduces estimation uncertainty by 23 % compared with methods that use only one model. Our analysis shows that temperature-driven losses (R2 = 0.61) are the main source of degradation more so than irradiance. The project demonstrates strong resilience with a net present value of 3.00 M$ an internal rate of return of 12.28 % and a levelized cost of energy of 0.092 $/kWh. The findings provide critical information that can help improve operations and maintenance strategies in arid regions. They also give evidence-based advice for improving Algeria's renewable energy policy particularly its 2035 solar targets.