Mohammed Boukhalfa

The power temperature coefficient (γ) of a photovoltaic–thermal (PVT) collector is usually taken from the datasheet. Determining it outdoors is difficult because irradiance and temperature vary together. This study evaluates how reliably γ can be estimated from a few field observations. Thirty observations were collected during three campaigns in Bacău, Romania, in 2024 on a 240 Wp liquid-cooled PVT collector operated at a fixed pump setting. Power normalised to 1000 W/m2 was regressed on front-surface temperature with campaign-specific intercepts. This conventional analysis yielded γ = −0.64%/°C (95% CI: −0.82 to −0.46), compared with the declared −0.45%/°C. The result was sensitive to model specification. Irradiance and panel temperature were strongly correlated (r = 0.84), and including irradiance as a covariate, which the data supported (p = 0.043), changed γ to −0.40%/°C (−0.72 to −0.09). Eleven specifications differing in covariates, first-observation exclusions and temperature variable produced estimates from −0.33 to −1.08%/°C. In one campaign, measured power averaged 19% above the nameplate-based expectation, indicating an inconsistency in the absolute measurement scale. In an hourly PVGIS-SARAH3 calculation for 2023, each 0.1%/°C change in γ altered annual electrical yield by 0.94%. The measurements are compatible with the datasheet coefficient but constrain it only to between about ±0.3 and ±0.7%/°C, depending on the specification.

Abstract In this article, a detailed performance analysis of a capillary heat pipe coupled with a parabolic trough collector is performed. The influence of different parameters on the overall system's performance was studied namely; beam radiation and the inclination of the PTC. Results showed that using a heat pipe as an absorber improves the performance of the PTC. At Tmax, the coupling of the heat pipe with PTC leads to a 33% increase in the system's global efficiency and a significant reduction in the heat losses by 46.55%. The inclined arrangement configuration improved the global efficiency of the system by 13%. The obtained results were compared with the experimental data provided by the literature and reasonable agreement was observed, thus confirming the model's validity.

The optical efficiency of a parabolic trough receiver (PTR) is influenced by the transmittance of the glass cover and absorptivity of the absorber plate.The transmittance of beam radiation through a glazing system as a function of incidence angle can be calculated using numerical integration technique. This will allow us to determine the effective transmittance-absorptance product (τα)effof the PTR. However, the determination of the transmittance of the glass cover is difficult since the angles of incidences of the solar radiation on the glass cover vary with the impact point.In this paper, the transmittance of the upper and the lower semi-cylindrical parts of the receiver, in addition to the transmittance of the whole receiver are calculated. The (τα)effand its dependency on the parabolic trough orientation and absorptance of some selective surfaces is investigated. Results showed that the optical performance depends on the optical properties of the materials and the orientation of the parabolic trough collector.