Modern solar air-heating units, widely used in low-temperature heat supply systems, exhibit certain limitations in efficiency due to pronounced diurnal and seasonal nonuniformity of solar insolation, as well as significant heat losses at low irradiance levels. Under these circumstances, there is an acute need for engineering-compact solutions that combine direct air heating with controllable thermal-energy accumulation. Of particular importance is the development of models that are experimentally reproducible and verifiable. The aim of this study was to formulate and experimentally validate an optical-thermal model of an integrated solar collector-accumulator with a variable opening angle of a louvred absorber. The model describes the dependence of the instantaneous efficiency on solar irradiance at fixed louvre opening angles – 0°, 45°, 60°, and 90° – and accounts for the division of the incoming energy between the air branch and the built-in water thermal accumulator. Based on a prototype housed in a single thermally insulated casing, bench tests were conducted with recording of the key parameters: solar flux density, inlet and outlet air-channel temperatures, water-heating dynamics, and air mass flow rate. The mathematical model used in the analysis was based on an energy balance with a linear dependence of efficiency on reduced temperature, while parameter identification was performed by the least squares method. The dynamics of the water subsystem were described by a first-order differential equation. The reliability of the model was supported by high explained-variance values, the absence of autocorrelation, and residuals consistent with a normal distribution. The work presented η(G) curves for the four louvre opening angles; at solar flux densities of 350, 650, and 1,000 W/m², the efficiencies achieved were approximately 0.36/0.50/0.56 for θ = 0°, ~0.33/0.48/0.55 for θ = 45°, ~0.32/0.47/0.54 for θ = 60°, and ~0.30/0.45/0.50 for θ = 90°. The average efficiency over G = 200-1,000 W/m² was about 0.435. It was shown that a moderate increase in the louvre opening angle to 45-60° reduces the efficiency of the air branch by 1-4 percentage points while simultaneously promoting more active charging of the water storage branch. The agreement between the model and the experimental data confirms its practical applicability and the absence of systematic error