Detailed analyses of melting processes in phase change material (PCM) glazing units, changes of direct transmittance as well as investigation of refraction index were provided based on laboratory measurements. The main goal of the study was to determine the direct light transmittance versus time under constant solar radiation intensity and stable temperature of the surrounding air. The experiment was conducted on a triple glazed unit with one cavity filled with a paraffin RT21HC as a PCM. The unit was installed in a special holder and exposed to the radiation from an artificial sun. The vertical illuminance was measured by luxmeters and compared with a reference case to determine the direct light transmittance. The transmittance was determined for the whole period of measurements when some specific artefacts were identified and theoretically explained based on values of refractive indexes for paraffins in the solid and liquid state, and for a glass. The melting process of a PCM in a glass unit was identified as a complex one, with interreflections and refraction of light on semi layers characterized by a different physical states (solid, liquid or mushy). These optical phenomena caused nonuniformity in light transmittance, especially when the PCM is in a mushy state. It was revealed that light transmittance versus temperature cannot be treated as a linear function.

The main goal of the paper was to numerically analyse the risk of overheating of the Energy Activated External Thermal Insulation Composite System (En-ActivETICS) as an example of Building Integrated Photovoltaics (BIPV). The analyses were conducted with the coupled power flow method (thermal and electrical) for 20 European cities. All locations were analysed considering the local climate in the context of building performance simulation as well as electricity production. The obtained results allowed for the determination of the risk of overheating, which can influence system durability, accelerated thermal ageing, and overall performance. It was revealed that the risk of overheating above 80 °C is possible in almost all locations; however, the intensity considerably differs between southern and northern Europe. The effect of latent heat storage for better thermal stabilization and overall performance was determined numerically for all locations. Finally, the improved solution with a phase change material (PCM) layer beside the PV panel was proposed individually for specific climatic zones, considering the required heat capacity. The maximum panel temperature for improved En-ActivETICS does not exceed 85 °C for any location.

The paper concerns the problem of the modeling of the thermal interaction between the phase change material (PCM) and photovoltaic (PV) panel, in the case of unventilated construction. The study aims to develop the numerical model of such a building element to support its proper future design under variable boundary conditions. The need for such a study comes from the realization of the research project which aims at developing a novel energy-activated thermal insulation composite system. Two different methods of PCM simulation using ESP-r software were compared. The model that was finally proposed was validated against experimental data, which proved its robustness. The MBE for the simulated and measured temperatures on the back of the PV panel did not exceed 2.0 °C and the maximum observed energy production difference was 4 Wh/m².

The paper presents comparative analysis of daylight conditions in office room simulated with two techniques of sky and surrounding modelling. The luminance distribution in the surrounding environment was determined using CIE standard sky model and image based lighting (IBL) technique. In IBL method the sky and surrounding environment was defined by high dynamic range (HDR) image. Used HDR images were captured by camera with fisheye lens with 180˚ viewing angle which enables the projection of the entire hemisphere of the sky and surrounding environment. Determination of daylight conditions were performed for two days characterised by overcast sky conditions. Simulations were conducted using Radiance Lighting Simulation and Visualization software. Obtained results show differences in luminance and illuminance distribution in analysed room for both techniques of sky and surrounding modelling. Reason of the observed divergences is uneven cloud layer distribution at HDR images and influence of surrounding environment visible at HDR images. IBL technique allow more precise modelling of daylight distribution, especially in urban environment where surrounding buildings and vegetation significantly effect on the light availability.

The use of concentrated solar irradiation for the improvement of electric generation improvement has been implemented on different scales, mainly in photovoltaic systems. High-concentration Fresnel lenses are widely chosen for this approach in large installations, while low-concentration systems are rather applied in medium-low scales. For the latter, the improvement on electric performance was revealed, even when no solar tracking was implemented. The presented work aims to analyse a low-concentration photovoltaic installation by a numerical approach. First, the reflective surfaces were designed geometrically considering the optimal slope determined for each month. Subsequently, different simulation techniques were used separately for prediction of solar irradiation and energy production. Three criteria were selected to analyze power generation: the highest increase in total annual solar irradiance on panels with reflective surfaces, the highest total annual solar irradiance collected, and the optimal slope of panels for the entire year. The increase in energy was found to not exceed 10% in the winter months. Whereas in the spring and summer months the energy improvement is about 15–20%. Moreover, it was observed that the temperature of the proposed concentration photovoltaic system increased significantly, reaching more than 90 °C, while for traditional PV panels it did not exceed 75 °C.