Thermal storage is very relevant for technologies that make thermal use of solar energy, as well as energy savings in buildings. Phase change materials (PCMs) are positioned as an attractive alternative to storing thermal energy. This review provides an extensive and comprehensive overview of recent investigations on integrating PCMs in the following low-temperature applications: building envelopes, passive systems in buildings, solar collectors, solar photovoltaic systems, and solar desalination systems. Moreover, techniques for improving heat transfer in PCM systems are described. All applications studies indicate that all applications improve their performance when applying a PCM. One of the most beneficiated technologies is the combined PV-Thermal systems (PVT), where some authors reported an increase in overall efficiency greater than 40%.

The current work reports a numerical investigation of the water produced and thermal performance of a solar still (SS). Using a SS for desalination is a proposal for low-income remote communities needing potable water. The study deals with the SS under five different concentrations of salt (0, 5, 10, 20, and 35 g/kg). Previous experimental results reported in the literature indicate that the increase in salinity leads to a decrease in productivity, so phase change material (PCM) was added under the water basin to counter the reduction. The mathematical model and numerical methodology were validated by comparing them with experimental results reported in the literature. The relative difference between temperatures was less than 2%, and for water production, it was less than 3.5%. The present mathematical model has the novelty of utilizing the water properties as a function of temperature and salt concentration, contrary to other models that use pure water properties. The results show that daily productivity decreases when the salinity increases from 0 to 35 g/kg. For each case, the time evolution of hourly and cumulate productivity is presented, as well as water temperature and the temperature difference between water and glass. Also, the behavior of heat flux between water and PCM is analyzed. The overall efficiency is calculated for all the cases.

Seaweed is of importance to the environment due to properties such as its CO₂ sequestration capability. On the other hand, plastic is a versatile material important to society. Unfortunately, the abundance of both plastics and seaweed represents a challenge due to the need of adequate waste management. At first, algae and plastics might not appear suitable for energy recovery; however, with co-gasification, the results are promising. This work presents a model to simulate the co-gasification of Chlorella vulgaris, Sargassum fluitans, and Sargassum natans with plastics. The effect of the gasification temperature (650–850 °C), equivalence ratio (0.25–0.45), and plastics/biomass ratio (0.0–1.0) on the produced gas’s lower heating value, tar concentration, and composition is assessed. Moreover, the environmental performance of using plastic to enhance the syngas produced from the co-gasification with sargassum is assessed using the life cycle assessment methodology. The results indicate that the lower heating value increases with the temperature and plastics/biomass ratio. Moreover, tar increases with the quantity of plastics, varying between 20 and 50 g/Nm³. Finally, adding plastics to algae during gasification reduces the variability in the syngas composition, simplifying the post-processing stage. With respect to environmental performance, gasification has an impact similar to those of pyrolysis and recycling, but the performance could improve with sufficient research and development.

In solar tower systems, the thermal receiver is a crucial element. Solar receivers may be exposed to high non-uniform heat fluxes, which requires consideration during their structural design. This paper presents a numerical study of the direct steam generation, thermal stress, and total deformations on a representative tube of an external solar receiver. A non-uniform distribution of solar heat flux on the receiver was considered. The sub-cooled boiling and the direct steam generation were analyzed in terms of the temperature field, the volumetric vapor fraction distribution, and steam quality. Under this configuration, the system can produce a steam quality of 0.113%. To develop the structural analysis of the tube, the internal and external temperature fields of its walls were introduced as boundary conditions. Numerical methodologies for direct steam generation, temperatures, and deformation were validated with experimental data. Since the base case presented high deformation (78.63 cm), the use of clips was proposed. Besides, the number, size, and location of the clips were tested. It was found that deformation can be reduced by about 99.1% by placing clips at different positions along the tube. However, the von-Mises stresses increased, but they did not reach the ultimate tensile strength.