Scientists in Egypt have investigated the effectiveness of using water and a mixture of aluminum oxide and calcium chloride hexahydrate to cool PV modules. Optimal performance was observed with a solution of 75% water, according to the research findings.
Scientists from Egypt’s Benha University have proposed a passive cooling technique for PV panels based on the use of water and a mixture of aluminum oxide (Al2O3) and phase change material calcium chloride hexahydrate (CaCl2H12O6). Phase change materials (PCMs) – compounds which can store thermal energy and help stabilize temperature – can absorb or release large amounts of ‘latent’ heat when they go through a change in their physical state, such as during melting and freezing.
The Benha research team applied various mixtures of their passive coolants to a 50 kW polycrystalline PV panel and compared performance during summer months in Cairo with that of an untreated panel.
The system involved the use of cooling unit, DC pump, valves, water flow meter and connecting pipes. Aluminum channels were fabricated for the water and the Al2O3/PCM mixture. The channels were placed under the two panels, which were south adjusted and oriented 30 degrees from horizontal.
The PCM mixture was heated to melting point to form a liquid and Al2O3 nanoparticles were added to it in the aluminum channels. “The dispersion of particles in the PCM liquid is done using an agitator bath with four different mass concentrations,” the group stated.
The researchers recorded PV current and voltage, front and rear panel surface temperatures, water inlet and outlet temperatures, solar irradiation, ambient air-dry bulb temperature and wind speed.
“Applying the cooling system, whether using water and/or [the] Al2O3/PCM mixture provides a noticeable drop in cell temperature compared with the uncooled [panel],” said the Egyptian team.
The researchers said a mixture of water and the Al2O3/PCM liquid outperformed the use of water alone and the best performance was recorded from 75% water and 25% Al2O3/PCM.
Although use of the Al2O3/PCM mixture alone did not produce the best results, removing the need for water for coolant purposes might be the optimal solution for solar installations, the researchers suggested.
The research findings are presented in the paper Performance enhancement of the photovoltaic cells using Al2O3/PCM mixture and/or water cooling-techniques, published in Renewable Energy and on the ScienceDirect website.
A similar technique, using CaCl2.6H2O–Fe3Cl2.6H2O eutectic as a phase change material, was recently proposed by scientists from India’s KPR Institute of Engineering and Technology and the National Engineering College.
Source: pv magazine