Solar Hot Water Systems and Materials of Construction :: essays research papers

The materials used in solar hot water systems must be carefully chosen to ensure that the unit will be efficient but also affordable. The efficiency of the conversion of sunlight energy to heat energy of the water depends on the materials of construction and the efficiency of heat transfer of the materials. Solar hot water systems use the processes of conduction to transfer the heat absorbed from the sun to the water and convection to move water through their structure. This assignment discusses the materials used in construction of solar hot water systems and their heat transfer properties. 2.0 Conduction Conduction is the process of transferring energy through a material from one point to another. Conductivity (k) is the rate at which the energy is transferred and its units are Watts per metre Kelvin or (W/mK). The higher the rate of conductivity the faster energy is transferred through the material. Conduction can occur in two different ways in solids; the first is by crystal vibration waves (phonons) where particles of high kinetic energy vibrate rapidly and bump into other particles to transfer energy from one point to another. The second way is by delocalised electrons or free moving electrons which transfer energy throughout materials much better than atoms do, as their energy to mass ratio is much higher than that of atoms. This allows the electrons to travel much faster throughout a substance and transfer energy faster. For a material to be a good conductor of kinetic or electrical energy it requires both methods of conduction, which is found in metals and some other materials (i.e. graphite). The conductivity of a solar hot water system’s materials are important ie. adequate insulation is required to prevent energy being lost to the unit’s surroundings. Materials for the pipes should not resist the transfer of thermal and kinetic energy being passed through the pipes to the water in the collector panel (shown in Fig 1.). The conductivity (k) of a material can be described by the following equation. The contribution of ke increases with free electron concentration. Copper is an abundant, cheap metal with great thermal and electrical conductivity. It is strong, malleable and ductile making it an ideal material for water pipes. Copper has a thermal conductivity (k) value of 398 W/mK, which is below silver’s thermal conductivity of 428 W/mK however still much larger than other metals such as Aluminium (247 W/mK) or steel (60 W/mK).