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Scottish Plastics and Rubber Association Scottish Plastics and Rubber Association

Potential for Plastics and Rubber in Low Cost Solar Thermal Collectors

George loumakis

George Loumakis, a physicist and renewable energy engineer and a research student in the School of the Built and Natural Environment at Glasgow Caledonian University, opened the SPRA meeting on Materials and Design with an overview of solar thermal collectors and then explored the potential of polymeric materials in the design of low cost solar collectors.

Although Scotland does not enjoy the same level of sunshine as some other countries, solar thermal collectors can still be effective enough to provide 30-40 % of hot water needs in domestic buildings and energy savings of up to £400 per year, taking into consideration the proposed tariff scheme of the Renewable Heat Incentive and further fuel savings from substituting conventional boilers with solar thermal collectors.

Glazed Flat Collector: active pumped system
Glazed Flat Collector: thermosiphon system
Most solar collectors are Glazed Flat Plate Collectors, with a transparent cover (usually glass), an absorber (usually aluminium) and pipes (normally copper) for circulating the heat transfer fluid (water or water with added anti-freeze). Insulation is another feature in some designs. Evacuated Tube Collectors work on the heat pipe principle, with evaporation and condensation of a fluid in a sealed pipe. Air Collectors, where the heat transfer medium is air are used mainly for space heating. Finally unglazed flat plate collectors have large areas and are used to heat swimming pools.

Installed glazed flat collector
Glazed Flat Plate Collectors are becoming more expensive because of the rising price of copper and aluminium but a significant contribution to the overall cost comes from assembly and installation, because of the weight of conventional designs. Using polymers is an attractive proposition because of lower material costs and lower installation costs because of the reduced weight. However polymers have limitations, such as durability and unattractive thermal properties.

For the glazing components, the polymer needs to have good transmittance, uv resistance, long term resistance to elevated temperatures and good general weathering resistance. The performance of PET and polycarbonate can be improved with the application of an acrylic capping layer. The absorber components require high thermal conductivity and high heat resistance for long periods, 80oC/16000 hours in water and 140oC/500 hours in air. Temperatures under stagnation conditions can reach up to 200oC which is demanding for commodity thermoplastics. Hydrolysis resistance is another important property. Thermal conductivity of unfilled polymers is of the order of 1000 lower than aluminium which presents a major challenge when incorporating polymer absorbers into the design of low cost solar thermal collectors.

Plastics Solar Thermal Collector

George’s research project is at an early stage and he is interested in talking to polymer suppliers about the potential for using plastics and rubber in low cost solar thermal collector designs. He believes there is scope for applications of recycled plastics.

mail to George Loumakis

Report by C Geddes, SPRA Hon Secretary April 2011

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