Designing a Solar Thermal Cylindrical Parabolic Trough Concentrator by Simulation

The focus on renewable energy in Malaysia gained momentum with the active involvement of the government and the private sector. This move can potentially help in diversifying the country's energy options besides relying on oil, natural gas, coal and hydropower. The scope of this paper is to look at the designing procedures of a solar thermal cylindrical parabolic trough concentrator (CPTC) by simulation. The designing effort starts off with the selection of certain parameters such as the aperture area and the diameter of the receiver to obtain the geometric concentration. Concentration ratios can be theoretically very high with the imaging concentrators of precise optica e emen s an con muous tracking, in the range of 10 to 40 000. A thorough analysis is necessary, where the optical precision and proper thermal analysis must be carried out to evaluate the performance of a CPTC. The results will clearly show that there must be an equilibrium achieved between the increasing thermal losses with the increasing aperture area, and the increasing optical losses with the decreasing aperture area for the optimization of the long-term performance of the CPTC. INTRODUCTION Improper use of fossil fuels has led to negative imbalance in the natural environment. The impact on the environment is fast surpassing the positive development brought about by the discovery of fossil fuels. One cannot deny that the exploitation of fossil fuels has brought about a better future for mankind, but if the environment is destroyed in the process, then proper ways and new resources must be introduced to strike a balance. Malaysia is keen on promoting the use of renewable energy which can help in diversifying the country's energy options besides relying on oil, natural gas, coal and hydropower. The National Energy Policy, introduced in 1979 aims to have an efficient, secure and environmentally sustainable supply of energy, which is moving parallel with the global efforts. The development plans for using both non-renewable and renewable energy resources were taken to be the main aim and the utilization objective outlined the need to use energy efficiently (Yap, 2002). The journey to embark on non-renewable energy technologies should be geared towards supplementing the conventional sources of energy. Since solar energy is readily available in Malaysia, it would be beneficial to fully exploit it. The scope of this paper is to look at the design procedures of a solar thermal CPTC. It is possible to achieve a temperature around 100°C with a flat plate collector, but for power generation or industrial purposes, concentrators playa vital role. Usually for comparison purposes, concentration ratio (CR) is introduced. Increasing ratios means increasing temperatures at which energy can be delivered and also increasing requirements for 1 International Rio3 Congress, World Climate and Energy Event, Rio de Janeiro, 1-5 December2003 precision in optical quality and positioning of optical systems. Concentration ratios can be theoretically very high with the imaging concentrators of precise optical elements and continuous tracking, in the range of 10 to 40 000. THEORY A solar thermal CPTC can be used to harness solar energy at rather high temperatures depending on the working fluid used. The level of concentration is restricted by the design parameters and is given as Eq.(l). Eq.(2) relates the CR to the acceptance half-angle and the best value is based on the sun's subtend angle of 0.54° with the highest CR at 212. Although the values look promising, the whole design process cannot be based only on these values. CR = sin~R 7tsin8c (1)