Design of a small-scale solar-stirling power system with a beam-down focus for rural electrification.

Abstract

In Ethiopia, off-grid rural electrification using renewable energy is a highly attractive energy option as a result of the scattered settlement of rural populations. Solar thermal energy has become very promising in recent years due to its abundance and clean energy in nature. This thesis presents the performance analysis of a solar thermal system consisting of a point-focus beam down system and a Stirling engine to power rural areas. The estimation of solar radiation was performed based on the sunshine hour model using the Angstrom-Prescott correlation. The predicted solar radiation data from different databases were compared and the study area was found to have enough solar radiation potential. The energy demand assessment for households of specified rural villages (in Goroba) was made. Microsoft Excel, EES, and Edraw max 7.9 are used for design calculation and analysis of the overall Beam-Down performance. The analysis is based on a theoretical design. Performance curves under varying operating temperatures and ambient conditions are presented. United Stirling 4-95 MKII Stirling engine of 25 kW rated power with 20MPa and hydrogen as working fluid is selected for the energy conversion unit. On the other hand, the heat flux and the temperature distribution at the final focal point of the concentrator and systems modeling are performed through Tonatiuh v_ 2.2.4.and Solidworks_2014, respectively. The result of Tonatiuh v_2.2.4 simulation shows that the flux distribution on the focal plane varies with the number of rays. For 1000W/m2 of DNI and the number of rays at 108 , the average flux is 56.65 kW/m2 . According to this simulation, the error decreases as the average heat flux as well as total power, increases. From the design process, the total output power that goes to the storage battery is estimated at 303.32kWhe, and the levelized cost of energy is about 0.11US$/kWhe. Therefore, the proposed system can be recommended as a viable option for rural electrification.