Browsing by Author "Lombard, Hans Jurgens"
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- ItemSmall solar organic rankine cycle for electricity generation(Stellenbosch : Stellenbosch University, 2015-12) Lombard, Hans Jurgens; Dobson, Robert; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: The global the demand for energy has risen dramatically in recent years and the cost of electricity has risen considerably. Local electricity sales prices followed the global trend, increasing by an average of 25% per annum from 2008 to 2012. This upward trend has opened the market for new technologies, such as renewable energy alternatives, better use of waste streams and low temperature power generation. The Organic Rankine Cycle is an example of a low temperature power generation cycle that can utilize a renewably energy source. The Organic Rankine Cycle is in essence a Rankine Cycle that employs a different working fluid than water. The primary objective of this thesis is to build a functioning ORC. The cycle is to utilize a low temperature (< 120°C) and pressure heat source to generate up to 1 kW of electricity. Each component has to be sized and bought or designed and manufactured. The performance of each component is to be predicted using theoretical mathematical models. This model will be validated through comparison with the experimental results obtained. The condenser has to be driven by natural convection in order to minimize the energy consumption of the system. Finally the feasibility of such a system will be investigated. The experimental Organic Rankine Cycle was run for several different scenarios and measurements were taken to characterize and evaluate the performance of this system. The performance of the system components was satisfactory in comparison with the design specifications with the exception of the boiler and scroll expander electric motor. The boiler capacity was experimentally determined to be 8 kW, much lower than the design capacity of 20 kW. The lowered boiler capacity inhibited the system performance by as much as 25%. The conversion efficiency of the scroll expander electric generator was low at 7%, but the scroll expander demonstrated an isentropic efficiency up to 47%. A theoretical model was developed to predict the thermodynamic performance of the system components. The theoretical model predicted the performance of the system components within 10%, except for the pump performance which deviated due to the bypass valve adjustment. A study was conducted to determine the feasibility of an Organic Rankine Cycle system. The study takes into account the initial capital cost, discount rate, operations and maintenance costs and system life span. The study found that the ORC is currently a viable option for remote, off-grid electricity generation with an levelized cost of electricity of R 2,55 compared to the Eskom tariff of R 3,90. The additional cost of line rental increases the Eskom tariff considerably. For urban generation the levelized cost of electricity for renewable sources is still higher (R 2,55) than the Eskom tariff (R 1,00), but the increasing Eskom tariff and decreasing cost of renewable energy solutions should see renewable energy technologies become a financially feasible solution by the year 2020.