Small solar organic rankine cycle for electricity generation

[摘要] ENGLISH ABSTRACT: The global the demand for energy has risen dramatically in recent years and the cost ofelectricity 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 hasopened the market for new technologies, such as renewable energy alternatives, betteruse of waste streams and low temperature power generation.The Organic Rankine Cycle is an example of a low temperature power generation cyclethat can utilize a renewably energy source. The Organic Rankine Cycle is in essence aRankine Cycle that employs a different working fluid than water. The primary objective ofthis 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 besized and bought or designed and manufactured. The performance of each component isto be predicted using theoretical mathematical models. This model will be validatedthrough comparison with the experimental results obtained. The condenser has to bedriven 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 andmeasurements were taken to characterize and evaluate the performance of this system.The performance of the system components was satisfactory in comparison with thedesign 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 thedesign capacity of 20 kW. The lowered boiler capacity inhibited the system performanceby as much as 25%. The conversion efficiency of the scroll expander electric generatorwas 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 thesystem components. The theoretical model predicted the performance of the systemcomponents within 10%, except for the pump performance which deviated due to thebypass 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 andmaintenance costs and system life span. The study found that the ORC is currently a viableoption for remote, off-grid electricity generation with an levelized cost of electricity ofR 2,55 compared to the Eskom tariff of R 3,90. The additional cost of line rental increasesthe Eskom tariff considerably. For urban generation the levelized cost of electricity forrenewable sources is still higher (R 2,55) than the Eskom tariff (R 1,00), but the increasingEskom tariff and decreasing cost of renewable energy solutions should see renewableenergy technologies become a financially feasible solution by the year 2020.

[发布机构] Stellenbosch University