Loading, modelling and costing of concrete and steel support structure designs : large wind turbines in South Africa

De Kock, Conrad Jeanne (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Wind energy has the potential to be a strong contributor to a more sustainable future. Globally it is a major player in the market and is expected to become more influential in the future. In South Africa the potential exists and major development is under way. A modern wind turbine has a horizontal axis orientation, three rotor blades, active pitch and face into the wind using yaw control. It has a steel monopole tower between 60m and 80m high with a reinforced concrete foundation. However, this design presents various problems for structural integrity, manufacturing and viability at heights above 80m. These constraints has led to a movement towards steel-concrete hybrid and full concrete towers. Such designs present an alternative and possibly more optimal solution for tower heights over 100 m. This hypothesis was tested for South African conditions. Steel and prestressed concrete tower designs were acquired for a 3MW reference wind turbine with 100m hub height. Towers were loaded according to local conditions and the structural soundness thereof was tested and proved. Structural parameters were optimized and material mass and volume were determined for each. A cost estimation and sensitivity analysis was performed for the following life-cycle phases: manufacture, construction and installation; transport; and disposal and recycling. Margins of cost between the tower designs were low enough for all three to be considered competitive alternatives at 100m in height. The cast-in-place prestressed concrete design was estimated to be the most affordable solution. However, its high sensitivity to variation in erection cost causes uncertainty and a higher financial risk. Furthermore, the steel tower was the most viable for low steel prices and high erection costs. For a larger foundation size it still remained a competitive alternative to the concrete towers. Overall the prestressed precast design was the most expensive. However, for high erection costs it was more affordable than the cast-in-place tower. For disposal and recycling the steel solution was a much more favourable financial alternative to the concrete design. However, salvage income does not contribute a significant gain compared to overall cost.

AFRIKAANSE OPSOMMING: Wind energie het die potensiaal om 'n sterk bydra te lewer tot 'n meer volhoubare toekoms. Wêreldwyd beklee dit 'n belangrike posisie in die mark en sal na verwagting meer invloedryk word in die toekoms. Suid-Afrika het baie potensiaal en grootskaalse ontwikkeling is aan die gang. 'n Moderne windturbine het 'n horisontale asoriëntasie, drie rotorlemme met aktiewe draai-aksie en word in die wind in gerig met behulp van beheersisteme. Dit het 'n silindriese staaltoring met 'n hoogte tussen 60m and 80m en 'n bewapende beton fondasie. Hierdie ontwerp bied egter verskeie probleme rakende strukturele integriteit, vervaardiging en lewensvatbaarheid vir hoogtes bo 80 m. Bogenoemde beperkinge het gelei tot 'n industriële beweging na staal-beton hibriedontwerpe en volle betontorings. Sulke ontwerpe bied 'n alternatief en moontlik meer optimale oplossing vir toringhoogtes bo 100 m. Hierdie hipotese is getoets vir Suid-Afrikaanse toestande. Staal en spanbeton toringontwerpe is verkry vir 'n 3MWverwysingswindturbine met 100m ashoogte. Die torings is belas vir plaaslike toestande en die bouvorm daarvan is getoets en bewys. Struktuurparameters is gebruik om geoptimeerde materiaalmassa en volumes vir elk te bepaal. 'n Kosteberaming en sensitiwiteitsanalise is vir die volgende lewensiklusfases uitgevoer: vervaardiging, konstruksie en installering; vervoer; en beskikking en herwinning. Kosteverskille was laag genoeg vir al drie ontwerpe om as medidingend beskou te word teen 'n hoogte van 100 m. Die insitu spanbetonontwerp is as die goedkoopste oplossing beraam, maar die toring se hoë sensitiwiteit vir variasie in oprigtingskostes veroorsaak onsekerheid en 'n oënskynlike finansiële risiko. Verder was die staaltoring die mees lewensvatbaar vir lae staalpryse en hoë oprigtingskostes. Dit was steeds mededingend met die beton torings ten spyte van 'n groter fondament. Die voorafvervaardigde spanbetonontwerp was oor die algemeen die duurste. Dit was egter goedkoper as die insitu toring vir hoë oprigtingskostes. Vir beskikking en herwinning was die staalontwerp 'n meer gunstige finansiële alternatief as die beton. In vergeleke met die totale koste van 'n toring het herwinning egter nie 'n beduidende wins bygedra nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97916
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