Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: As the push continues for increased use of renewables on the electricity grid, the problem of energy storage is becoming more urgent than ever. Flywheels with wound, composite rotors represent an efficient and environmentally friendly option for energy storage. They have already been applied successfully for voltage control on electrical rail networks and for bridging power in backup UPS systems, but lately they have also proven useful for grid-scale frequency regulation. For flywheels to be deployed on a wider scale, the high cost associated with the technology will have to be addressed. An important driver of cost is the density at which energy can be stored. Currently, flywheel designs do not consistently achieve high energy density, and this study investigates the reasons for this. A critical analysis is made of the design methodologies that have been proposed in the available literature, and some improvements are suggested. Most notably it is shown that significant improvements in energy density may be possible if the design optimization problem is formulated carefully. In addition, the problem of material selection is discussed, because material properties have a significant influence on energy density. Some guidance is given for flywheel designers on how to choose an optimal set of materials without invoking undue computational effort. It is hoped that these suggestions may be carried forward as a topic of further research. / AFRIKAANSE OPSOMMING: Namate die aanvraag vir hernubare energie op die elektrisiteit netwerk vergroot, word die probleem van energie berging van kardinale belang. Vliegwiele met silindriese rotors van samegestelde materiale bied ’n effektiewe en omgewingsvriendelike opsie vir energieberging. Hierdie tipe vliegwiele is reeds suksesvol aangewend vir spanningsbeheer op elektriese spoornetwerke en om oorbruggingskrag te voorsien aan rugsteun sisteme. Meer onlangs is hulle ook nuttig bewys vir die regulasie van frekwensie op die elektrisiteit netwerk. Grootskaalse aanwending van vliegwiele kan egter slegs oorweeg word indien die hoë koste van die tegnologie aangespreek word. Een van die onderliggende redes vir die hoë koste van vliegwiele is die relatiewe lae digtheid waarby energie geberg kan word, en hierdie studie ondersoek die redes hiervoor. Die ontwerpmetodiek wat in die beskikbare literatuur voorgestel is, word krities geanaliseer en ’n paar verbeteringe word aanbeveel. Mees noemenswaardig is die opmerklike verbeteringe in energie-digtheid wat soms moontlik is indien die optimerings-probleem deurdag geformuleer word. Omdat materiaaleienskappe ’n bepalende invloed op energie digtheid uitoefen word die probleem van materiaalseleksie ook verder bespreek. ’n Paar riglyne vir die seleksie van ’n optimale stel materiale sonder om oordrewe berekenings-inspanning te veroorsaak, word aan vliegwielontwerpers gegee. Hierdie voorstelle kan hopelik in die toekoms verder deurgetrap word as onderwerp vir verdere studies.