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# An investigation into the use of the vanadium redox flow energy storage system for peak-shaving and load-leveling

Diko, Mpho (2003-04)

Thesis (MScEng)--University of Stellenbosch, 2003.

Thesis

ENGLISH ABSTRACT: This thesis investigates the credibility of the vanadium redox flow energy storage system, sometimes termed vanadium redox battery (VRB). The focus is on the use of this technology in peak-shaving and load-leveling applications. The initial problem is to find a suitable mathematical model for representing the daily load profile. A sinusoidal function is identified as an elementary approximation of the first order. Due to the periodicity characteristics that are inherent in a daily load profile, the Fast Fourier Transform (FFT) algorithm is identified as a mathematical model that closely resembles a load profile. The main theme in this thesis is the determination of an optimal solution during the peak-shaving process. In this particular context, the optimal solution refers to the following: With the energy capacity of the VRB and the power rating of the entire system considered as the constraints, the interest is on (i) the constant power that the VRB can deliver in order to bring down the maximum demand quite significantly, (ii) and the time interval in which this constant power is delivered. Therefore, the VRB power delivered during peak-shaving (PVRB) and the corresponding time interval are the main two parameters under consideration in the optimization process. The mathematical algorithm that can be used to determine suitable values for these two parameters is developed. Maple" V 5.1 is used for determining the solution analytically. The obtained results are verified by simulation with Excel". The investigation into the economic benefits that may be derived from the utilization of the vanadium energy storage device is also presented.

AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die waarde en toepassing van die vadium "redox" vloei energie stoorstelsel (VRB). Die fokus is op die gebruik van hierdie tegnologie om pieklas te verminder en om laste meer egalig te maak. Die aanvanklike probleem is om 'n geskikte wiskundige model vir die daaglikse las-profiel te kry. Deur gebruik te maak van sinus-komponente en die toepassing van die Vinnige Fourier Transform (FFT) is hierdie probleem opgelos. Die hooftema van hierdie werk is om 'n analitiese oplossing te vind vir die optimale toepassing van die konsep vir pieklas vermindering. In hierdie konteks verwys die optimale oplossing na die volgende: Met die gegewe verrnoe van die VRB stelsel en drywingsvermoe van die kragelektronika is die vrae rondom (i) die konstante drywing wat die VRB kan lewer om die maksimum aanvraag van die las beduidend te verminder en (ii) die tydsduur waarin dit plaasvind. Dus is die twee veranderlikes waarvoor oplossings in die optimale proses gesoek word die drywing (PVRS) en die tyd-interval daarvan. Die wiskundige algoritme is met die hulp van Maple® V5.1 ontwikkel. Die resultate is daarna met behulp van simulasies in Excel® getoets. 'n Analise van die moontlike ekonomiese voordele is ook ondersoek.

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