Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Central receiver power plants generate renewable electricity by exploiting the
energy provided by the sun. The conditions experienced in the Northern Cape
region of South Africa provide the ideal conditions for the development of these
plants. Without a storage medium these plants have capacity factors in the range
of 25-30%. The inclusion of a thermal energy storage medium provides the ability
to increase the capacity factors of these plants. Although storage increases the
costs, it results in better utilisation of the power block and a decrease in the
levelised electricity cost (LEC). Eskom intends building a 100MWe central
receiver dry cooled power plant in the Upington region. This research identifies
the appropriate storage medium and ideal storage capacity to achieve the lowest
LEC.
A literature survey was performed to identify the different methods of storage that
are available. The different storage methods were evaluated and the best storage
medium for a central receiver power plant based on the developments of the
various storage technologies was identified.
To determine the costs associated with a central receiver power plant, data
published by NREL was used. Different plant parameters were required to
evaluate the costs. A power plant model based on efficiencies and energy balances
was created to determine the required plant parameters. It provided the ability to
determine the effect of changing different plant parameters on the LEC and
estimate the plant output. The power block parameters were initially varied to
determine the most efficient power block configuration. Once the most efficient
power block configuration was identified the solar field and storage parameters
were varied to determine the plant configuration which resulted in the lowest
LEC.
The most efficient power block configuration of 0.4206 was found for a system
comprising of six feedwater heaters with the feedwater temperature of 230°C,
main steam pressure 140 bar and an exit steam generator salt temperature of
290°C. A solar multiple of 3.0 with 16 hours of storage resulted in a LEC of
R1.41/kWh with no system constraints. A capacity factor constraint of 60%
resulted in a solar multiple of 1.8 with 8 hours of storage and a LEC of
R1.78/kWh. / AFRIKAANSE OPSOMMING: Sonkragaanlegte met sentrale ontvangers wek hernubare elektrisiteit op deur
sonenergie te ontgin. Die klimaat in die Noord Kaap-streek van Suid-Afrika is
ideaal vir die oprigting van hierdie aanlegte. Sonder ’n bergingsmedium is die
kapasiteitsfaktore van sulke aanlegte ongeveer 25-30%. Met die insluiting van ’n
bergingsmedium vir termiese energie kan die kapasiteitsfaktore egter verhoog
word. Hoewel berging aanlegkoste verhoog, lei dit terselfdertyd tot beter
aanwending van die kragblok en ’n afname in die konstante eenheidskoste van
elektrisiteit (LEC). Eskom beplan om ’n droogverkoelde kragaanleg van 100 MW
met ’n sentrale ontvanger in die Upington-streek op te rig. Hierdie navorsing was
dus daarop toegespits om die mees geskikte bergingsmedium en ideale
bergingskapasiteit te bepaal om die laagste moontlike LEC uit die aanleg te
verkry.
’n Literatuurstudie is onderneem om die verskeie beskikbare bergingsmetodes te
bestudeer. Die verskillende metodes is beoordeel, waarna die beste
bergingsmedium vir ’n kragaanleg met ’n sentrale ontvanger op grond van die
ontwikkelings in die verskillende bergingstegnologieë bepaal is.
Om die koste van ’n kragaanleg met ’n sentrale ontvanger te bepaal, is
gepubliseerde data van die Amerikaanse Nasionale Laboratorium vir Hernubare
Energie (NREL) gebruik. Verskillende aanlegparameters was egter nodig om die
koste te beoordeel. Dié parameters is gevolglik bepaal deur ’n kragaanlegmodel
op grond van doeltreffendheidsfaktore en energiebalanse te skep. Sodoende kon
vasgestel word watter uitwerking veranderinge in die verskillende parameters op
die LEC sou hê, en kon die aanleguitset geraam word. Die kragblokparameters is
aanvanklik afgewissel om die doeltreffendste kragbloksamestel te bepaal. Nadat
dít bepaal is, is die sonenergieveld en bergingsparameters weer afgewissel om vas
te stel watter aanlegsamestel die laagste LEC tot gevolg sou hê. Die beste termiese benuttingsgraad is behaal vir ʼn stoom siklus met ses water
verhitters en ʼn water temperatuur van 230 °C by die ketel se inlaat, ʼn stoom druk
van 140 bar, en sout uitlaat temperatuur van 290 °C. ʼn Vermenigvuldigingsfaktor
van drie vir die heliostaat veld, en 16 uur termiese energie storing gee ʼn
opwekkingskoste van R 1.41/kW/h indien daar geen beperkings op die grootte of
koste van die stelsel geplaas word nie. Indien die kapitaal uitgawe ʼn perk van
60 % op die kapasitiet van die stelsel plaas, verander die optimale ontwerpspunt
na ʼn vermenigvuldigingsfaktor van 1.8, en die termiese stoorkapasitiet verlaag na
8 uur. In hierdie geval is die opwekkingskoste R 1.78/kWh.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86276 |
| Date | 04 1900 |
| Creators | Madaly, Kamalahasen |
| Contributors | Hoffmann, J., Gauche, P., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xiv, 85 p. : ill. |
| Rights | Stellenbosch University |
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