Solar Thermal Technology in South Africa
Transcript of Solar Thermal Technology in South Africa
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1. Introduction
Society has become dependent on electricity in order to function. Current methods of
electricity generation make use of non-renewable fossil-fuels in order to produce energy.
These sources are not sustainable and are leading to a rapid rate of climate change. For this
reason, experts are increasingly looking towards renewable sources of energy such as the
sun.
The ever-present sun provides solar energy. South frica in particular receives approximately
!"## k$h%m& of '(irect )ormal *rradiance+, according to Siemens South frica !#!. For
this reason, South frica/s geographical position makes solar energy the optimum option for
future electricity supplies. This report will be focusing on the two methods of solar energy
conversion, photovoltaic and solar thermal, while concentrating mainly on the latter.
Furthermore, the advantages and disadvantages of solar thermal energy production will be
discussed, with particular focus on the economic and efficiency factors. This will allow a
conclusion to be established as to whether solar thermal energy is a viable option for South
frica in terms of satisfying the growing electricity demand.
2. General Overview of Solar Energy
Solar energy is produced by harnessing the power of sunlight. Sunlight can be reflected,
absorbed or transmitted How Photovoltaic Cells work [S.a.]). Solar energy production
manipulates the absorption property in order to create energy.
3. Types of Solar Energy Production0ltimately there are two types of absorption processes to manufacture energy from the sun.
1hotovoltaic active solar cells convert light energy from the sun/s rays immediately to direct
current (C electricity. Solar thermal passive systems indirectly convert heat energy into
electricity via steam turbines, 2ust as fossil-fuelled power plants do.
3.1 Photovoltaic Solar Systes
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1hotovoltaic cells absorb photons from light rays sunlight. (ue to the photoelectric effect,
this absorption process causes electrons to be released resulting in a potential difference
between the various conducting layers of the photovoltaic cell. This potential difference, or
voltage, causes electrons to consistently flow between the layers in order to e3ualise this
difference and is called electricity.
These cells can be designed to cover surfaces in everyday life such as buildings, e.g.
transparent solar power windows were recently invented by Sharp in 4apan 56hlum. !#!.
draw-back of this solar process, however, is the necessity for batteries. $hen the
wavelength of the sunlight is not great enough, the photoelectric effect does not take place,
thus batteries are needed to store electricity for these periods e.g. overcast and cloudy
days. This increases the total cost of this process.
3.2 !oncentrated Theral Solar Systes
Concentrated thermal solar systems CS1 use mirrors and%or lenses to focus light received
from a wide area onto a smaller surface, concentrating and intensifying the thermal heat
energy onto this specific surface. This concentrated heat can be utilised for various industrial
processes but is specifically used in the energy industry to make steam. This steam then
powers a steam turbine, thereby generating electricity.
3.2.1 Types of !SP Systes
ll concentrated solar power CS1 systems essentially comprise of a mirror heliostat and
an area that receives the reflected heat energy receiver. 7owever, each system utilises
these elements differently8
I. Parabolic Trough
These heliostats are trough shaped and reflect the heat energy onto a central pipe
positioned inside the curved surface. These may be placed on a single 9ast-$est
axis allowing maximum absorption. This is the most common CS1 used in the world
although it is currently only used to support other fossil-fuelled power plants.
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"ig. 1 Para#olic Trough Syste.
Source: Working of CSP Parabolic Trough !#!. :;nline< vailable8 http8%%techbells.blogspot.com%!#!%#=%working-of-csp-parabolic-
trough.html :!#> 5ay !<
II. !inear "resnel
This system is similar to the parabolic trough system? however, flat heliostats areused in place of parabolic-shaped ones. This flat design allows for more light to be
captured and reflected onto the central pipe.
"ig. 2 $inear "resnel Syste
Source: Co#$act !inear "resnel %eflector !##" :;nline< vailable8 http8%%2cwinnie.bi@%wordpress%ApB!=# :!#> 4une !<
III. Power Tower&Central %eceiver
*n this type of CS1 technology, multiple heliostats are positioned so as to focus
reflected light onto a central tower or receiver. The tower contains molten salt, a
means of storing heat energy see section >.!.!. 9ach individual heliostat is
positioned on two axes in order to directly track the sun.
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"ig. 3 Power Tower Syste.
Source: Concentrate' Solar Ther#al Power :S.a.< :;nline< vailable8 http8%%en.wikipedia.org%wiki%ConcentratedDsolarDpower :!#>
5ay !<
I(. ish Stirling& Parabolic ish
parabolic-shaped heliostat is used to concentrate all reflected light onto a centrally
mounted receiver. Eecause the receiver is mounted onto the individual dish, the
system can also move on two axes.
"ig. % &ish Stirling'Para#olic &ish Syste
(Source) ah Ge. !#. *iant Parabolic'ish Photo *aller+. :;nline< vailable8
http8%%xaharts.org%$hirlwheelDdir%reflectingDdisks%reflectingDdisks.html :!#> 4une !<
3.2.2 *dvantages of !SP Systes
The most obvious benefit is the renewable factor. 1rogressively, society is considering the
environment and the greenhouse-effect with every action made and hence interest in solar
energy/s capabilities is growing 3uickly.
3.2.2.1 Thermal Storage and Hybridisation
ma2or advantage of CS1 unlike 1H technology is that it is able to store the heat energy
received via a compound8 molten nitrate salt. This is called thermal storage. 1otential storage
periods range from nine to ! hours (ersatilit+ of CSP. [S.a.])? hence, energy can potentially
be supplied throughout the day. This capability makes CS1 not only useful as an individual
power source, but may also be built in close proximity to already existing plants in order to
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ease the electricity demand during peak hours. This method of using more than one energy
source to produce power is called hybridisation. Such practises are a good mid-term solution
for countries, such as South frica, experiencing demands that surpass supply.
3.2.2.2 Scalability
Furthermore, concentrated solar thermal technology is modular or scalable. The process can
take place at various scales. t household level it is already being used in the form of solar
water heaters. Specifically, CS1 systems can be built to satisfy a small town # kilowatts or
to connect to a larger, national grid up to ## ### kilowatts, CSP , How it works- [S.a.]).
ccording to 56hlum !#!, 'it can be used for many different purposes+. *nvestors seem
to fear the fact that CS1 technology is relatively new. 7owever, this modular ability allows
CS1 pro2ects to be scaled up swiftly and hence the development of CS1 plants is able to be
a multi-phased process.
3.2.2.3 Economic Benefits
s mentioned previously, CS1 technology is renewable and its solar source is free of charge.
Currently South frica spends billions annually in harvesting coal, ac3uiring nuclear stock
and other forms of potential energy all of which will run out in the future. Solar energy, as a
source, will cost our country nothing. Thus, once a CS1 plant is established, the only costs
incurred would be running costs, unlike our current, non-renewable energy sources. 'Solarthermal power currently leads the way as the most cost-effective solar technology on a large
scale+, Solar Ther#al nerg+: an In'ustrial %e$ort [S.a.]).
Furthermore, CS1 has a 2ob creation potential 'greater than other forms of renewable
energy+, S/0s first solar $lants: CSP in action. [S.a]). 4obs are created directly through the
construction and maintenance of plants and indirectly through the industry they bring to the
areas of establishment. Currently there are two concentrated solar thermal plants being built
in 0pington and as a result there has been a boost in their micro economy.
3.2.3 &isadvantages
4ust like any energy source, the advantages are accompanied by disadvantages. The
challenge for scientists and engineers is to compress and limit these disadvantages to a
minimum.
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3.2.3.1 Intermittence and Unpredictability
1ossibly the largest concern of solar energy producers is the inconsistency of solar radiation.
single day of dark clouds should not undermine the energy needs of a country. South
frica, with its high levels of ()* see >.!. fortunately is not as susceptible to this factor. *n
the same way, dust particles also cause intermittence. Solar thermal technology must be
properly maintained in order to obtain maximum efficiency. This may include the removal of
any dust or dirt particles that block rays from striking the heliostats. This being said, solar
energy is still only 'variable+ and certainly not 'unreliable+, as Chiras !##" correctly states.
3.2.3.2 Economic ra!bac"s
0nfortunately, the reality is that solar technology is still in its early stages of development and
hence is still expensive. 9ven more so when considering 'the cost of re3uiring back-up
energy are generally not included in the assumed production costs+, according to 56hlum
!#!. There are few full-scale, independent concentrated thermal solar power plants in the
world unlike coal-fired power plants, for example, which produce #I of the world/s energy
$orld Coal ssociation :S.a.<. For this reason, it investors are not as willing to invest large
sums of money into the development and installation of the technology. ;ne must also
consider, however, that many current non-renewable forms of energy production are heavily
subsidised by the government. ;nce policies start changing and the technology becomes
cheaper, it will be much more appealing to investors and politicians.
3.2.% !SP + a eans to satisfy South *frica,s Energy -euireents
ccording to Euthele@i !#!, South frica/s power deficits estimates around J ### ### and
># ### ### kilowatts a year. ;ur energy situation is concerning and even more so when
considering the rapid rate of annual population growth. )evertheless, the government is aware of
this issue as seen by the recent policies and plans that have been proposed. ;ne such plan is
the Kenewable 9nergy Feed-*n Tariff K9F*T that was announced in !##". )d2obeni !#!,
reveals that our government 'seeks to introduce = L## ### kilowatts of renewable energy online
by !#>#. Solar thermal technology is exactly what our country needs to meet this goal.
(irect normal irradiance ()* measures the solar radiation received by m& of land. *n South
frica, values of up to !"##kwh%m& are not unusual in some provinces, according to the
(epartment of 1ublic 9nterprises !##=. The exact map of ()* measurements can be seen
below in figure J. This confirms clean energy solutions manager of S )ational 9nergy
(evelopment, Thembaka@i 5ali/s statement8 'it would soon be cheaper to develop energy using
solar radiation than fossil fuels because of frica/s sun exposure. *f the continent took full
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%. !onclusion
*n comparison to other renewable energy sources, solar energy is progressively becoming
the preferred type of renewable energy among experts. There are namely two types of solar
energy systems8 photovoltaic and concentrated thermal. CS1 in particular is advantageous
when considering its uni3ue thermal storage and hybridisation capabilities, the 2obs the
technology creates and the savings it would provide in the long term considering sunlight is a
free energy source. *n the same light, the technology has its drawbacks that are similar to
most renewable energy technology8 it is intermittent and is currently still 3uite expensive
relative to present energy producing technology such as coal processing.
Considering all these factors, CS1 will be the best option for a country such as South frica
when taking into account our significant levels of ()* and the electricity deficit we experience
annually. CS1 technology is the future of South frican energy production.
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energy-.>=J=.html. :!#> 5arch N<
Chiras, (an. !##". Power fro# the Sun: /chieving nerg+ In'e$en'ence. )ew
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