8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 1/10

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

1

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 2/10

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.

2

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 3/10

"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.

3

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 4/10

"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

4

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 5/10

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.

5

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 6/10

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

6

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 7/10

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 8/10

%. !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.

8

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 9/10

. -eferences)

Euthele@i, ). !#!. !aw stan's between S/ an' chea$ solar energ+. :;nline<

 vailable8 http8%%www.iol.co.@a%business%law-stands-between-sa-and-cheap-solar-

energy-.>=J=.html. :!#> 5arch N<

Chiras, (an. !##". Power fro# the Sun: /chieving nerg+ In'e$en'ence. )ew

Society 1ublishers. #-N

Concentrate' Solar Power a ke+ technolog+ for sustainable $ower generation in

 /frica. :;nline< vailable8

http8%%www.siemens.co.@a%en%newsDpress%news!#!%concentrated-solar-

power.htm.html. :!#> 5arch N<

Concentrate' Solar Power. :;nline< vailable8

http8%%en.wikipedia.org%wiki%ConcentratedDsolarDpower.html. :!#> 5arch "<

CSP , How it works. :;nline< vailable8

http8%%www.solarpaces.org%CS1DTechnology%cspDtechnology.htm.html. :!#> 5arch "<

(epartment of 1ublic 9nterprises !##= Strategicall+ I#$ortant evelo$#ent .

:;nline< vailable8 http8%%www.info.gov.@a%view%(ownloadFilectionAidB"J="  :!#>

5ay !<

(ontigney, 9. / brief su##ar+ of Solar nerg+. :;nline< vailable8

http8%%www.ehow.com%factsDJL#NNLDbrief-summary-solar-energy.html.html. :!#>

5arch ><

Fluri, T.1. !##". The potential of concentrating solar power in South frica. nerg+

Polic+- >=!8 J#=J-J#L#

How Photovoltaic Cells wok. :;nline< vailable8

http8%%www.solarenergy.net%rticles%how-photovoltaic-cells-work.aspx.html. :!#>

5arch ><

*nstitute for 9nergy Kesearch. :S.a.<. Solar. :;nline< vailable8

http8%%www.instituteforenergyresearch.org%energy-overview%solar%.html. :!#> 5arch ><

9

8/20/2019 Solar Thermal Technology in South Africa

http://slidepdf.com/reader/full/solar-thermal-technology-in-south-africa 10/10