1. A REVIEW OF SOLAR ENERGY TECHNOLOGIES ;
A COMPARATIVE ANALYSIS
Adun Humphrey Hugh Balogun Enitan Adeleke
Department of Energy Systems Engineering Department of Energy Systems Engineering
Cyprus International University Cyprus International University
Haspolat-Lefkosa, Via Mersin 10, Turkey Haspolat-Lefkosa, Via Mersin 10, Turkey
ABSTRACT
This paper gives an overview of different solar technologies; Photovoltaics, Concentrated Photovoltaics,
solar thermal technologies, and solar chimney. Considering the climatic side-effects of fossil fuels to
the environment coupled with increasing energy demands, there is a neeed to profer a lasting solution
to the climate change prolem. A rapid growth of renewable energy in terms of research & development,
technological advancements and installations in the world has been witness in the last 10 years. Solar
energy is a tremendous alternative to fossil fuels in energy production. The sun being the source of solar
energy produces an energy sufficient to meet 24-hours global energy need in one hour. To fully harness
this resource, several technologies have been made, some still in experimetal stage like the solar
chimney, while technologies like photovoltaics, parabolic trough and solar tower are already
commercialised.Given the technical advancement in solar energy technologies, coupled with favorable
financing and investments, the future holds great prospects in energy production. As the cost of PV
technology is expected to continue, it will become more economically advantageous. PV hybridization
with CSP is design that will increase the commercialisation of CSP technology. Though Solar chimney
is in its experimental stage,it holds an interesting alternative to solar energy production for regions with
low technological expertise and financial capacity. This is because local materials can be utilised in its
production.
1. INTRODUCTION
It is a worth noting fact that all renewable energy source is directly or indirectly dependent on the sun.
The sun is somewhat of an infinite solution to human needs; as the radiation that reaches the earth is
about 885 million Terawatts hours (TWh) every year – 3500 times the energy that humans will consume
in 2050 (IEA, 2011; 2014b)[15]. This enormous radiation is sufficient to cater for the totalenergy needs
of the globe. Though, there have been an exponential growth of solar energy technologies only recently
(in the last decade),solar energy is not a new technology. The oil rise in the 1970s neccessitated the first
major effort to exploit the sun forpower production by the US. From the 7th century through to 1200AD,
several experimetal procedures of concentrating sunrays using magnifying glasses to produce energy
have been done. Hurace de Saussue, a Swiss scientist is credited with building the world’s first solar
collector in 1767 [15].
World’s solar electric generation had 88.8% growth from 2008 to 2012 [4], an indication of the
increasing contribution of solar energy to growing energydemands of the world. However,due to certain
factorslike economic policies, technological deficiencies, lack of sufficient investments and many more,
the use of fossil fuels still constitute a major chunk of energy resource for production. Considering the
continous growth of energy demands, an example of which occured in 2008, where total energy

2. consumed reached 474 ExaJoules [4], solar energy still lags far back in meeting these demands. These
growth of energy needs comes as a result of the high rising economic growth of developing countries.
About 80% of world’s energy consumption is still dependent on hydrocarbon energy sources [2].
This paper gives an overview of solar energy technologies. For the purpose of comparative analysis, the
solar technologies has been subdivided into three; PV/CPV, Solar thermal electric power and Solar
Chimney/Solar downdraft.
2.SOLAR ENERGY TECHNOLOGIES
The annual radiation receieved on the earth annualy is about 1000W/m2
[1], although this value is
heavily dependent on time and geographical location. Solar energy technolgy concepts is hinged upon
capturing this radiations for production of power or for other basic purposes like heating and cooling
houses, water heating and the likes. Technological advancements of solar technologies aim to produce
better efficiencies of utilising more of the radiations that the earth receive although this only does not
guarantee commercial utilisation. In the industrial market, solar technology is categorised into PV and
solar thermal market [1]. PV technology utilises semiconductors for direct conversion of sunlight into
electricity. Based on the materials used for production, PV is subdivided into monocrystalline,
polycrystalline, thin-film and most recently, a more efficient module called Concentrated Photovoltaics.
Although PV technologies only account for just 0.9% [8] of the total electricity generation, it is a
commercially dependable technology, with prospects as it is gradually expanding due to reduction of
cost [7]. The Renewable Energy Network stated that the largest growth in 2014 was PV, wind and
hydropwer.CPVis a more of an economic upgrade of the PVtechnology asit usesa collectors (asagainst
solar cells in panels) to focus the sunlight onto a high efficiency a cell, therebycutting cost in production.
Solar thermal account for 0.4% of the global electricity generation at the end of 2014Solar thermal
technologies use only direct irradiations from the sun to heat a working fluid that turns water to
steam.this steam is used in a conventional staem turbine for electricity generation [9]. The collectors
focus this radiations onto a receiver which could be a line focus (parabolic trough) or a point focus
(parabolic dish and solar tower). Also called Concentrated solar power, this technology accords more
efficiency because of the ability to ensure thermal strorage for peak demands. Hybrid systems is also
utilised for base load outputs. Solar thermal are subdivided by the type of collectors used and they are ;
parabolic trough, parabolic dish, Linear Fresnel, and solar tower. Parabolic is the most commercialised
of the CSP technology with about 90% of total solar thermal installations.
Solar chimney and solar downdraft technology are renewable energy sources that are still in the
experimential stages. The solar chimney technology is uses the basic physics concept that hot air rises.
And so collectors are used to concentrated the sun radiation in a green house, utilising the earth as a

3. natural staorage system. Air rushes to a chimney and is used to turn a turbine placed horizontally in the
chimney [10]. There are no major commercial application of the solar chimney, though the experimental
project in Manzares, Spain in 1986 provides a model for future designs and economic estimations. This
estimations would be considerably correct because the principles of design and opeartions are thesame
[11]. The solar downdraft is a similar technology to the solar chimey. It uses the principle of dense air
falls, and so water is sprayed at the top of the chimey, which makes the air at the top denser than the
outside air. The air that falls is used to drive a turbine [12]. Though no data on a working pilot plant
have ever been collected, Altmann and Czisch have made projections of its efficiencies and cost of
electricity generation using computational models [13].
2.1.CURRENT INSTALLED CAPACITY OF THE SOLAR TECHNOLOGIES
With greaterawarenessofnegative climatic effectsoffossil fuels and effortsto cut co2 emmissions,there
is growth of solar technology in the world, with more research and practical applications as alternative
means to meeting growing energy demands.
2.1.0 Photovoltaics : As at the end of 2014, the total capacity of PV installation is about 177GW,
contributing about 0.9% to the renewable share of global electricity production [14]. The commercial
modules of PVs are the crystalline sillicon (mon
o-sillicon and poly-silicon) and thin film. The c-si accounts for about 85-90% of the total PV
installations while the thin film constitute about 10-15%[7].
Figure 1: solar PV Global capacity 2004-2014 [14]
Figure 2: solar PV Additions 2004-2014
From the graph above, it is seen that there is a 97.9% growth of PV technology from 2004 to 2014.

4. 2.1.1 Solar Thermal Energy (Concentrated Solar Power) : The total CSP installed capacity as at the
end of 2014 is 4.4GW. Spain and US have most installations compared to other areas of the world [14].
Figure 3: Global cumulative growth of STE capacity Source : REN 2015
Table 1 : Progress in STE since 2009 Source : REN 2015
From the table above, it is seen that there is an increase of about 86.4% growth of CSP technology in
the world from 2004 to 2014.
The parabolicd trough remains the most mature and dominant CSP technology as several innovations
took place between 2007-2009. Their solar to electricity conversion can reach than 15% (annual mean
value) [15].
2.1.2 Solar Chimney/Solar downdraft : Enviromision, an Australian based company has reported
progress in the first solar chimney in India this year. The 50MW solar chimney plant will be completed
in 2017 [16].
2.2 LEVELISED COST OF ENERGY(LCOE)
The technical feasisibility of renewable energy being able to replace fossil fuels has never been in doubt
especially with the technical advancement of the technologies and working fluids; the economic
feasibility remains an impediment [5]. The economic feasibility of solar technologies is analysed using
Levelised cost of energy. The LCOE is a financial tool used for evaluating the cost of electricity

5. produced by a generator. Calculating the LCOE requires considering the cost of the energy generating
system and the energy generated over its lifetime to provide a cost in $/kWh (or $/MWh or cents/kWh)
[5].
2.2.0 Photovoltaics :There are varied estimates for the LCOE of PV systems. This is because of diverse
report assumptions, complex relationships of local prices of electricity, different prices of solar PV
(dependent on suppliers) and geographical attributes. The discripancy that results from the inconsistent
data of the LCOE values results in misguided policy making. A more efficient methodology of
[5]
Calculation of LCOE is given above which covers the discount rate, grid parity, initial investment, solar
life, system costs and degaradation rate.
Figure 4 : LCOE for energy output versus initial cost of the system for a zero interest loan, discount rate
at 4.5%, degradation rate of 0.5%yr and 30 yr lifetime.
The REN 2014 reports that the cost of electricity from new built PV systems varies from USD 90 to
USD 300/MWh. This is depending on the type, size and the cost of the systems,maturity of markets and
cost of capital.
2.2.1 Solar Thermal Energy (Concentrated Solar Power) : The LCOE of CSP Plants are dependant
upon severalfactors. They are the investment cost,plant’s capacity and storage system, efficiency, local
DNI, the O&M and the cost of capital. İn tertms of plants’s thermal storage system, it is estimated that
a lower storage results in a lower LCOE especially for a solar Tower.

6. For a parabolic Trough, the LCOE is estimated to have between USD 0.20 and O.33 KW/h. For a solar
Tower system, it is estimated that the LCOE is between USD 0.16 and 0.27 KW/h. However these
estimations are dependent on the geographical location, size of the storage,and particulars of the project.
İt is important to know that the DNIof a location also affectsthe LCOEof a plant. The LCOEis expected
to expected to decline by 4.5% for every 100KW/hm2/year that the DNI exceeds 2100KW [5]. Upon
this premise, it can be deduced that the LCOE of the parabolic Trough Noor Project in Morroco (which
is the largest parabolic trough plant in the world), with DNI of 2700KW/h will have an estimated LCOE
of between USD 0.045 – 0.0745 KW/h.
The LCOE of the stirling dish and Fresnel system will be slightly higher because they are in their early
stage of development, though sufficient data have not been gotten for their operations.
Table 2 : total installed cost of PT and ST
Figure 5 : LCOE cost of a PT of 100MW as a function of size and storage [5]
From figure 7, it is seen that the size of a thermal storage results in the value of the LCOE. A higher
storage capacity has a corresponding increase in LCOE.
Concentrated Photovoltaics : The calculated value of LCOE for a region having a DNI of
2000KW/(m2
a) is estimated at 0.102 – 0.142 KWh/Euro, with current cost installation of 10MW
estimated at about 1400-2200 Euro/KW (source : GTM 2013, industry survey) [21]
Figure 6 : LCOE by solar irradiation (DNI in KWh/m2
a) in 2013 [21]

7. Solar Chimney: The economic analysis of a solar chimney power plant is made upon several factors
that include; capital cost, operation cost and maintenance cost. Although there is no major commercial
solar chimney power plant to model the economics of its operation, data for calculating the LCOE will
be retrieved from the work of J.Schlaich[18] and will be applied to a plant if constructed in India [17].
The total chimney cost and the total capital cost of the solar chimney power plant is given in table 3 and
4 respectively.
Table 3 : Total chimney cost for different capacities [17]
Table 4 : Capital cost of SCPP for different capacities
And so, the LCOE computation is made using formulas;

8. (1) (2) (3)
Equation 1 represents the present cost over the lifetime period of the plant; i = inflation rate,f= inflation
rate, Af= cash flow at the end of first year
Euation 2 representsanannual equivalent costover the lifetime of the plant; C = capital cost of the plant.
Equation 3 represents the calculation of the LCOE; P = power output in KWh
From the mathematical simulation above, the LCOEfor solar chimney is evaluated as shown in the table
5 and figure 6;
Table 5: LCOE at different interest and inflation rate
Figure 7 : LCOE for different capacities[17]
Summarily, it is estimated that the LCOE for 5 MW is USD 0.22, for 30MW is USD 0.1475 and for
200MW is given as USD 0.1298. It is seen that the LCOE reduces as the plant size increases.
3. RESULTS
The present state of solar energy is only a glimpse of what the future holds for renewable energy
production.

9. The falling price of solar PV has made the technology cost-competitive with fossil fuels in the market.
At the end of 2014, about 40GW was installed [15], pointing to the fact that the PV technology is a
rapidly growing solar technology. İt is estimated that solar PV installed capacity will rise to about
302GW by 2030 producing 505TWh of energy and 632GW by 2050 producing about 1036TWh of
energy. İn order to facilitate this growth, improvements and innovations is to be made in the PV
technology with respect to material use. The concentrated solar photovoltaic, an advancement in PV
technology will further scale-up the commercialisation of the technology. This is because of the
reduction of cost of construction thereby making it more cost effective.
Table 7: Projections of LCOE for newly built CSP plant with storage
‘Munner et. al described the solar PV electricty as the solution of future energy changes [3].
Projections of CSP plants with thermal storage show a reduction in LCOE. This is because most of the
CSP installations have been built in places with relatively low DNI like spain [15], hence requiring
higher capital in construction to make for better efficiency of the plant. Upon more main stream
installations in areas with higher DNI [15] like the ongoing project in Morocco, other MENA regions,
and the likes, the technology will become more mature, hence reducing cost of capital. İt is expected
that by 2050, the total CSP installations will be about 2500 TWh. This estimation is however hinged on
improvement in CSP designs like Linear Fresnel and Sterling dish, designs of receivers and working
fluids.
Table 8 : Technology development for facilitation of CSP growth

10. From the table above, point 9 states the hybridization of PV and CSP as a incentive for CSP growth.
This is because of the rapid decrease in the PV technology which ultimately could make for a slow
expansion of the CSP technology, because of negative cost comparativeness. And so, because PV
offers a good match for consumption peaks and cost effectiveness,there is a technological shift
towards a hybrid PV-CSP design where PV offers low cost day-time generation [15].
Figure 8 : Hybrid STE-PV system
The high effciency of CPV compared to that of PV has made it a fast growing solar technology.CPV is
very advantageous in location with high DNI as the output of the solar cells is not reduced at high
temperature like conventional silicon cells. There is a trend towards larger installations of CPV.
Figure 9 : Future forcast for CPV capacity installations [21]
There is a high potential of the solar chimney to contribute to the global renewable electricity generation.
As there is a gradual shift from the lack of awareness and initiative towards this technology, growth in
technical inputs and advancements in solar chimney designs is on the rise . New designs like Floating
solar chimney proposed by Jorge Scheach, sloped solar updraft power plant that optimises collector
slope, counter rotating turbines for better efficiencies etc are springing forth [20]. Also, it is undisputable

11. that the SCPP will directly affect the economy as will create more jobs compared to other solar
technologies. This is so because, SCPP is labor intensive for construction [10].
The table 9 shows the cost of production of electricity in terms of the investment per MWh. It is seen
that, in comaprison to CSP, PV technology,(and with fossil fuels), SCPP have smaller capital
expenditure per MWh/year. This estimation makes it a competitive option for solar energy generation
in the future.
Table 9 : Production cost of MWh and Investment cost [19]
Method of Electricity Generation MWh Direct
production cost
in Euro
Investment in EURO
per produced
MWh/year
Mode of operation
and capacity
Concentrating Solar CSP 180 2000 Continuous with
thermal storage 30%
Solar Updraft Tower (Concrete
Solar Chimney)
155 ~2000 Continuous ~ 50%
Float Updraft Tower Less than 60 Less than 50 Continuous ~ 50%
Photovoltaic PV 280 3000 Intermittent 15-17%
The float Updraft Tower is seen to have a favourable cost of MWh production,even compared to the
solar updraft tower. This is because it optimises the cost of construction, as there is no expenditure
incurred on using concrete in building the chimney.
4. CONCLUSION
This purpose of this paper is to present an analysis of Solar energy technologies; Photovoltaic,
Concentrated Solar Power,Solar Chimney in terms of their impact in energy production. Comparative
analysis is also made asto make forcastinto what the future holds for these technologies. With continual
growth in energy demands in the world, the ability of renewable energy to compete with conventional
fossil fuels is key in energy analysis. Relatively newsolar technologies that are still in their experimental
stages or not yet commercialised like solar downdraft, Linear Fresnel are not detailed in this paper, as
sufficient data is not available for making concrete future renewable projections .
The CSP technologies though late on commercialisation behind the PV technology is cyrrently gaining
grounds in R & D and in capacity installations. The lowering cost of PV makes it a competitive
technology in the energy market. An hybrid system of PV-CSP will further scale-up its growing trend.
Solar Chimney power plants are an interesting alternative for electricity generation because of the
simplicity in its technical operations. Also, it an option for countries with lack of sophisticated technical
infrastructures as local materials can be employed in the construction of SCPP.

12. İt is worthwhile to mention that favourable policy acts are vital to the growth of solar energy
technologies in the world.
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