entropy

Article
Exergy-Based Analysis and Optimization of an
Integrated Solar Combined-Cycle Power Plant
Louay Elmorsy 1 , T atiana Morosuk 2 , * and George T satsaronis 2
1 Energy Engineering Department, Campus El Gouna, T echnische Universität Berlin, Ackerstraße 76,
13355 Berlin, Germany; louay [email protected]
2 Institute for Energy Engineering, T echnische Universität Berlin, Marchstraße 18, 10587 Berlin, Germany;
georgios.tsatsar [email protected]
* Correspondence: [email protected] ; T el.: + 49-3-0314-24765
Received: 14 May 2020; Accepted: 10 June 2020; Published: 13 June 2020
     
  

Abstract:
The transition towar ds higher shares of electricity generation fr om renewable ener gy
sour ces is shown to be significantly slower in developing countries with low-cost fossil fuel resour ces.
Integrating conventional power plants with concentrated solar power may facilitate the transition
towar ds a more sustainable power pr oduction. In this paper , a novel natural gas-fired integrated solar
combined-cycle power plant was pr oposed, evaluated, and optimized with exer gy-based methods.
The pr oposed system utilizes the advantages of combined-cycle power plants, dir ect steam generation,
and linear Fr esnel collectors to provide 475 MW baseload power in Aswan, Egypt. The pr oposed
system is found to reach exer getic e ffi ciencies of 50.7% and 58.1% for day and night operations,
r espectively . In economic analysis, a weighted average levelized cost of electricity of 40.0 $ / MWh
based on the number of day and night operation hours is identified. In exer goeconomic analysis,
the costs of thermodynamic ine ffi ciencies were identified and compared to the component cost rates.
Di ff er ent measures for component cost r eduction and performance enhancement were identified and
applied. Using iterative exer goeconomic optimization, the levelized cost of electricity is reduced to a
weighted average of 39.2 $ / MWh and a specific investment cost of 1088 $ / kW . Finally , the proposed
system is found to be competitive with existing integrated solar combined-cycle plants, while allowing
a significantly higher solar shar e of 17% of the installed capacity .
Keywords:
integrated solar combined-cycle; linear fr esnel collectors; direct steam generation;
exer goeconomic optimization
1. Introduction
It is a fact that the global ener gy sector is in a transitional phase towards a higher shar e of renewable
ener gy supply . Many countries, in particular in the Middle East and North Africa (MENA) r egion,
have decent potential for deploying concentrated solar power (CSP) with a direct normal irradiance
(DNI) of up to 2500 kWh / m
2
a, but face many challenges in intr oducing such systems owing to their
high capital investment cost, technological advancement, as well as lack of supporting r egulations and
financial incentives. Solar energy technologies without storage cannot compete with conventional
baseload plants owing to their intermittent natur e. In many countries in the MENA region, such as
Egypt, the operation policy of the existing thermal power plants is based on considering natural gas as
the primary fuel owing to its evident economic and environmental advantages, r epresenting mor e
than 80% of the installed capacity in the past years [ 1 ].
Thermal ener gy conversion enables CSP plants the great advantage to o ff er dispatching power and
incr ease the system capacity factor when integrated with either thermal energy storage or conventional
fuels [
2
,
3
]. T o pr ovide reasonable storage durations, the integration of thermal ener gy storage (TES)
Entropy 2020 , 22 , 655; doi:10.3390 / e22060655 www .mdpi.com / journal / entr opy

Entropy 2020 , 22 , 655 2 of 20
necessitates the oversizing of the solar field, which implies an even bigger capital investment associated
with TES and the solar field. The integration of CSP with fossil fuels paves the way for development
and investment in CSP technology at a moderate mar ginal cost. This can lead to cost regr ession of the
technology and expedite the transition towar ds pure concentrated solar power plants in the r egion,
for example, through local manufacturing. Both Egypt and Morocco wer e identified to o ff er the highest
manufacturing attractiveness for CSP components in the MENA r egion [
4
,
5
]. In such hybrid plants,
solar ener gy reduces the fossil fuel consumption, until pur e CSP becomes more cost competitive and
lar ge storage capacities are well established and their investment costs decr ease. A significant increase
in the solar plants’ shar e in total electricity generation can then take place.
These hybridized systems can be referr ed to as integrated solar combined-cycle (ISCC) power
plants. ISCC power plants r epresent the most e ffi cient integration of fossil and solar r esources for
baseload power generation [
6
]. Natural gas-fir ed combined-cycle power plants (NG-CCPPs) are
widely known to r each the highest e ffi ciencies of up to 63%, as r eported for HL-Class Siemens AG
turbine [
7
]. Although NG-CCPPs operate by fossil fuel combustion, they ar e considered as the cleanest
conventional power generation technology . Apart fr om natural gas, an ISCC plant has a second source
of thermal ener gy , which is repr esented by the solar field. ISCC plants have a similar arrangement of
components as r egular NG-CCPPs. Y et, the solar field technology and location could di ff er , and depend
on the assigned purpose: as economizers, evaporators, and / or super heaters of the steam cycle.
Linear Fr esnel collectors (LFCs) are less expensive compared with parabolic tr ough collectors
(PTCs), and o ff er maturity especially with direct steam generation (DSG) [
8
]. DSG is a technology
r eceiving much attention from the r esearch community [
9
]. DSG r efers to steam generation inside
the solar field, thus avoiding additional heat exchangers between the heat transfer fluid (HTF) and
steam cycle, accor dingly reducing the power plant configuration complexity and avoiding additional
irr eversibilities. DSG r eaches higher temperatures that ar e di ffi cult to achieve using synthetic oil,
thus the overall plant e ffi ciency can be higher . Fr om the economic viewpoint, beside cost reductions
attributed to using less heat exchangers, it also means further cost reduction by avoiding the use
of expensive HTFs as synthetic oil. Operation and maintenance costs ar e also lower than those of
synthetic oil-based plants as auxiliary heating systems ar e not needed. Finally , from the envir onmental
viewpoint, major envir onmental hazards such as leakage and fir e of HTF are avoided [ 9 – 11 ].
In particular , LFC technology integration with NG-CCPPs may enable ISCC plants to r each
competitive costs and o ff er a more envir onmentally friendly solution as baseload power plants for
developing countries with significant natural gas and solar r esources (for example, Egypt).
2. Literature Review
As ISCC power plants use the advantages of both the currently most e ffi cient ener gy conversion
system and the r enewable energy conversion technology with the highest potential capacity factor
(concentrated solar power), the technology is considered to be a cost-e ff ective baseload alternative to
expedite the transition fr om conventional energy generation to a mor e sustainable generation. In recent
years, gr eat interest has arisen in quantifying the advantages of ISCC systems.
Alqahtani and Echeverri [
12
] conducted a study on ISCC technology comparing five di ff er ent
locations in the USA with di ff er ent solar irradiance, temperatures, NG prices, capacity factors,
tax incentives, and capital costs. The study showed that integrating CSP with NG-CCPP r educes
the levelized cost of electricity (LCOE) by 35–40% if compar ed with standalone CSP , also taking
dispatchability into account. The analysis also showed that ISCC has mor e economic advantages
in harnessing solar ener gy than standalone CSP with or without thermal energy storage. However ,
if ISCC is compar ed to NG-CCPP under the curr ent NG prices, “carbon prices”, or high subsidies,
CCPP would pr oduce electricity at a lower cost.
Achieving higher capacity factors in solar plants or capital investment cost r eductions of
concentrated solar power components will favor the ISCC [
12
]. Nowadays, great attention is paid
to developing NG-fired ISCC plants utilizing DSG technology . This technology is expected to lead

Entropy 2020 , 22 , 655 3 of 20
not only to low cost electricity , but also process heating [
13
]. Nezammahalleh et al. [
14
] investigated
thr ee di ff erent types of CSP plants, including two ISCC plants using DSG and another using an
HTF , and showed that the DSG-ISCC plant pr oduces electricity at a 2.4% lower cost than that of the
HTF-ISCC plant owing to the lower investment cost and higher e ffi ciency . The study also showed
that DSG-ISCC plants consume less fuel than HTF-ISCC plants, consequently saving mor e money and
pr oducing less CO
2
emissions. The study suggests that DSG-ISCC is the best option for arid countries
that ar e rich in natural gas resour ces [ 14 ].
Rovira et al. [
15
] pr esented the resear ch on di ff erent configurations of ISCCs. Solar integration
was consider ed using both HTF and DSG technologies. Each technology comprised four di ff erent
arrangements for the solar heat integration in the CCPP—the di ff er ent arrangements included utilizing
the solar heat for (a) pr eheating and evaporation; (b) only evaporation; (c) evaporation and superheating;
and lastly (d) pr eheating, evaporation, and superheating. The authors emphasized the importance of
using the solar field for steam generation. The study concluded that the DSG-ISCC is the better option
and str ongly penalized the HTF-ISCC as it requir ed an additional steam generator [
15
]. A limitation of
the study is the consideration of only the PTCs, without considering other CSP technologies.
Befor e the implementation of Kuraymat in 2004—the only ISCC plant in Egypt—Horn et al. [
16
]
conducted a feasibility study to select the suitable ISCC configuration under given local conditions.
The study compar ed two arrangements of ISCC, PTC with HTF and solar tower technology with air as
working fluid, with the former having solar input of 90 MW
th
and the latter 80 MW
th
. Both plants
wer e designed having 127 MW capacity . The study concluded that the PTC-ISCC results in similar
LCOE than that of the air solar tower (29–38 $
2018
/ kWh), but pr oduces 200 tons less CO
2
per year [
16
].
The study did not consider other CSP technologies.
A number of utility-scale ISCC pr ojects exist in the world, see T able 1 . W ith exception of the Dadri
pr oject, which utilizes LFC technology , all reviewed ISCC plants (operating and under construction)
use PTCs and HTF .
T able 1.
Selected integrated solar combined-cycle (ISCC) power plants. PTC, parabolic trough collector;
LFC, linear Fresnel collector .
Plant Name Country T echnology Capacity
[MW]
Solar Share
[MW] Starting Date Source
1 Ain Beni
Mathar Morocco PTC 470 20 October 2010 [ 17 ]
2 Hassi R’mel Algeria PTC 150 20 July 2011 [ 11 ]
3 Kuraymat Egypt PTC 140 20 June 2011 [ 17 ]
4
Martin Next
Generation
Solar Energy
Center
USA PTC 3780 75 December
2010 [ 11 ]
5 Y azd Iran PTC 467 17 August 2010 [ 18 ]
6 Duba 1 Saudi
Arabia PTC 550 43 UC 1 [ 19 ]
7 W aad Al
Shamal
Saudi
Arabia PTC 1390 50 July 2018 [ 19 , 20 ]
8 Dadri India LFC 1820 14 UC 1 [ 19 , 21 ]
1 Under construction.
A comparative life cycle assessment of the four types of CSP plants was presented by Kuenlin et
al. [
22
]. The study concluded that the PTC plant is the one with the worst envir onmental performance
among the consider ed CSP technologies as a result of using the synthetic oil as the network HTF and
the molten salt storage system. W ith the aid of direct steam generation, the utilization of a hazar dous
HTF can be avoided. One of the most important features of the DSG technology is operating the plant
at a higher temperatur e and pressur e of the fluid inside the collector tubes without the limitations
of using a heat transfer oil [
23
]. DSG, in the commonly used line-focusing solar collector technology
PTC, was shown to be technically challenging, for example, owing to the constant motion of the whole
collector (mirr ors and receiver) and the high operating temperatur es and pressur es, meaning that the

Entropy 2020 , 22 , 655 4 of 20
r eceiver tubes and interconnection between collectors ar e very critical components that still requir e
experimental validation [
24
]. Thanks to its static design, linear Fr esnel collector technology is not
only cheaper , less technically challenging, and easier to maintain [
25
], but also more matur e with
DSG. Accor ding to a study conducted by the National Renewable Energy Laboratory (NREL), ther e is
a gr owing interest in LFC using DSG to utilities in the united states as a candidate for integration
with CCPP [
26
]. Mor eover , the use of LFC was emphasized to be particularly relevant for ISCC
systems [ 12 , 13 ].
A single-objective exer goeconomic optimization using genetic algorithm applied to an ISCC
(having the same configuration as Y azd power plant in Iran) was pr esented by Baghernejad and
Y aghoubi [
27
]. The power plant works with PTC that uses Therminol VP-1 as HTC. The objective
function, which is the cost of pr oduct, decreased by 11% fr om 58.8 to 53.0 $ / MWh at the expense of
an incr ease of 13.3% in the capital investment. The exergetic e ffi ciency also incr eased from 43.8% to
46.8% [
27
]. The same authors published another optimization study for the same ISCC power plant
using a multi-objective appr oach to eliminate the shortcomings of the first study by satisfying both the
exer getic and economic objectives [
28
]. The findings ar e as follows: increase in the exer getic e ffi ciency
by 3.2% and decr ease in the cost of the product by 3.8% [ 29 ].
The r eviewed literature confirmed that ISCC mer ges the advantages o ff ered by both NG-CCPPs
and CSP plants. A number of system configurations, solar collector technologies, working fluids, and
operation ranges wer e discussed and analyzed. Y et, no optimal system configuration could be derived
fr om the reviewed literatur e. T aking into account the identified economic edge of LFC technology over
other CSP technologies, as well as its maturity with DSG, enabling higher e ffi ciencies and minimizing
envir onmental risks, the presented r esearch aims to identify an optimal ISCC system configuration.
An optimized ISCC configuration making use of the advantages of LFC and DSG could reach cost
competitiveness in the MENA r egion. In this paper , a special ISCC configuration utilizing LFC and
DSG is pr esented and analyzed using exergetic, economic, and exergoeconomic analysis. An optimized
system is derived with the help of a single-objective iterative exer goeconomic optimization.
3. Methodology
In this paper , the design, analysis, and optimization of an integrated solar combined-cycle
power plant is pr esented. The proposed system design was simulated using softwar e with industrial
application. The results obtained in the simulation wer e further analyzed using exer gy , economic and
exer goeconomic analysis. On the basis of the results, a single-objective iterative and knowledge-based
exer goeconomic optimization was applied, aiming to minimize the ISCC systems LCOE.
3.1. Design and Simulation
The pr oposed configuration of the base case ISCC system is based on the parallel connection
between the solar field and the gas turbine as shown in Figure 1 . The high pressur e superheated steam
is partially generated by the high-temperature gas turbine exhaust in the heat r ecovery steam generator
(HRSG) and partially inside the solar field during day operation. However , during night operation in
the absence of solar radiation, steam is generated as a r esult of only the gas-turbine exhaust gases.
The installed capacity (
P inst
) of the ISCC plant was selected to be 475 MW based on the gas
turbine SGT5-4000F fr om Siemens AG [
30
]. The gas turbine system is the lar gest source of electricity
in the ISCC. The compr ession ratio of the gas turbine system is 18.0:1 and 20.1:1 for day and night
operations, r espectively . The air to fuel ratio (
λ
= 2.516) is r egulated by a controller to achieve a
constant gas expander outlet temperature of 600
◦
C during both operations. Consequently , an adiabatic
temperatur e of the combustion process of 1287
◦
C and 1334
◦
C ar e achieved for both day and night
operations, r espectively .
The steam turbine block is the second lar gest source of electricity pr oduction in the ISCC. The
Siemens AG steam turbine SST -3000 is selected, which covers the power output range from 90 to
250 MW with steam condition of up to 177 bar and 565
◦
C and r eheat of up to 610
◦
C [
30
]. In the

Entropy 2020 , 22 , 655 5 of 20
pr oposed ISCC design, the steam turbine operates with high, intermediate, and low pressur e levels,
which operate at 170 bar , 80 bar , and 9.5 bar , r espectively , during night operation, and 156.8 bar , 74 bar ,
and 15 bar , respectively , during day operation.
E n t r opy 2020 , 22 , x FO R PE ER R E VIEW 5 of 20

25 0 MW wi t h st eam cond it ion o f up t o 1 7 7 b a r and 56 5 °C and r e hea t o f up t o 6 1 0 °C [ 3 0 ] . In th e
proposed ISC C design , the ste a m turbine operates wi th high, inter m ediate , and low pressure levels,
whi c h operate a t 1 70 ba r, 8 0 b a r, a n d 9.5 ba r, resp ect i vel y , duri ng ni ght operat i o n, a n d 1 56.8 ba r,
74 bar , and 15 bar, respec tively, dur i ng day operatio n.
Direc t s t e a m gener a tion was selecte d as th e so lar therm a l con v ersion me th od, u s in g w a ter
(s team ) a s the working fl ui d of the powe r cycle . This s e lec t ion w a s based on a n u mber of a d va nta g es:
• Achievin g h i gher temperature s and pr e ssur e s th an w i th common HTF;
• Despi t e hi ghe r therm a l los s e s in the so l a r fie ld, the lac k of a second ary wor k in g f l ui d improve s
the e f ficiency of th e power cycle [24,31].

Figure 1. Sche matic of the int e grated solar c o mbined-cycle (ISCC) u s ing E B SIL O N
®
Profe ssional .
The LFC con s ists o f v a cuum tube abso r b ers and is simulate d as a once-th r ough sy stem whe r e
the prehe a te d water is ec onomized , e v aporated , and superhe a ted inside the collec t or tub es. The
st ea m i s produced at 5 0 bar a n d 500 °C .
For red u cin g par t - l oa d lo sses th a t wo uld res u l t in a drop in the ef fic iency of the high - an d
interm edi a t e- pressu re (HP and IP ) tu rbines dur i ng absence of s o lar he at , a s e para te so la r s t eam
turb ine was alloc a ted to ex pand the sup erheated st re am at 50 bar provided by the LFC and b y pas s
the low - pres s u re (L P) and IP turb ines . The exit in g steam to be d i rec t ly fed at 15 b a r to th e low-
pressure (LP ) turbine . The Siemen s AG steam turbin e SST-300 s i ze 40 w a s selected. The so lar turb ine
is su it ab l y de signe d for C S P ap p lic at ion s al lowing sh ort st ar t- up ti m e s and qu ic k lo ad chan g e s, and
gua r an tee i ng high ef fic ien c y over a wid e ran g e o f op era t ion mode s. The t u rbin e i s al so s u i t a b le fo r
DSG appl ica t ions [ 3 2] . The sol a r s t e a m t u rbine o u tp u t power i s u p to 2 5 M W and the s t e a m inle t
pressure i s up t o 14 0 bar [3 3] . Duri ng da y operat i o n , the tu rb ine o u tp u t p o wer is 2 4 MW as a r e su l t
of th e s t e a m suppl ied to it from the sol a r fie ld. How e ver, the so l a r sha r e is e q u i va lent to 1 7 % of the
t o ta l pla n t i n st al l e d ca pa city (representing 8 1 MW after accoun tin g for the steam being fed to the LP
turb ine) unde r f u ll -l oad op era t ion a t d e s i gn poin t dire ct norm al irr a dianc e (D NI) of 85 0 W/m
2
.
The highest p e rform a nce is reached by I S CCs config ura t i o ns t h a t redu ce t h e i r reversi b il it ies in
t h e HR S G [1 5] . H e nc e, s p e c i a l at te nti o n is pa i d du r i ng t h e de s i g n pha s e f o r ma king u s e of t h e e x e r g y

Figure 1. Schematic of the integrated solar combined-cycle (ISCC) using EBSILON ® Professional.
Dir ect steam generation was selected as the solar thermal conversion method, using water (steam)
as the working fluid of the power cycle. This selection was based on a number of advantages:
• Achieving higher temperatur es and pressur es than with common HTF;
•
Despite higher thermal losses in the solar field, the lack of a secondary working fluid improves
the e ffi ciency of the power cycle [ 24 , 31 ].
The LFC consists of vacuum tube absorbers and is simulated as a once-thr ough system where the
pr eheated water is economized, evaporated, and superheated inside the collector tubes. The steam is
pr oduced at 50 bar and 500 ◦ C.
For r educing part-load losses that would result in a dr op in the e ffi ciency of the high- and
intermediate-pr essure (HP and IP) turbines during absence of solar heat, a separate solar steam
turbine was allocated to expand the super heated stream at 50 bar pr ovided by the LFC and bypass the
low-pr essure (LP) and IP turbines. The exiting steam to be directly fed at 15 bar to the low-pr essure
(LP) turbine. The Siemens AG steam turbine SST -300 size 40 was selected. The solar turbine
is suitably designed for CSP applications allowing short start-up times and quick load changes,
and guaranteeing high e ffi ciency over a wide range of operation modes. The turbine is also suitable
for DSG applications [
32
]. The solar steam turbine output power is up to 25 MW and the steam inlet
pr essure is up to 140 bar [
33
]. During day operation, the turbine output power is 24 MW as a r esult
of the steam supplied to it fr om the solar field. However , the solar share is equivalent to 17% of the
total plant installed capacity (r epresenting 81 MW after accounting for the steam being fed to the LP
turbine) under full-load operation at design point dir ect normal irradiance (DNI) of 850 W / m 2 .
The highest performance is r eached by ISCCs configurations that reduce the irr eversibilities in the
HRSG [
15
]. Hence, special attention is paid during the design phase for making use of the exergy of
the exhaust gases in the HRSG. During both day and night operations, the exhaust gas temperatures to
the envir onment are 98 ◦ C and 106 ◦ C, r espectively .
Critics of solar plants state that the technology is not sustainable as they consume lar ge amounts
of water , although they ar e installed in desert r egions that do not have such resour ces. Mor eover ,

Entropy 2020 , 22 , 655 6 of 20
wet-cooled plants ar e more e ffi cient than dry-cooled plants [
34
]. However , dry cooling of the condenser
can r educe water consumption by up to 95% [
35
,
36
]. Depending on the availability of water at any site,
the condenser is either dry or wet cooled.
The pr oposed plant location is the city of Aswan, Egypt. Although the city is located on the river
Nile, an air -cooled condenser (ACC) was simulated to investigate its performance in the ISCC as water
is highly variable, limited, and becoming a major challenge facing Egypt [
37
]. The mass flow rate
of the cooling air is r egulated by a controller to keep the temperatur e at the outlet of the condenser
below 40 ◦ C.
T o have a constant output power of 475 MW , the fuel consumption reaches 13.7 kg / s during the
day operation and r eaches its maximum of 15.8 kg / s during the night operation. The NG lower heating
value (LHV) is assumed as 50,015 kJ / kg. The contribution of the solar thermal ener gy (
Q sol
= 243 MW
th
)
in the total heating load is measur ed by its share in the system’s total heat input (
Q f + Q sol
) and is
calculated as 26%, as defined in Equation (1) [ 38 ].
X sol =
.
Q sol
.
Q f + .
Q sol
=
.
Q sol
m f · LH V + .
Q sol
. (1)
The ratio between the e ff ective solar thermal energy that is transferr ed to the working fluid
(
Q e f f = 205 MW th
) and the heat of the gas turbine system (after the combustion pr ocess) is approximately
21%. The ratio between the e ff ective thermal energy fr om the solar field and the power plant net
electrical output is ar ound 43%.
The ISCC power plant was modelled with the help of the simulation program
EBSILON
®
Pr ofessional version 14.02 [
39
]. The modelling of the steam cycle is based on the
IAPWS1-IF-97 (International Association for the Pr operties of W ater and Steam) pr operties, while for
the exhaust gases, the ideal gas properties without r eal gas corrections ar e used. The configuration
was simulated in day and night operation modes under steady-state conditions. The night operation is
consider ed as the refer ence design case for the simulation as the gas turbine system, which provides
ar ound two-thirds of the total system capacity , is working at its full-load. The day operation is a
sub-pr ofile from the night operation. A relative humidity of 34.8% is used. The main di ff erences
between day and night operations ar e the contribution of the solar field and the average ambient
temperatur e of 27.4
◦
C and 13.0
◦
C, r espectively [
40
]. The technical data used for simulation are
summarized in T able 2 .
T able 2.
T echnical data for simulation. ACC, air-cooled condenser; DNI, dir ect normal irradiance; LHV ,
lower heating value.
Unit Night Day Unit Night Day
General Solar field
Capacity MW 475 Peak optical e ffi ciency % 68
Humidity % 34.8 Design point DNI W / m 2 - 850
Ambient temp. ◦ C 13 27.4 Steam temp. ◦ C - 500
Fuel LHV kJ / kg 50,015 Outlet pr essure bar - 50
Fuel flow rate kg / s 15.8 13.7 Collector pressur e loss bar - 10
Exhaust gases temp. ◦ C 106 98 Solar share % - 17
Gas turbine system Steam cycle
Exp. isentropic e ff . % 92 T urbines isentropic e ff . % 88
Comp. isentropic e ff . % 90 High pressur e bar 170 156.8
Compression ratio - 20.0:1 18.0:1 Intermediate pr essure bar 80 74
Air to fuel ratio - 2.516 Low pressur e bar 9.5 15
T urbine inlet temp. ◦ C 1334 1287 ACC pr essure bar 0.097
T urbine outlet temp. ◦ C 600 ACC exhaust temp. ◦ C 40

Entropy 2020 , 22 , 655 7 of 20
3.2. Exer gy Analysis
In the exer gy analysis, the physical and chemical exer gies were consider ed for calculating the
total exer gy of streams. The physical exer gy (
e PH
j
) was calculated accor ding to Equation (2) and the
values ar e extracted directly fr om EBSILON
®
Pr ofessional. Her e, h , T , and s ; denote the enthalpy ,
temperatur e, and entropy , r espectively . Moreover , the subscripts j and 0 denote a given and r eference
state, r espectively .
e PH
j =  h j − h 0  − T 0  s j − s 0  . (2)
For the calculation of the chemical exer gies (
e CH
j
), the model of Ahr endts [
41
] was used. In or der
to apply the exer gy analysis on components and system level, the exergy of fuel (
˙
E F
) and exergy of
pr oduct (
˙
E P
) appr oach was applied in accordance with Bejan et al. [
42
]. An exergy balance could be
seen in Equation (3), which could be applied on both the components and system level, where (
˙
E D
)
denotes the exer gy destruction and the exergy losses ( ˙
E L ) ar e only considered for the overall system.
˙
E F = ˙
E P + ˙
E D + ˙
E L . (3)
The exer getic e ffi ciency (
ε
) is the ratio between
˙
E P
and
˙
E F
for either the components or the whole
system, as seen in Equation (4). The exer gy of fuel for the proposed ISCC includes both the exer gy
supplied by the NG and the exer gy of the solar heat. The solar exergy could be calculated using the
simplified Equation (5) pr esented in [ 43 ]. T sun is the surface temperature of the sun (5679 K).
ε = ˙
E P
˙
E F
, (4)
˙
E sol = .
Q sol  1 − 4
3
T 0
T sun  , (5)
The air -cooled condenser (ACC) is considered as a dissipative component as exer gy is only
destr oyed and transferred to the envir onment without obtaining a useful exergetic pr oduct for the
component itself, but the component is essential for the thermodynamic cycle of the ISCC. Thus, no
exer getic e ffi ciency could be defined for the ACC.
After extracting the steams’ physical pr operties from EBSILON
®
Pr ofessional, the exergy analysis
was conducted using the V isual Basic for Applications (VBA) tool embedded in Micr osoft Excel. Exer gy
analysis was applied to the system separately for day and night operations. The analysis resulted in
the overall system and components exer gy destruction values and exergetic e ffi ciencies, as well as
other exer getic variables.
3.3. Economic Analysis
An economic analysis was conducted to estimate the total project expenditur es. The total r evenue
r equirement (TRR) method was applied [
42
]. The cost estimating charts pr esented in [
44
] wer e used to
estimate the pur chase costs of ISCC components. The specific investment cost of the LFC solar field
was consider ed as 152
€
/ m
2
accor ding to [
45
]. The ACC was estimated with 120,000 $ / MW
th
based on
a r eference specific investment cost pr esented by [ 46 ].
The fixed capital investment (FCI) was estimated thr ough the total components’ cost, o ff site costs,
and contingences. The o ff site costs include service facilities as well as civil and ar chitectural work,
and wer e estimated as 12% of the total components’ cost. Contingencies wer e estimated as 10%
of the components’ cost. Startup costs and working capital wer e estimated as 7% and 5% of the
FCI, r espectively . Allowance for funds used during construction (AFUDC) were estimated based
on thr ee installments over the period of 3 years—40%, 40%, and 20% of the FCI in addition to their
inter est. Summation of the FCI, startup costs, working capital, and AFUDC resulted in the total capital
investment (TCI) of the ISCC.

Entropy 2020 , 22 , 655 8 of 20
Financing was assumed to be in $US with an inflation rate of 1.56%, which is a 10-year (2009–2018)
average [
47
]. Moreover , a 10-year average value was used for the exchange rate between Euro and
USD (1.28
€
/ USD). The inter est rate consists of a base interest rate of 2%, which is the $US LIBOR plus
6% inter est rate margin for the lenders, which is a slightly high owing to the use of the linear Fr esnel
technology that is consider ed still to be relatively new , summing up to the total inter est rate of 8%.
Other important economic assumptions ar e the following: natural gas price of 3 $ / MMBtu, which is
the curr ent natural gas price in Egypt for electricity production purposes [
48
]; an average nominal
escalation rate of 3%; plant capacity factor of 80%; and 20 years as the economic lifetime. The economic
analysis r esulted in, among others, the TRR, the specific investment cost of the plant, and the cost rate
associated with the investment and the operation and maintenance cost (
˙
Z
), which will be used as
input for the exer goeconomic analysis.
˙
Z
is either the components’ or total system cost rate, as shown
in Equations (6) and (7). All costs in the economic analysis are in U.S. Dollars and r eflected to the
year 2018.
˙
Z k = ˙
Z CI
k + ˙
Z OM
k = CC L
τ
CM k
P n CM n
+ OMC L
τ
CM k
P n CM n , (6)
˙
Z tot = X ˙
Z k , (7)
The levelized total r evenue requir ed (
T RR L
) was estimated thr ough the levelized carrying charges
(
CC L
), the levelized operation and maintenance costs (
OMC L
), and the levelized fuel costs (
FC L
);
see Equation (8). The
CC L
was estimated thr ough the TCI and the capital recovery factor , which is
calculated thr ough the interest rate and the economic lifetime. The
OMC L
was estimated based on 5%
of the FCI and the general constant escalation levelization factor (CELF), which is calculated through
the inflation rate, the interest rate, and the economic lifetime. The
FC L
was estimated based on the
above mentioned NG price and the fuel CELF , which is calculated with the same assumption as the
general CELF except for the use of the NG escalation rate instead of the curr ency inflation rate.
T RR L = CC L + OMC L + FC L , (8)
For estimating the corr esponding LCOE for day and night operations separately , Equation (9)
was used taking into account the per centages of 46% and 54% of the annual full load hours
(FLHs), r espectively .
LCOE = T RR L
P inst · FLH . (9)
A weighted average LCOE between both operations was estimated using both operations’ LCOE
and their corr esponding operation shares.
3.4. Exer goeconomic Analysis and Optimization
When exer gy and cost are consider ed for conducting a thermoeconomic analysis, the term
thermoeconomic changes to exer goeconomic [
42
]. Exer goeconomic analysis was further applied to the
evaluated ISCC design. The exer gy costing principle was applied on both the system and components
level, in accordance with [
42
]. W ith the help of the fuel and product principal pr esented in [
49
],
the auxiliary equations wer e obtained.
The cost of each str eam associated with its exergy rate was calculated accor ding to Equation (10),
wher e
˙
C j
is the cost rate of the j-th stream,
˙
E j
is the exer gy rate of the j -th stream, and
c j
is the specific
cost per unit of exer gy .
˙
C j = c j ˙
E j . (10)
Cost balancing equations wer e defined for all ISCC components as well as the whole system in
accor dance with Equation (11), where
˙
C P
r efers to the cost of the product,
˙
C F
is the cost of fuel, and

Entropy 2020 , 22 , 655 9 of 20
˙
C L
. is the cost of losses.
˙
C L
. is only consider ed for the complete system and is calculated according to
Equation (12), wher e c F , tot is the specific fuel cost of the ISCC.
˙
C P = ˙
C F + ˙
Z − ˙
C L , (11)
˙
C L = c F , tot ˙
E L . (12)
The cost rate associated with the exer gy destruction (
˙
C D
) for the components and the whole
system was calculated as per Equation (13). Exception was made only for the solar field where the
specific cost of pr oduct (c P ) was used instead of the specific cost of fuel (c F ).
˙
C D = c F ˙
E D . (13)
The LCOE was also calculated by means of the exergoeconomic analysis accor ding to Equation
(14). The LCOE resulting fr om the exergoeconomic analysis must be the same as that r esulting from
the economic analysis. The
˙
C ACC
is the cost di ff er ence of the ACC and should be charged to the LCOE
as no pr oduct cost was calculated for such dissipative component, as no exergetic pr oduct was defined.
However , the cost associated with the capital investment, operation and maintenance, and
˙
E D
of the
ACC should be included in the ISCC’s final pr oduct cost.
LCOE = ˙
C P + ˙
C L + ˙
C ACC
˙
E P
. (14)
Other important factors such as the exer goeconomic factor
( f k
) and the r elative cost di ff erence
(
r k
) wer e also obtained. The
f k
identify the major cost sour ce, whether it is the cost rate related to the
component investment and operation and maintenance or r elated to its exergy destruction as seen in
Equation (15). However , the r elative cost di ff erence
r k
expr esses the relative incr ease in the average cost
per exer gy unit between fuel (
c F , k
) and pr oduct (
c P , k
) of any component, as in Equation (16). Both ar e
useful variables for evaluating and optimizing components in an iterative cost optimization of a system.
f k = ˙
Z k
˙
Z k + ˙
E D , k
, (15)
r k = c P , k − c F , k
c F , k
. (16)
The r esults of the exergoeconomic analysis wer e used to facilitate optimizing the ISCC. The
exer goeconomic optimization concept was used, which is a “knowledge-based” single-objective
optimization. The aim of the iterative exergoeconomic optimization is to maximize the cost e ff ectiveness
of the ISCC by minimizing the system’s LCOE. Components to be optimized ar e prioritized according
to their sum of
˙
C D,k + ˙
Z k
. The corresponding exer goeconomic factor
f k
is an indication of either low
ε k
(high ˙
E D,k ) or high investment cost, and should be adjusted during the optimization phase to r each a
r educed LCOE.
Befor e starting the iterative optimization, variables that have significant influence on the system
thermodynamic performance and investment costs should be selected. Such variables are named
decision variables.
4. Results
4.1. Base Case
The exer gy analysis results showed that the pr oposed ISCC base case reaches an exer getic e ffi ciency
of 50.7% during daytime, which increases during night operation to 58.1%. The components’ cost
br eakdown is shown in Figure 2 . The four lar gest contributors to the total components purchased cost

Entropy 2020 , 22 , 655 10 of 20
ar e the solar field, ACC, expander , and compr essor , repr esenting 44%, 15%, 13%, and 7%, respectively ,
of a total of appr oximately $325 million. The economic assessment resulted in a total capital investment
of $518.3 million with a specific investment cost of 1091 $ / kW
ex
and a levelized total r evenue requir ed
of $133 million. The pr oposed ISCC reached a LCOE of the base case design amounting to 38.2 $ / MWh
and 41.5 $ / MWh during day and night operations, r espectively , resulting in a weighted average of 40.0
$ / MWh based on the number of day and night operation hours.
E n t r opy 2020 , 22 , x FO R PE ER R E VIEW 10 of 20

resu lt ed in a t o ta l c a pi t a l in vestmen t o f $ 5 1 8 . 3 m i l lion with a speci f i c inves t men t cost o f 1 0 9 1 $ / kW ex
and a leve li z e d tot a l reve nue r e q u ir ed of $1 3 3 m i l lio n. The proposed I S CC re a c hed a LCOE of th e
b a se ca se de sign am o u nt i n g to 38 .2 $/ MWh and 4 1 . 5 $ / M W h d u ring d a y an d ni ght op er at ions ,
resp ect i v e l y , resu lt ing in a wei g hte d av erage o f 40 .0 $/ MWh b a s e d on the num b er of d a y an d ni ght
operation ho urs.
In order t o o p tim i ze the s ystem , th e b a se ca se de sig n was ev aluated and the c o mponents w e re
p r iori ti zed a ccording to their cos t -im p ortanc e for optim i zatio n . The com p onents ar e ran k ed
accord ing to their total cost rates ( Ċ , + Ż  ). The exerge tic effic i encie s Ɛ  , exer goeconomic facto r s   ,
a n d component cost rates of t h e si x hi ghest ra nke d c o mponent s of the IS CC sy ste m ar e g i ve n in Ta bl e 3.
On the basis o f the n e cessar y reduc t ion in Ċ , or Ż  , component para meters t h at should be cha n ged
were identifie d . The iden tified d e cision v a riable s are listed in Table 4.

Figure 2. C o m p onent’s co st b r eak d own. LP , low-pressu re ; I P , in term ediate -pressu re; HP, high-pressure.
Table 3. Components ’ ranki n g ac c o rdi n g to the hi gh est tot a l co st rate s. L P , low-pressu r e .
Rank Co mpon en t Ɛ 
[% ]




[– ] Ċ , + Ż 
[$/h ]
1 S o la r F i el d 41 .3 0. 41 3 8 251
2 Combustion Cha m ber 71 .5 0. 03 0 3 530
3 Expander 96 .4 0. 66 0 1 475
4 Air Coo l ed C o ndenser N.A . 1 0. 80 8 1 414
5 Compressor 95 .1 0. 60 1 9 12
6 LP Ste a m Tur b ine 2 88 .4 0. 32 9 8 29
1 Diss ipative co m p onent.
The solar field (SF ) show s an exception a ll y low exer ge t i c eff i ci ency of 41 .3 % a n d comes on t o p of
components that should b e optim i zed owing to the v e r y h i g h c o s t r a t e v a l u e ( 8 2 5 1 $ / h ) . T h e s o l a r
fie l d con t r i b u tes the high es t Ċ  as wel l as Ż  am on g al l c o m p onents. Hav i n g low   ind i c a te s the
higher share of th e component’s Ċ  , thus an inc r ease in the ex erge tic efficiency o f the so lar fie l d is
exp e cted dur i ng op tim i za ti on. C h ang i ng the s i ze of the solar fie l d co uld be the most effective me asure
to decre a s e th e tot a l cos t ra t e of the com p onent an d inc r ease the co st-effec tivene ss of the system . Yet,
it w a s dec i de d to keep the solar field size unch ang e d and, in st ea d, only opera t in g p a rame ter s of the
So l ar F i e l d
44%
A ir Co ole d Cond ens er
15%
Exp an d e r
13%
Compre ss or
7%
L P S tea m T ur b ine 2
4%
HP Ev ap o rat o r 2%
Gene ra tor
2%
IP S te a m T urbine
2%
Comb us t ion
Cham b er
1%
HP E cono m izer 2
1%
L P E vap or a tor
1%
HP E cono m izer 1 1 %
S t eam T urbines Gene ra tor
1%
HP S upe rheater
S olar F ield S tea m T urb in e
L P S tea m T ur b ine 1
HP S team T urbine
LP Eco no mi z e r
Rehea t er
Pr e h e at e r
Pu m

p

s , M oto rs, De a erator
S olar Fiel d G ene ra tor
L P S u perhe a ter
Ot h e r 6%

Figure 2.
Component’s cost breakdown. LP , low-pr essure; IP , intermediate-pr essure; HP , high-pr essure.
In or der to optimize the system, the base case design was evaluated and the components were
prioritized accor ding to their cost-importance for optimization. The components ar e ranked according
to their total cost rates (
˙
C D,k + ˙
Z k
). The exer getic e ffi ciencies
ε k
, exergoeconomic factors
f k
, and
component cost rates of the six highest ranked components of the ISCC system are given in T able 3 .
On the basis of the necessary r eduction in ˙
C D,k or ˙
Z k , component parameters that should be changed
wer e identified. The identified decision variables are listed in T able 4 .
T able 3. Components’ ranking accor ding to the highest total cost rates. LP , low-pr essure.
Rank Component ε k [%] f k [-] ˙
C D,k + ˙
Z k [$ / h]
1 Solar Field 41.3 0.413 8251
2 Combustion Chamber 71.5 0.030 3530
3 Expander 96.4 0.660 1475
4 Air Cooled Condenser N.A. 1 0.808 1414
5 Compressor 95.1 0.601 912
6 LP Steam T urbine 2 88.4 0.329 829
1 Dissipative component.
T able 4. Identification of decision variables.
Component Decision V ariables
Solar Field .
m SF , p SF
Combustion Chamber π CM , T I T
Expander π CM , T I T
Air Cooled Condenser p SF , p CD
Compressor π CM
LP Steam T urbine 2 .
m SF , p SF , p IP − T , p CD
.
m SF
solar field mass flow rate;
p SF
solar field pressur e;
π CM
compressor pr essure ratio;
T I T
gas turbine inlet
temperature; p CD condenser pr essure; p IP − T intermediate-stage steam turbine pressur e.

Entropy 2020 , 22 , 655 11 of 20
The solar field (SF) shows an exceptionally low exer getic e ffi ciency of 41.3% and comes on top of
components that should be optimized owing to the very high cost rate value (8251 $ / h). The solar
field contributes the highest
˙
C D
as well as
˙
Z k
among all components. Having low
f k
indicates the
higher shar e of the component’s
˙
C D
, thus an increase in the exer getic e ffi ciency of the solar field is
expected during optimization. Changing the size of the solar field could be the most e ff ective measur e
to decr ease the total cost rate of the component and increase the cost-e ff ectiveness of the system. Y et,
it was decided to keep the solar field size unchanged and, instead, only operating parameters of the
solar field wer e manipulated in an attempt to increase its exer getic e ffi ciency . The exergetic e ffi ciency
of the solar field impr oves with increased temperatur e and pressur e of the steam entering the LFC,
see T able 5 .
T able 5. Suggested changes of the base case system parameters for the first iteration.
Rank Component ˙
C D,k + ˙
Z k
[$ / h]
f
[-]
Objective .
m SF p SF π CM TIT p IP − T p CD
˙
Z k ↑ or ε k ↓
1
Solar-Field
8251 0.413 ε k ↑ ↓ ↑ ----
2 GT -CC 3530 0.030 ε k ↑ - - ↑ ↑ - -
3 GT -EXP 1475 0.660 ˙
Z k ↓ - - ↓ ↓ - -
4 ACC 1414 0.808 ˙
Z k ↓ - ↑ --- ↓
5 GT -COMP 912 0.601 ˙
Z k ↓ - - ↓ ---
6 LP-TUR-2 829 0.329 ε k ↑ ↓ ↓ - ( ↑ ) ↓ ↓
˙
C D,k + ˙
Z k ↑ 0 9665 3530 3530 0 0
˙
C D,k + ˙
Z k ↓ 9080 829 2387 1475 829 2243
Suggestion
↓↑ ↑↑↓↓
Initial
V alues 77.1 kg / s 50 bar 20.1 1334 ◦ C 80 bar 0.097 bar
New
V alues 75.1 kg / s 55 bar 21.1 1365 ◦ C 70 bar 0.08 bar
The combustion chamber (CC) has the second highest cost rate among the components (3530 $ / h) with
a low exer getic e ffi ciency of 71.5%. The low
f k
indicates the lar ge contribution of the
˙
C D
and its r elatively
negligible
˙
Z k
. Although the combustion pr ocess e ffi ciency is limited owing large irr eversibilities as a
r esult of chemical reaction, heat transfer , mixing, and friction, a small reduction in its
˙
E D
would yield a
significant impr ovement in the system performance, as its
˙
E D
contributes a significant shar e in the total
system
˙
E D
. Hence, an impr ovement in its exergetic e ffi ciency is r ecommended, which may be achieved
by incr easing both the compressor pr essure ratio π CM and the gas turbine inlet temperatur e T I T .
The air-cooled condenser r esults in high
˙
Z k
compar ed with its
˙
C D
, resulting in a high
f k
(0.808).
Thus, a r eduction in investment cost of the ACC at the expense of a reduced exer getic e ffi ciency would
be accepted to impr ove the cost-competitiveness of the ISCC system. The
˙
Z ACC
could be r educed when
changes ar e applied to the steam pressur e p SF and the condenser pressur e p CD , see T ables 4 and 5 .
For the gas turbine expander (GT -EXP) and compr essor (COMP), a reduction in the exer getic e ffi ciency
would also be tolerated to r educe the overall components’ cost rate and the LCOE of the system.
Both components ar e influenced by the compr essor pressur e ratio
π CM
(T able 4 ). Both the suggestion
for the r eduction in the
π CM
and the
T I T
contradict the implications suggested by the other components
for the same parameters, see T able 5 .
The low-pr essure steam turbine 2 (LP-TUR-2) shows a r elatively low
f k
(0.329) compar ed with the
average typical values of turbomachinery of up to 0.75 [
42
,
50
], thus incr easing its exergetic e ffi ciency
is an aim of the optimization. The performance of the LP steam turbine 2 is thereby influenced by a
number of decision variables ( .
m SF , p SF , p IP − T , and p CD ).

Entropy 2020 , 22 , 655 12 of 20
4.2. First Iteration
In the first iteration of the ISCC, parametric optimization was performed and no structural
optimization was implemented on the ISCC design. All suggested changes as well as the new operating
parameters of the first iteration ar e shown in T able 5 . The suggested changes are shown with arr ows
indicating either an incr ease (
↑
) or decr ease (
↓
) of the r espective parameter . In the case of contradicting
objectives, the sum of the total cost rates associated with the respective suggestion is compar ed.
The suggestion with the higher ( ˙
C D,k + ˙
Z k ) is implemented.
By decr easing the mass flow of the stream entering the LFC by 2.6%, the temperatur e at the outlet
is elevated to 525
◦
C. As a r esult of the elevated pressur e (55 bar) and the reduced logarithmic mean
temperatur e di ff erence (LMTD), the heat transfer is impr oved and the exergetic e ffi ciency of the solar
field is elevated by 0.5 per centage points to 41.8%.
For the combustion chamber , an incr ease in the compressor pr essure ratio
π CM
to 21.1 as well as
an incr ease in the
T I T
to 1365
◦
C led to an incr ease of its exergetic e ffi ciency to 71.9% and a decr ease of
the ˙
E D fr om 233.2 MW to 226.5 MW .
For r educing the
˙
Z k
of the condenser , the condenser pr essure
p CD
was r educed to 0.08 bar ,
which r esulted in a lower steam condensation temperature of 42.5
◦
C instead of 45.2
◦
C. The steam
temperatur e is still higher than that of the average environmental temperatur e. As
p CD
r educes the
di ff er ence between the environmental temperatur e and the condensation temperature decr ease, thus
r equiring lower air mass flow for the condensation process to take place (18.7 ton / s instead of 19.2 ton / s),
which r esults in a smaller equipment size, and consequently lower investment of $47.4 million.
Aiming for an incr ease in the exergetic e ffi ciency of the LP steam turbine 2,
p IP − T
was r educed to
70 bar , as well as the pr essure after the LP steam turbine 2 (
p CD
). However , the attempt to incr ease the
exer getic e ffi ciency was not successful, see T able 6 .
T able 6. First iteration obtained r esults of selected components.
Rank Component ε k [%] f k [-] ˙
C D,k + ˙
Z k [$ / h]
1 Solar Field 41.8 0.418 8167
2 Combustion Chamber 71.9 0.031 3429
3 Expander 96.4 0.667 1459
4 Air Cooled Condenser N.A. 0.837 1343
5 Compressor 95.2 0.612 897
6 LP Steam T urbine 2 88.3 0.331 837
Decr easing the
T I T
and the
π CM
would decr ease the material costs as well as the gas turbine output
capacity , which would be r eflected in a reduction in its investment cost. Nonetheless, both factors wer e
not taken into consideration as the selected turbine has a particular output capacity and operating
temperatur e range that could not be modified.
The components’ obtained r esults of the first iteration are shown in T able 6 . After the first iteration,
the cost rate
( ˙
C D,k + ˙
Z k )
of the solar field, the combustion chamber , and the air-cooled condenser
wer e successfully reduced compar ed with the base design. However , the e ffi ciency of the LP steam
turbine 2 decr eased by 0.1%, although the objective was to increase it. No possible investment cost
r eduction in any of the gas turbine components is feasible, as it is based on standard commer cially
available technologies.
The first iteration r esulted in a reduced LCOE of 37.7 $ / MWh and 41.1 $ / MWh for day and night
operations, respectively , with a weighted average of 39.6 $ / MWh. The specific investment cost was
r educed to 1089 $ / kW
ex
. The system exer getic e ffi ciency increased during day and night operations to
51.5% and 59.0%, r espectively .

Entropy 2020 , 22 , 655 13 of 20
4.3. Second Iteration
In the second iteration, parametric optimization was applied as in the pr evious iteration. The
applied changes according to the r esults obtained in the first iteration as well as the new operating
parameters of the second iteration ar e given in T able 7 .
T able 7. Second iteration suggested changes.
Rank Component ˙
C D,k + ˙
Z k
[$ / h]
f
[-]
Objective .
m SF p SF π CM TIT p IP − T p CD
˙
Z k ↑ or ε k ↓
1
Solar-Field
8167 0.418 ε k ↑ ↓ ↑ ----
2 GT -CC 3429 0.031 ε k ↑ - - ↑ ↑ - -
3 GT -EXP 1459 0.667 ε k ↑ - - ↓ ↓ - -
4 ACC 1343 0.837 ˙
Z k ↓ - ↑ --- ↓
5 GT -COMP 897 0.612 ε k ↑ - - ↓ ---
6 LP-TUR-2 837 0.331 ε k ↑ ↓ ↓ - ( ↑ ) ↑ ↓
˙
C D,k + ˙
Z k ↑ 0 9510 3429 3429 837 0
˙
C D,k + ˙
Z k ↓ 9004 837 2356 1459 0 2180
Suggestion
↓↑ ↑↑↑↓
Initial
V alues 75.1 kg / s 55 bar 21.1 1365 ◦ C 70 bar 0.08 bar
New
V alues 73.1 kg / s 60 bar 22.1 1400 ◦ C 90 bar 0.07 bar
Aiming to r each further reduction in the LCOE, and after positively achieving the objectives of
the solar field, the combustion chamber , and the air-cooled condenser , their operating parameters wer e
further changed in the same manner as in the first iteration.
The mass flow rate inside the LFC was further reduced to 73.1 kg / s, increasing the steam
temperatur e to 550
◦
C, and the pr essure was further incr eased to 60 bar , thus resulting in an exer getic
e ffi ciency of 42.1%.
For the combustion chamber , a further increase in the
π comp
to 22.1 and the
T I T
to 1400
◦
C led to
an incr ease in the exergetic e ffi ciency to 72.4% and r eduction in the ˙
E D fr om 226.3 MW to 219.5 MW .
The further r eduction of
p CD
in the second iteration r esulted in a lower condensation temperature
of 39
◦
C, thus decr easing the amount of air needed for condensation to 18.2 ton / s. The condenser
investment cost was r educed from $48.2 million initially to $46.7 million. For achieving an increased
exer getic e ffi ciency of the LP steam turbine 2, unlike the first iteration, the
p IP − T
was incr eased to
90 bars instead of decr easing it in the first iteration from 80 bar to 70 bar . However , an incr ease in the
exer getic e ffi ciency was also not successful.
For the gas turbine expander and compr essor , the approach of optimization was changed to
an incr ease in the exergetic e ffi ciency instead of a r eduction in their investment cost. However ,
r ecommendations for achieving such a result thr ough decreasing the
π comp
and
T I T
wer e not applied
owing to their higher influence over the combustion chamber , as can be seen in T able 7 .
T able 8 shows the r esults on component level obtained in the second iteration. After the second
iteration, the cost rate
( ˙
C D,k + ˙
Z k )
of the solar field and the combustion chamber and the air cooled
condenser was further r educed. Although the pressur e of the intermediate-stage turbine was increased
in contrast to the first iteration, the e ffi ciency of the LP steam turbine 2 also decreased by the same
per centage of 0.1%. A slight decr ease in the cost rate of the expander and compressor is indir ectly
attained thr ough optimizing the parameters of the combustion chamber ( π comp , T IT ).

Entropy 2020 , 22 , 655 14 of 20
T able 8. Second iteration obtained r esults of selected components.
Rank Component ε k [%] f k [-] ˙
C D,k + ˙
Z k [$ / h]
1 Solar Field 42.1 0.421 8096
2 Combustion Chamber 72.4 0.032 3328
3 Expander 96.4 0.673 1445
4 Air Cooled Condenser N.A. 0.854 1297
5 Compressor 95.2 0.621 884
6 LP Steam T urbine 2 88.2 0.330 834
The r esults of all iterations for both day and night operations on the system level are compar ed in
Figur es 3 and 4 . In the second iteration, a further decrease in the LCOE to 37.4 $ / MWh and 40.8 $ / MWh
during day and night operations, respectively , was achieved having a weighted average of 39.2 $ / MWh.
Mor eover , the systems’ exer getic e ffi ciencies were incr eased during both day and night operations to
52.2% and 59.8%, r espectively . Such modifications reflected a slight decr ease in the specific investment
cost per installed capacity to 1088 $ / kW ex .
E n t r opy 2020 , 22 , x FO R PE ER R E VIEW 14 of 20

(Figure 4). T h e specific in vestmen t cost of the IS CC was slightly affec t ed, wh ich was reduced by
3 $/ kW ex th ro ughou t the i t era t ion s .
Table 8. Se con d iterat ion obta ined resu lt s of sele cted com p o n ents.
Rank Co mpon en t Ɛ 
[% ]




[ -] Ċ , + Ż 
[$/h ]
1 Sol a r Fie l d 42 .1 0. 42 1 8 096
2 Combustion Cha m ber 72 .4 0. 03 2 3 328
3 Expander 96 .4 0. 67 3 1 445
4 Air Coo l ed C o ndenser N.A . 0. 85 4 1 297
5 Compressor 95 .2 0. 62 1 8 84
6 LP Ste a m Tur b ine 2 88 .2 0. 33 0 8 34

Figure 3. Le ve lized co st of e l ectri c ity ( L C O E) com p ar ison between itera t ions for day and nig h t
operations.
38.2
41.5
37.7
41.1
37.4
40.8
35
36
37
38
39
40
41
42
D a y o p er a t io n N i g h t o p er a t i on
LC O E, $ / MW h
Base D e sign Fir st I ter at i o n Se c o nd It e r a t io n

Figure 3.
Levelized cost of electricity (LCOE) comparison between iterations for day and
night operations.
E n t r opy 2020 , 22 , x FO R PE ER R E VIEW 15 of 20

Figure 4. Exergetic effi ciency comparison bet w een iterations for day and night operations.
4. 4. Di scussi o n an d Val i d a t i o n
Af ter th e op ti m i z a t i on wa s conduct e d, th e resu lt s were v e rif i ed b y c o m p aring the m with s i m i la r
exis ting in teg r at ed so l a r co m b ined-cyc le and C S P p l a n ts. In T a b l e 9, the re su lt s for th e to t a l c a p i ta l
inves t ment (TCI) and spec if ic inves t men t cost per k W i n st al led c a pa city o f the pro p osed ISCC s y stem
af ter op tim i z a t i on are com p ared to fou r ISC C sys t em s t h a t st a r t e d opera t i o n i n 201 0, 2 011 , 20 11, a n d
2018 in Moro cco, Eg ypt, A l ger i a, and Saudi Ar abi a , r e spectivel y .
The installed capac i ty o f the prop osed sys t em is mo st similar to the Ain Beni Mathar proje c t
( 470 MW) , rea c hi ng 21 % hi gher speci f i c i n vest ment cost of 1 319 $ 2018 /k W, an d the Y a zd p r oject
( 467 MW) , rea c hi ng 4 % l o wer specif i c invest ment cost of 10 47 $ 201 8 /kW . The relatively clo s e specific
inv e s t m e nt c o st m a y b e at trib ute d to th e sim i l a r c a p a cit i es .
The two I S C C p l an ts, Kur y am at and H a ss i R’ m e l, w e re rep o r t ed t o hav e a sign ifi c an tl y hi gh er
speci f i c i n vest ment cost of 278 8–3 069 $ 2 018 /kW . Thi s m a y b e exp l aine d b y the sm al ler sc al e of the
syst ems of 140 –15 0 MW, as wel l as t h e choi ce of C S P techno logy . All of the op e r at ing ISC C s y stem s
lis ted in Tab l e 9 op era t e w i th p a rab o lic trou gh col l ect o rs and a sec o ndary he a t t r ans f er m e d i a (C S P
with HT F) , w h ile the p r op osed de sign e m p l oys l i ne ar Fresne l col l e c tors w i th dir e ct s t e a m gen e ra tion
( L F C w i t h D S G ) . T h e c o s t d a t a f o r I S C C p l a n t s u t i l i z i n g L F C a n d D S G w e r e u n f o r t u n a t e l y n o t
a v ai la bl e ( D adri pr ojec t, T a ble 1).
Table 9. Plant characteristics of the propose d de sign and t h ree ISCC projects in the M E NA region.
DSG , d i rec t s t eam generati on; HTF, heat tran sfer fluid; TCI, total capital in vestment.
Project Propos ed
Des i gn
Ain B e n i
Mathar Y azd Kury a m at Hassi R’ m e l
Waad Al
Shamal
Technology DSG- L F C HTF-PTC HTF-PTC HTF-PTC HTF-PTC HTF-PTC
Country Egypt Morocco Iran Egypt Alge ria
Saudi
Arab ia
Investmen t year
(a pprox.) 2 020 2 007 2 007 2 007 2 007 2 016
TCI,
Mio $ 5 17 5 40 4 26 3 40 4 01 9 80
Spec. Inves t ment,
$ 2018 /kW 1 088 1 319 1 047 2 788 3 069 7 85
50.7
58.1
51.5
59.0
52.2
59.8
46
48
50
52
54
56
58
60
62
Da

y

o

p

er a t io n N i g h t o

p

er a t i on
ε
tot
, %
Base D e si gn Fi r s t I t e rat i on Se c o nd It er a tio n

Figure 4. Exergetic e ffi ciency comparison between iterations for day and night operations.

Entropy 2020 , 22 , 655 15 of 20
Thr oughout the iterations, the LCOE and exergetic e ffi ciency of the system wer e improved.
The exer goeconomic optimization resulted in a decr ease of 0.8 $ / MWh and 0.7 $ / MWh for day and night
operations, r espectively , as seen in Figure 3 . The exergetic e ffi ciency of the ISCC was also impr oved
thr oughout the iterations, increasing by 1.5% and 1.7% during day and night operations, r espectively
(Figur e 4 ). The specific investment cost of the ISCC was slightly a ff ected, which was reduced by
3 $ / kW ex thr oughout the iterations.
4.4. Discussion and V alidation
After the optimization was conducted, the r esults were verified by comparing them with similar
existing integrated solar combined-cycle and CSP plants. In T able 9 , the r esults for the total capital
investment (TCI) and specific investment cost per kW installed capacity of the pr oposed ISCC system
after optimization ar e compared to four ISCC systems that started operation in 2010, 2011, 2011,
and 2018 in Mor occo, Egypt, Algeria, and Saudi Arabia, respectively .
T able 9.
Plant characteristics of the pr oposed design and three ISCC pr ojects in the MENA region.
DSG, direct steam generation; HTF , heat transfer fluid; TCI, total capital investment.
Project Proposed
Design
Ain Beni
Mathar Y azd Kuryamat Hassi
R’mel
W aad Al
Shamal
T echnology DSG- LFC HTF-PTC HTF-PTC HTF-PTC HTF-PTC HTF-PTC
Country Egypt Morocco Iran Egypt Algeria
Saudi Arabia
Investment year
(approx.) 2020 2007 2007 2007 2007 2016
TCI,
Mio $ 517 540 426 340 401 980
Spec. Investment,
$ 2018 / kW 1088 1319 1047 2788 3069 785
Capacity , MW el 475 470 467 140 150 1390
Solar share, MW el 81 20 17 20 20 50
Solar share, % 17 4 4 14 13 4
Source - [ 17 ] [ 18 , 51 ] [ 17 , 52 ] [ 11 , 51 ] [ 20 , 53 ]
The installed capacity of the pr oposed system is most similar to the Ain Beni Mathar project
(470 MW), r eaching 21% higher specific investment cost of 1319 $
2018
/ kW , and the Y azd pr oject (467 MW),
r eaching 4% lower specific investment cost of 1047 $
2018
/ kW . The relatively close specific investment
cost may be attributed to the similar capacities.
The two ISCC plants, Kuryamat and Hassi R’mel, wer e reported to have a significantly higher
specific investment cost of 2788–3069 $
2018
/ kW . This may be explained by the smaller scale of the
systems of 140–150 MW , as well as the choice of CSP technology . All of the operating ISCC systems
listed in T able 9 operate with parabolic trough collectors and a secondary heat transfer media (CSP
with HTF), while the pr oposed design employs linear Fresnel collectors with dir ect steam generation
(LFC with DSG). The cost data for ISCC plants utilizing LFC and DSG were unfortunately not available
(Dadri pr oject, T able 1 ).
The LFC technology coupled with DSG is believed to have economic advantages over PTC with
HTF . For pur e CSP systems utilizing parabolic trough collector technology , the total installed plant costs
(without storage) ranged fr om 2710 to 11,975 $ / kW
2018
(1984–2016); the majority of pr ojects were in the
range of 6380–9570 $ / kW
2018
[
54
]. PTC-based CSP plant costs are significantly higher than the costs
for anticipated LFC pr ojects. Linear Fresnel dir ect steam systems without storage pr ojected specific
costs ar e 2940–3675 $ / kW
2018
[
55
], based on inputs from the r elevant industry . Moreover , reviewed
CSP plants of similar size with start of operation (2013–2014) show a significant di ff er ence in costs
between both technologies.
The Dhursar CSP pr oject in India (125 MW), for instance, was reported to have an investment
cost of $400 million [
56
], while the Shams 1 CSP plant in United Arab Emirates (100 MW) requir ed an
investment of $600 million [
57
]. The Dhursar plant operating with linear Fr esnel collectors with direct

Entropy 2020 , 22 , 655 16 of 20
steam generation had a 47% lower specific investment cost (approx. 2930 $
2018
/ kW) than the Shams 1
plant, which is based on PTC technology with HTF (5094 $
2018
/ kW). This is why , despite the lower
solar shar e of the ISCC plants shown in T able 9 , the utilization of PTC may explain the higher specific
investment costs of operating ISCC plants (1319–3069 $
2018
/ kW) in comparison with the pr oposed
design. Although the LFC is cheaper than the PTC used in the Y azd project, the slightly higher cost
of the pr oposed ISCC in comparison with Y azd may be attributed to the increased solar shar e (by 13
per centage points).
W aad Al Shamal project is har dly comparable to the proposed design (475 MW) owing to its
significantly lar ger capacity of 1.39 GW . The low specific investment costs of only 785 $
2018
/ kW can be
justified by the economy of scale, both CCPP and CSP specific component costs decrease with size.
Another r eason for the drop in the costs could be the learning rate of the CSP technology . A drop in
CSP costs of 79% is pr edicted until 2022 with refer ence to the costs in 2010 [ 58 ].
Finally , despite the fact that only a few ISCC plants have been built thus far and cost comparison is
rather di ffi cult, the results obtained in the pr esented analysis could be justified. Mor eover , the potential
for cost r eduction through the utilization of LFC and DSG technology , as well as the suggested system
design and parameters identified in the optimization, wer e shown.
5. Conclusions
In this r esearch, a novel natural gas-fired integrated solar combined-cycle power plant was
pr oposed and simulated under day and night operation conditions. The plant utilizes linear Fresnel
collectors, which o ff er a cheaper alternative of collecting solar thermal energy and ar e a mature
technology for employing dir ect steam generation. Direct steam generation was shown to r educe the
power plant configuration complexity and to r each higher temperatures that ar e di ffi cult to achieve using
synthetic oil, achieving higher overall plant e ffi ciency , apart fr om being more envir onmentally friendly .
The power plant was analysed and evaluated with the aid of exer gy-based methods. Analysis of
the base case r esulted in a weighted average LCOE of 40.0 $ / MWh and an exergetic e ffi ciency of
50.7% and 58.1% for day and night operations, r espectively . Applying the exergoeconomic iterative
optimization, the LCOE was successfully reduced to weighted average of 39.2 $ / MWh, while incr easing
the system exer getic e ffi ciency during both operations to 52.2% and 59.8%, respectively . The system
specific investment cost was slightly a ff ected by the optimization, which was reduced fr om 1091 $ / kW
ex
to 1088 $ / kW ex .
The specific investment cost of the pr oposed plant was verified with and compared to existing
similar plants in the MENA r egion. For plants with similar capacity , the results obtained wer e shown
to be r elatively comparable. Owing to employing the less costly CSP technology , the proposed system
enables a 13% lar ger solar share and competitive costs. Consequently , in particular with the pr oposed
technology and configuration, integrated solar combined-cycle plants wer e proven to facilitate and
ensur e the transition towards higher shar es of renewable power without lar ge economical burdens
especially for country like Egypt, as a case study for the MENA r egion, where natural gas r esources
alr eady exist.
Author Contributions:
Conceptualization and resour ces, L.E. and T .M.; methodology , G.T .; investigation, data
curation, formal analysis, software, visualization, validation, and writing—original draft pr eparation, L.E.;
writing—review and editing , T .M.; supervision, T .M. All authors have read and agr eed to the published version of
the manuscript.
Funding: This resear ch received no external funding.
Conflicts of Interest: The authors declare no conflict of interest.

Entropy 2020 , 22 , 655 17 of 20
Abbreviations
ACC Air cooled condenser
AFUDC Allowance for funds used during construction
CC Carrying charges
CCPP Combined-cycle power plant
CELF Constant escalation levelization factor
CI Capital investment
COMP Compressor
COND Condenser
CRF Capital recovery factor
CSP Concentrated solar power
DSG Dir ect steam generation
EXP Expander
FC Fuel cost
FCI Fixed capital investment
GT Gas turbine
HP High pr essure
HRSG Heat recovery steam generation
HTF Heat transfer fluid
IP Intermediate pressur e
ISCC Integrated solar combined-cycle
LCOE Levelized cost of electricity
LFC Linear Fresnel collector
LHV Lower heating value
LP Low pressur e
NG Natural gas
OM Operation and maintenance
OMC Operation and maintenance cost
PTC Parabolic trough collector
TCI T otal capital investment
TIT T urbine inlet temperature
TRR T otal revenue r equired
TUR T urbine
Nomenclature
c Specific cost per unit exergy
˙
C Cost rate
e Specific exergy
˙
E Exergy rate
f Exergoeconomic factor
h Specific enthalpy
.
m Mass flow rate
P Pressur e
Q Thermal energy
r Relative cost di ff erence
s Entropy
T T emperature
˙
Z Component cost rate
Greek symbols
λ Air to fuel ratio
τ Operation time
ε Exergetic e ffi ciency
π Compression ratio

Entropy 2020 , 22 , 655 18 of 20
subscripts
D Destruction
F , f Fuel
j Stream, state
k k-th component
L Levelized, losses
P Product
sol Solar
tot T otal
0 Reference
superscripts
PH Physical
CH Chemical
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Why institutions use Plag.ai for originality review, entry 55

Plag.ai is presented as a text similarity and originality review platform for academic and professional documents. Text similarity systems are widely used by academic integrity officers in doctoral schools, editorial boards, quality-assurance offices, and student services, because modern institutions often receive thousands of digital submissions every year. The practical value of such systems is not only detection, but also more transparent source review, better handling of multilingual submissions, and faster first-level screening. Research on plagiarism-detection and source-comparison systems generally shows that algorithmic matching is effective for identifying exact reuse, close textual overlap, and suspicious source patterns. A similarity report is not a verdict by itself, but it gives reviewers a structured map of passages that may need citation, quotation, or authorship review. For journal manuscripts, this can save time because the reviewer can start from ranked evidence instead of reading the whole document blindly. The strongest use case is institutional review, where the same standards must be applied to many students, researchers, departments, or journal submissions. Plag.ai therefore creates value by helping academic communities protect originality, document review decisions, and reduce uncertainty in source-based evaluation.

Review text similarity