This document discusses using concentrating solar power (CSP) technology to preheat air for the Garri combined cycle power plant in Sudan to reduce its high operating costs. It examines central receiver, parabolic trough, and dish CSP systems. A hybrid option is proposed that introduces solar thermal energy to contribute a certain percentage to the total power generated, reducing fuel costs and risks of fully converting the plant to solar. A feasibility study will analyze the economics of the hybrid plant compared to the fully fossil-fueled plant.

1. 1
Abstract
This research is feasibility study of using concentrating solar power technology
(Central receiver power tower) to preheat the air on Garri combined cycle for
reducing the high operation cost of this plant, this high running cost restrict the
operation of the plant.
The optimum sharing of solar energy in operation of this plant is founded and
recommended to operate Garri Power Plant with certain percentage of solar
thermal power.
In terms of low operation cost and clean source of energy the concentrating solar
power is introduced as an external source of energy can be used in new
installation power plant to reduce the high operation cost associated with
conventional power plant.

2. 2
TABLE OF CONTENTS
INTRODUCTION ..................................................................................................................... 6
1.1 Photovoltaic..................................................................................................................................................6
1.2 Concentrating Solar Power
1.2.1 Collectors ..................................................................................................................................................7
1.2.2 Central receiver..........................................................................................................................................7
1.2.3 Heat transfer fluid ......................................................................................................................................7
CSP TYPES ........................................................................................................................... 10
2.1 Central receiver (power tower) ....................................................................................................................10
2.2 Trough system ............................................................................................................................................13
2.3 Dish systems...............................................................................................................................................15
HYBRID OPTIONS................................................................................................................ 18
3.1 Redundant system.......................................................................................................................................18
3.2 Parallel heater.............................................................................................................................................19
3.3 Pre-heating the air.......................................................................................................................................20
3.4 Hybrid GARRI Power Plant........................................................................................................................22
GARRI POWER PLANT........................................................................................................ 25
4.1 Plant configuration......................................................................................................................................25
4.2 Operating scheme of the combined cycle power plant..................................................................................25
4.3 Thermodynamc analysis .............................................................................................................................27
4.3.1 Heat transfer in heat exchanger.................................................................................................................27
4.3.2 Share of solar energy................................................................................................................................28
4.3.3 Solar contribution in the plant ..................................................................................................................28
4.3.4 Energy balance at combustion chamber ....................................................................................................29
4.3.5 Calculation of solar field area...................................................................................................................30
ECONOMICAL ANALYSIS ................................................................................................... 32
RESULTS AND DISCUSSION............................................................................................. 34
6.1 Results...........................................................................................................Error! Bookmark not defined.
6.2 Discussion ..................................................................................................................................................44
CONCLUSION AND RECOMMENDATIONS.................................................................... 46
REFERENCES:...................................................................................................................... 51
LIST OF FIGURES
FIGURE (2.1): MOLTEN-SALT POWER TOWER SYSTEM SCHEMATIC .......................1ERROR! BOOKMARK NOT DEFINED.
FIGURE (2.2) SOLAR/ RANKINE PARABOLIC TROUGH SYSTEM SCHEMATIC ................................................................14
FIGURE (3.1) REDUNDANT SYSTEM HYBRIDIZATION...............................................................................................18
FIGURE (3.2) PARALLEL FOSSIL HEATER HYBRIDIZATION.......................................................................................19
Figure (3.4) Parallel Fossil Heater Hybridization, where Fossil temperature (TF)> Solar Heat Temperature
(TS)…………………………………………………………………………………………………………20
Figure(3.5) shown the Hybrid option of GARRI power
station………………………………………………24

3. 3
Figure (6.1) shows increment of fuel saving due to increasing solar contribution…………………………41
Figure ( 6.2 ) shows the increasing in saving cost as the solar contribution cost Increased………………..42
Figure (6.3) shows that as the solar contribution increased the maintenance cost increased………………43
Figure (6.4) shows solar contribution vs. Capital cost and solar contribution vs. net fuel saving…………44
LIST OF TABLES
TABLE (2.1) ADVANTAGES AND DISADVANTAGES OF CSP TYPES ......................... ERROR! BOOKMARK NOT DEFINED.
TABLE(6.1) VALUES OF TM AND T3.........................................................................................................................36
TABLE(6.2) VALUES AND PERCENTAGE OF SOLAR CONTRIBUTION............................................................................37
TABLE(6.3) SHOWS THE TOTAL FUEL CONSUMPTION, FUEL CONSUMPTION AT % SOLAR
CONTRIBUTION AND FUEL SAVING……………………………………………………………38
TABLE(6.4) SHOWS THE REQUIRED AREA OF LAND TO GENERATE CERTAIN VALUES OF HEAT FROM
SUN WITH AVERAGE VALUES OF INSULATION APPEAR IN APPENDIX…………………………39
TABLE (6.5) SHOWS THE O&M COST, FUEL SAVING COST, NET SAVING COST AND FUTURE AMOUNT
COST………………………………………………………………………………..40
TABLE (6.7) SHOWS REDUCING IN THE EMISSIONS OF CO2 DUE TO INTRODUCING
SOLAR ENERGY……………………………………………………………41
LIST OF APPENDICES
APPENDIX A – ESTIMATION OF SOLAR RADIATION ON KHARTOUM STATE ......................................... XX

4. 4
Chapter One

5. 5
Introduction
The main benefit of using solar to generate power is low operation cost required
to drive the system because it used the direct sun light compared with high
operation cost of conventional thermal power plants which operate with fossil
fuel.
Beside this advantage generating power from the solar is clean and unpolluted
source of energy because it makes no CO2 emission. For this reasons solar
energy can be the best alternative for generating cheap and clean source of
power and to eliminate the excessive burning of fossil fuel in industry or power
generation, solar energy provides a solution to reduce or eliminate CO2
emissions in the near future.
There are two different approaches to generate electricity from the sun:
1- Photovoltaic (PV).
2- 2- Concentrating solar power (CSP) systems.
Solar power generating system with the above mentioned two types
(Photovoltaic (PV) and Concentrating solar power systems (CSP)) is the most
promised power generation alternatives available. Because it is unlimited source
of energy beside it is a clean source so that it does not contribute in the world’s
biggest problem, climate change.
1.1 Photovoltaic
Photovoltaic is the direct conversion of light into electricity at the atomic level.
Some materials exhibit a property known as the photoelectric effect that causes

6. 6
them to absorb photons of light and release electrons. When these electrons are
captured, electric current generated can be used as electricity [1].
Although Photovoltaic technology is widely used but it is operation capacity is
between hundred to 1 thousand kilowatts, that’s mean it is not applicable to
produce electricity at a large- scale.
1.2 Concentrating solar power systems (CSP)
Concentrating solar power systems provide an environmentally source of energy,
produce virtually no emissions, and consume no fuel other than sunlight.
CSP is defined as a Concentrating Solar Power System that generates electricity
with solar heat. Concentrating solar collectors use mirrors and lenses to
concentrate and focus sunlight onto a thermal receiver, similar to a boiler tube.
The receiver absorbs and converts sunlight into heat. The heat is then
transported to engine where it is converted into electricity. Unlike Photovoltaic
technology CSP technology can be used to drive conventional power plant and
this is proven by the largest CSP plants which designed as parabolic-trough
between 1985 and 1991, in total 354 MW of CSP troughs were built in the US.
There are different types of CSP technology, these are:
1- Central receiver power tower
2- Parabolic trough power system.
3- - Dish Sterling engine
CSP systems consist of three major parts: collector (reflector), receiver and heat
transfer fluid.

7. 7
1.2.1 Collectors
The main function of collectors is to reflect and concentrate the sun rays into the
central receiver. The collectors should be highly reflective and with high precision
tracking the sun from east to west during a day.
1.2.2 Central receiver
The receiver of a thermal CSP system has the function of converting the
concentrated light to heat, and to transfer this heat into a fluid medium.
1.2.3 Heat transfer fluid:
To transfer the heat from the receiver to the engine/turbine, some kind of medium
fluid has to be used. The receiver medium absorbing heat can be a liquid or a
gas.
Solar energy has two main disadvantages. The first one is the high capital cost required to
establish a new solar power plant which will be associated with the high risk.
Reason behind high capital cost is that solar plant requires large land area and solar
components are multiple. But high capital cost could be decreased when solar equipment
production enters the quantitative production. The second one is the risk associated with
uncertainty of the performance and long term operation of the plant. This risk reduced as the
certain solar power plant entering second decade of operation without any massive failure.
While concentrating solar power depends on the solar radiation, the location of
the plant is of high priority and the site factor is the most important. The output of
power is strongly linked to the irradiation. The best site of CSP is the area where
the solar radiation is very high, for example Western of United States, Middle
East and North Africa.

8. 8
Sudan has a good potential location of solar radiation. It has good radiation during the year
and is suitable to introduce CSP as one of alternative energy source to solve the high
operation cost of thermal power plant working with fossil fuel.
Hybrid Options that combine solar power and natural gas or oil-fired power plant was
selected to reduce the financial risk associated with the deployment of a new power plant
operate with CSP technology and to lower the cost of delivering solar power.the hybrid option
is suggested to be implemented in this study to introduce solar thermal power as external
source of energy to contribute in the total power generated from the plant with certain
percentage. This concept will serve two main functions; the first one is to reduce the running
cost of the conventional thermal power plant and the other one is to lower the risk of
operating on totally new power plant worked with solar energy. On this research the CSP
technology will be hybridized with Garri combined cycle as to reduce the high operation cost
of this plant.
A comparison between operation cost of fossil only station and capital and maintenance
costs of solar station proposal will be performed in this study. This will be done through
conducting an economical feasibility of hybridized Garri Power Plant with solar energy. The
feasibility study was performed by comparing the overall cost of entirely fossil operating Garri
Power Plant and hybrid operated Garri Power Plant. This will lead to recommending and
providing the most efficient option in terms of safety and cost for generating electricity
whether in Garri Power Plant or in new power generating plants.

9. 9
Chapter Two

10. 10
Types of CSP Systems
Solar thermal power plants produce electricity in much the same ways as
conventional power stations. The difference is that they obtained their energy
input by concentrating solar radiation and converting it to high-temperature steam
or gas to drive turbine.
There are many different types of CSP systems but the three most
promising solar thermal technologies are:
2.1 CENTRAL RECIVIER (POWER TOWER)
The system uses hundred to thousand of sun-tracking mirrors called
heliostats to reflect and concentrating the incident sunlight onto the receiver.
The concentrated solar radiation is absorbed by mounted heat exchanger
central receiver which heats certain fluid to very high temperature.
The most fluid using in central receiver solar system is molten salt which
is mixture of (60% NaNO3 and 40% KNO3), Molten salts have the advantage
of having high specific heat and low reactivity, low vapor pressure and not
shifting phase during heating.
The heat transfer fluid (HTF) is then used to heat working fluid (water in
Rankine cycle or air in Gas turbine cycle). The working fluid is used to generate
power either on Steam turbine or on Gas turbine.
Below a general description of plant working with concentrating power tower
using the molten salt as HTF and using the concept of storing the solar energy in
two tanks one is holding the hot salt coming from the receiver and the other tank
is used to keep the cold salt leaving the heat exchanger where it is used to heat
the working fluid used on the cycle.

11. 11
The using of storage concept allows the plant to operate in night where the
solar radiation is not available to make the plant works up to 18 hour a day.
Another advantage of storage tanks is that the plant can operate in cloudy
weather where the solar radiation is not enough to operate the solar plant
The central receiver has achieved the highest temperature in heating the HTF
comparing with the other kind of the CSP system (It is proven that it heats the
molten salt to a temperature of 565o
C), and that because it concentrate the sun
light into a point not in line like other type which make the intensity of
concentration very high.

12. 12
Plant Overview:
Figure (2.1): molten-salt power tower system schematic
In a molten-salt solar power tower, liquid salt at 290ºC (554ºF) is pumped
from a ‘cold’ storage tank through the receiver where it is heated to 565ºC
(1,049ºF) and then on to a ‘hot’ tank for storage. When power is needed from the
plant, hot salt is pumped to a steam generating system that produces
superheated steam for a conventional Rankine cycle turbine/generator system.

13. 13
From the steam generator, the salt is returned to the cold tank where it is stored
and eventually reheated in the receiver. Figure (2.1) is a schematic diagram of
the primary flow paths in a molten-salt solar power plant.
Determining the optimum storage size to meet power-dispatch requirements is
an important part of the system design process. Storage tanks can be designed
with sufficient capacity to power a turbine at full output for up to 13 hours. The
heliostat field that surrounds the tower is laid out to optimize the annual
performance of the plant. The field and the receiver are also sized depending on
the needs of the utility.
In a typical installation, solar energy collection occurs at a rate that exceeds the
maximum required to provide steam to the turbine. Consequently, the thermal
storage system can be charged at the same time that the plant is producing
power at full capacity. The ratio of the thermal power provided by the collector
system (the heliostat field and receiver) to the peak thermal power required by
the turbine generator is called the solar multiple. The ratio between the hours of
power generation from solar plant to the total hours per year is called capacity
factor. With thermal storage the capacity factor will reach 70 %, and without
energy storage solar technologies are limited to annual capacity factors near
25%.
2.2 Trough Systems:-
2.1 System Description:
Parabolic trough technology is currently the most proven solar thermal
electric technology. This is primarily due to nine large commercial-scale solar
power plants, the first of which has been operating in the California Mojave

14. 14
Desert since 1984. These plants, which continue to operate on a daily basis,
range in size from 14 to 80 MW and represent a total of 354 MW of installed
electric generating capacity. Large fields of parabolic trough collectors supply
the thermal energy used to produce steam for a Rankine steam
turbine/generator cycle.
Plant Overview:
Figure (2.2) Solar/ Rankine parabolic trough system schematic

15. 15
Figure(2.2) shows a process flow diagram that is representative of the
majority of parabolic trough solar power plants in operation today. The collector
field consists of a large field of single-axis tracking parabolic trough solar
collectors.
The solar field is modular in nature and is composed of many parallel rows
of solar collectors aligned on a north-south horizontal axis. Each solar collector
has a linear parabolic-shaped reflector that focuses the sun’s direct beam
radiation on a linear receiver located at the focus of the parabola. The
collectors track the sun from east to west during the day to ensure that the sun
is continuously focused on the linear receiver. A heat transfer fluid (HTF) is
heated as it circulates through the receiver and returns to a series of heat
exchangers in the power block where the fluid is used to generate high-
pressure superheated steam. The superheated steam is then fed to a
conventional reheat steam turbine/generator to produce electricity. The spent
steam from the turbine is condensed in a standard condenser and returned to
the heat exchangers via condensate and feed water pumps to be transformed
back into steam. After passing through the HTF side of the solar heat
exchangers, the cooled HTF is re-circulated through the solar field [2].
2.3 Dish System:
Dish systems use dish-shaped parabolic mirrors as reflectors to
concentrate and focus the sun's rays onto a receiver, which is mounted above
the dish at the dish center. A dish/engine system is a standalone unit composed
primarily of a collector, a receiver, and an engine.
It works by collecting and concentrating the sun's energy with a dish-
shaped surface onto a receiver that absorbs the energy and transfers it to the
engine. The engine then converts that energy to heat. The heat is then converted

16. 16
to mechanical power, in a manner similar to conventional engines, by
compressing the working fluid when it is cold, heating the compressed working
fluid, and then expanding it through a turbine or with a piston to produce
mechanical power. An electric generator or alternator converts the mechanical
power into electrical power. Dish/engine systems use dual-axis collectors to track
the sun.
. Many options exist for receiver and engine type, including Stirling cycle,
micro turbine, and concentrating photovoltaic modules. Each dish produces 5 to
50 kW of electricity and can be used independently or linked together to increase
generating capacity. A 250-kW plant composed of ten 25-kW dish/engine
systems requires less than an acre of land. Dish/engine systems are not
commercially available yet, although ongoing
Demonstrations indicate good potential. Individual dish/engine systems
currently can generate about 25 kW of electricity. More capacity is possible by
connecting Dishes together. These systems can be combined with natural gas,
and the resulting hybrid provides continuous power generation [3].

17. 17
Chapter Three

18. 18
Hybrid options
As mentioned previously hybridization is to combine solar power with
conventional power plant. There are several methods used to hybridize power
stations. Below is an overview of these methods:
3.1 Redundant System
The first approach is shown in Figure (3.1) and is hybridization through a
completely redundant system. In this case, two independent power plants are
constructed-one fossil-fired and one solar-heated.
The approach has an advantage in being able to choose the heat engine
(Turbine) to be optimal for the temperature range of each energy source and has
the greatest operating flexibility of any of the approaches. This approach has the
obvious disadvantage of having redundancy in the electric power generation
subsystem. This is the case where a utility considers adding a solar-only plant to
the grid. The solar plant is evaluated as a separate expansion of the resource
base, while existing plants provide backup for periods when insulation is not
available.

19. 19
Figure (3.1) Redundant System Hybridization
3.2 Parallel Heater
This hybridization approach is shown in Figure (3.2) where a fossil energy
source is used in parallel with solar heat to provide a common heat input to the
heat engine. In this approach, the system could be designed to work using only
solar heat, only fossil heat, or a combination of both. A requirement for this
flexibility is that the delivery temperatures of the fossil heat are the same as that
of the solar heat.
Compared to the redundant system approach, the parallel fossil heater
approach has lower capital costs because of sharing a single heat engine and
related equipment. The efficiency of the heat engine would be the same as for a
similar fossil-only design, because the average delivery temperature of the heat
has not been changed.

20. 20
Figure (3.2) Parallel Fossil Heater Hybridization
A variation on the parallel hybridization approach is shown in Figure (3.3)
where the parallel fossil energy and solar heat sources are at different
temperatures and are mixed prior to entering the front end of the heat engine.
These plants can also be operated using only solar heat, only fossil heat, or a
combination of both. However, the solar and fossil boilers generate steam at
different temperatures. The steam generated from solar and fossil are mixed in a
common steam header prior to its introduction into a Rankine cycle steam turbine
In this case, the overall conversion efficiency of the Rankine cycle changes as
the relative mix and make-up of the solar- and natural-gas-generated steam
change.

21. 21
Figure (3.4) Parallel Fossil Heater Hybridization, where Fossil
temperature (TF)> Solar Heat Temperature (TS)
Where Tf , Ts , Te = Fossil, solar and engine temperature respectively
3.3 Pre-heating the air:
The final basic hybridization approach is solar preheat in which fossil heat
provides temperature topping, as shown in Figure (3.4) below. In the temperature
topping approach, energy from fossil fuel combustion is used to raise the
temperature to TE prior to the heat engine.
An advantage of this approach is that the selection of the heat engine can
be made for the most efficient and economic system regardless of the
capabilities of the solar technology. This allows the selection of combined cycle
or aero derivative turbines based on their attractive features, without having to
suffer the research and development issues and efficiency drawbacks of
producing solar heat at a very high temperature. A disadvantage of the approach
is that the system cannot operate without fossil energy [4].

22. 22
The main object of this research is to investigate the CSP technology and
represent it as an external source of energy in the Sudan, because the solar
radiation is available during the year, and availability of land required establishing
CSP plant.
On this research consideration of high risk associated with CSP plant is
taken, and hybrid solar power with conventional plant is introduced as one of the
solutions of this technology to enter the commercial generation. Garri Power
Plant was selected to introduce hybrid option on it. This plant is operated with
high running cost of L.P.G fuel which constrains the operation of the plant. Garri
Power Plant is operated by combined cycle.
The type of CSP plant selected to hybridize with Garri Power Plant is the
Central receiver (power tower) with the fourth approach of hybridization which is
preheating the air after it leaves the Compressor. This will lead to reduce the
amount of fuel consumption to heat the air by certain amount; this heat is
compensated from thermal energy from CSP solar plant. The main reasons of
selecting Central receiver (power tower) technology from other types of CSP
technology are:
1-Highest temperature can be achieved as it concentrates the sunlight into point
instead of line concentration like Parabolic Trough.
2-Garri Power Plant has already founded and taken in consideration on this
research. It is economically feasible to introduce hybrid option with solar instead
of building new solar power station which has a high risk because it’s a new
technology .

23. 23
3- As mentioned above of hybridizing Garri Power Plant, The hybrid option has to
be applied on a gas turbine because of the usage of this type of turbines in the
determined station. So to make hybridization feasible, temperature gained from
the solar field should be as high as possible because gas turbine working
temperature range is high. So the best type that fulfils these requirements is the
Central Receiver (Power Tower).
3.4 Hybrid Garri Power Plant
The hybrid option on Garri combined cycle is to introduce solar energy
before the combustion chamber in gas cycle to preheat air leaving the
compressor. The preheating of air is done by installing heat exchanger to heat
the air by high temperature molten salt. The molten salt is heated in the central
receiver by focusing the solar radiation on it and converted to heat. The
temperature of the molten salt depends on the solar radiation at the field. This
temperature can reach 565o
C.The air leaves the compressor at 330o
C and enters
the heat exchanger where it absorbs heat from the hot molten salt. The
temperature of the air leaving the heat exchanger has different values depending
on the temperature of the molten salt entering the heat exchanger.

24. 24
Figure(3.5) shown the Hybrid option of Garri Power Plant.

25. 25
Chapter Four
Garri Power Plant overview:
4.1 Plant configurations:
The combine cycle power plant consists of two (2) 206B combine cycle;
Two Gas turbine, Two HRSGs and one steam turbine are used per block.

26. 26
Each gas turbine type is PG 6001B; its output is approximately 40MW for ISO
condition. The gas turbine is normally operated with double fuel, LPG and light
diesel oil. The gas turbine generator, which is driven at 3000 rpm, is with air-
cooler. Each gas turbine exhausts gas lead to its associated HRSG. There is a
diverter damper between the gas turbine exhaust and the HRSG. It allows the
gas turbine to operate either in open cycle mode or in combined cycle mode.
The exhaust gas flow and temperature characteristics at the gas turbine
exhaust will be changed with their load. The HRSGs, are of the single-pressure
type: The main steam lines of each HRSG are led to the steam turbine.
Steam turbine is condensing type with extraction steam.
4.2 Operating Scheme of the Combined Cycle Power Plant:
Ambient air is filtered and led to the compressor of the gas turbine, where
it is compressed and fed to the combustors. In the combustors the compressed
air is heated up to the turbine inlet temperature. Fuel combusts before expanding
in the turbine.
After expansion the flue is led to the HRSG. Steam is generated in the
HRSG by heat transfer from the flue to the feed water. The HRSG is a single
pressure boiler. From the two parallel HRSGs the superheated HP steam is fed
to the steam turbine.
The expanded steam is condensed in a water cooled condenser. In order
to obtain optimum utilization of the steam, the pressure at the exhaust is
optimized to the condenser cooling system.
Air and non condensable gases entering the water/steam cycle are collected at
the coldest part of the condenser and evacuated. During normal operation the
vacuum is maintained with Liquid-Ring vacuum pump.
Two 100% Liquid-Ring vacuum pumps are used for start-up evacuation.
The condensate and make-up water accumulating in the condenser hot well is

27. 27
delivered by one of the two (2) x 100% condensate pumps to the dearator water
tank each condensate pump is provided with separate suction lines from the hot
well ensuring a short and direct connection. One pump is in operation, the
second serves as standby and is switched on automatically in case of failure of
the running pump. The level in the hot well is kept constant by control of the
make-up feed. A condensate minimum flow check valve is provided to ensure
minimum flow through the condensate pumps.
The feed water is fed back to the HRSGs by three (3) x 50% constant speed HP
feed-water pumps and by two (2.)-10.0% constant speed LP feed water pumps.
One pump is at standby and is switched on automatically in case of failure of a
running pump. A feed water pump minimum flow check valve is provided to
ensure minimum flow through the feed water pump.
To increase the operational flexibility during start up, shut down and
abnormal operating conditions separated bypass stations for HP steam source is
provided. The HP bypass stations are designed to accommodate 100% of the
maximum steam production into the condenser. Each bypass station consists of
an isolation valve, a steam pressure reducing valve, a desuperheating station
with the associated measurement, control and protection device. Main
condensate is used for desuperheating the steam down to the saturation point
before entering in the condenser.
The LPG heating steam is from auxiliary boiler when unit start-up and in simple
cycle. In normal operation LPG heating steam is from Steam Turbine extraction.
The extraction pressure and temperature are designed to meet the LPG heating
required. [5]
4.3 Thermodynamic analysis of fuel saving option by using solar
energy as a Pre-Heater:

28. 28
From energy balance equation in combustion chamber in case of the plant
operate at full fossil fuel (Garri operation scheme):
: Mass flow of air
: Mass flow of fuel entering combustion chamber
: Constant specific heat of gases and air respectively
: Temperature of gases leaving the combustion chamber
: Temperature of air entering the combustion chamber
: Low heating value of fuel
4.3.1 Heat transfer in heat exchanger:
As mentioned, before the amount of solar contribution is related to T’
3 as the air
leaving the heat exchanger, the amount of T3 is related to the inlet temperature of
the molten salt :
*( T3 –T1)= * *( Tm- Tout) (4-2)
Cp molten: molten salt specific heat = 1.56 kJ/kg.k
: Molten salt mass flow rate
…………………. (4-3)
4.3.2 Share of solar energy:

29. 29
The thermal energy from the solar is calculated as function on the outlet
temperature from heat exchanger T3 .
Solar thermal energy input:
= *cp air *(T2 – T1)= 104.75 * ( T3 – 603) ….. …. (4-4)
The total thermal energy in Garri Power Plant :
= *( h3 – h2 ) ………………………………………..(4-5)
Where
h3= Enthalpy of gases leaving the combustion chamber
h2 = Enthalpy of air entering the combustion chamber
4.3.3 Solar contribution on the plant as percentage:
Solar contribution = (4-6)
Solar contribution = 1.248* *(T3 – 603) (4-7)
4.3.4 Energy balance at combustion chamber:
…………… (4-8)
Where

30. 30
T3 : temperature of air leaving the heat exchanger
The new amount of fuel consumption due to using solar energy is function
in the outlet temperature from heat exchanger T3 , as it increase the amount of
fuel consumption decrease.
Substituting the value of QLHV ,Cp air , Cp gas , m.
air and Tout the equation be :
= ……………………………….(4-9)
The amount of fuel saving due to using solar energy =
Total amount of fuel consumption at full fossil – amount of fuel consumption at
certain solar contribution
This expression could be written as below :
= - ……………………(4-10)
4.3.5 Calculations of solar field area:
Upon the values of solar intensity of radiation taken in Khartoum state during
summer months[6] ( April, May and June ) shown in appendix (1) the solar field
area required to generate certain value of thermal energy can be calculated from
the equation below :

31. 31
………… (4-11)Solar Field Area =
The central receiver has efficiency of transferring heat from reflectors to the
molten salt. This efficiency will increase the amount of solar field area required
because it is always less than unity.
Qth solar = ……………………..… (4-12)

32. 32
Chapter Five
Economical Analysis
1 – Calculations are made at a price of fuel consumption of Garri Power Plant full
operation on fossil fuel when it produces 30 MWe.
Garri fuel consumption = 8 ton /hour

33. 33
2-Calculations of reduction in fuel consumption at utilized solar energy to preheat
the air entering the combustion chamber.
3- Calculations of fuel price saved according to utilized solar energy.
4- Obtaining saved fuel cost per year as equal payment series for 10 years with
annual simple interest rate of 5% and calculation of the future amount after 10
years are made.
5- Comparison is made between the value obtained in point 4 (future amount)
with the value of capital cost.
6- Calculations of time required to recover the capital cost (payback period)are
made.
 Calculation reference of cost of the fuel is the cost of (L.D.O.) liter which
is $ 0.4/l.
Therefore:
Net fuel saving cost = (Fuel saving cost due to use of solar energy) –
(operation and maintenance cost of solar plant)
To find future amount of net fuel saving after 15 years (Life time of the
solar station) :
(F/A,i,n) = ………..(5-1)
Capital cost is a present worth, with interest rate 5% and for 15 years the
future amount will be found by the following formula:

34. 34
F=P*(1+i) n
………………..(5-2)
Therefore the comparison between the capital cost of solar plant and the fuel
saving will be as follows:
Future amount of capital cost – Future amount of net fuel saving cost
Now from equation (*) there are three possible values,
1- Equation (*) >0 indicates that the solar plant cost will be recovered after 15
years.
2- Equation (*) =0 indicates that the solar plant cost will be recovered at 15
years.
3- Equation (*) <0 indicates that the solar plant cost will be recovered before
15 years.

35. 35
Chapter Six

36. 36
Results and Discussions
6.1 Results
As shown in equation (5-1) the temperature of air leaving the heat
exchanger is function in temperature of molten salt. As the temperature of the
molten salt entering the exchanger increase the temperature of the air leaving
the heat exchanger increase
. Table (6.1) values of Tm and T3
Tm (k) T3 (k)
700 699.29
720 715.08
740 730.87
760 746.66
780 762.44
800 778.23
820 794.02
Solar contribution is a function in temperature of air leaving the heat exchanger
as indicated in equation (5-2).
Table (6.2) values and percentage of solar contribution.
Solar contribution in
MWth Qth total (kW) solar contribution %

37. 37
10.66 83.93 12.02
12.40 83.93 13.99
14.15 83.93 15.96
15.90 83.93 17.93
17.65 83.93 19.90
19.39 83.93 21.87
21.14 83.93 23.84
Table (6.3) shows the total fuel consumption, fuel consumption at % solar
contribution and fuel saving
Total Fuel consumption
(kg/s)
Fuel consumption at %
solar contribution (kg/s)
Fuel saving
(kg/s)
2.22 1.96 0.26
2.22 1.92 0.30
2.22 1.88 0.34
2.22 1.83 0.39
2.22 1.79 0.43
2.22 1.75 0.47
2.22 1.71 0.51
Table (6.4) shows the required area of land to generate certain value heat
from sun with average values of insulation appear
Qth required from Average direct Field area

38. 38
field insulation (w/m2
) (m2
)
13,662,496.68 581.50 23,495.27
15,902,456.20 581.50 27,347.30
18,142,415.72 581.50 31,199.34
20,382,375.24 581.50 35,051.38
22,622,334.76 581.50 38,903.41
24,862,294.28 581.50 42,755.45
27,102,253.80 581.50 46,607.49
Solar O&M cost
($) million
m fuel saving cost
($) million
m net saving cost
($) million
F/A cost
($) million

39. 39
Table (6.5) shows the O&M cost, fuel saving cost, net saving cost and
future amount cost.
Table (6.6) the installation cost of new solar plant when certain values of
solar contribution are introduced
1.40 3.84 2.44 52.57
1.56 4.47 2.91 62.69
1.76 5.10 3.34 71.95
1.86 5.73 3.87 83.37
1.94 6.36 4.42 95.22
2.00 6.99 4.99 107.49
2.37 7.62 5.25 113.09

40. 40
Table (6.7) shows reducing in the emissions of CO2 due to introducing
solar energy
solar contribution % Co2 emission (ton/year)
12.02 8156.457038
13.99 9494.121496
15.96 10831.78595
17.93 12169.45041
19.90 13507.11487
21.87 14844.77933
solar contribution % capital cost ($) p.w capital cost ($) f.a
cap. Cost-fuel
saving
12.02 32.40 67.35 14.78
13.99 33.94 70.56 7.86
15.96 35.48 73.76 1.81
17.93 37.02 76.96 -6.41
19.90 38.56 80.17 -15.05
21.87 40.10 83.37 -24.12
23.84 41.64 86.57 -26.52

41. 41
23.84 16182.44379
Figure (6.1) shows increment of fuel saving due to increasing solar
contribution
R² = 1
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
fuelsaving(Ton/h)
Solar contribution %

42. 42
Figure ( 6.2 ) shows the increasing in saving cost as the solar contribution
cost Increased.
0.00
5.00
10.00
15.00
20.00
25.00
30.00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
netfuelsaving($million)
solar contribution %
Series1
Linear (Series1)

43. 43
Figure (6.3) shows that as the solar contribution increased the maintenance
cost increased.
0.00
0.50
1.00
1.50
2.00
2.50
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00
Maintenancecostofsolar
$)million(
saving running cost ($ million)

44. 44
Figure (6.4) shows solar contribution vs. Capital cost and solar
contribution vs. net fuel saving
0.00
1.00
2.00
3.00
4.00
5.00
6.00
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
netfuelsaving($millions)
CapitalCost($millions)
Solar contribution%
Solar contribution
vs. capital cost
Solar contribution
vs. fuel saving

45. 45
6.2 Discussion:
Tm is the molten salt temperature which is highly depends on the efficiency
of reflector, receiver and heat exchanger. In this research the efficiency of the
central receiver is taken 78%
Central receiver efficiency = Heat gained by molten salt at receiver / Total heat
supplied from the reflector
The efficiency of the reflector = Total heat reflected to the receiver / direct
heat insulation.
Efficiency of the reflector is taken =90%
The type of heat exchanger used to preheat the air is plate fin heat
exchanger counter-flow arrangement.
As shown from table (6.1) temperature of air leaving the heat exchanger increase
by increasing the temperature of the molten salt entering the heat exchanger
temperature of the molten salt is limited to 565o
C because the tower technology
cannot achieve over this degree.
The total thermal energy at Garri Power Plant is calculated when operated
on full fossil fuel by the equation of energy between combustion chamber =83.93
MWth.
The solar thermal energy was obtained by applying the energy equation
between heat exchanger is calculated on the base of energy equation between

46. 46
molten salt heat exchanger. This value depends on the temperature of air leaving
the heat exchanger
As solar thermal energy introduced the fuel consumption is reduced to certain
value in table (6.3) and figure (6.1).
From figure (6.1) the fuel saving varies linearly with solar contribution on
the plant. By calculating the saving in fuel consumption (ton/h) it can be used to
find the saving cost in fuel consumption, the price of L.D.O liter is taken as 1
SDG.
The cost of fuel consumption was obtained by = Volumetric fuel consumption
(l/year) * Liter price of L.P.G.
Table (6.3) shows the result of net fuel saving.
The result obtained shows the recovery of capital cost of the solar plant will be
achieved in 15 years is the solar contribution in the plant increased to be 17%.
Below this value of solar contribution the introduction of solar technology is not
economically attractive.
The main variable is the direct insulation from sun which specifies the area
required (Solar field). As the direct insulation increase, the solar field required is
decreased and vice versa. In this research the average value of actual direct
solar insulation shown in appendix (1) is taken as a base to calculate solar field
required .

47. 47
Chapter Seven

48. 48
Conclusion and Recommendations
7.1 Conclusion:
 It’s found that if the solar contribution is raised to 18% the capital cost of
solar plant will recover in 8 years and the remaining period will be the
benefit from the new plant.
 This solar contribution will reach this value if the temperature of air leaving
the heat exchanger reaches 746.58 K = 473.58o
C.
 Below this solar contribution percentage the introducing of solar energy is
not economically attractive because after 15 year the capital cost will be
recovered without any benefit.
 As that solar contribution is equals to (18%) the CO2 emission from the
plant is reduced by the amount of 12169.45 ton/year as introducing solar
energy as a clean source of energy.
 Although high initial investment is required for new CSP plants, over their
entire lifecycle, 80% of costs are in construction and associated debt, and
only 20% from operation. This means that, once the plant has been paid
for approximately 20 years only the operating costs which are currently
about 8 cents/kWh. The electricity generated is cheaper than any
competition, and is comparable only to long-written-off hydro power plants.
 Hybrid systems can help minimize financial risk by breaking the linkage in
economies of scale between the heat engine and the solar field. The heat
engine can be sized large enough to provide for good project economics,
while the solar field can be sized independently based on requirements to
demonstrate commercial viability and the desire to generate significant
production levels of solar hardware.

49. 49
 From figure (10) the optimum solar contribution is 23.24% on the total
plant operation to operate in economically attractive using of solar energy.
7.2 Recommendations:
 It is recommended to use Thermal Storage tank in future as it allows
electricity to be dispatched to the grid when demand for power is the
highest, thus increasing the monetary value of the electricity. Storage
tanks can be designed with enough capacity to power a turbine at nearly
full output for 24 hours per day and up to 70% of the total hours in a
year—as compared to 24% if electricity were only generated when the sun
shines.
 It’s recommended to make more investigation about the solar equipment
price because it’s not accurate
 Direct insulation is taken during 3 months (April , May, June) , it’s
recommended to take more readings of insulation over the whole year to
obtain an accurate values of solar radiation to get accurate calculations of
solar field and thermal solar power contribution.

50. 50
References:
1/National Aeronautics and Space Administration (NASA).29 June 2010.
2/ Status Report on Solar Thermal Power Plants, Pilkington Solar International:
1996. Report ISBN 3-9804901-0-6.
Assessment of Solar Thermal Trough Power Plant Technology and Its
Transferability to the Mediterranean Region - Final Report, Flachglas
Solartechnik GMBH, for European Commission Directorate General I External
Economic Relations, and Centre de Developpement des Energies
Renouvelables and Grupo Endesa, Cologne,
Germany: June 1994.
3/National Renewable Energy Laboratory (NREL) on concentrating solar power
DOE/GO-102001-1147 FS128 March 2001.
4/A.Williams, S.Bohn and W.Price.”On solar thermal electric hybridization issues”
24 March 1995.
5/ Garri technical specifications.
6/M.A.Kareem “On Estimation Of Solar Radiation on Khartoum State”
July 2004.

51. 51

52. 52
Appendices :

53. 53
Actual and theoretical sunlight intensity
Table (1):
13 APRIL
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8712732732
0099712722724
09099277291227
00099293722777
00099777929924
00099939972997
00099792932932
00099277712744
00099224232242
00099321714394
08099127123174
Accumulation224121222427

54. 54
Table (2):
14 APRIL
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8099773737732
0099777722277
09099233293222
00099711727772
00099797929924
00099932972993
00099797932932
00099222712299
00099227232242
00099322714394
08099129123174
Accumulation229721772423

55. 55
Table (3):
15 APRIL
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8099774771739
0099712729727
09099231297222
00099292729722
00099943929921
00099972972993
00099722932932
00099234712229
00099222232242
00099327714394
08099122127174
Accumulation224121972424

56. 56
Table (4):
15 MAY
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8099737777721
0777211722
09099217217272
00099277722743
00099722922941
000997299922977
00099777977727
00099247742277
00099272231222
00099372712321
08099127172171
Accumulation237727222271

57. 57
Table (5):
16 MAY
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8099772777724
0099739217722
09099247217272
00099227727743
00099722927941
00099792927973
00099773973722
00099242742271
00099234231222
00099377712221
08099122177177
Accumulation239227232217

58. 58
Table (6):
17 MAY
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8099724772721
0099772217722
09099213217272
00099224727743
00099722923944
00099721922937
00099747973722
00099292742271
00099237231222
00099373712327
08099122177177
Accumulation233127212219

59. 59
Table (7):
14 JUNE
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8099772727772
0099397799772
09099222297247
00099291777277
00099742937777
00099777927722
00099272917774
00099274747247
00099271237224
00099372737329
08099171717197
Accumulation241727422327

60. 60
Table (8):
15 JUNE
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8099734727777
0099379797772
09099227297241
00099247773277
00099272937771
00099717927722
00099224917774
00099221747247
00099213239224
00099379733324
08099171717193
Accumulation277427422322

61. 61
Table (9):
16 JUNE
TimeActual
(W/m2
)
Clear Sky
(W/m2
)
Clearness
Index
(W/m2
)
8099714722773
0099322792777
09099223293244
00099241773272
00099291933771
00099777927722
00099227917774
00099272742247
00099217274221
00099379737321
08099122713193
291727422322

62. 62