Heliostat Power Plant 2019-20

CHAPTER 1
Introduction
This seminar aims to give a global overview on the various solar towers that
are operating and under construction. First an outline of the Solar Tower (ST)
technology and the different components that make up a tower plant, namely, the
heliostats, receivers, Heat Transfer Fluid (HTF), and power cycles employed, is
discussed. A list of the available literature on the various operational plants is also
presented. This is followed by a brief description of existing ST plants (operational
and under construction) and a subsequent overall assessment of certain parameters of
the plants.

In the CSTEP report “Engineering Economic Policy Assessment of

Concentrated Solar Thermal Power Technologies for India” published in 2012, a brief
idea was given about the ST technology, its components, some brief assessment of
parameters for the existing plants worldwide as well as a techno-economic viability
study of ST technology in India. The present report is an extension to the review
portion of the aforementioned report after carrying out a more detailed study of
available literature and also updating the various data in the current (2014) scenario.
The receiver (which is located at the top of the tower) is one of the most crucial
components of a tower plant.

The type of receiver used will be the key to deciding many parameters which
are chosen while modelling a plant, for example, the type of heliostat field, its layout,
the heat transfer fluid to be used etc. Therefore, an assessment of existing power
plants is made depending upon the type of receiver being used. The gross costs of the
plants per MWe (of equivalent capacity) is discussed subsequently. The conclusion
discusses the challenges and opportunities with respect to this technology in the
Indian scenario. The global review on ST technology is carried out in this study to
provide a bench mark for the design studies under Indian conditions.

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CHAPTER 2
2.1 Litterateur Survey
Heliostat power pant is a nascent technology as compared to the parabolic
trough technology. The growth of the ST technology in the past decade has been
significant and is increasing enormously. In this section, the available literature on
existing ST plants and their characteristics is presented. Burgelata et al., 2011 have
given an overview of the Gem solar plant, the first commercial tower plant with
molten storage. The work describes the characteristics, construction, start up and
operation of the plant . Zunft et al., 2011 have done an experimental evaluation of the
storage subsystem and performance calculation of the Jülich Solar Power Tower.
They set up a test facility at the plant to monitor performance as well as the storage
subsystem of the plant. The results from the analysis carried out affirm that the plant
(including the storage system) is functioning to its full capacity. They also confirmed
that cycling can be done at high discharge rates of heat transfer accompanied by low
heat losses . Koli et al., 2009 have done an analysis of the Jülich Tower plant.

This seminar describes the mechanism of the plant with the aim of using it to
as a means to devise methods, mechanisms and procedures that will help in the
construction and operation of plants using similar technology in the future . Xu et al.,
2010 have performed the modelling and simulation of the 1 MW Dahan ST plant.
They discuss the generation of response curves for various solar irradiance changes
and have shown that the receiver outlet pressure and flow change moderately,
regardless of radiation changes. However, the receiver response is more rapid to outlet
temperature and power . Quero et al., 2013 have studied the operation experience of
the Solugas ST plant, which is the first solar hybrid gas turbine system developed at
the MW scale. They concluded that while the plant is operating satisfactorily in its
capacity, further modifications like incorporation of storage, turbine improvements
and receiver distribution can be incorporated . Tyner et al, 2013 have designed a
reference plant using eSolar’s modular, scalable molten salt power tower. They
proposed a thermal modular design for a plant using these heliostats after performing
a detailed risk assessment. Meduri et al., 2010 carried out the performance
characterization and operation of eSolar’s Sierra Suntower plant . Siva Reddy et al.,
2013 have done a review of the various state of the art solar thermal plants worldwide.
They have performed a comparative study of the parabolic trough, parabolic dish and
solar tower systems in terms of economic viability. They concluded that the parabolic
dish technology provides electricity at a lower cost per unit in comparison with the
other two technologies. Zhang et al., 2013 have performed a review of CSP
technologies and talks about the advantage of the power tower technology.They also
give a method to estimate the hourly beam radiation flux from available monthly

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CHAPTER 3
3. Heliostat power plant and its Components
Heliostat power plant which is also referred to as Central Receiver uses a large
number of heliostats, having dual axis control system (one about the vertical axis and
the other about the horizontal axis). These heliostats reflect the solar radiation
(impinging on their surface) to a stationary receiver located at the top of a tower. This
concentrated solar energy incident on the receiver is converted to thermal energy,
which is carried by the HTF passing through the receiver. The thermal energy of the
HTF is transferred to the working fluid of the power cycle, thereby generating
electricity. The advantage of ST is that a high geometrical concentration ratio ranging
from 200 to 1000 can be achieved. Consequently, temperatures of the order of 1000°C
can be reached with suitable HTFs.

The high temperature leads to an increase in the power cycle efficiency. As a

result of this, potentially, an overall solar to electric conversion efficiency of around
28% can be achieved. (1) Thermal energy storage and hybridisation can also be
incorporated similar to the parabolic trough case. Further, molten salt can be used
both as HTF and thermal storage medium. Given the potential of higher efficiency,
ST with molten salt/water/air as HTF has gained momentum in recent years.
However, there are a lot of variations in the design of heliostats, Global Review of
Solar Tower Technology receivers, HTF and also in the power block. Hence, a
common description for all the power plants is not possible. It must be pointed out
that many details of the components were not available in open literature. Green
technology is the future of this society. It's main goal is to find ways to produce
technology in ways that do not damage or deplete the Earth's natural resources.
In addition to not depleting natural resources, green technology is meant as an
alternative source of technology that reduces fossile fuels and demonstrates less
damage to human, animal, and plant health, as well as damage to the world, in
general.

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Next, green technology is so that products can be re- used and recycled. The
use of green technology (clean technology) is supposed to reduce the amount of waste
and pollution that is created during production and consumption. The most important
and urgent concern and want for green technology is for energy purposes. We need
better, more efficient was to produce energy without burning all the world's coal and
using all the world's fossil fuels and natural resources. These rippling mirrors are able
to track sunlight throughout the day and reflect it on to the tower where it is converted
into solar energy. The energy created at the plant is sufficient enough to power 6000
homes. The name of the site is PS10. There are few such CSP (Concentrated Solar
Power) sites in the world. The Proponents of CSP state that the technology has the
potential to generate energy for the entire United States

Figure 3: Heliostat Power Plant

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3.1 Heliostats

Heliostats are conventionally flat or slightly curved mirrors mounted on a

backup steel structure, which can be controlled or tracked about two axes, one
horizontal and other vertical, so as to tilt the heliostats to reflect the solar rays to a
fixed receiver on top of a tower. The aperture areas of the heliostats that have been
used in various plants vary considerably from 1 m2 to 120 m2, but all heliostats
within a plant have the same aperture area. Some developers (for example,use small
heliostats and claim that the advantages are mass production, easy handling &
installation, smaller wind loads because of size and proximity to ground. Heliostats of
1 m2 have a single flat mirror. However, if such small mirrors are used, the number of
heliostats and controllers will increase. Heliostats of 120 m2 area (2; 3) have 28
curved facets (seven rows & four columns). While using such large heliostats, each
facet has to be canted properly, so that the receiver could be made as small as possible
thereby increasing the concentration ratio. As a result of using large heliostats, the
number of heliostats and controls reduces. However, in these cases, the structure of
the heliostat has to withstand large wind loads and the control system has to be more
powerful. New concepts such as target aligned heliostats have also been explored.
These heliostats use a tracking mechanism and are mounted and aligned to the
receiver (target). This method can also be used to track asymmetrical heliostats.

Figure 3.1 Heliostat

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3.2 Receivers

The receiver is one of the most important parts of tower plants. There are two
types of receivers: tubular and volumetric. Tubular receivers are used for liquid HTF
such as water, molten salt, thermic oil, liquid sodium and Hitec salt, and volumetric
receivers use air or supercritical CO2 as HTF. The type of receiver depends on the
type of HTF and power cycle (Rankine or Brayton) used in the system. A brief
description of the receivers is discussed in the following section.

Figure 3.2 Receivers

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3.2.1 Tubular Receivers

In tubular receivers, the HTF passes through a number of vertical tubes and gets
heated by the radiant flux reflected from the heliostats. There are two types of tubular
receivers: External cylindrical receivers and cavity receivers.

 External Cylindrical Receivers

In external cylindrical receivers vertical tubes are arranged side by side, in a
cylindrical fashion and the radiant flux from the heliostats impinges from all
directions. This is shown in Figure Since the receiver is exposed to atmosphere; it is
subjected to higher convection losses.

Figure 3.2.1 (a): External Cylindrical Receiver used in Crescent Dunes Power
Tower

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 Cavity Receivers
The cavity receiver consists of welded tubes kept inside a cavity in order to
reduce convection losses. The heliostat field is arranged within the range of possible
incident angles onto the receiver. Cavity receiver can be either be a single or dual
cavity type. A single cavity receiver will have solar field on one side of the receiver
while the dual cavity receivers will have solar field on either sides of the receiver.
Figure 3 and show the single cavity receiver and dual cavity used in the PS 10 and
Sierra sun tower plants respectively. Global Review of Solar Tower Technology

Figure 3.2.1 (b): Cavity Receiver used in PS-10

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3.2.2 Volumetric Receivers

Receivers which use air as HTF are made of porous wire mesh or metallic/ceramic
foams. The solar radiation impinging on the volumetric receivers is absorbed by the
whole receiver. Volumetric receivers are of two types: open volumetric and
closed/pressurised volumetric. Figure 5 and Figure 6 give a schematic representation
of them.

 Open Volumetric Receivers

In open volumetric receivers, ambient air is sucked through the porous receiver
where air gets heated up by concentrated solar energy. The outer surface of the
receiver will have a lower temperature than inside the receiver because the incoming
air from the ambient cools the surface and avoids damage to the material. Jülich tower
plant uses a porous silicon carbide absorber module as receiver. The air gets heated up
to about 700°C and is used to generate steam at 485°C, 27 bar in the boiler to run the
turbine. The schematic representation of the open volumetric receiver used in Jülich
Plant is shown in Figure 5 (Source: Report Article: The Solar Tower Julich - A
research and demonstration plant for central receiver systems).

Figure 3.2.2(a): Schematic of Open Volumetric Receiver

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Closed Volumetric Receivers

Closed volumetric receivers are also called as pressurized volumetric

receivers, in which the HTF (usually air) is mechanically charged through the receiver
by a blower and the receiver aperture is sealed by a transparent window. The HTF
will get heated up at the dome shaped portion of the receiver by the concentrated solar
energy and the heated air will be used either in a Rankin cycle via heat exchanger or
in a Brayton cycle for generating electricity. The schematic of a closed volumetric
receiver is shown in Figure 6 (Source: European Commission Report: Solar hybrid
gas turbine electric power system).

Figure 3.2.2(b): Schematic of the Pressurised Volumetric Receiver

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3.3 Heat Transfer Fluid

Different types of HTFs can be used in ST based on the type of receiver and
power cycle employed in the system. The HTF used in the operational ST plants are
water, molten salt and air. Other possible candidates are liquid sodium, Hitec salt and
synthetic oil. The merits and demerits of these HTFs are given in Table 1. A brief note
on the use of each of the principal HTFs is given below.

3.3.1 Water

When water is used as HTF, the solar field generates steam directly (Direct
Steam Generation) and the Rankine steam cycle is used for power generation. As the
HTF is itself water, it eliminates the need of a heat exchanger in order to transfer the
heat from the HTF to water (or steam) which is used to drive the turbine in the power
block. The minimum temperature at inlet is around 250°C while the maximum
possible temperature that has been achieved with water is 566°C.

3.3.2 Molten salt

In the case of molten salt as HTF, a heat exchanger is used to transfer the
thermal energy from the HTF to water in order to generate steam. Rankine steam
cycle is used for power generation. Use of molten salt as HTF allows easy thermal
storage. When the plant is not in operation, HTF from the receiver has to be drained
out as the freezing temperatures of the molten salt are relatively high, around 238°C
(5). It can be noted that using molten salt as the HTF is preferred in a ST system
rather than a PT system as gravity helps aid the draining of the molten salt at the end
of the day in order to prevent it from freezing in the pipes. PT system, this HTF will
have to be pumped out to drain the pipes and this is not very convenient as some
auxiliary power source will be required for this purpose. Molten salt is salt which is
solid at standard temperature and pressure (STP) but enters the liquid phase due to
elevated temperature. A salt that is normally liquid even at STP is usually called a
room temperature ionic liquid, although technically molten salts are a class of ionic
liquids. Molten salts have a variety of uses. Cyanide and chloride salt mixtures are
used for surface modification of alloys such as carburizing and nitrocarburizing of
steel. Cryolite (a fluoride salt) is used as a solvent for aluminium oxide in the
production of aluminium in the Hall-Héroult process. Fluoride, chloride, and
hydroxide salts can be used as solvents in pyroprocessing of nuclear fuel. Molten salts

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(fluoride, chloride, and nitrate) can also be used as heat transfer fluids as well as
for thermal storage. This thermal storage is commonly used in molten salt power
plants. A commonly used thermal salt is the eutectic mixture of 60% sodium
nitrate and 40% potassium nitrate, which can be used as liquid between 260-550 °C. It
has a heat of fusion of 161 J/g, and a heat capacity of 1.53 J/(g K). Experimental salts
using lithium may have a melting point of 116 °C while still having a heat capacity of
1.54 J/(g K).Salts may cost $1,000 per ton, and a typical plant may use 30,000 tons of
salt.Regular table salt has a melting point of 800 °C and a heat of fusion of 520 J/g.

Figure 3.3.2: Molten salt

3.3.3 Air

Air is used as a HTF when the receiver used is a volumetric receiver, as

discussed in the previous section. However, the receiver design is rather complex and
also one disadvantage is that air has poor heat transfer properties (thermal
conductivity, film coefficient etc) and therefore, the efficiency of heat transfer to the
power block is not very high. However, when a CO2 Brayton cycle is being used, this
is minimised to some extent. Compressed air has better heat transfer properties as
compared to uncompressed air as it is denser. Air at higher temperatures of the order
of 1000°C gives rise to better heat transfer properties but the material constraints of
the HTF carrying pipes will have to be considered. Also air does not require cooling
water and hence is advantageous especially in locations where water availability is a
problem.

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3.4 Power Cycle

The power block is also a very important component of the plant as it is here
that the solar energy collected by the receiver is converted to a more usable form
which is electricity. The two main power cycles used in ST plants are discussed in the
following sections.

3.4.1 Rankine cycle

In the Rankine cycle, the working fluid is water. Here the water is heated up
(either directly if HTF used is water, or in a heat exchanger when HTF used is not
water) and converted to steam.

Figure 3.4.1: Ranking Cycle

This dry saturated vapour expands through a turbine generating power. After leaving
the turbine, at low pressure, the low quality steam now passes through a condenser
where it is converted to a saturated liquid state (water). This is now pumped from low
pressure to a high pressure. Heat is taken up by this sub cooled water while getting
converted to steam (at constant pressure) and the cycle repeats. Figure 7 gives the
schematic diagram of the working of a Rankine cycle. The only difference here is that
instead of being heated in a conventional coal-fired boiler, water (the working fluid) is
heated by solar energy.

3.4.2 Brayton Cycle

One of the potential advantages envisaged in ST technology is the use of

compressed air as HTF to raise its temperature to about 1000°C to run a turbine on
Brayton cycle. This is yet to be proven commercially. The Brayton cycle has the same
processes as the Rankine cycle, however it does not operate within the vapour dome.
It operates at much higher pressures and temperatures.

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Merits & Demerits of HTF used in Heliostat Power Plants HTF

HTF Merits Demerits

Water For steam Rankine cycle, water Dissimilar heat transfer

being the working fluid, the coefficients in liquid, saturated
need for heat exchanger is vapour and superheated gas
eliminated. phases. Consequent problems
with temperature gradient and
Eliminates the costs associated thermal stress to be tackled Flow
with the salt or oil based HTFs. control problems with varying
solar flux Thermal Storage for
long hours difficult
Molten Salt Stable and non-toxic and High melting point (~222°C);
(KNO3 + environmentally benign. High Needs auxiliary heating to
NaNO3) thermal conductivity and prevent solidification Highly
thermal capacity. Operating corrosive at elevated
temperatures can go up to temperatures
560°C.
Air High temperatures of the order Poor heat transfer properties
of 1000°C can be utilized. (conductivity and film coefficient
etc.) compared to other fluids.
Complex receiver design
Liquid Sodium Higher solar field outlet Handling is difficult Accidental
temperatures are possible and leakage is highly hazardous
thus higher power cycle
efficiencies Low Melting Point
(97.7°C) High boiling point
(873°C)
Hitec Salt Temperatures are limited to Melting point is 142°C 535°C
less than

Synthetic Oil Operating temperature limited Freezes at 15°C which limits the
to 390°C power cycle efficiency

Table 1: Merits & Demerits of HTF used in Solar Tower Plants HTF

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CHAPTER 4
4. Arrangement of heliostat power plant

Receiver

Cold storage tank

Steam generator Turbine

Generator

Hot storage tank

Water storage tank

Condenser

Figure 4.1: Arrangement of heliostat power plant

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CHAPTER 5
5.1 Operation of heliostat power plant

5.1.1 PS 10

The Planta Solar 10 (PS 10) plant is the world’s first commercial ST plant to
be constructed near Seville in Spain. It is the first plant producing grid connected
solar power using tower technology. It is a 10 MWe plant. The technologies used by it
are – glass-metal heliostats, pressurised water thermal storage system (with 1 hour
storage capacity) and a saturated steam turbine (HTF used is water). The receiver
system used in this tower is the cavity receiver system with a tower height of 115m.
The plant uses 55 ha (550000 m2) of land area with 624 heliostats. Each heliostat has
an aperture area of 120m2. Since the heliostat size is so large, keeping the mirrors
clean and dust-free is a major challenge. The solar receiver which is at the top of the
tower produces saturated steam at 275°C (6).

5.1.2 Jülich Power Tower

This 1.5 MWe capacity power tower in Germany is an experimental 60m high
tower plant. It uses a volumetric receiver with non-compressed air as the HTF. Due to
the poor heat transfer coefficient of air, the efficiency of this plant is not so high. The
working fluid is water. It also has 1.5 hours of storage capacity. It uses 2153 heliostats
each of 8.2 m2 area. The heliostats and tower are spread across a land area of 80000
m2. It is a demonstration plant. This plant started operation in 2008 (7). The air (HTF)
is heated up to 700°C and is used to heat water (in the power cycle) up to 500°C at
pressures of 100 bars (8).

5.1.3 PS 20

Planta Solar 20 (PS 20), a tower plant which started operation in 2009 is
beside PS 10 at Seville in Spain. It is a 20 MWe capacity plant with a tower 165m
high. This plant occupies 80 ha (800000 m2) of land area. It is made up of the glass-
metal 120m2 area heliostats as the PS 10 plant, but 1255 in number. This plant also
has a cavity receiver (9). This tower is higher than the PS 10 tower by 50m. The land
area /MW is lower for the PS 20 plant, however, the mirror area/ MW is higher.

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5.1.4 Sierra Sun Tower

This plant, which started in 2009 is one of the operating power tower plants in
the United States. It is located in Lancaster, California. The 5 MWe capacity project
site occupies 8.1 hectares (81000 m2) in an arid valley in the western corner of the
Mojave Desert at 35°N. It has 24360 heliostats of 1.136m2 each. It uses a tower
height of 55m. The HTF used is water. This plant has two towers and hence two
receivers. One is the dual cavity type and the other is the external rectangular receiver
type (10).

5.1.5 Gemasolar Thermosolar Plant

The Gemasolar Thermosolar plant, which started operation in 2011, is the first
commercial high-temperature solar plant using molten salt as the HTF and storage
medium, which provides 15 hours of thermal storage with an annual capacity factor of
about 75%. This plant is located in Spain. Here the HTF reaches temperatures of
565°C. The land area occupied by this plant is 1950000 m2. It has a 140m high tower
and a capacity of 20 MWe. It has 2650 heliostats, 120 m2 each. The plant has been
able to supply uninterrupted power for a complete day to the grid, using thermal
transfer technology developed by SENER (11). The receiver is 8m in diameter and
10m high.

5.1.6 ACME Bikaner

This is a 2.5 MWe capacity plant which was set up in 2011 in Bikaner,
Rajasthan, India. This plant has a total of 14280 heliostats each with an area of
1.136m2. The heliostats used in this plant are manufactured by eSolar. They are
smaller than the industry norm, allowing for pre-fabrication, mass-manufacturing, and
easy installation, thereby reducing production and installation costs (12). The Plant
was supposed to be a 10MWe but it is running at reduced capacity (only one unit is
operational) (13).

5.1.7 Dahan Power Plant

This plant is situated in Beijing, China and started operating in 2013. It is a 1

MWe plant for experimentation and demonstration. It uses 100 heliostats each of 100
m2 area. Each heliostat has 64 facets. The tower height is 118m. It uses a cavity

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receiver with water as the HTF. The receiver tilt angle is 25° and receiver aperture
size is 25 m2. The water is heated to about 400°C at the outlet of the receiver (14). It
has one hour of thermal storage. The storage system is a combination of high
temperature and low temperature oil storage tanks and a set of heat exchangers (15).

5.1.8 Solugas Plant

This plant is a 4.6 MWe capacity plant located in Spain. The construction for
this plant was finished in early 2012. It is built over a land of area 60000m2 (16). It
uses 69 heliostats of 121 m2 area each. It has a 75 m high tower. Since the area of
each heliostat is high it is made up of 28 facets. The cavity receiver is located at a
height of 65m with an inclination of 35° with the horizontal. The diameter of the
receiver is 5 m, however, the sun’s rays areconcentrated to an area of 2.7 m diameter.
The length of the receiver is 6 m and it has a cylindrical cavity region. (17).This plant
uses a Brayton cycle and uses air as HTF (18).

5.1.9 Themis Solar Tower

This is a 2 MWe capacity tower constructed for research and development

purposes. It is located in France. This solar tower plant is the refurbished and
upgraded version of the tower initially built in the seventies to test a 10 MWth scale
electricity to concentrated solar energy production facility. It uses a new high
performance, high precision heliostat tracking system which will allow the receiver
temperature to reach 900°C. It has 201 mirrors to concentrate the solar energy on top
of a concrete tower of 101 m height (19). The HTF employed is compressed air. (20).

51.10 Ivanpah Solar Electric Generating Station (ISEGS)

This project is a 392 MWe capacity plant in Ivanpah, California. It is a

commercial plant which covers 14170000m2 with 173500 heliostats, each with an
area of 15 m2. The tower height is 140m (21). This plant is made up of three units
(three towers and their respective heliostat fields) and utilizes BrightSource energy's
'luz power tower' (LPT) 550 technology (22). This plant started operation in
December 2013. This plant uses a Solar Receiver Steam Generator (SRSG) wherein
the boiler is contained in the receiver itself.

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CHAPTER 6

6. Assessment of Existing Solar Tower Plants

An assessment of the existing ST plants is discussed in this section where the overall
efficiency of solar to electric energy conversion is discussed. Also, the mirror and
land area per MWe of capacity is explored, the various layouts are described, receiver
size estimation is carried out and the tower height of the plants with respect to their
capacity is assessed.

6.1 Overall Efficiency of Conversion of Solar to Electric Energy

The efficiency of conversion of solar to electrical energy is as follows: The values of

overall efficiency for the various existing plants are also included in and lie in the
range of 15.51 to 17.30.

6.2 Comparison of Mirror Area and Land Area for Existing Plants

Important information such as capacity, solar resource, land area used, total heliostat
aperture area, number of hours of storage etc., of the ST plants have been presented in
Table 2, Table 3 and Table 4 for plants in operation and under development. From
this data, one can observe that the mirror area and land area per MWe of rated
capacity vary from plant to plant due to variations in thermal storage hours. Hence it
is necessary to normalise the mirror/land area requirements taking into consideration
the number of hours of thermal storage.In order to take into account the thermal
storage, it is assumed that plant with no thermal storage can generally operate for nine
hours. If ଢଢ hours of thermal storage have been provided, then the mirror area and
correspondingly the land area has to be increased (9+ ଢଢ)/9 times compared to the
plant with no thermal storage. A comparison of the mirror area and land area with
rated and equivalent capacity for plants that are operational and under construction is
made separately for each type of receiver used.

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6.2.1 Mirror Area

Table 6 gives the normalised values of the mirror area with respect to rated and
equivalent capacity. It can be seen from the table that the mirror area per MWe of
equivalent capacity (m2/ MWe) of plants using cavity receivers range from 5999 to
6750 and for plants using external receivers range from 3781 to 6633. It can also be
seen that both Rice Solar and Crescent Dunes plants have lesser mirror area compared
to other plants as these two sites have a higher solar resource.

6.2.2 Land Area

Table 7 gives the utilisation of land area per MWe of rated and equivalent capacity.
The land area per equivalent capacity (hectares/ MWe) for plants with cavity receivers
ranges from 1.3 to 4.5 and for plants with external receivers ranges from 2 to 3.7.
Here the variation could be due to the type of receiver employed, sizes of heliostats
used and further due to the variations in packing density.

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CHAPTER 7
7. Cost of Heliostat Power Plant Technology

The data available on the gross costs for the existing tower plants is limited.
The gross cost of the PS 10 Plant (cavity receiver) is about Rs.19 crores per MWe
million Euros (47)). The gross cost for the Dahan Plant (cavity receiver) is
approximately Rs. 20 crores per MWe (32 million CNY (48)). The overall cost of the
Gemasolar plant (external cylindrical) is Rs. 36 crores per MWe (419 million USD
(49)). This is data depicted in Table 10. Data for most of the other existing plants was
not available. The costs of some of the components of the ST, namely the heliostat
field, receiver and tower for specific capacities according to some reports are given in
Table 2.

Plant Capacity TES Equivalent Cost/ Eq.

(hours) Capacity capacity
(MW) (Rs.Crore/MW)
PS 10 11.02 1 12.2 18.62
Gemasolar 20 15 53.3 36.44
Dahan 1.5 1 1.67 19.76

Table 2: Available Gross Costs of Plants

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Heliostat Power Plant Component Costs

Solar Field Capacity Receiver

Heliostat Receiver Tower (MW) Type
Source Field (Rs./kWth)
(Rs./m2)

CSIRO 6674 893 1363 100

2011 (50) Rs./kWth

UNDP 12090 14950 3.37E+08 Rs. 20 External

2012 (51) Cylindrical

UNDP 12090 5525 20 Cavity

2012 (51) 2.73E+08
Rs.
SANDIA 9000 6390 2610 100 External
REPORT, Rs./kWth Cylindrical
2011(52)

ECOSTAR 8250 6875 1.1E+08 17 Cavity

2004 (53) Rs.

ECOSTAR 7810 6380 3.06E+08 50 Cavity

2004 (53) Rs.

Table 3: Heliostat Power Plant Component Costs

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CHAPTER 8
8. Challenges for Heliostat Power Plant Technology Deployment in
India

India has limited experience in the development of power tower systems.

Apart from a couple of small scale demonstration plants, there have been no plants in
the pipeline for India. ACME company in India have partnered with e-solar, USA in
developing a 2.5 MWe (to be scaled up to 10 MWe) tower plant in Bikaner,
Rajasthan. The heliostat field for the 2.5 MWe plant set up utilises small size flat
mirrors of 1.16 m2. The advantage of small size heliostats is that they are easy to
handle and install but a major disadvantage is that they require more number of
controllers for tracking. The plant, of 2.5 MWe, was commissioned in 2010. However
it is not running to its full capacity. Some of the possible problems were attributed to
lack of sufficient Direct Normal Irradiance (DNI), difficulties in tracking and
accumulation of dust on the mirror. SunBorne energy is setting up a 1 MWth ST
system, with support from Ministry of New and Renewable Energy (MNRE),
Government of India, at the National Institute of Solar Energy (NISE), Gurgaon. The
primary aim of this demonstration plant is to devise a method to optimise the heliostat
field (using Titan tracker heliostats) using volumetric air receiver while
simultaneously having a provision for thermal storage. This plant is planned to be set
up using regional indigenous resources for most of the system components

The challenges for using ST technology in India are as follows:

Dust on the heliostats reduces its life and efficiency. Most of the areas in India with
abundant solar irradiation (for example, Gujarat and Rajasthan) are areas which are
prone to very high dust factors. In these cases maintenance of each heliostat is of
prime importance which is not an easy task in a field with thousands of mirrors.

There are only three suppliers of molten salt HTF globally, namely, SQM, Haifa
Chemicals and Durferrit Salts and Auxillary Products. Lack of domestic suppliers of
HTF is one of the main challenges in implementing ST plants with storage (as molten
salt storage is the most efficient presently). This is due to the fact that the major cost
contributor of any storage system is the storage medium.

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Absence of an established supply chain for the main ST components is also a major
challenge. One of the most important components of ST technology, namely, the
receiver, does not have even a single indigenous manufacturing unit in India. At the
international level as well, there are only a handful of manufacturers resulting in
extremely costly receivers.

Unlike the parabolic trough which has a well-established supply chain and
standards, ST, due to its variants in technology has seen limited suppliers as well as
standards. Furthermore there is no benchmarking for reliability testing of ST
components. Due to this, market acceptability of in-house manufactured components
reduces. As a result of the lack of demand, even components for which a domestic
market can be set up, the question of sustainability looms at large.

There exists no policy support or incentive from the government for setting up of
ST plants as well as promoting hybridization. This is also a huge challenge which
currently hinders the implementation of ST plants in India.

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CHAPTER 9
9. Opportunities for Technology India
India is situated between 8°N to 37°N latitude and 70°E to 96°E longitude. For
these geographical coordinates, the sun is in the southern side for a larger part of the
year and on the northern side for a smaller duration annually for any particular
location. Based on this geographical positioning, the opportunities for ST deployment
in India are as follows:

High temperatures in the range of 300 to 565°C are possible with the use of
suitable HTFs. The presence of higher operating temperatures results in a higher
power cycle efficiency as well as number of hours of storage.

India has a good solar zone with high solar resource (DNI values) almost
throughout the year which has the potential to be tapped. The best sites in India,
receive around 2100 kWh/m2/annum which is at par with most of the existing tower
plants. This sets the benchmark for commercial viability of this technology under
Indian conditions.

The land requirement for ST plants can be fulfilled by utilising the huge wastelands
present in India. Approximately 472200 km2 of wasteland is available in India (55).
Even if 1% of this land is utilised for solar projects the potential goes beyond India’s
current installed capacity. Hence land constraint is not a deterrent to growth of ST
technology in India.

Since ST technology does not require land of constant slope, terrains (of up to 5°
difference) need not be filled in or levelled. This reduces the construction time and
installation (set up) cost.

The manufacture of low cost heliostats is possible as there is considerable

availability of low iron content glass in India which is necessary for the fabrication of
heliostats. Further, the structural designing and manufacture of heliostat support
structure, the requisite drive mechanisms and tower can be accomplished in India at
lower costs.

Establishment of an indigenous market for receiver technology, external cylindrical

and cavity receivers can be done since for both these technologies, once the

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specifications are known, the manufacturing and fabrication process is relatively

straightforward.

Due to availability of biomass resource in India hybridisation with biomass can be

achieved in order to increase the Plant Load Factor (PLF) of the plants. The total
capacity of grid connected solar projects in India currently stands at 2632 MW as on
March 31st, 2014 (56). The contribution from CSP in Phase-1 has been very less as
compared to the contribution of Photovoltaic (PV) based systems. Some of the
reasons for the slow deployment of CSP in India are: availability of solar resource
data, delay in importing key components of the plant (mirrors, HTF etc.), obtaining
financial closure etc. However, CSP is expected to play a significant role in the
coming phases of the Jawaharlal Nehru National Solar Mission (JNNSM), given the
mandate of 30% capacity addition from CSP (57). Assuming that 30% of the target
could be tapped from solar thermal technologies, the CSP share will be around 6000
MW. Based on present maturity levels of ST technology, it is assumed that it can
contribute around 30% of the CSP share resulting in approximately 1800 MW of
installed capacity by 2022. Using a mix of cavity and external cylindrical receiver
technologies, the approximate land required per MW is about three hectares resulting
in a land requirement of 54 km2 for the 1800 MW target.

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CHAPTER 10
10. Applications

Recently, there has been a renewed interest in solar tower power technology,
as is evident from the fact that there are several companies involved in planning,
designing and building utility size power plants.

This is an important step towards the ultimate goal of developing

commercially viable plants. There are numerous examples of case studies of applying
innovative solutions to solar power. Beam down tower application is also feasible
with heliostats to heat the working fluid.

The Pit Power Tower combines a solar power tower and an aero-electric
power tower in a decommissioned open pit mine. Traditional solar power towers are
constrained in size by the height of the tower and closer heliostats blocking the line of
sight of outer heliostats to the receiver.

The use of the pit mine's "stadium seating" helps overcome the blocking
constraint. As solar power towers commonly use steam to drive the turbines, and
water tends to be scarce in regions with high solar energy, another advantage of open
pits is that they tend to collect water, having been dug below the water table.

The Pit Power Tower uses low heat steam to drive the pneumatic tubes in a
co-generation system. A third benefit of re-purposing a pit mine for this kind of
project is the possibility of reusing mine infrastructure such as roads, buildings and
electricity.

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CHAPTER 11

11. Advantages
1. Renewable Energy Source – Among the several benefits of solar panels, the most
important thing is that solar energy is truly a renewable resource. It can be utilized in
all areas of the world and is available every day. We can never run out of solar energy
unlike some of the other sources that are being used excessively. Solar energy is
readily accessible and available to us for as long as we have the sun which according
to scientists is going to stay for at least next 5 billion years. The cost of solar panels
has also fallen by 75% that should encourage everyone to go for solar.

2. Provides energy security – Another top benefit of installing solar panels is that no
one can go and buy or turn sunlight into a monopoly. Combined with the ease of solar
panels, this also provides a notable solar power advantage of energy security. This is
why governments are investing huge amount of money into the development and
installation of solar power systems.

3. Decrease the carbon footprint – Solar power decreases your carbon footprint as
well. Carbon dioxide has been known to cause global warming that is causing havoc
on our Earth further causing glaciers to melt, animals to be endangered and shorelines
to erode. For example, solar power can help conserve more than 16000 gallons of
water per year and also decrease dependence on non-renewable sources of energy.
Reducing the mileage from 15,000 to 10,000 can save more than a ton of CO2 which
is around 15% of the average person’s footprint.

4. Technology Development – The technology in the solar power industry is

continuously advancing and improvements are sure to intensify in the future.
Innovations in nanotechnology and quantum physics can increase the effectiveness of
solar panels or increase multi-folds the electrical output.

5. Low Maintenance Costs – Solar power systems don’t require a lot of

maintenance. All you need to do is keep them relatively clean. The reliable solar
power companies give 20-25 years of warranty. There is no wear and tear and the
inverter is the only part that needs to be changed after 5-10 years. Basically, there is
very little spending on maintenance and repair work. For example, the average cost of
an annual inspection for a household rooftop solar PV system is approximately
$150.00

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6. Diverse Uses – Solar energy can be used for diverse purposes such as to generate
electricity or heat. It can also be used to produce electricity in areas without access to
energy grid, to distill water in regions with limited water supplies, power satellites in
space, in residential properties and recreational homes. These are some of the most
popular diverse uses of solar power.

7. Reduce electricity bills and Increase Savings– As some of the energy needs will
be met by the solar power system, the energy bills are sure to drop. It also depends on
the size of the solar panel system and the electricity usage. Not only you will save on
the bill, but also generate more electricity than you can use, the surplus of which will
be exported back to the grid provided it is connected. For example, you have a
consumption of 10,000 kWh and if the solar panels produce 10,000 kWh or more, you
will end up saving a lot on your electricity bills. The average electric bill can be as
low as $10 or lower. So has this sparked your interest in solar energy? If yes, you can
contact Amplus Energy Solutions one of the best solar power companies. It is a leader
in providing distributed solar and energy solutions to industrial and commercial
customers in India.

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CHAPTER 12
12. Conclusion
As seen from the existing plants, most of the tower plants are employing either the
external cylindrical or the cavity type receiver. By using molten salt one can achieve
high temperatures along with thermal storage for a long duration. The main advantage
of using molten salt is that it can be used both as the HTF as well as the storage
medium. India has indigenous manufacturers of components such as mirror, support
structure and power block components. However, as pointed out earlier, the
experience in designing and manufacturing of receivers is limited. Therefore, given
the considerations mentioned above, the system configuration that could be ideal for
Indian conditions are:

Molten salt as HTF and storage medium,

External cylindrical receivers with a larger north side field or cavity receiver with
north side field.

Thermal storage for utility scale plants, as it can provide reliable and dispatch able
power and further help in meeting the peak-time demands.

Biomass hybridisation which would require more R&D.The total installed capacity
of the ST plants worldwide is shown in Table 12 (58). It has been compared with the
Parabolic Trough technology to see the growth potential of ST in the next few years.

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CHAPTER 13
13. References
1. IRENA, ISE-ETSAP and. Concentrating Solar Power Technical Brief. 2013.

2. William, B Stine and Michael, Geyer. Power from the Sun. [Online] 2001.
[Cited: ] http://www.powerfromthesun.net.

3. DLR. 10 MW solar thermal power plant for southern Spain. s.l. : European
Commission, 2005. Final Technical Progress Report.

4. Tracking and ray tracing equations for the target-aligned heliostat for solar
tower. Xiudong Wei, Zhenwu Lu, Weixing Yu, Hongxin Zhang, Zhifeng Wang.
2011, Elsevier.

5. Archimede Solar Energy.

http://www.archimedesolarenergy.it/molten_salt.htm.

6. NREL. August 2012.

http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=38.

7. NREL. Feb 2013.

http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=246.

8. Ju ̈lich Solar Power Tower-Experimental Evaluation of the Storage Subsystem

and Performance Calculation . Zunft, Stefan. 2011, Journal of Solar Energy
Engineering.

9. NREL. August 2012.

http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=39.

10. NREL. Aug 2012.

http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=63.

11. NREL. Oct 2011.

http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=40.

12. NREL. Feb 2013.

http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=262.

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