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Solar Power Stations - Part 3 |
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150 MW, CSP stations in Spain, 3 Parabolic trough of Solnova
and 2 Power Towers - PS10 and PS20. |
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Andasol Solar Power Station
in Spain,
Parabolic
trough, 150 MW |
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1-
Current Technology -
Concentrated Solar Power technology,
CSP technology |
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CSP (Concentrated Solar Power) is used to produce electricity (sometimes called solar
thermoelectricity, usually generated through steam). Concentrated-solar
technology systems use mirrors or lenses with tracking
systems to focus a large area of sunlight onto a small area. The
concentrated light is then used as heat or as a heat source for a
conventional power plant (solar
thermoelectricity). The solar concentrators used in CSP systems can often
also be used to provide industrial process heating or cooling, such as in
solar air-conditioning.
Concentrating technologies exist in 5 common forms, namely
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Parabolic Trough,
-
Solar Power Tower,
-
Fresnel Reflector,
-
Dish Stirling/Engine,
-
Enclosed Trough.
Although simple, these solar concentrators are quite far from the
theoretical maximum concentration.
For example, the parabolic-trough concentration gives about 1/3 of the
theoretical maximum for the design acceptance
angle, that is, for the same overall tolerances for the system.
Approaching the theoretical maximum may be achieved by using more
elaborate concentrators based on nonimaging
optics.
Different types of concentrators produce different peak temperatures
and correspondingly varying thermodynamic efficiencies, due to differences
in the way that they track the sun and focus light. New innovations in CSP
technology are leading systems to become more and more
cost-effective. |
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A- Parabolic
Trough |
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Reference:
1- Simplified Methodology
for Designing Parabolic Trough Solar Power
by Ricardo Vasquez Padilla
University of South Florida,
rsvasque@mail.usf.edu
2011
2- Parabolic Trough
Collector Overview
by Dr. David W. Kearney
National Renewable Energy Laboratory,
Golden CO
Workshop 2007 |
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A
Parabolic Trough consists of a linear parabolic reflector that
concentrates light onto a receiver positioned along the reflector's
focal line. The receiver is a tube positioned directly above the
middle of the parabolic mirror and filled with a working fluid. The
reflector follows the sun during the daylight hours by tracking
along a single axis. A working fluid
(e.g. molten salt)
is heated to 150–350 °C (423–623 K (302–662 °F)) as
it flows through the receiver and is then used as a heat source for
a power generation system.
Trough systems are the most developed CSP technology. |
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1- Gallery,
Parabolic Trough Solar Stations |
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Part of the 354 MW SEGS
solar complex in northern San
Bernardino County, California. |
Parabolic trough at a plant near Harper
Lake,
California |
 |
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Andasol Solar Power Station
in Spain,
Parabolic
ttrough, 150 MW |
Nevada Solar
Parabolic Trough in USA, 64 MW |
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1- Design
of
PTC |
PTCs are
composed of parabolic trough-shaped mirrors, which
reflect the incident radiation from the sun on
the solar receiver tube. The receiver tube
is located at the focus of a parabola in whose
sides the mirrors are located.
As shown in Figure
A, the circulating
Heat Transfer
Fluid (HTF) passes through
the receiver and is heated up
by the radiant energy absorbed. Then, the HTF is
collected to be sent to the
power block, where it passes through a series of heat
exchangers and produces superheated
steam at high temperatures. The superheated steam
flows through a steam turbine where
rotational mechanical work is then converted into
electricity.
A solar field consists of hundreds of Solar Collector
Assemblies, which are independently
tracking assemblies of parabolic trough solar
collectors.
Each SCA has the following
components: metallic support structure, mirrors, solar
receiver, and collector balance
of the system.
Figure B shows
different parts of a Solar Collector Assembly (SCA)
for a LS3 solar collector. In
order to reach the operational conditions, the Solar
Collector Assembly (SCA) are arranged in a series
configuration normally known as a loop.
The length of the loop depends on the PTC
performance, but as shown in Figure
C, it usually has
a U shape to minimize the pressure drop through
the pipe header. Usually the PTCs are
oriented North-South and tracking the sun from
east to west, but this also depends on the
land constraints.
The economic feasibility of PTC solar plants is based on
finding the optimum size for a
given electric output. The preliminary analysis is
performed by the integration of the complex
models and components, which are integrated to
simulate real operating conditions.
This dissertation proposes the development of a simple
methodology for the initial design
of parabolic trough solar systems based on
physical models. The methodology is focused
in obtaining a preliminary optimum design through
a simplified methodology based on
correlations obtained from detailed component
simulations. This methodology is expected
to be great help for engineers for the design and
performance analysis of parabolic trough
solar systems. |
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2-
Schematic Diagrams |
A-
The troughs are usually
designed to track the Sun along one axis,
predominantly north–south. A heat transfer
fluid (HTF), such as synthetic thermal oil or
a mixture of Molten Salt, runs into the
absorber tube and transfers the thermal energy
to a conventional steam turbine power cycle,
generating electricity. In particular, the
fluid is heated to approximately 400° C by the
sun’s concentrated rays and then pumped
through a series of heat exchangers to produce
superheated steam.
The steam is converted in to
electrical energy in a conventional steam
turbine generator, which can be either part of
a conventional steam cycle or integrated into
a combined steam and gas turbine cycle.
Parabolic Trough plants, then, consist
of 2 parts:
A Solar
Field,
constituted by reflecting panels that
concentrates the solar energy. Receiving tubes
convert this energy into high-temperature heat
which can be stored for some hours.
A Power
Generation Plant where
a traditional turbine power generation system
produces electricity. |
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B-
Parabolic Trough technology consists of
installing rows or loops of parabolic
trough-shaped mirror reflectors that are used
to collect the solar radiation and concentrate
it onto a thermally efficient receiver tube
placed in the trough’s focal line. The fluid
is heated up to approximately 400°C by the
concentrated sun’s rays and then pumped
through a series of heat exchangers to produce
superheated steam. The steam is converted to
electrical energy in a conventional steam
turbine generator, which can either be part of
a conventional steam cycle or integrated into
a combined steam and gas turbine cycle. This
fluid can also be used to heat a storage
system consisting of two tanks of molten salt. |
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3-
Efficiency
The trough is usually aligned on a north-south axis, and rotated
to track the sun as it moves across the sky each day. Alternatively,
the trough can be aligned on an east-west axis; this reduces the
overall efficiency of the collector due to cosine loss but only
requires the trough to be aligned with the change in seasons, avoiding the
need for tracking motors. This tracking method approaches
theoretical efficiencies at the spring and fall equinoxes with less
accurate focusing of the light at other times during the year. The
daily motion of the sun across the sky also introduces errors,
greatest at the sunrise and sunset and smallest at solar noon. Due
to these sources of error, seasonally adjusted parabolic troughs are
generally designed with a lower concentration
acceptance product.
Parabolic trough concentrators have a simple geometry, but their
concentration is about 1/3 of the theoretical maximum for the same acceptance
angle, that is, for the same overall tolerances of the system to
all kinds of errors, including those referenced above. The
theoretical maximum is better achieved with more elaborate
concentrators based on primary-secondary designs using nonimaging
optics
which may nearly double the concentration of conventional parabolic
troughs
and are used to improve practical designs such as those with fixed
receivers. |
 |
A diagram of a
parabolic trough solar farm (top), and an end view of how a
parabolic collector focuses sunlight onto its focal
point. | |
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4- Commercial
plants
Most commercial plants utilizing parabolic troughs are hybrids; fossil fuels are
used during night hours, but the amount of fossil fuel used is
limited to a maximum 27% of electricity production, allowing the
plant to qualify in the US as a renewable energy source. Because they are hybrids and include
cooling stations, condensers, accumulators
and other things besides the actual solar collectors, the power
generated per square meter of area varies enormously.
As of 2014, the largest
solar thermal power systems using parabolic trough technology
include, the 354 MW SEGS
plants in California, the 280 MW Solana
Generating Station that features a molten
salt heat storage, the 250 MW Genesis
Solar Energy Project, that came online in 2014, as well as the
Spanish 200 MW Solaben Solar Power Station, the 200 MW Solnova
Solar Power Station, and the Andasol
1 solar power station, using a
Eurotrough-collector.
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Array of
parabolic
troughs. | | |
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B- Solar
Power Tower |
Reference,
Technical
Paper:
1- Progress
Towards
Cost-Competitive
Solar Power
Tower Plants
by K.L. Santelmann, D.T. Wasyluk, and
B. Sakadjian
Babcock & Wilcox Power Generation
Group, Inc.,
Barberton,
Ohio, U.S.A.
Presented to: Power-Gen Middle
East, 2014,
Abu Dhabi,
United Arab
Emirates |
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In Solar
Thermal Tower Power plants, hundreds or even
thousands of large two-axis tracked mirrors are
installed around a tower. These slightly curved
mirrors are also called heliostats; a computer
calculates the ideal position for each of these,
and a motor drive moves them into the sun. The
system must be very precise in order to ensure
that sunlight is really focused on the top of the
tower. It is here that the absorber is located,
and this is heated up to temperatures of
500–1000 °C (773–1,273 K (932–1,832 °F)) . Hot air
or molten salt then transports the heat from the
absorber to a steam generator; superheated water
steam is produced there, which drives a turbine
and electrical generator. Power-tower development
is less advanced than trough systems, but they
offer higher efficiency and better energy storage
capability. |
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1- Gallery,
Solar Power Tower Stations |
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PS10 solar power tower, 11
MW, in Spain,
has 624 mirrors reflecting the sun to the 40
storey tower, with some night-time storage
capacity. |
20 MW, CSP in Spain - PS10
Solar Power Plant in the foreground, with PS20
in the background. |
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5 MW Sierra SunTower, located in
Lancaster, California |
The
THEMIS solar power tower in the Eastern
Pyrenees - France, 2 MW,
has 201 mirrors reflecting the sun which
heated a boiler (a cavity lined with coolant
tubes) at the top of a 100 m tower where the
coolant (molten salts) carried the thermal
energy to a vapour generator, itself powering
an electric turbine. |
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solar technology using a
central power tower the middle of a circle of
mirrors, 10 MW, in Daggett California. |
Small
sized Concentrating Solar Power system |
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Ivanpah solar towers station
in the Mojave Desert - California, 400
MW,
uses
an array of small, flat mirrors on heliostats
that track the sun and focus its rays on a
central "power tower" where the generator is
located. |
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2- Schematic
Diagrams |
2.1- Power
Tower System Plant
Power tower systems consist
of numerous large, flat, sun-tracking mirrors,
known as heliostats that focus sunlight onto a
receiver at the top of a tower. The heated
fluid in the receiver is used to generate
steam, which powers a turbine and a generator
to produce electricity. Some power towers use
water/steam as the heat-transfer fluid.
Individual commercial plants can be sized to
produce up to 200 megawatts of electricity. |
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2.2-
Solar Power Tower
System Plant without Thermal storage, Single
or Multiple Receivers
In this arrangement, solar energy is
concentrated by a field of heliostats (mirror
assemblies) onto one or more tower-mounted
solar receivers which absorb the energy and
convert feedwater into superheated steam. The
superheated steam, at high temperature and
pressure, is piped directly to a steam
turbine-generator to produce electrical power.
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The Sierra SunTower plant in Lancaster, California is a direct-steam
plant with two power towers capable of
supplying up to 5 MW of clean, renewable
energy to the grid.
This
direct-steam plant
design changes the cost structure
dramatically via thousands of
independently controlled heliostats
organized into modular collector fields.
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2.3- Schematic
of two types of Tower Receiver of solar
thermal tower power plant |
2.3a- Solar
Tower, Open Volumetric Air Receiver Concept
This type of solar tower is the open
volumetric receiver concept (2-2a). A
blower transports ambient air through the
receiver, which is heated up by the reflected
sunlight. The receiver consists of wire mesh
or ceramic or metallic materials in a
honeycomb structure, and air is drawn through
this and heated up to temperatures between
650°C and 850°C. On the front side, cold,
incoming air cools down the receiver surface.
Therefore, the volumetric structure produces
the highest temperatures inside the receiver
material, reducing the heat radiation losses
on the receiver surface. Next, the air reaches
the heat boiler, where steam is produced. A
duct burner and thermal storage can also
guarantee capacity with this type of solar
thermal power plant.
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2.3a- solar
thermal tower power plant, Open Volumetric
Air Receiver |
2.3b- Solar
Tower, Pressurized Air Receiver Concept
The volumetric pressurized air receiver concept
(2.2b) offers totally new
opportunities for solar thermal tower plants.
A compressor pressurizes air to about 15 bar;
a transparent glass dome covers the receiver
and separates the absorber from the
environment. Inside the pressurized receiver,
the air is heated to temperatures of up to
1100°C, and the hot air drives a gas turbine.
This turbine is connected to the compressor
and a generator that produces electricity. The
waste heat of the gas turbine goes to a heat
boiler and in addition to this drives a
steam-cycle process. The combined gas and
steam turbine process can reach efficiencies
of over 50%, whereas the efficiency of a
simple steam turbine cycle is only 35%.
Therefore, solar system efficiencies of over
20% are possible.
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2.3b-
solar thermal tower power plant,
Pressurized Air Receiver (with combined
gas and steam turbine cycle) |
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3-
Economic
By varying the size of the solar
field, solar receiver, and size of the thermal
storage, plants can be designed with annual
capacity factors ranging between 20 and 65%.
Economic studies have shown that levelized
energy costs are reduced by adding more
storage up to a limit of about 13 hours (~65%
capacity factor). While it is true that
storage increases the cost of the plant, it is
also true that plants with higher capacity
factors have better economic utilization of
the turbine, and other balance of plant
equipment |
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C-
Fresnel Reflector |
Design and Analysis of
Rooftop
Linear
Fresnel
Reflector
Solar
Concentrator
|
(372 KB pdf
file)
download |
References:
1- Advanced
CSP Teaching
Materials,
Chapter 6 -
Linear
Fresnel
Technology
by Matthias Günther
2- Linear
Fresnel
Reflector
based Solar
System,
Operations &
Maintenance
Manual
by UNDP-GEF Project on Concentrated
Solar Heat
Ministry of New & Renewable Energy
Government
of India
3- AUGUSTIN
FRESNEL 1
PROJECT:
Design,
Construction
and Testing
of a Linear
Fresnel
Pilot Plant
in the
Pyrenees
by David Itskhokine, Patrick
Lécuillier
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Linear Fresnel solar CSP
technology produces energy as heat through the
use of long and narrow segments of mirror that
pivot to reflect the sunlight onto a fixed
absorber tube located at the common focal line
of the reflectors called Linear Fresnel
Reflectors. This energy can be used either
directly in the form of heat, either in the
form of electricity after conversion.
Solar thermal energy is collected and
concentrated with mirror reflectors equipped
with tracking devices to maximize the amount
of solar energy collected over the day. The
reflected sunrays are focused on a receiver
tube located on the focal axis of the
reflectors. Inside the tube, a heat transfer
fluid circulates - water in this case -
which is heated, evaporated and superheated
by the concentrated solar energy.
With the control of a two-phase flow within
the receiver tube, Solar Euromed’s Linear
Fresnel solar CSP technology allows the use of
water and steam directly as heat transfer
fluid. It simplifies the overall solution, by
preventing the need of a potentially toxic and
pollutant fluid heat transfer fluid and of a
steam generator. The steam produced can then
be transferred to a Rankine thermodynamic
cycle, wherein a steam turbine coupled to an
alternator converts thermal energy into
electricity |
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Linear Fresnel Reflectors for Direct
Steam Generation |
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1- Gallery,
Linear Fresnel
Solar Power
Systems |
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9
MW, Novatec Solar’s Fresnel technology station in
Australia, uses parallel rows of flat mirrors to
focus direct solar irradiation onto a linear
receiver. Water that is conveyed through the
absorber tubes is directly evaporated or
superheated in a temperature range from 270°C to
above 500°C depending on the steam application.
The cleaning of the mirrors is done by cleaning
robots using very less water to save valuable
water in this arid region |
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2- Schematic Diagram of Linear Fresnel Solar CSP |
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Linear Fresnel Solar Systems
An array of nearly flat reflectors concentrate solar radiation onto elevated inverted linear receivers. Water flows through the receivers and is converted into steam. This system is linear-concentrating, similar to a parabolic trough, with the advantages of low costs for structural support and reflectors, fixed fluid joints, a receiver separated from the reflector system, and long focal lengths which allows the use of flat mirrors. The technology is seen as a potentially lower-cost alternative to trough technology for the production of solar process heat and steam.
Linear Fresnel reflector (LFR) also based on solar collector rows or loops. However, in this case, the parabolic shape is achieved by almost flat linear facets. The radiation is reflected and concentrated onto fixed linear receivers mounted over the mirrors, combined or not with secondary concentrators. One of the advantages of this technology is its simplicity and the possibility to use low cost components. Direct saturated steam systems with fixed absorber tubes have been operated at an early stage of use of LFR technology. This technology eliminates the need for HTF and heat exchangers. Increasing the efficiency depends on superheating the steam. Superheated steam up to 500°C has been demonstrated at pilot plant scale and first large commercial superheated LFR plants have begun recently their operation. |
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Note:
Fresnel Reflectors (FR) plants are
similar to PT plants but use a series of
ground-based, flat or slightly curved mirrors
placed at different angles to concentrate the
sunlight onto a fixed receiver located several
meters above the mirror field.
Each line of
mirrors is equipped with a single axis tracking
system to concentrate the sunlight onto the fixed
receiver. The receiver consists of a long,
selectively-coated tube where flowing water is
converted into saturated steam (DSG or Direct
Steam Generation). Since the focal line in the FR
plant can be distorted by astigmatism, a secondary
mirror is placed above the receiver to refocus the
sun’s rays. As an alternative, multi-tube
receivers can be used to capture sunlight with no
secondary mirror. The main advantages of FR
compared to PT systems are the lower cost of
ground-based mirrors and solar collectors. |
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Compact Linear Fresnel Reflectors (CLFRs) to
concentrate energy on water pipes, which produce
steam to drive turbines |
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Schematic Diagram of Linear Fresnel
Solar CSP, in Frensh | |
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3- Examples,
Linear Receiver for LFR Collector |
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Geometry Fresnel reflector |
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Schematic design of a Solar
single-tube receiver |
Solar single-tube receiver with
compound parabolic shaped secondary concentrator
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Schematic design of a Solar
multipe tube receiver |
multiple tube receiver with simple
trapezoidal secondary reflector |
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4- Concentrated
Linear Fresnel Reflectors CLFR, The next
generation of Concentrating Solar Power |
Benefits of CLFR:
-
Sturdy, Low
Cost Construction
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Primary
Components Steel, Glass, Water
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Efficient Use
of Land
-
Air Cooled;
Minimal Water Use
-
No Toxic
Materials
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Easily
Protected from Hail and Dust Storms
- Can be
hybridized with fossil fuel plants
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CLFR for direct steam
generation to be used in electric power
production or process heat in Australia. |
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5- Conclusion |
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Compared to other technologies, the investment costs per square meter of collector field using linear Fresnel technology tend to be lower because of the simpler solar field construction, and the use of direct steam generation promises relatively high conversion efficiency and a simpler thermal cycle design. The Fresnel design uses less expensive reflector materials and absorber components. It has lower optical performance and thermal output but this is offset by lower investment and operation and maintenance costs.
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There are almost more than 200MW LFR plants in operation or under construction. After a first pilot scale application in Australia, a few new pilot plants have been tested in Spain and in the United States. In 2012, the first commercial 30-MW Puerto-Errado 2 plant began its operation in Spain. France has already implemented two linear Fresnel pilot plants and is currently building two new commercial plants with this technology of 9 and 12 MW respectively, named Llo and Alba Nova 1 plants constructed respectively by CNIM and SOLAR EUROMED. In Australia, there are two plants running with this technology of 6 and 9.3 MW respectively. There is also one 44-MW plant under construction at Kogan Creek. In India, Reliance has completed and connected to the grid in November 2014 at Dhursar in Rajasthan a 125MW CLFR plant designed and constructed by AREVA Solar. |
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D- Dish
Stirling/Engine |
EuroDish, Stirling
System
Description
|
(854 KB pdf
file)
download |
Reference:
1- Price
Model of the
Stirling
Engine
by Isabelle Gadré, Johanna Maiorana
KTH School of Industrial Engineering
and
Management,
STOCKHOLM
2- 30 kW
Maintenance,
Free Solar
Dish Engine
by Infinia FOA Program
Austin, Texas, 2008 |
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A
dish Stirling or
dish engine system consists of a stand-alone parabolic
reflector that concentrates light onto a receiver positioned at
the reflector's focal point.
The reflector tracks the Sun along two
axes. The working fluid in the receiver is heated to
approximately 250–700 °C
(523–973 K (482–1,292 °F)).
This fluid
or gas is
then used to
generate
electricity
in a small
piston or Stirling
engine or a
micro
turbine,
attached to
the
receiver.
Parabolic-dish
systems
provide high
solar-to-electric
efficiency
(between 31%
and 32%),
and their
modular
nature
provides
scalability.
Parabolic dish could be
applied individually in remote locations, or
grouped together for small-grid (village power, 10
KW) or end-of-line utility (100 MW) applications.
The electricity has to be used immediately or
transmitted to the gird as the system has no
storage device.
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1- Gallery,
Stirling/Engine
Dish Power
Systems |
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2- Dish Design
The solar dish
design is
relatively new and quite different from the
other concentrated solar power designs due to
the fact that it usually doesn’t use steam and
a turbine to produce electricity. Instead, a
reflective disc that is similar to the shape
of a satellite dish, focuses sunlight onto
something called a Stirling engine . The
engine is positioned in front of the
reflective dish by an arm attached to the dish
(see images below). This is a very unique
non-combustible engine that functions by using
temperature differences . The Stirling
engine has a fixed amount of gas sealed within
. Heating one end of the Stirling engine
with concentrated sunlight creates a large
temperature difference from the opposite end
of the engine. Therefore, the hot
temperature at one end causes the gas to
expand and move towards the cooler end.
As a result, the gases flow within the engine
chamber, which in turn makes the engine run. The Stirling
engines can then be used to create
electricity. |
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solar dish
design |
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 |
 |
Stirling Energy Systems Solar Dish |
Stirling Energy Systems
Station in the Imperial Valley of Southern
California, 300 MW, consists of 12,000
dishes |
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3- Schematic Diagram
Dish/engine systems
use
parabolic dishes of mirrors to direct and
concentrate sunlight onto a central engine
that produces electricity. The dish/engine
system produces relatively small amounts of
electricity compared to other CSP
technologies-typically in the range of 3 to 25
kilowatts.
The
Solar Concentrator,
or dish, gathers the solar energy coming
directly from the sun. The resulting beam of
concentrated sunlight is reflected onto a
thermal receiver that collects the solar heat.
The dish is mounted on a structure that tracks
the sun continuously throughout the day to
reflect the highest percentage of sunlight
possible onto the thermal receiver.
The Power Conversion Unit includes the thermal
receiver and the engine/generator. The thermal
receiver is the interface between the dish and the
engine/generator. It absorbs the concentrated
beams of solar energy, converts them to heat, and
transfers the heat to the engine/generator. A
thermal receiver can be a bank of tubes with a
cooling fluid—usually hydrogen or helium—that
typically is the heat-transfer medium and also the
working fluid for an engine. Alternate thermal
receivers are heat pipes, where the boiling and
condensing of an intermediate fluid transfers the
heat to the engine.
The engine/generator system is the subsystem that
takes the heat from the thermal receiver and uses
it to produce electricity. The most common type of
heat engine used in dish/engine systems is the
Stirling engine. A Stirling engine uses the heated
fluid to move pistons and create mechanical power.
The mechanical work, in the form of the rotation
of the engine's crankshaft, drives a generator and
produces electrical power. |
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Dish/Engine
Power plant -
Concentrator and Power Conversion Unit. |
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4-
Solar Powered Stirling Engine, Parabolic Dish |
Parabolic Dish systems
use satellite-like mirror dish(es) to focus the
light onto a singlecentral receiver in front of
the mirror. They so far have the highest
heat-electricity conversion efficiencies among all
CSP designs (up to 30 %). The size of the
concentrator is determined by its engine. A dish/Stirling
system’s concentrator with a nominal maximum
direct normal solar insolationof
1000 W/m2 and a 25-kW capacity has a
diameter ofapproximately 10 meters. It could
also run on a single Brayton cycle, where
air, helium or other gas is compressed,
heated and expanded into a turbine.
"Parabolic dish could be applied individually
in remote locations, or grouped together for
small-grid (village power, 10 KW) or
end-of-line utility (100 MW) applications.
The electricity has to be used immediately
or transmitted to the gird as the system has
no storage device".
Intermittent
cloud cover can cause weakening of highly
concentrated receiver source flux. Sensible
energy storage in single-phase materials was
proposed to allow a cylindricalabsorber
element not only absorb the energy but also
store it in its mass, thus reducing the
amplitude of cloud cover transients. Although
this design only allows short period energy
storage, potential longer time storage
technology would make parabolic dish more
appealing
 |
Stirling
Energy System Inc.’s 300 MW commercial
solar thermal power plant in California |
|
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Dish/engine system schematic. The dish
that follows the sun on two axes focuses
the sunlight onto one single point on a
receiver posed right in front of the
mirror. |
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5- EuroDish
Stirling System |
Dish-Stirling
Systems are small power generation sets
which generate electricity by using direct
solar radiation. The capacity of a single
unit is typically between 5 and 25 (50) kWel.
Dish-Stirling Systems consists of the
following components:
-
Parabolic solar concentrator
-
Tracking
system
-
Solar
heat exchanger (Receiver)
-
Stirling engine with generator
The parabolic concentrator
reflects the incoming solar radiation onto a
cavity receiver which is located at the
concentrator’s focal point. The solar
radiation is absorbed by the heat exchanger
(receiver) and thus heats the working gas
(helium) of the Stirling engine to
temperatures of about 650 oC. This heat is
converted into mechanical energy by the
Stirling engine. An electrical generator,
directly connected to the crankshaft of the
engine, converts the mechanical energy into
electricity (AC). To constantly keep the
reflected radiation at the focal point
during the day, a suntracking system rotates
the solar concentrator continuously about
two axes to follow the daily path of the
sun. The electrical output of the system is
proportional to the size of the reflector.
Technical
Data:
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Concentrator:
Diameter
8.5 m
Projected area
56.7 m²
Reflectivity
94 %
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Tracking and Control:
Drive
servo motor
Control system PC,
micro controller
Remote control
telephone / WWW
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Stirling engine:
Type
single acting, 90° V-engine
Swept volume
160 cm³
Gross power output 9 kW
Net power output 8.4 kW
Grid connection 400 V, 50 Hz, 3
phase
Receiver gas temperature 650 °C
Working gas
helium
Gas pressure
20-150 bar
Power control
pressure control
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F-
Enclosed trough |
Reference:
1-
Construction
of an
Enclosed
Trough
Enhanced Oil
Recovery -
EOR system
in South
Oman
by B. Biermana
SolarPACES 2013 |
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Enclosed trough systems are used to produce process
heat. The design encapsulates the solar thermal system within a
greenhouse-like glasshouse. The glasshouse creates a protected environment
to with stand the elements that can negatively impact reliability and
efficiency of the solar thermal system.
Lightweight curved solar-reflecting mirrors are suspended from the ceiling
of the glasshouse by wires. A single-axis tracking
system positions the mirrors to retrieve the optimal amount of
sunlight. The mirrors concentrate the sunlight and focus it on a network
of stationary steel pipes, also suspended from the glasshouse
structure. Water is carried throughout the length of the pipe, which is
boiled to generate steam when intense solar radiation is applied.
Sheltering the mirrors from the wind allows them to achieve higher
temperature rates and prevents dust from building up on the mirrors.
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GlassPoint Brings 7 MW of Enclosed Trough CSP
On-Line in Oman |
GlassPoint pilot plant, South Oman |
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robotic cleaning system automatically washes
the roof of the glasshouse at night |
Lightweight mirror installation, 3 workers, no
crane, no work at height |
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1- Description |
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The enclosed trough is a variant of the
technology parabolic trough
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The design encapsulates the solar thermal
system within a greenhouse-like glasshouse.
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The glasshouse creates a protected
environment to withstand the elements that
can negatively impact reliability and
efficiency of the solar thermal system.
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Lightweight curved solar-reflecting mirrors
are suspended from the ceiling of the
glasshouse by wires. A single-axis tracking
system positions the mirrors to retrieve the
optimal amount of sunlight.
-
The mirrors concentrate the sunlight and
focus it on a network of stationary steel
pipes, also suspended from the glasshouse structure. Water is
carried throughout the length of the pipe,
which is boiled to generate steam when
intense sun radiation is applied. Sheltering
the mirrors from the wind allows them to
achieve higher temperature rates and
prevents dust from building up on the
mirrors.
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2- Schematic
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The Solar Steam Generation
Pilot (SSGP) plant has a solar field footprint
of 17,280 m 2,
with a peak output of over 7 MW thermal. The
Enclosed trough system is protected by a glass
structure, which is similar to an agricultural
greenhouse. Lightweight parabolic mirrors (4
of Fig 1) are hung within the glasshouse (2 of
Fig 1). The glasshouse provides structural
support and isolates the solar collectors from
wind and moisture.
Roof washer.
The
enclosed trough glasshouse structure is fitted
with an automated roof washing system (1 of
Fig 1) capable of cleaning the entire roof
surface each night. The majority of wash water
is returned in the gutter system and can be
recovered for re-use. Dust infiltration is
minimized by positive pressure from an
air-handling unit (6 of Fig 1), which provides
filtered, dried air at slight overpressure
within the structure in all conditions.
Reflector.
Due to
the absence of wind forces acting on the
collectors, a lightweight parabolic reflector
can deliver consistently high optical
accuracy. Total weight of the mirror and frame
is only 4.2 kg/m.2
The lightweight reflector enables a simple
cable drive aiming system. The fully
automatic control system delivers less than
0.5 mrad pointing error at hundreds of points
within the glasshouse.
Receiver.
The low
system weight allows the entire mirror system
to be suspended from the fixed receiver
system. This fixed receiver eliminates all
moving parts from the high-pressure direct
steam receiver system. Tubular glass shields
minimize heat losses from convection (3 of Fig
1). The receivers are suspended from the
structure by steel rods (5 of Fig 1).
Boiler.
This
system is specifically designed to mimic a
conventional oilfield OTSG boiler process, and
accommodates feed water, with total dissolved
solids as high as 30,000 ppm, and produces 80%
quality steam at 100 bar.
Water tank.
An 80-m3
upright, insulated water tank was added to the
system during the year to improve overall
performance. |
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Fig 1 - Shematic
of Enclosed trough solar system |
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3- How Enclosed Troughs work
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Step One - There are no solar
panels in a GlassPoint system. instead,
large curved mirrors are suspended inside an
agricultural glasshouse.
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Step Two - The mirrors
automatically track the sun throughout the
day, focusing sunlight on a stationary
boiler tube containing water
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Setp Three - The
concentrated sunlight heats the water to
efficiently produce high-pressure steam
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com |
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