Declaration Certified that the Report entitled Solar Thermal
Power plant submitted by Raval Dhaivat Jaladhi with Enrollment No.
A20422411018 on 13th April 2015 is his own work and has been
carried out under my supervision. It is recommended that the
candidate may now be evaluated for his work by the University.
Raval Dhaivat Jaldhi
B.Tech+M.Tech (MAE)
AcknowledgementI, Raval Dhaivat Jaladhi of B.tech + M.tech (MAE;
8th Semster), Amity School of Engineering and Technology (A.S.E.T),
Amity University Rajasthan, gratefully acknowledge the guidance,
support and co-operation of all the faculty members of A.S.E.T for
completing my report on Solar Thermal Power Plant.
I would like to heartily thank Mr. Laxman Kumar Pandey whose
encouragement, guidance and support from the start till the end of
my report enabled me to develop an understanding of the topic.
I have gained a lot of knowledge about this topic and think that
it is a good way of improving our knowledge on new
technologies.
Raval Dhaivat Jaladhi
B.Tech+M.Tech (MAE)
Semster:-8th
Table of Contents
1. Introduction1.1
1. Introduction
Solar Thermal Power Plant:-Solar thermal power plants use the
sun's rays to heat a fluid to high temperatures. The fluid is then
circulated through pipes so that it can transfer its heat to water
and produce steam. The steam is converted into mechanical energy in
a turbine which is then converted into electricity by a
conventional generator.Solar thermal power generation works
essentially the same as power generation using fossil fuels, but
instead of using steam produced from the combustion of fossil
fuels, the steam is produced by heat collected from sunlight. Solar
thermal technologies use concentrator systems to achieve the high
temperatures needed to heat fluid.For thermodynamic reasons high
temperatures are required to achieve the utmost efficiency. Such
high temperatures are reached by increasing the energy flux density
of the solar radiation incident on a collector.
According to the type of solar radiation concentration, solar
thermal power plants are subdivided into:- Concentrating (point and
line focussing) systems.1. Solar tower power plants (i.e.central
receiver systems) as point focussing power plants,2. Dish/Stirling
systems as point focussing power plants 3. Parabolic trough and
Fresnel trough power plants as line focussing power plants.
Non-concentrating systems.1. Solar updraft tower power plants2.
Solar pond power plants
Process of solar thermal power generation:-
Concentrating solar radiation by means of a collector system;
Increasing radiation flux density (i.e. concentrating of the solar
radiation onto a receiver), if applicable; Absorption of the solar
radiation (i.e. conversion of the radiation energy into thermal
energy (i.e. heat) inside the receiver); Transfer of thermal energy
to an energy conversion unit; Conversion of thermal energy into
mechanical energy using a thermal engine (e.g. steam turbine);
Conversion of mechanical energy into electrical energy using a
generator.
Concentrating (point and line focussing) systems:-
Parabolic trough plants: - The solar field of a parabolic trough
plant contains numerous parallel rows of collectors that comprise
parabolic curved dishes and concentrate sunlight onto an absorber
tube that runs along a focal line, thus producing temperatures of
about 400 C. The heat carrier here is circulating thermal oil which
absorbs the generated heat and creates steam at an approximate
temperature of 390 C in a heat exchanger; the steam is then used to
drive a steam turbine and a generator to generate electricity as in
conventional power plants. The principal share of solar thermal
power generation in Spain is currently supplied by numerous
parabolic trough plants each with a capacity of 50 MW, the majority
of which have thermal storage for about seven hours of operation
without sun.
Fresnel collectors: - Long, only slightly curved, flat mirrors
concentrate the solar radiation onto a fixed absorber tube, thus
directly heating and vaporising water. In comparison with the
parabolic trough, the investment outlay in terms of the reflecting
surface is lower due to the simpler basic concept; on the other
hand, the comparative annual efficiency is lower. Two Fresnel power
plants with a total capacity of 31 MW have been put into operation
in the Spanish province of Murcia.
Solar towers: -In solar tower power plants, the solar radiation
from hundreds of automatically positioned dishes is concentrated on
a central absorber at the top of the receiver. The significantly
higher concentration of sunlight than in parabolic trough
collectors, for example, also allows for higher temperatures of up
to about 1,000 C. This allows for greater efficiency, particularly
when using gas turbines, and is therefore likely to lead to lower
electricity costs.The first commercial solar tower power plant in
Europe, the PS10, which has an installed capacity of 10 MW, was
commissioned in 2007 in Seville, Spain; it was supplemented in 2009
with the PS20, a twin solar tower power plant. In mid-2011, the Gem
solar tower power plant was connected to the grid in the province
of Seville. It has a capacity of 20 MW and uses a thermal molten
salt storage system that allows for up to 15 hours of storage at
rated power, thus providing electricity from solar energy around
the clock during the summer months. In October of 2013, a solar
power plant with a capacity of 420 MW went on the grid in the USA,
and another with 120 MW is about to be commissioned.
Dish / Stirling systems: - In dish/Stirling systems, a parabolic
dish concentrates the solar radiation onto the heat receiver of a
downstream Stirling engine, which then converts the thermal energy
into mechanical power or electricity. Efficiencies of over30 per
cent are achieved. There are prototype systems at the Platform
Solar, for example, in Almeria, Spain. These plants are
particularly suitable as stand-alone systems. They also offer the
possibility of interconnecting several individual systems to create
a solar farm, thus meeting an electricity demand from ten kW to
several MW.
Solar Pond: - A salinity gradient solar pond is an integral
collection and storage device of solar energy. By virtue of having
built-in thermal energy storage, it can be used irrespective of
time and season. In an ordinary pond or lake, when the sun's rays
heat up the water this heated water, being lighter, rises to the
surface and loses its heat to the atmosphere. The net result is
that the pond water remains at nearly atmospheric temperature.
Thesolar pond technologyinhibits this phenomena by dissolving salt
into the bottom layer of this pond, making it too heavy to rise to
the surface, even when hot. The salt concentration increases with
depth, thereby forming a salinity gradient. The sunlight which
reaches the bottom of the pond remains entrapped there. The useful
thermal energy is then withdrawn from the solar pond in the form of
hot brine. The pre-requisites for establishing solar ponds are: a
large tract of land (it could be barren), a lot of sun shine, and
cheaply available salt (such as Sodium Chloride) or bittern.
Solar Updraft Tower: -Thesolar updraft tower(SUT) is
arenewable-energypower plantfor generating electricity fromsolar
power. Sunshine heats the air beneath a very wide greenhouse-like
roofed collector structure surrounding the central base of a very
tallchimneytower. The resultingconvectioncauses a hot air updraft
in the tower by thechimney effect. This airflow driveswind
turbinesplaced in the chimney updraft or around the chimney base to
produceelectricity. Plans for scaled-up versions of demonstration
models will allow significant power generation.
Solar TowerDish/ StirlingParabolic troughFresnel CollectorSolar
PondSolar updraft Tower
Typical Capacity(MW)30-2000.01-110-20010-2000.2-530-200
Real Capacity(MW)100.025800.350.05
Concentration Factor600-1000Up to 300050-9025-5011
Efficiency in %10-2815-2510-239-1710.7-1.2
Operation Modegridgrid/ islandgridgridgridgrid
Concentration factors and technical parameters of selected solar
thermal power generation technologies.
2. Solar Tower Power StationA solar power tower, or central
receiver, generates electricity from sunlight by focusing
concentrated solar energy on a tower-mounted heat exchanger
(receiver). This system uses hundreds to thousands of flat,
sun-tracking mirrors called heliostats to reflect and concentrate
the sun's energy onto a central receiver tower. The energy can be
concentrated as much as 1,500 times that of the energy coming in
from the sun.Energy losses from thermal-energy transport are
minimized because solar energy is being directly transferred by
reflection from the heliostats to a single receiver, rather than
being moved through a transfer medium to one central location, as
with parabolic troughs.Power towers must be large to be economical.
This is a promising technology for large-scale grid-connected power
plants. Power tower technology is in the early stages of
development compared to parabolic trough technology.
Main principals and components: Central receiver systems in the
tower Mirrors tracking the course of the sun in two axes
(Heliostats) Heliostats reflect the direct solar radiation onto a
receiver, centrally positioned on a tower. In the receiver,
radiation energy is converted into heat and transferred to a heat
transfer medium (E.g. air, liquid salt, water/steam). This heat
drives a conventional thermal engine. To ensure constant parameters
and a constant flow of the working medium also at times of
varyingSolar radiation, either a heat storage can be incorporated
into the system or additional firing using e.g. fossil fuels (like
natural gas) or renewable energy (like biofuels) can be used.
Heliostats: -
Heliostats are reflecting surfaces provided with a two-axis
tracking system which ensures that the incident sunlight is
reflected towards a certain target point throughout the
day.Heliostats commonly concentrate sunlight by means of a curved
surface or an appropriate orientation of partial areas, so that
radiation flux density is increased.
Faceted glass/metal heliostat.Metal membrane heliostat
Heliostats consist of: The reflector surface (e.g. mirrors,
mirror facets, other sunlight-reflecting surfaces) A sun-tracking
system provided with drive motors Foundations and control
electronics.
The individual heliostats orientation is commonly calculated on
the basis of: The current position of the sun The spatial position
of the heliostats The target point.
The target value is communicated electronically to the
respective drive motors via aCommunication line. This information
is updated every few seconds.The concentrator surface size of
currently available heliostats varies between 20 and150 m2; to
date, the largest heliostat surface amounts to 200 m.
Controller: - Heliostats are usually centrally controlled and
centrally supplied with electrical energy. As an alternative,
autonomous heliostats have been developed which are controlled
locally. There, the energy required for the control processor and
the drives is provided by Photovoltaic cells mounted parallel to
the Reflector surface.
Heliostat fields: -The layout of a heliostat field is determined
by technical and economic optimization:Heliostats located closest
to the tower present the lowest shading, Heliostats placed north on
the northern hemisphere (or south on the southern hemisphere) show
the lowest cosine losses.Heliostats placed far off the tower, by
contrast, require highly precise tracking and, depending on the
geographic location, have to be placed farer from the neighbouring
heliostats.Notes:Cosine losses: -of the earthThe cost of the land,
the tracking and the orientation precision thus determine the
economic size of the field.For about half the cost of the solar
components