solar turbine plants

not for publication 1

SOLAR TURBINE PLANTS

By

Sujitkumar patel (14me089)

CHAMOS Matrusanstha department of Mechanical Engineering

CHARUSAT


INTRODUCTION

A Solar thermal power plants works on solar energy received from solar radiation through collectors.

The radiant energy from the sun is captured by solar collectors and transmitted for suitable working fluid

A solar turbine employs Rankine cycle in lower temperature range and Brayton cycle in high temperature range

Earth receives 1.783*10^14 KJ solar energy per second. Sunshine available for long hours in tropical countries like India. Blythe solar power project (California) working on solar turbine plants.


ELEMENTS OF SOLAR POWER PLANT


RANKINE CYCLE POWER PLANT


BRAYTON CYCLE POWER PLANTS


SOLAR COLLECTORS

Any surface which receives solar radiation and transmits it to a receiver or absorber is a collector of solar energy

Types of collectors:

1. Low temperature collectors

2. Medium temperature collectors

3. High temperature collectors


LOW TEMPERATURE COLLECTORS

Here solar radiation is received by bank of tubes mounted on a black metallic absorber plate.

In these collectors large surface for collecting both direct and diffuse radiation can be obtained without employing any suntracking mechanism.

Energy losses in these collectors are mainly due to heat losses by conduction,convection and radiation.


MEDIUM TEMPERATURE COLLECTORS

For absorbing heat at higher temp. solar radiation is directed on the receiver by concentrating devices.

Concentration ratio

=area of concentrator/receiver surface area

=Ac/Ar



Optical efficiency=Qr/Qc

Where ,

Qc=Ic*Ac Collector efficiency=Qu/Qc

Qu=Qr-losses


HIGH TEMPERATURE COLLECTORS

These are concentrating collectors which can produce receiver temperature above 350 degree.

They require accurate sun tracking by employing large number of heliostats


Heliostats

On account of the changing position of sun every day during the year, the solar radiation can neither be collected nor directed on the receiver properly in a fixed collector receiver system.

A collector which continuously tracks the sun is called heliostat.

The concentration ratio obtained by employing n heliostats.

The position of the individual heliostats in the field, besides other factors,depends upon geographical location of the place.


SOLAR RECEIVERS

The receiver absorbs the heat from the solar radiation flux transmitted by the collector.

The coolent or primary fluid can be heated to high temperatures. Majority of receivers for solar turbine power plants are located on high stands or

towres for receiving radiation flux from collectors. Types of collectors

1. External receivers

2. Cavity receivers

3. Tubular receivers


External receivers In this type of receiver the tubes carrying the primary fluid or working fluid are

provided on the external surface of the vertical body. On account of the configuration of the external receivers large arrays of

heliostats around them can be employed to transmit the solar radiation flux on the coolant tubes.


Cavity receivers

Here solar energy is supplied to the coolant tubes , which are mounted on the inside surface of a large enclosure.

Since a large number of coolants tubes have to be accommodated inside the cavity.


Tubular receivers

It consists of a row of coaxial tubes as shown in fig.

The outer tube is made from transparent material which receives solar radiation.

Heat losses are further reduced by providing proper insulation


Central receiver system


Distributed receiver system


Solar energy storage


Solar ponds A solar pond is a large water body which is employed to receive solar energy through

collected by its suface.it is a collector receiver system built into it. The temperature in a water body surface is exposed to solar radiation is higher at the

surface and lower at the bottom. The hot layer of water nearer the bottom acts as sensible heat storage. heat is

extracted from this layer by pumping hot brine to the evaporator of the plants.


Solar ponds


Solar turbines

The section brings together the role and performance of thr various components of the solar turbine power plants in terms of the turbine output and efficiency of plant.

The solar turbine output, along with the net efficiency of the plant,effects of collector receiver size and the land area required.these factors determines the capital cost of plant.

The selection of working fluid and coolant are also important because they decide the major design parameters of the components of the plant.


Solar turbines


Net efficiency

Graph shows the variations of the efficiencies of the collectors and turbine plants.

The thermal efficiency of plant increases with the inlet temp. of the working fluid .

In some temperature range the gain in thermal efficiency due to higher fluid temp. is offset by the significantly lower collector efficiency.


Advantages

Fuel cost is zero. No extraction of fuel and transportation is required. No fuel processing is needed Power produced by without environmental pollution. With energy storage systems can be used in special situations

when other power plants are not available. Solar power plants can be easily operate in remote places like

islands.


disadvantages

Availability of sunshine is not continuous. For continuous power supply large heat storage system is needed Collection of solar energy produces large areas of shadows which

can create ecological problems. Expensive sun tracking system is required. Overall efficiencies of solar turbine power plant is low.