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					            SOLAR THERMAL POWER GENERATION
               AND SEA WATER DESALINATION

                                       Stephen Kaneff
            Energy Research Centre, The Australian National University/ ANUTECH
                              Canberra A.C.T. Australia 0200




ABSTRACT
     In the past 3-4 decades, technological advances have allowed three
mainstream solar concentrating collector technologies to reach a stage which
indicates excellent potential to attain economic viability- given appropriate
conditions – in comparison with current energy supply sources. An additional
advantage is the lack of significant environmental degradation when using the
solar resources. Although a late starter, dish technology carries the best
prospects for economic success; as well as providing the highest temperatures,
the most widespread applications and the most cost-effective systems when
using large collectors, suitably designed. Parabolic trough systems have
received the greatest attention over the years, but although apparently the
simplest of the technologies, suffer from limitations in maximum efficient
temperature of operation; and economic factors are not as favorable as those
for dish systems. Central Receivers can be located, in relation to technological
and economic performance, between dishes and troughs.
     An important feature of most solar thermal technologies is the ability to
utilize the waste from the heat to work conversion processes in order to effect
cogeneration, especially to drive distillation plant, using as feedstock, saline
water sources such as sea water, underground or surface water. These features
are extremely important attributes, since economic and environmental aspects
are improved and potable water is a commodity even scarcer than electric
power in many parts of the world. In the case dishes producing high
temperatures, various thermochemical processes permit solar energy to power
solar-driven chemistry and as a result can provide non-polluting or less-
polluting liquid and gaseous fuels and especially allow the long term storage of
energy. These issues are addressed in the paper.
    Keywords: Dishes, central receivers, troughs, solar power, solar-driven
desalination, solar fuels, energy storage.




June 2005         University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2   19
Solar Thermal Power Generation and Sea Water Desalination




                                                     .
      .
                   (dish technology)

          .
                      (Prabolic trough)
                                                                                 .

                                  .
                                                                         (central receivers)
                                                                 .

          .

                                       .


                                             .



1. INTRODUCTION

    The seemingly docile power of the sun has not proved easy to
harness, except for needs which utilize the resource naturally-growing
of food, provision of warmth and generally the maintenance of life
without recourse to specific hardware utilization. Technological
applications of the more-indirect means of solar energy use – via wind
and the power of falling water, together with the burning of wood –
came first and have been well established for many hundreds of years
and more. But major changes initiated some 300 years ago, caused
onset of the Industrial Revolution, as a result of the ready applicability
of fossil fuels (and the burning of increasing amounts of wood). The
consequent provision of high temperature heat enabled the introduction
of thermal, chemical and metallurgical processes which made
practicable and led to the recent vast industrial developments. As a
consequence, much if not most of our technology – thermal, chemical
and metallurgical – is now fossil-fuel-driven.




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                                                                            Stephen Kaneff (19-46)



     In these energy providing processes, the greater part of the fossil-
fuel-supplied heat appears usually in the form of ‘waste’ heat, resulting
from the imperfections of the processes themselves and causes thermal
pollution of the biosphere, adding to the material pollution resulting
from the processes of burning of the fossil fuels. These problems were
recognized almost from the time of their first significant occurrence, but
have remained unsolved for economic reasons, lack of adequate
knowledge and particularly while-ever their magnitude was regarded as
relatively inconsequential and consequently ignored.
    But realization of the deleterious effects stemming from the burning of
fossil fuels, caused effort by some-more than 150 years ago-to be directed
to the application of solar heat to serve the same function as fossil-fuel
provided heat. These efforts initially determined means to power heat
engines-notably the work of Mouchot in France who was able from 1860 to
1880 to develop and install early solar driven machinery. In recent years,
the general progress of technology and especially the advent of large
concentrating collectors and energy conversion machinery is leading to the
availability of economical solar provided electricity and process heat. In
addition, although in its early stages, the evolution of solar-driven chemistry
via thermochemical, photochemical and other processes, is leading to the
achievement of practical systems for economically transporting and storing
large amounts of energy respectively over long distances and for long
periods of time. This contributes to the potential to supply base-load solar
power and to the realisation of solar-fossil combined systems. The solar-
driven production of modified hydrocarbon and non-hydrocarbon-based
liquid and gaseous fuels is made practicable, together with the production
of a wide range of chemicals which currently depends on the burning of
fossil fuels. Developments in these directions are currently ongoing and
can be expected to contribute substantially to the use of solar energy in the
coming years.
     Solar-based technology has further great potential, including: highly
efficient solar-driven power generation based on large Brayton Cycle
Systems, with air as the heat transport medium, operating during good
sunshine, combined with a back-up synthetic fuel produced from the



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Solar Thermal Power Generation and Sea Water Desalination



solar gasification of hydrocarbon materials or the use of
thermochemically stored heat or solar-produced non-hydrocarbon fuels,
to maintain continuous or even base-load operation; the realization of
solar-driven photochemical processes; the use of combined
thermochemical/ photochemical processes to realise efficient solar-
driven reactions; the production of hardware-based photosynthesis –and
many other processes for application on small or large scale.
     That the above mentioned processes – already developed or potentially
practicable – are now available or are being seriously studied with a view to
utilization, has resulted from a general forward march of technology which
allows effective economical hardware to be employed for all aspects of
required systems. A major advance in relation to economical solar
collection and concentration has been the advent, in recent years, of large
paraboloidal dish concentrating collectors [1-5] which have made
practicable the building of cost-effective solar thermal systems whose
economic potential increases with size of system.

2. CONCENTRATING SOLAR COLLECTORS AND COLLECTOR
   ARRAYS
     Collection/concentration systems are a key to the technological and
economic viability of the above technology, the evolution of which is
still ongoing. Unfortunately, various misunderstandings, especially
regarding temperature of collection and utilization have arisen regarding
the use of specific technologies.
     Mouchot’s basic ideas of 150 years ago were forward thinking and
essentially valid. He understood the benefits of high temperature
collection and the corresponding heat to work conversion processes, but
was unable to employ the then existing forms of technology to provide a
successful economic realisation of his concepts. Thus his overall
efficiencies were low and costs were relatively high.
    Many contemporary workers misinterpreted the reasons for Mouchot’s
incomplete success in his developments and surmised that by using lower
temperature collection with associated lower losses, these lower losses



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                                                                           Stephen Kaneff (19-46)



would more than offset the lower heat engine performance at the lower
operating temperatures – resulting in better overall technological
performance and economics. But they were unable to do better using lower
temperature systems and for similar basic reasons – inadequate level of
technological development generally. The expectation of lower losses from
lower temperature parabolic trough collectors did not more than
compensate for the inherently poorer conversion efficiencies of the heat to
work conversion machinery operating at lower temperatures.

    It is of considerable practical importance to note that the above
aspect of higher temperature vs. lower temperature solar collection and
conversion systems, still escapes the notice of many who pursue
parabolic trough systems and who may not be adequately aware of the
relative economic advantages ensuing from the use of higher
temperature collection and conversion systems, for example based on
paraboloidal dishes.

    Over the past 3-4 decades, the practically important means for
collecting and concentrating solar thermal energy have resolved into
three related but economically different technologies – dishes, central
receivers and parabolic troughs, illustrated in Figure 1.




            Figure 1. The normally available solar concentrating collectors.




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Solar Thermal Power Generation and Sea Water Desalination



    As is well known, the thermodynamic effectiveness of paraboloidal
dishes, central receivers and parabolic troughs decreases in the order
stated, for fundamental reasons involving loss mechanisms as
discussed in many references over the years. Systems using these
collectors, being dependent on the properties of the collectors, also
become less favourable in the same order. Thus paraboloidal dish
systems are favoured because on their higher potential Carnot
efficiencies when driving many processes, consequent on their higher
temperature potential and better economics (lower cost per kilowatt
thermal provided) so long as dishes are large and built economically.
Because of their advantages performance-wise and economically, this
paper concentrates on large paraboloidal dishes and systems employing
such dishes.

    Although the potential performance of dishes is well known, there
have been many reasons to expect that their apparent complexity
mitigates against good economics. However, this view is not valid
when large collectors (eg 400 m2 aperture and large) are involved,
along with employing a specific means to achieve lightweight rigid
structure [4-10].

    Figures 2a and 2b portray respectively the early SG 3 collector
which first provided electricity to the Australian East coast Grid in June
1994 [10] and the Fifth Generation collector, designated the Power Dish
Mark 3. This latter unit, although of the same generic technology and
with the same efficiency, is of 430 m2 aperture and has fewer
components; it has been rationalized for easier production and, as a
consequence, is more economical to manufacture and install.

     In the case of the Power Dish Mark 3 Collector, a dish frame
carrying 46 triangular curved mirror panels is pivoted to move on a
horizontal axis supported by a base frame rotating on a vertical axis
supported by bogies (trolleys) moving on a level circular steel rail fixed
to the ground and restrained to provide sideways constraint. A computer
control system ensures that the collector always faces the sun squarely
when in operation, actuation being effected by hydraulic ram drives on



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                                                                                Stephen Kaneff (19-46)



each axis, taking their control signals from transducers defining the
positions of each axis and relating these to the positions dictated by a
model of sun position at each moment, derived from the computer.




                Figure 2a. Perspective view of 400m2 aperture collector – SG3.




  Figure 2b. The 400m2 aperture power disk (Mark3) – perspective view with dish at 60 elevation.




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Solar Thermal Power Generation and Sea Water Desalination



     Control causes each collector axis to point in the correct orientation to
ensure that tracking occurs with adequate accuracy to allow the receiver to
be properly illuminated with concentrated solar energy with no spillage and
to convert solar heat into high quality steam with high efficiency. This
steam flows via two rotary joints to ground level into an insulated steam
main which conveys it to the central plant, with losses and costs designed to
be minimal. The control system also enables all operating functions to be
performed and for the collector to respond to appropriate signals from the
central plant, including ‘start’ and ‘stop’. The system is protected against
various abnormal situations, including receiver overheating and the advent
of strong winds (producing vertical dish orientation).

    The Power Dish is designed to maintain sun-tracking up to winds of
60 km/h in power applications. At higher wind velocities, solar resources
are rarely adequate or suitable for providing useful energy. An ever-
vigilant wind monitoring system causes the collector to move to the
survival (vertically-facing) position when wind velocity exceeds 60
km/h. The technology takes advantage of the inherent high optical
concentration achievable by paraboloidal dishes, combined with
structural configuration and detail which provide frame rigidity adequate
to maintain focal region characteristics constant, irrespective of dish
orientation or wind velocity. Specific energy density distributions can be
provided for the focal region by design, to meet particular applications –
for example, high quality steam with high efficiency for the inlet of a
steam turbine.

    Appropriate receiver design can result in very high efficiency of
conversion from direct beam solar energy to high quality steam at
temperatures and pressures beyond those required for any steam turbine (eg.
>700°C, >160 Bar); consequently the dishes can supply steam directly to
any solar thermal system of steam turbines – large or small.

2.1 Structural Advantages

   High precision structural components for the collectors are produced
by automated machinery; no adjustment is needed during or after


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                                                                           Stephen Kaneff (19-46)



installation. The precision of the structure resides in the members which
produce a high rigidity, light weight structure – manufactured by
existing industrial processes with tight tolerances achieved at reasonable
cost. Assembly is practicable in the field by relatively ‘unskilled labour’;
without jigs or special tools. The technology produces collectors of
exceptional focal region stability with a ground-hugging profile which
reduces wind loads and structural costs (due to minimal wind resistance)
and facilitates access.

     New or high cost materials or techniques are not required – steel,
concrete and glass being the main construction elements. Mirror
reflector panels are sufficiently accurate to obviate the needed for field
alignment (the structure allowing the fitting of whatever quality reflector
panels are appropriate).

2.2 Hardware and System Validity

    Hardware components and systems employed in solar power
systems need to be reliable and well proved in the field. The ‘Power
Dish’ has achieved this standing due to its evolution resulting from a
long line of developments in the field of practical working solar thermal
power systems, including White Cliffs [11], Albuquerque [12], and SG 3
[1,2,13,14]. These systems have worked in the field for long periods, in
the case of White Cliffs, for a decade.

2.3 Collector Performance

    The Power Dish Mark 3 collector is a member of the SG 3
generic class of collectors with technological improvement,
retaining the benefits of geometric and optical properties and
thermodynamics of the class, but achieved at reduced cost.
Performance in converting water by concentrated direct beam solar
energy to high quality steam follows the characteristics described in
detail in Kaneff [1,2,13,14] in accordance with Figures 3a-e.
(Figures 3a-c are taken from the Ph.D. project measurements on the
SG 3 collector by Dr. Glen Johnston [6]).



June 2005     University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2       27
Solar Thermal Power Generation and Sea Water Desalination




           Figure 3a. Percentage power within radius for various target plate positions.




                Figure 3b. Concentrated solar flux distribution across focal plane.




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                                                                               Stephen Kaneff (19-46)




     Figure 3c. Measured and design predicted flux distributions for slope error of 6 mrad.




                          Figure 3d. ’Top Hat’ semi cavity receiver.




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Solar Thermal Power Generation and Sea Water Desalination




        Figure 3e. Dish collection, conversion and supply efficiency vs. steam conditions
                        and insolation levels (Mirror Reflectivity 96%).


    In summary, for example, the conversion efficiency to produce
steam at 500°C and pressure of 5 MPa, for insolation in the range 400 to
1100 W/m2, is about 90% (steam enthalpy at ground level to direct
beam input) for a collector with clean mirrors. This results in very high
annual conversion efficiency, since the energy received over the above
insolation range amounts to some 95% of the annual incident energy. As
the efficiency of conversion falls off below 400 W/m2, the remaining
incident solar energy is collected with lower, but still useful efficiency;



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                                                                              Stephen Kaneff (19-46)



moreover, the energy involved amounts to less than 5% of the total
received. Useful heat is still collected (notwithstanding losses) for
insolation levels below 100 W/m2, this heat is valuable during the first
minutes of system warm-up, or as supplementary heat to a back-up
system, or for co-generation.




            Figure 4. Applications of paraboloidal dish systems vs size of system.



2.4 Advantages of Size for Dishes

    So long as dishes do not become too large for the wind loading to
become overwhelming, there is substantial technological and economic
advantage in the use of large dishes because:


June 2005        University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2       31
Solar Thermal Power Generation and Sea Water Desalination




Figure 5. Layout for 374 power dish array for 50MWe solar thermal power station (dish centers
                                     only are indicated).


           There are fewer components needed per MWe;
           Each component can be more sophisticated, effective, efficient
           and cost-effective;



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                                                                               Stephen Kaneff (19-46)



            When used in an array, large dishes provide broader land areas
            in between dishes and rows of dishes, which allows the land to
            be readily, without much impediment, cultivated or used for
            other purposes, apart from solar energy collection. Close spacing
            is practicable, with reduced costs and solar again;
            Lower coasts for manufacture, installation and O & M apply; and
            Reduced costs of energy supply/KW thermal result, a factor
            which improves with the number of dishes produced.

3. SOLAR THERMAL POWER SYSTEMS USING LARGE DISHES
     Earlier studies were carried out to ascertain feasibility and economics
of dish-based systems. With advent of the current Power Dish [16], several
new studies employing systems such as illustrated in Figures 6a and 6b, in
which fossil back-up is employed to provide continuity, have been made.
An important feature involves the utilization of all heat gained from the sun,
no matter what its quality. This produces economic advantage as well as
facilitating control of the solar system, since high quality heat is fed directly
to the turbine; lower quality heat is enhanced by the fossil fuelled
superheater still lower quality heat is fed to the boiler; while even lower
quality heat is diverted to the low temperature sections of the system, most
of which are existing standard components in thermal technology. Studies
have included (in collaboration with groups as indicated):

 1992               Prefeasibility Study for a 2 MWe solar power station
                    for Tennant Creek for the Northern Territory Power
                    and Water Authority.
 1993-1994          Full Feasibility Study for the Tennant Creek solar
                    thermal power station, in collaboration with a
                    Consortium of Mainland Utilities and ERC staff;
 1995-1996          Feasibility Study for 2 MWe Grid-Connected Solar
                    Dish/Central plant for Rajasthan;
                    Study for a 10 MWe Grid-Connected Dish/Central
                    plant for Uttar Pradesh;



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Solar Thermal Power Generation and Sea Water Desalination




 1997                 Feasibility Study for a 1 MWe Dish Array feeding a 60
                      MW Steam turbine, in collaboration with Transfield;
                      Study for 2.6 MWe Dish Array feeding a 200 MW
                      steam turbine;
 1997-1998            58 MWe Grid-connected generating plant with MED
                      Sea Water Desalination Plant producing 52 ML pure
                      water per day, for North Coast NSW;
                      20 MWe and 10 MWe plant as alternatives to the above
 1999                 Prefeasibility Study for a 24 MWe solar thermal plant
                      for Whyalla for Whyalla Council, providing 20 ML
                      pure water/day from solar waste-heat-driven MED
                      desalination plant.




              Figure 6a. Basic diagram for multimegawatt power system with coal,
                                  oil or natural gas fired boiler.




34        University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2   June 2005
                                                                               Stephen Kaneff (19-46)




                     Figure 6b. Solar array powering steam turbine section
    and optionally providing compressed air heating for gas turbine combined cycle system.



    Figures 6a and 6b give typical functional diagrams for steam and
gas turbine combined cycle systems respectively for a typical
optimized solar array. Optimization follows the work of Carden and
Bansal [15] and in the case of a 50 MWe, 374-Dish system, layout of
the array is given in Figure 5, which is typical for systems of this size
and much larger.



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Solar Thermal Power Generation and Sea Water Desalination



4. ECONOMIC ASPECTS

    When the latest developments for large 400m2 aperture paraboloidal
dish collectors (with high efficiency and low cost) are incorporated and
combined in suitable arrays feeding central plant, excellent economic
potential can arise, sufficient to place such systems at the forefront of
solar thermal technologies which are valid for smaller systems, but
whose advantages increase with size of system.

     A feature of such systems, already mentioned, is the wide scope for
applications in different sizes and for different purposes, as indicated in
Figure 4. At the start of new technological developments, in the absence of
an established market, it is not easy to report with assurance on system
costs. However, due to the substantial amount of interaction with and
participation of both Utilities and Industry, a degree of confidence exists to
support the economic potential in applications involving power systems.
Economic performance is dependent on many factors, not only on the cost
of manufacturing, assembling and installing hardware and developing
strategies for operation, maintenance and optimization, but especially on
solar resources, which vary over wide limits and with time in any given
location. Figure 7 shows (Australian Currency), the effect on levellised
electricity cost for a small 20 dish system feeding a large turbogenerator at
different Insolation levels and for different dish costs (which also may
depend on the capacity of the plant to build the systems).

4.1 Comparison of Dish-Based Solar Thermal with Other
    Renewable Energy Costs

    Table 1 compares, on the basis of recent published information,
various renewable energy technologies. The wide ranges of costs arise
because of different system sizes and (as already mentioned) due to a
non-established market as yet for many of the technologies. It can be
noted that Solar Thermal Dish-based power in greater than small sizes, is
becoming competitive with fossil-fuel-based power, in spite of there
being no benefits granted because of the low pollution levels; but there
are benefits now being provided in some areas through the operation of


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                                                                                        Stephen Kaneff (19-46)



‘green power’ premiums which are set to proved a deserved advantage.
The cost provide in Table 1 are expressed in Australian dollars.




            Figure 7. Indicating cost of electricity vs. cost of dishes and solar resources.


                       Table 1. Indicative costs of selected renewable energies.
Energy Source      Relevant        Special Size      Cost     Cost     Potential    Reference
                  Technology                      $A/MWhe    Trends    Contrib.
Biomass          Direct Comb.       1-300 MW       60-200     Decr.   Significant   Chegwidden, Wright, Redding
                 Gasification            "         30-100       "          "
Geothermal      Heat exch.turb       100 MW        90-130       "          "        Wright
Hydro (small)   Hydro turb, gen     0.1-10MW       40-250     Incr.     Small       Chegwidden, Wright, Redding
Landfill Gas      Gas engine         1-5 MW        50-100    Static    Limited      Chegwidden, Wright
Photovoltaics   Non-Concentr.         0.5MW        300-500    Decr.   Significant   Chegwidden, Wright,
                Concentrating       0.004MW         250?        "     Significant   Redding, Blakers
Solar Thermal        Dish          0.01-200MW      50-250       "     Significant   Kaneff, Cheg. Wr. Redd. Blak.
                    Tower           1-200MW        200-280      "     Significant   Grimaldi, Osuna et al.
                    Trough          1-200MW        200-250      "     Significant   (10MWe)
                                                                                    Chegwidden
Tidal           Low head hydro       60MW          80-300    Static    Limited      Chegwidden, Wright
                 Turbine gen.
Wastes          Gasifier/gaseng.    5-15 MW        60-200    Decr.    Significant   Chegwidden, Wright
Wave               Various          0.1-4MW       100-200    Decr.    Significant   Chegwidden, Wright, Redding
Wind            Wind turb. Gen      0.1-3MW       60-120     Decr.    Significant   Cheg.Wright.Blakers Redding




June 2005            University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2                37
Solar Thermal Power Generation and Sea Water Desalination



4.2 Comparison of Dish-Based High Temperature Solar Heat
     with Natural Gas Heat

    All costs are in $ Australian ($AUD)–February 2001 rates of
exchange are $AUD 1 ~ $US 0.53, but this does not provide a true
comparison of values for technological systems.

    The current ‘Power Dish’ designs can challenge the cost-
effectiveness of high quality heat provided by the burning of natural gas
either in gas-fired boilers, or for powering gas turbines with or without
the use of combined cycles. Without making a detailed comparison of
operating systems in each case, it is useful to provide relative indicative
costs for supplying solar heat and natural gas heat to the point of use. In
the generation of electricity, the means for conversion of the high quality
heat by specific kinds of plant (steam turbogenerator or gas turbine etc.)
is not a factor, since such conversion machinery can be powered by heat
from either source.

     Natural Gas Heat Costs: If natural gas delivered to the point of use
     costs $3.0/GJ, which is on the low side for systems considered here:

     Cost of the fuel itself = 300 cents per 1000/3.6 kWh thermal (1 GJ-
     278 kWh) (ie. = 1.08 cents per kWh thermal)

     Adding various hardware and handling costs, pumping, storage,
     leakage losses, O & M costs and others, increases this amount by
     factors which depend on the application.

     For a relevant but low increase, applying levellised energy gives:

     Cost of Gas Energy to provide high quality heat                             1.2+ cents per
     kWh thermal (for gas at $3.0/GJ)

     Salary Array Heat Costs: Using Standard AS3595 – 1990 Energy
     Management Programmes – Guidelines for financial Evaluation of a




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                                                                            Stephen Kaneff (19-46)



     Project, published by Standards Australia for calculating present
     values; and the following parameters:

     Discount Factor = 8%

     30 year plant lifetime with refurbishment at 5% capital cost after 10
     years, 10% of installed cost at 20 years and with 20% residual value
     at 30 years;

     Direct Beam solar Resources = 2200 kWh/m2/annum (This is on the
     low side of solar resources for much of inland Australia – and for
     many parts of the world – where for sunny sites, Insolation ranges
     from 2300 to 3000 kWh/m2/annum);

     Collectors of 430 m2 aperture and overall conversion efficiency –
     including reflectivity and receiver absorptivity of over 90%, at an
     insolation level of 950 W/m2 and output steam = 550ºC, supplying
     heat via a heat transport network of 4% loss,

     Power/dish fed to turbine             430 x 0.9 x 0.95 x 0.96 = 353 kW
     thermal.

     Total output/dish per annum              353 x 2200 = 776,000 kWh/annum
     thermal.

     For an installed Collector cost = $100,000 + $6000av./collector for
     the heat transport network, using the above Standard,

     Total discounted cost = (100,000 + 6,000) x 1.1758 = $ 124,600

     Total discounted output = 776,000 x 11.2572 = 8,740,000 kWh
     thermal

     Levellised energy cost = 124,600 x 100/8,740,000 = 1.4 cents/kWh
     thermal

     For an installed Collector cost = $75,000 + $5,000av./collector for
     the heat transport network,



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Solar Thermal Power Generation and Sea Water Desalination



     Total discounted cost = (75,000 + 5,000) x 1.1758 = $94,060

     Levellised energy cost = 94,600 x 100/8,740,000 = 1.08 cents/kWh
     thermal

    To achieve these installed solar collector costs requires present
designs to be rationalized for production and installation processes (as
well as gaining the necessary purchase advantages and other related
aspects) which correspond to factory production processes set up for
several thousand units. This is not an impractical requirement, noting
that one 100 MWe electricity generating system requires some 700
collectors each of 430m2 aperture.

     In the above approximate analysis, system overall generation costs are
similar whether solar energy or gas is employed, taking account of the
intermittent nature of solar operation. The above begs the question of
storage and continuous solar operation, but indicates that systems
employing collectors with installed costs of about $100,000 or less in areas
of reasonable sunshine, can compete economically with natural gas for
electricity generation. This competitiveness improves as solar resources
increase and/or the cost of natural gas increases above $3.0/GJ. Cooperative
systems fare better still due to better capacity factors.

5. SOLAR SYSTEM WASTE-HEAT DRIVEN DESALINATION

    Potable water is even more important to many worldwide than is
electricity. Sea water, saline surface or underground waters may be used
as feedstock for desalination plant which can be powered by waste heat
from solar thermal dish-based systems. Figure 8 shows the exergy
requirements (available heat) to achieve desalination by various
processes which are in use.

     The rejected heat from solar thermal/ thermochemical electricity
generation systems can be employed readily to power desalination plant,
utilizing much of the waste heat normally discarded in the cooling water
of thermal heat-to-work conversion machinery. That is, the fuel costs to



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                                                                            Stephen Kaneff (19-46)



achieve desalination are obviated, as is the need to create pollution from
the burning of fossil fuels.




                Figure 8. Exergetic comparison of desalination systems.


     Commercially available desalination plant can be employed,
particularly plant which is designed to operate at low first stage
temperatures, as this reduces greatly the maintenance requirements of the
desalination equipment; it also allows the first cell of the desalination plant
to be connected to the steam turbine exhaust to effect steam condensation to
advantage. This results in relatively small reduction in performance of the
turbine. Figure 9 illustrates this means for achieving both electricity and
water production economically. Other arrangements are possible.

     By suitable design and overall system configuration, combined
electricity and potable water plants can provide a cost-effective approach
to providing valuable needs for much of the world. A recent assessment
[5], supported by outside Consultants has indicated an electricity cost of
$65/MWe (qualifying for a green power premium of $20/MWe) and a
water cost of $0.82/kilolitre. Both of these costs are competitive in the
area concerned. A larger plant than the 24 MWe and up to 20 megalitres


June 2005      University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2       41
Solar Thermal Power Generation and Sea Water Desalination



of water per day, in an area of better sunshine (~2200 kWh/m2/annum),
would have better economic returns.




       Figure 9. Solar thermal dish-based electricity generation with waste-heat driven desalination.
          The MED plant provides condensation for the turbine, as utilized by SIDEM of Paris.




42        University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2                June 2005
                                                                                Stephen Kaneff (19-46)



    Suitable large concentrating solar collectors are already available as
a commercial product. A wide range of processes can, with the benefit of
appropriate R & D, be also realized commercially within a short time by
employing the system ‘waste heat’ energy. When applied to the
remediation of saline soils, desalination and salt separation, such solar
thermal plant can provide:

     -      Viable solar electricity generation;
     -      Production of Salts or Concentrated Brine as valuable salable items;
     -      Land Reclamation and general environmental improvement;
     -      Provision of Process Heat (low to very high temperatures);
     -      Water for Horticulture – especially for hydroponics and high
            value crops;
     -      Water for Aquaculture and associated processes;
     -      Supply of Ultra-Pure Water (Pharmaceutical and Boiler Quality);
     -      Low-quality heat for building, greenhouse heating and crop-drying;
     -      The establishment of Industries associated with the above activities;
     -      Improvement of wealth and quality of life generally for local
            inhabitants; and
     -      Generation of Intellectual Property in relation to the above,
            leading to income-earning potential, both directly and from
            application elsewhere.

6. CONCLUSIONS

    Areas which can exploit solar resources with benign environmental
consequences are clearly those regions with good solar resources –
which can be used for the benefit of the regions themselves and to the
world as a whole;

   Starting with present commercially-available solar technology and a
good R & D and manufacturing infrastructure, solar-based technology can be


June 2005          University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2       43
Solar Thermal Power Generation and Sea Water Desalination



expanded in the directions indicated above to become a major energy source,
as fast as the appropriate resources are applied to achieve these results.

     The present circumstances whereby existing energy providers of oil,
coal and gas, transport this energy worldwide from points of availability to
points of use, could gradually evolve to include increasingly the similar
transport of solar produced fuels, especially in the earlier stages with the
inclusion of solar – modified fossil fuels. Present oil, coal and gas providers
would be in a good strategic position to take advantage of these developments,
especially since their basic energy infrastructure already exists; moreover,
their solar resources are usually excellent, thereby providing additional
advantage. Economic aspects are becoming favourable for the use of large
dish-based systems, especially if associated with desalination.

REFERENCES
[1]     S., Kaneff, Viable Solar Thermal Electricity Generation, in Power
        Generation Technology 1994, Sterling Publications, London,
        (1994a), pp. 105-109.
[2]     S., Kaneff, Solar Generator 3: 400 m2 Paraboloidal Concentrator”,
        Solar Progress, Vol. 15, No. 3, (1994b), pp. 4-5.
[3]     S., Kaneff, A 400 m2 Aperture ‘Power Dish’. Proc. 35th Annual
        Conference of the Australian and New Zealand Solar Energy
        Society (ANZSES), Solar 97, Ed. T. Lee, Canberra December 1-3,
        Paper 90, (1997), pp. 7.
[4]     S., Kaneff, Viable Distributed Dish/Central Plant Solar Power:
        Status, New Developments, Potential, in Journal of Physics IV,
        France, Vol. 9, No. 3., (1999a), pp. 195-200.
[5]     S., Kaneff, Prefeasibility Study: 24 MWe Solar Thermal Paraboloidal
        – Dish – Based Plant for Whyalla – with recommendations for
        Waste-Heat-Driven Desalination of Seawater. Report to Whyalla
        Council, July (1999b), pp. 221.
[6]     S., Kaneff, On the Design of Viable Paraboloidal Dish Solar
        Collector Systems, Proc. Congress of International Solar Energy
        Society (ISES), Kobe, Japan, 4-8 September 1989, Edis Horigome,
        Kimura, Takakura, Nishimo and Fuji (Pergamon Press, Oxford
        1990), 2: (1990a), pp. 1303-1307.



44        University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2   June 2005
                                                                            Stephen Kaneff (19-46)



[7]    S., Kaneff, Large Paraboloidal Dish Solar Arrays, Keynote
       paper, Proc. Annual Australian and New Zealand Solar Energy
       Society Annual Conference, University of Auckland, 28
       November-1 December, Solar ’90, Edis Bansal, Raine and
       White, (1990b), pp. 25-36.
[8]    S., Kaneff, Paraboloidal Dishes of 400 m2 Aperture and Larger, Proc.
       International Solar Energy Society (ISES) Solar World Congress,
       Budapest, 23-27 August, Vol. Solar Thermal, (1993a), pp. 6.
[9]    S., Kaneff, On the Evolution, Over Four Generations, of
       Paraboloidal Dish Solar Thermal Electric Power Systems,
       Proceedings of the Sixth International Symposium on Solar
       Thermal Concentrating Technologies, sponsored by International
       Energy Agency (IEA), CIEMAT et al, Mojacar, Spain, 28
       September – 2 October, Vol. 2, (1993b), pp. 903-917.
[10]   S., Kaneff, Final Report on the First Large Dish Solar Thermal
       System for the New South Wales Department of Energy, January
       1997; Updated May 1998, (1997-1998).
[11]   S., Kaneff, “The White Cliffs Project: Overview for the Period
       1979-89 Publ. NSW Office of Energy, Sydney. ISBN 0 7305 6954
       3, (1991), pp. 241.
[12]   C.P., Cameron, and D.M., Harvey, A Small Community Solar
       Experiment #2 ModuleTest Results, Sandia Report No. SAND88-
       2802, UC-237, May, (1991), pp. 121.
[13]   S., Kaneff, The ANU/ANUTECH 400 m2 Aperture Paraboloidal
       Concentrating Collector- Details and Performance. Energy
       Research Centre Report, June (1995), pp. 43.
[14]   S., Kaneff, Solar Generated Electricity: A Comparison of
       Available Technologies Proc. National Engineering Conference,
       Darwin, 21-24 April, (1996), pp. 465-470.
[15]   P.O. Carden, and P.K., Bansal, Optimisation of Steam-Based
       Energy Transport in Distributed Solar Systems, Solar Energy Vol.
       49, pp. 451-461. (Also 1991 ERC Report), (1992).
[16]   A., Blakers, Solar and Wind Electricity in Australia, Australian
       journal of Environmental Management, December, (2000).
[17]   A., Chegwidden, Markets for Renewable Energy Products:
       Overview from a Utility Perspective, Proceedings of the 6th
       Renewable Energy Technologies & Remote Area Power Supplies
       Conference, Sydney, 8-10 March, (2000), pp. 17.



June 2005      University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2       45
Solar Thermal Power Generation and Sea Water Desalination



[18] P.,Grimaldi, and I., Grimaldi, Solar Tres: Proposal of a Solar-Only
     24 hour Operation Solar Tower Plant for Southern Spain,
     Proceedings of the 10th SolarPACES International Symposium on
     Solar Thermal Concentrating Technologies ‘Solar Thermal 2000’,
     Sydney, 8-10 March, (2000), pp. 57-58.
[19] G.H.G., Johnston, Focal Region Modelling and Characterization of
     Paraboloidal Dish Solar Concentrators, PhD Thesis, The
     Australian National University, January, (1997), pp. 280.
[20] S., Kaneff, Multi-Megawatt Dish-based Solar Thermal
     Electricity Generating Plant with Optional Co-Generation,
     Proceedings, 10th SolarPACES International Symposium on
     Solar Thermal Concentrating Technologies, ‘Solar Thermal
     2000’, Sydney, 8-10, (2000).




46        University of Sharjah Journal of Pure & Applied Sciences Volume 2, No. 2   June 2005

				
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