太阳能热利用 热发电 光伏发电 论文

Solar Thermal Power Plants

prepared for the EUREC-Agency

drafted version with status of May 03, 2000

prepared by

M. Becker*, W. Meinecke*, M. Geyer*, F. Trieb*, M. Blanco**, M. Romero**, Ferrière, A. ***1 Introduction, Potential and Strategic Summary

In solar thermal power plants the incoming radiation is tracked by large mirror fields whichconcentrate the energy towards absorbers. They, in turn, receive the concentrated radiationand transfer it thermally to the working medium. The heated fluid operates as in conventionalpower stations directly (if steam or air is used as medium) or indirectly through a heatexchanging steam generator on the turbine unit which then drives the generator.

To make solar high flux, with high energetic value originating from processes occurring at thesun's surface at black-body-equivalent temperatures of approximately 5800 K usable fortechnical processes and commercial applications, different concentrating technologies havebeen developed or are currently under development for various commercial applications.Such solar thermal concentrating systems will undoubtedly provide within the next decade asignificant contribution to efficient and economical, renewable and clean energy supply.

This paper deals with three different technologies for solar thermal power plants making useof concentrating solar energy systems (Figure 1), namely by

parabolic troughs,

central receivers (towers) and

parabolic dishes.

The White Paper of the European Commission for a community strategy and action plan onrenewable energies of 1997 foresees at least 1 GWe of those systems implemented inEurope by the year 2010. This objective can be achieved by a scenario of a number of 25 to30 commercial solar thermal power plants with 30 to 50 MWe unit size each and distributedalong the South of Europe.

These solar thermal technologies comply with the prime objectives and key research,technology, and demonstration actions of the Fifth Framework Programme of the EuropeanCommission, because

their developments will enhance the deployment of solar energy systems for bulk

electricity production and the conservation of fossil energy, consequently preserving theenvironment in particular with respect to their high potential to contribute to the reductionof the CO2 emissions,

they reduce the generating costs of solar power plants, and thus contribute to ensure

durable and reliable energy services at affordable costs in the medium- to long-termrange,

___________________________

* DLR; Köln, Stuttgart and Almería

** CIEMAT; Madrid and Almería

*** CNRS; Odeillo

太阳能热利用 热发电 光伏发电 论文

they will provide the European industry with a privileged technological position, thus

opening industrial growth possibilities not only to the internal market of southernEuropean countries but also to the export of equipment and services in the field of solarplant installations; in some respect, the solar specific technology required in most casesis also accessible to the local industries; the opportunity to create links with developingcountries and their markets is self-evident,

they have the potential to contribute to the social objectives of the European Union as to

the quality of life, health, safety (including working conditions) and job creation; theerection of such plants at undeveloped areas in southern Europe can create newopportunities of industrial fabrication, of assembling and of operation and maintenance.So, solar thermal power plant technologies are important candidates for providing a majorshare of the clean and renewable energy needed in the future, because

solar thermal power stations are among the most cost-effective renewable power

technologies; they promise to become competitive with fossil-fuel plants within the nextdecade,

solar thermal power stations are already today of well-proven and demonstrated

technology; since 1985 nine parabolic trough-type solar thermal power plants inCalifornia have fed more than 8 billion kWh of solar-based electricity into the SouthernCalifornian grid, demonstrating the soundness of the concept,

solar thermal power stations are now ready for more intensified market penetration;

accelerated grid-connected applications will lead to further innovation and cost reduction.However, no new commercial solar thermal power plants have been built since the last two80 MWe parabolic trough plants (SEGS VIII and IX) were connected to the SouthernCalifornia grid in 1991 and 1992 respectively, due to the following main reasons:

financial uncertainties caused by delayed renewal of favourable tax provisions for solar

systems in California

financial problems and subsequent bankruptcy of the U.S./Israeli LUZ group, the first

commercial developer of private solar power projects

rapid drop of fossil energy prices and following stable energy prices at low levels since

years world-wide

required large unit capacities of solar thermal power stations to meet competitiveconditions for the generation of bulk electricity, resulting in financing constraints due to theinherently large share of capital costs for solar installations

rapidly decreasing depreciation times of capital investments for power plants due to the

deregulation of the electricity market and the shift to private investor ownership of newplant projects world-wide

dropping specific prices and enhanced efficiencies of installed conventional power plant

installations, particularly of combined cycle power plants

missing favourable financial and political environments for new initiatives for the

development of solar thermal power plant projects in sunbelt countries.

Fortunately, the chances for solar thermal projects in the next decade have increased in themeantime significantly, because

interest rates and capital costs have fallen drastically in Europe with the introduction of the

Euro for the benefit of capital-intensive projects such as solar thermal power plants,

the EU policy firmly supports an 8 % reduction in gas emissions by doubling the share of

renewable energies of the EU energy balance from 6 to 12 % by the year 2010,

a recent expertise of the World Bank predicts solar thermal cost reductions below

6 US cents/kWh after the year 2010, convincing the Global Environment Facility (GEF) tosupport barrier removal and market introduction of solar thermal power in developing

太阳能热利用 热发电 光伏发电 论文

countries. India, Egypt, Morocco and Mexico have now applied within the GEFOperational Programme for about 50 million US-Dollar GEF grant for each project tocover their incremental costs of solar thermal power projects.

With positive experiences in construction and operation of the first European demonstrationpower plant projects being under development (50 MWe THESEUS on the Crete island inGreece; 10 MWe Planta Solar (PS 10) in Southern Spain), other projects are expected tofollow. Until the year 2015, the market potential for solar thermal power plants is estimated atleast with 7 GWe in southern Europe, representing a CO2 reduction potential of up to 12million tons per year.

These projects represent a cost reduction potential of 20 % compared to the last built 80MWe SEGS IX plant in California. Projected electricity production costs can then come downto 14 Euro cents/kWh (in pure solar mode, without any grant). However, electricity costs ofsolar power plants operating in the solar/fossil hybrid mode (as encouraged by the EU FifthFramework Programme) could fall to as low as to 8 Euro cents/kWh in the short-term period.Research and development programmes in Europe and in the USA are aimed at reducingthe electricity costs furthermore in the long-term run.

The Mediterranean Member States of the European Union will surely be counting on solarthermal power plants as an excellent option for achieving the mentioned goals in theirnational policies. This is the case in Spain, where solar energy has been given specialpriority. It is expected that the new Spanish legislation on renewable electricity generation willallow solar thermal power plants to earn an additional 18 Euro cents/kWh on top of theconventional electricity price, which will undoubtedly favour the short-term construction ofcommercial solar thermal power plants in Spain.

2 Achievements, Present Situation, Main Barriers and Vision on the Way Forward

2.1 Parabolic Trough Systems

Trough systems use linear concentrators of parabolic shape with highly reflective surfaces,which can be turned in angular movements towards the sun position and concentrate theradiation onto a long-line receiving absorber tube (see Figure 1). The absorbed solar energyis transferred by a working fluid, which is then piped to a conventional power conversionsystem.

The used power conversion systems are based on the conventional Rankine-cycle/steamturbine generator or on the combined cycle (gas turbine with bottoming steam turbine).Trough power plants are highly modular and are already applied up to 80 MWe unit capacityusing a thermal oil heat transfer system. Total power plant capacities of above 100 MWe areactually projected for solar/fossil “hybrid” integrated solar combined cycle systems (ISCCS)with equivalent solar field capacities of 30 to 40 MWe in order to help introduce the systemson the energy market of sunny countries in the near to medium term, e. g. in the countrieswith GEF support mentioned above.

Energy Service Sector and Role of Technology:

Parabolic trough power plants represent today the most mature solar power plants with 354MWe of commercial solar electric generating systems (SEGS) parabolic trough power plantsconnected to the Southern California grid since the 1980’s (Figure 2). These plants have unitcapacities of 14 MWe (SEGS I), 30 MWe (SEGS II to VII) and 80 MWe (SEGS VIII and IX).With more than two million square meter of total glass mirror area of current troughtechnology they have generated more than 8 TWh of electricity since 1985. The 30 MWSEGS plants of Kramer Junction with an annual insolation of over 2700 kWh/m²a haveverified generating costs of 15 US cents/kWh during high-priced daytime slots (mainly for

太阳能热利用 热发电 光伏发电 论文

peak-load demand by air conditioning), with allowance to generate up to 25% of the annualoutput by supplementary natural gas-firing. (The equivalent pure solar costs would be 20 UScents/kWh); the 80 MW SEGS plants of Harper Lake with the same annual insolation haveverified generating costs of 12 US cents/kWh, also with allowance to generate up to 25% ofthe annual output by supplementary natural gas firing. (The equivalent pure solar costswould be 16 US cents/kWh). They have gained record values of an annual plant efficiency of14 % and of a daily solar-to-electric efficiency near 20 % as well as peak efficiencies up to21.5 %. The annual plant availability exceeded 98 % and the collector field availability morethan 99 %. The performance of the plants have been improved continually during theoperation time. The five plants at the Kramer Junction site (SEGS III to VII) have during thelast five years achieved a 30 % reduction in operation and maintenance costs. In addition,key trough-component manufacturing companies in Europe and its associated partners havemade considerable advances.

Parabolic trough plants may be designed as quasi-solar-only plants for peak-load (as theSEGS plants with about 2,000 equivalent solar full-load hours per year and with 25 %supplementary fossil firing) or in the future on an annual average up to 100 % solar share,applying thermal energy storage systems. Plant concepts favourable for the marketintroduction are hybrid ISCCS plants for mid-load or base-load operation, with solar sharesbetween 10 and 50%.

Technology Shortages:

Parabolic trough systems have the following technology shortages:

The upper process temperature is currently limited by the heat transfer thermal oil to

400°C.

The heat transfer thermal oil adds extra costs of investment and of operating and

maintenance.

Depending on national regulations, environmental constraints from ground pollution by

spillage of thermal oil could occur.

Some absorber tubes are still object of early degradation; reasons are the risk of

breakage of absorber envelope glass tubes with loss of vacuum insulation anddegradation of the absorber tube selective coating.

High winds may break mirror reflectors at field corners.

Low-cost and efficient energy storage systems have not been demonstrated up to now. The direct steam generation trough technology is still in a developmental stage.Current Projects:

While the European Commission supports only pure solar plants, the World Bank/GEF focuson the integration of parabolic troughs into combined-cycle plants (ISCCS) in sunnydeveloping countries. On the above mentioned background, various commercial power plantdevelopment projects with unit outputs of 50 to 310 MWe and large solar fields of parabolictrough collectors are currently promoted or are in a progressive planning stage by Europeanand U.S. project developers with grants of the World Bank/GEF or other co-funds world-wide,namely in:

50 MWe solar thermal power plant THESEUS on the Crete island; promoted by

German and Greece companies; solar field of approximately 300,000 m2;, 112

GWh of pure solar electricity per year

Various 50 MWe plants group in southern Spain; promoted by international

industrial group; based on the new Royal Decree on the support of renewable

electricity generation

135 MWe natural-gas-fired ISCCS plant in Kuraymat at the Nile river; 30 MWe

equivalent solar capacity; promoted by industrial groups; with allocated 40 to 50

million US-Dollar GEF grant

太阳能热利用 热发电 光伏发电 论文

capacity; promoted by industrial groups; with allocated 40 to 50 million US-

Dollar GEF grant

140 MWe naphta-fired ISCCS plant in Mathania/Rajasthan; 35 MWe equivalent

solar capacity; promoted by industrial groups; with allocated 49 million US-

Dollar GEF grant and 100 million US-Dollar loan of the German KfW-bank

Feasibility study for the implementation of a 100 MW natural gas fired combined

cycle plant with a 200 000 – 400 000m² parabolic trough field in the desert of

Yazd contracted with its own national funds.

310 MWe natural-gas-fired ISCCS plant in the Northern Mexican desert; 40

MWe equivalent solar capacity; promoted by industrial groups; with allocated 40

to 50 million US-Dollar GEF grant.

The German/Spanish R&D project generates direct steam using LS 3-trough collectors at thePSA in southern Spain (DISS project, schedule 1996 – 2001, Figure 3). This new concept isexpected to produce a cost reduction over the SEGS plants of between 20 and 30 percent.Future solar-only solar thermal power plants are planned with potential use of solar energystorage systems in order to enlarge the solar capacity or solar share and to ultimatelyminimize the CO2 emissions. The EuroTrough R&D project of an European group underSpanish industrial leadership is in progress with EU co-funds since 1998 with the goal toreduce the costs of an advanced European trough collector on the basis of the proven LS 3-collector type.

Competitors, Cost Situation and Vision of Cost Range:

Competitors are the current conventional grid-connected fossil fuel-fired power plants,particularly the modern natural gas-fired combined cycle plants in mid-load or base-loadoperation mode.

Installed plant capital costs of the Californian SEGS Rankine-cycle trough systems with on-peak power operation fell from 4,000 US Dollar/kWe to under 3,000 US Dollar/kWe between1984 to 1991, mainly due to scaling-up effects from 30 to 80 MWe units and due to serieseffects. The 50 MWe THESEUS plant will already meet the near-to-mid-term cost targets setforth in the EU Fifth Framework Programme for solar power systems with 2,500 Euro/kWeinstalled. Projected electricity production costs for a next 50 MW parabolic trough plant at aSouthern European site with 2400 kWh/m²a like on the Island of Crete are then at 14 Eurocents/kWh (in pure solar mode without any grant), or at 18 Euro cents/kWh at a site with2000 kWh/m²a like in Southern Spain. However, in hybrid mode with up to 49 % fossil-basedpower production, the electricity costs could drop to as low as 8 Euro cents/kWh.

Installed trough field costs have dropped to 210 Euro/m² of current or near-term installedcollector technology (based on the LS-3 type). They are expected to fall below 200 Euro/m²for enhanced collectors and larger production rates in the medium-term and to 130 to 110Euro/m² for high production rates in the long-term. 15 % discount on the U.S./European pricelevel of solar installations may be projected for developing countries due to lower labourcosts.

As analyzed by the above mentioned World Bank expertise on solar thermal power plants,installed plant capital costs of near-term trough plants are expected in the range of 3,500 to2,440 Euro/kWe for 30 to 200 MWe Rankine-cycle (SEGS type) plants and of about 1,080Euro/kWe for 130 MWe hybrid ISCCS plants with 30 MWe equivalent solar capacity forU.S./European construction price scenario. The projected total plant electricity costs rangefrom 10 to 7 Euro cents/kWh for SEGS type plants and less than 7 Euro cents/kWh forISCCS plants, which however are not assessed to have lower electricity costs thanconventional gas-fired combined cycle pants.

太阳能热利用 热发电 光伏发电 论文

The expected drop of the installed capital costs of grid-connected ISCCS trough plants willresult in electricity costs of 6 Euro cents/kWh in the medium-term period and of 5 Eurocents/kWh in the long-term run (200 MWe Rankine-cycle plant without and with storage).There is the promising long-term potential of Rankine-cycle trough plants to compete withconventional peaking Rankine-cycle plants (coal-fired, oil-fired) at good solar sites. The long-term application of direct steam generation trough technology has even higher expectance inthe future due to its promising cost reduction potential.

2.2 Central Receiver Systems

Central receiver systems use heliostats to track the sun by two axes mechanisms followingthe azimuth and elevation angles with the purpose to reflect the sunlight from manyheliostats oriented around a tower and concentrate it towards a central receiver situated atopthe tower (see Figure 1). This technology has the advantage of transferring solar energy veryefficiently by optical means and of delivering highly concentrated sunlight to one centralreceiver unit, serving as energy input to the power conversion system.

In spite of the elegant design concept and in spite of the future prospects of highconcentration and high efficiencies, the central receiver technology needs still more researchand development efforts and demonstration of up-scaled plant operation to come up tocommercial use. Its main attraction consists in the prospect of high process temperaturesgenerated by highly concentrated solar radiation to supply energy to the topping cycle of anypower conversion system and to feed effective energy storage systems able to cover thedemand of modern power conversion systems.

The solar thermal output of central receiver systems can be converted to electric energy inhighly efficient Rankine-cycle/steam turbine generators, in Brayton-cycle/gas turbinegenerators or in combined cycle (gas turbine with bottoming steam turbine) generators. Grid-connected tower power plants are applicable up to about 200 MWe solar-only unit capacity.Conceptual designs of power plant units of above 100 MWe have been analyzed for ISCCSplants.

Energy Service Sector and Role of Technology:

The technical feasibility of the central receiver (tower) technology has been proven world-wide between 1981 and 1986 by operation of six research or proof-of-concept solar powerplant units ranging from 1 to 5 MWe capacities and by one pilot demonstration plant (SOLARONE with water/steam receiver) connected to the Southern California grid, totaling to a netelectric capacity of 21.5 MWe with an installed heliostat mirror area of about 160,000 m².However, the central receiver technology has not been used commercially up to now.

The 10 MWe SOLAR ONE pilot demonstration plant was operated in California from 1982 to1988 with steam as the heat transfer medium. Rebuilt to the 10 MWe SOLAR TWO plant, itwas successfully operated with a molten salt-in-tube receiver system and a two-tank moltensalt storage system from 1997 to 1999 (Figure 4), accumulating several thousand hours ofoperating experience and delivering power to the grid on a regular basis. Solar Two hassuccessfully demonstrated grid-connected operation and successful tests of dispatching thegenerated energy as designed. This concept is the basis for the U.S. efforts for tower plantcommercialization; it has the potential of more than 15 % annual solar-to-electric plantefficiency and of annual plant availability of over 90 %.

Different receiver heat transfer media have been successfully researched (water/steam,liquid sodium, molten salt, ambient air). Two of the proof-of-concept power plants have beenconverted to central receiver test bed facilities on the largest European solar test center, thePlataforma Solar de Almería (PSA) in Spain (Figure 5), and two further large test facilities areactually available for R&D activities in the USA and in Israel. Today, promising advanced

太阳能热利用 热发电 光伏发电 论文

systems refer to the European volumetric air receiver technology and to the U.S. molten salt-in-tube receiver technology; both concepts are assessed to be the most mature andpromising central receiver technologies for mid- to long-term grid-connected power plantapplications. The heliostat technology, which is available at near-to-commercial conditions inEurope (Germany, Spain) and in USA already today, comprises glass-metal and stretchedmembrane heliostat types of 70 to 150 m² reflective surface area.

More recent European activities have demonstrated that high-flux characteristics aremaximized in high-intensity/high-efficiency volumetric air receivers in either open or closedcycles, in which the concentrated solar energy irradiates fine wire mesh or ceramic foamstructures, transferring the energy by convection directly to air in the attractive temperaturerange of 700 to 1,200°C. Tests conducted at the PSA in a joint German/Spanish projectbetween 1993 and 1995 within the PHOEBUS Technology Programme Solar Air (TSA) withthe German 2.5 MWth pilot experimental plant showed the feasibility and prospects of thevolumetric air receiver system concept with ceramic energy storage system.

Plants may be designed as solar-only plants for peak-load (with about 2000 equivalent full-load hours per year) or in the future up to 100 % solar share on an annual average. Hybridplant concepts, which are favourable for the phase of market awareness and expansion, areISCCS plants for mid-load or base-load operation.

Future solar-only solar tower plants have the good long-term perspective for high conversionefficiencies and for use of very efficient energy storage systems by utilization of hightemperatures in order to enlarge the solar capacity or solar share. In addition, they have thepotential to be applied to other high-temperature heat processes (e.g. process heat, solar-chemical processes).

In 1999 the World Bank expertise assessed the central receiver power plants to be currentlyless favourable for the start of commercialization and market introduction versus Parabolictrough systems due to less advanced plant maturity and lack of demonstration of commercialoperation of up-scaled unit size. Consequently, new up-scaled demonstration centralreceiver projects are required before these systems can be considered to be commerciallyready.

Technology Shortages:

Central receiver systems have the following technology shortages:

No successful scaled-up central receiver plants are available for commercial

demonstration up to now, although more than six experimental and pilot demonstrationcentral receiver plants were successfully operated world-wide since 1981.

Currently promising technologies (the molten salt-in-tube receiver technology in USA and

the volumetric air receiver technology in Europe, both with energy storage system) areproven only by one pilot demonstration unit (10 MWe SOLAR TWO) with two years ofoperating experience and by one pilot experimental unit (2.5 MWth PHOEBUS-TSA) withsome years of operating experience.

Not yet verified is the good potential projected for the improvement of solar system

performance and for cost reductions.

Not yet verified are projections of the installed plant capital costs, operation and

maintenance costs, electricity costs, solar subsystem performance, operationalcharacteristics and of the annual plant availability.

The industrial demonstration of volume production of heliostat components is still missing.Current Projects:

European activities related to the technical and economic feasibility of central receiverdemonstration power plants have already started. Two 10 MWe projects are currently underdevelopment to take credit of the Spanish Royal Decree of December 1998 with special legal

太阳能热利用 热发电 光伏发电 论文

classifications of premium payments for renewable or solar electricity and of subsidies of thesolar investment from the EC Fifth Framework ENERGY Programme in its 1999 call forproposals. The projects are namely in:

demonstration of hybrid solar tower power plants (ISCCS) for integration of

20 MW of solar saturated steam into a conventional combined-cycle power plant;

terminated due to budgetary reasons after the detailed engineering phase in

1998

Sevilla promoted by Spanish and German companies; application of German

PHOEBUS volumetric air receiver/energy storage technology; use of Spanish 90

m2 glass-metal heliostats (Figure 6)

companies; application of U. S. molten-salt technologies for receiver and energy

storage; use of new Spanish low-cost heliostats with reduced dimensions.

In addition, the following R&D projects concerning central receiver components or systemsare being promoted or are in progress, namely in:

the PSA proposed by European group under Spanish industrial leadership;

application for next central receiver projects after PS 10; with co-funds of the EC

Fifth Framework Programme

receivers at the PSA proposed by DLR together with CIEMAT (Figure 7);

application for solar preheating of gas turbine combustion air in combined-cycle

plants

low-cost heliostats with advanced technologies

receiver facility of Weizmann Institute of Science (WIS) with tower reflector; for

solar thermal or thermal-chemical applications

receiver test facility; application for synthetic gas production by solar reforming of

natural gas; use of 400 kWth high-temperature volumetric air receiver (DLR).

Competitors, Cost Situation and Vision of Cost Range:

Competitors are the current conventional grid-connected fossil fuel-fired power planttechnologies, particularly the modern natural gas-fired combined cycle plants in mid- or base-load operation mode.

Specific installed capital costs of built central receiver pilot plants are yet too high. There areno electricity costs of commercial scaled-up plants available today. Economic analyses showmore cost uncertainties versus trough plants due to less mature technology. Central receiverplants, however, will take credit from their potential of favourable application of hightemperature and energy storage systems. But the addition of a long-time energy storagesystem is not reducing the electricity costs, it is increasing the plant performance and thecapacity factor.

As analyzed by the above mentioned World Bank expertise, installed plant capital costs ofnear-term central receiver plants are expected in the range of 4,300 Euro/kWe (next130 MWe ISCCS plant with 30 MWe solar-generated capacity with storage) to3,300 Euro/kWe (next 100 MWe Rankine-cycle plant with storage) for U.S./Europeanconstruction price level, with the range of predicted total plant electricity costs of about 14 to12 Euro cents/kWh.

太阳能热利用 热发电 光伏发电 论文

In Europe, new near-term tower project developments in Spain have indicated the validationof installed plant capital costs in the order of 2,700 Euro/kWe by central receiver power plantwith Rankine-cycle and small energy storage system, with the range of predicted total plantelectricity costs of 20 to 14 Euro cents/kWh.

The actual range of installed heliostat field costs is 180 to 250 Euro/m² for small productionrates in the USA, and 140 to 220 Euro/m² in Europe. 15 % discount on the U.S/Europeanprice level may be projected for developing countries due to lower labour costs. Heliostatfield costs are expected to drop below 100 Euro/m² at high production rates in the long-termperiod.

Central receiver plant projects will benefit from similar future cost reduction effects asmentioned for parabolic trough plants. By the expected evolution of total plant costs of grid-connected central receiver plants, the total plant electricity costs will drop to 8 to 7 Eurocents/kWh in the medium-term period (100 MWe Rankine-cycle plant or 100 MWe ISCCS,both with storage) and to 5 Euro cents/kWh in the long-term period (200 MWe Rankine-cycleplant with storage), as has been analyzed by the mentioned World Bank expertise. Long-term central receiver plants are expected to produce electricity at approximately 25% lowerelectricity costs than similar sized trough plants. There is the promising long-term potential ofRankine-cycle central receiver systems to compete with conventional peaking Rankine-cycleplants (coal-fired, oil-fired) at good solar sites. As mentioned above for ISCCS trough plants,also ISCCS central receiver plants are not expected to have lower electricity costs thanconventional gas-fired combined cycle plants.

2.3 Parabolic Dish Systems

Dish systems use parabolic reflectors in the shape of a dish to focus the sun’s rays onto adish-mounted receiver at its focal point (see Figure 1). In the receiver a heat-transfer mediumtakes over the solar energy and transfers it to the power conversion system, which may bemounted in one unit together with the receiver (e. g. receiver/Stirling engine generator unit)or at the ground. Due to its ideal optical parabolic configuration and its two axes control fortracking the sun, dish collectors achieve the highest solar flux concentration, and thereforethe highest performance of all concentrator types in terms of peak solar concentration and ofsystem efficiency. These collector systems are restricted to unit capacities of some 10 kWefor geometrical and physical reasons.

The dish technology is applicable to off-the-grid power generation, i. e. at remote places or atisland situations. Dish systems may optionally be arranged in large dish arrays in order toaccumulate the power output from the kWe capacity up to the MWe range. It requires somemore continued R&D activities and demonstration before start of market introduction.

The power conversion subsystem of dish systems is mainly based on the Stirling enginegenerator system, but also on the water/steam powered turbine or piston engine generatorsystem or on the gas turbine generator system. Peak-load by solar-only operation or bysolar/fossil "hybrid" operation with solar shares may range from 50 to 100 % on an annualaverage.

Short-/medium-term turn-key dish/Stirling systems are projected with the option of hybriddish/Stirling operation, i. e. with supplementary combustion of natural gas integrated into thereceiver component. Such systems are currently under development and are expected to beavailable for first demonstration projects in the near-term run.

太阳能热利用 热发电 光伏发电 论文

Energy Service Sector and Role of Technology:

Several small power systems for off-the-grid solar thermal electricity generation withparabolic dish unit sizes in the range of 5 to 25 kWe have been proven their technicalfeasibility in several experimental, prototype and demonstration projects world-wide since theend of the seventies. Dish/Stirling systems have excellent possibilities for high conversionefficiencies due to their potential of high process temperatures in the Stirling engine. Therecord energy yield was experienced by a 25 kWe U.S. dish/Stirling system with a solar-to-electric system efficiency of 30 %. The current advanced dish/Stirling technologydevelopment is performed mainly by European (German) and U.S. industries and institutions,developing the most promising unit capacities of 10 kWe (German units) and 25 kWe (U.S.units). These systems are under proof-of-reliability operation in the USA and in southernSpain. The concept of stretched-membrane dish concentrators, currently under proof-of-reliability testing mainly on the PSA using German advanced technologies, holds greatpromise for further reduced cost in order to make them competitive with Diesel stations inremote areas or on islands. The tools required for a small-series production of 100 units peryear are also being developed.

Technology Shortages:

Parabolic dish systems have the following technology shortages:

The electricity output of single dish/Stirling unit is limited to small ratings of e. g. 25 kWe

due to geometric and physic reasons (exception: Australian big dish designed for use of a50 kWe steam engine or turbine generator).

Large-scale deployment has not yet occurred.

No commercial demonstration has been performed up to date.

Not yet demonstrated or verified are projections of capital costs, operation and

maintenance costs, electricity costs, system performance and of the annual plantavailability over the long run.

The predicted potential for improvements of solar system performance and of cost

reductions is still to be verified.

Hybrid systems have inherent low-efficient combustion and have to be proven.

No adequate energy storage system is applicable or available.

The establishment of industrial large volume production of dish components and Stirling

engines is needed for entry into appropriate market segments.

Current Projects:

The following R&D and demonstration projects concerning dish/Stirling systems are beingpromoted or are in a progressive stage of development or demonstration, namely in:

successful operation for proof of continuous operation of six German

dish/Stirling pre-commercial units with 9 to 10 kWe ratings of Schlaich,

Bergermann & Partner (SBP) at the PSA (three DISTAL I-systems since 1992

and three DISTAL II-systems since 1997, Figure 8); over 30,000 operating

hours accumulated by the DISTAL I-systems up to now; promising advanced

heat pipe receiver types and Stirling engines currently under development and

testing for proof of system reliability; new 9 to 10 kWe dish/Stirling units under

way for testing on the PSA within the EuroDish R&D programme with EU co-

funds since 1998 (goal: cost reductions by advanced structures for

commercialized European dish/Stirling systems)

group in collaboration with Stirling Energy Systems (SES) consortium using a

25 kWe Dish/Stirling unit of McDonnell Douglas (MDAC) for erection in the

South-east of Spain

太阳能热利用 热发电 光伏发电 论文

nd generation prototype

systems for extended testing in the South-west USA; projects will possibly be

shortened or stopped due to dropping public R&D funds in the short term run

2 pilot experimental “big dish” project with capacity of up to

150 kWth under scientific testing at the Australian National University (ANU)

since 1994; designed for power generation using a 50 kWe steam engine

generator or for co-generation applications by solar steam production;

alternative to the small-unit philosophy described above.

The Australian government is presently funding a 2.6 MWth solar power plant project2 consisting of eighteen 400 m “big dish” units which will inject solar generated steam directlyinto the steam turbine of an existing coal-fired power station. Another 400 m2 dish collectorunit was recently sold to the Israeli solar test center in the Negev desert for solar R&D testbed purposes.

Competitors, Cost Situation and Vision of Cost Range:

Competitors for dish/Stirling systems are conventional small-scale off-grid generationsystems with unit ratings of the kWe-range up to about 10 MWe in peak- or mid-loadoperation at remote places, i. e. the gas oil- or heavy fuel oil-powered Diesel enginegenerators, particularly in developing sunbelt countries and on islands with relatively highfuel costs.

Experienced dish cost trends show a drastic reduction of installed dish collector costs:1,250 Euro/m² (40 m² Shenandoah, USA, 1982), 300 Euro/m² (91 m² MDAC, USA, 1985),200 Euro/m² (44 m² LaJet, USA, 1986) and 150 Euro/m² (44 m² German SBP stretched-membrane dish, 1992).

The today’s installed plant capital costs of a first stand-alone 9 to 10 kWe dish/Stirling unit is10,000 to 14,000 Euro/kWe and of actual near-term units 7,100 Euro/kWe (at 100 units/yearproduction rate). The most attainable near-term goal of electricity costs is less than 15 Eurocents/kWh. In the medium- to long-term run, dish/Stirling systems are expected to havedrastically decreasing installed system costs, which are projected with growing number ofdish units produced in series. The goal of the European EuroDish project: drop from7,100 Euro/kWe (100 units/year) to 3,700 Euro/kWe (1,000 units/year) to 2,400 Euro/kWe(3,000 units/year) and to 1,600 Euro/kWe (10,000 units/year), but not below that price leveldue to the inherently very high modular technology. Medium- to long-term installed dishcollector costs are predicted in the range of 125 to 105 Euro/m² for high-production rates.Advanced dish/Stirling systems have the promising medium- to long-term potential tocompete with similar sized Diesel generator units at sunny remote places or islands.3 Goals for Research, Development and Demonstration (RD&D)

There are the following main goals for solar thermal power plants:

units of equivalent solar capacities of 10 MWe or even more favourable 100 MWe in theMediterranean area to ensure a significant contribution to the environmentally benignelectricity production in Europe. In this respect, Spanish and Greek initiatives will play adecisive role, enjoying the support of the European Union.

essence, the most important features and cost-reducing items considered are thequalification and demonstration of direct steam generation for parabolic troughs, thereliable utilization of volumetric air and molten salt receiver techniques for central receiver

太阳能热利用 热发电 光伏发电 论文

systems, the hybrid operation of saturated steam central receiver systems and of thehybrid operation of dish/Stirling systems.

link proven solar thermal and conventional technologies through optimized integration ofsolar thermal energy into fossil-fired power plants, particularly into combined cycle powerstations. Such applications are not only door openers for solar applications, but in factrepresent a most realistic strategy.

obligatory. As a short-term goal, guaranteed electricity delivery from a buffer storage orshort-period storage capacity is advisable, and as a long-term objective solar-onlyoperation from large storage capacities.

4 Roads to the Market

Solar thermal power plants have the potential to generate well-priced bulk electric powertogether with hydro power stations and with large wind energy converter arrays. They have,therefore, the potential to effectively contribute to the international efforts to reduce climaticgas emissions from fossil-fired electricity generation. They also can take profit from thealready proven high-voltage direct current transmission system in order to link good solarsites of the Mediterranean area by grid-connection with consumers of high electricity demandat less sunny locations.

All three solar thermal power plant technologies are approaching readiness for the marketintroduction, although with different technological and commercial availability:

the parabolic trough technology already today and still more improved with the direct

steam generation technique in the near-term period,

the central receiver technology and the dish/Stirling technology in the near-term to

medium-term run.

Figures 9 and 10 show the status of international developments and the evolution of thelevelized energy costs of parabolic trough and central receiver power plant projects.

The GEF’s Operational Programme provides financial support for specific solar thermalpower applications in sunbelt countries, as mentioned above.

It is recommended that the roads to the market be pursued step-by-step, implying speedymarket introduction of proven SEGS-type parabolic trough plants, the implementation of afirst limited series of commercial central receiver power plants and the consequent use ofdish/Stirling applications in appropriate market segments.

After the first step of identifying the most probable market segments through market analysis,awareness and acceptance, all solar thermal power technologies have to be demonstratedby stages until finally ensuring commercial introduction within the next decade. As forsolar/fossil hybrid solutions, solar systems should be demonstrated by coupling toconventional power plants in order to optimally combine the technical concepts and theireconomies, particularly during the market introductory phase. However, theserecommendations should be taken with a certain measure of flexibility so that they remainadaptable to circumstances and do not become intolerant of local requirements. Recentnational and regional experiences like in Spain, in the USA and in Australia do demonstratethe open-minded strategies required for a successful implementation of solar thermal powerplants. In a world in which recognition of differences is more patent and more important everyday, the only viable strategies for introducing a new technology are those which integrate theuser or receiver of the technology in the definition of the strategy itself and are respectful ofsocial circumstances and the expectations of those to whom the solution is proposed.

太阳能热利用 热发电 光伏发电 论文

4.1 Roads to the Market of Parabolic Trough Systems

Parabolic trough systems will proceed the following main items on their road to the market: Projection on the success of current parabolic trough collector system experience and on

the low-risk approach to advance the state of the trough technology by several stepsduring the next decade, in order to reach the necessary synergy of technologydevelopment and market awareness/expansion/acceptance

Hybrid ISCCS plants using current trough technology; hybrid plant design optimization

and optimized linkage to conventional power plants or to co-generation plants

Improvements of trough collector key elements by optimized design, e.g. optimized steel

structures, absorber tubes of increased lifetime and better maintainability; specialoperation and maintenance tools and equipment; improvement of procedures

Standardized designs of hybrid ISCCS cycles with equivalent solar unit capacities of 30 to

50 MWe and of solar Rankine-cycles with more than 30 MWe up to 200 MWe

Advanced trough collector/reflector design concepts, e. g. mirror facets with front surface

or film reflectors of high reflectivity, lighter and strengthened mirror panels

Application of direct steam generation trough technology ready for commercialization

Development and application of efficient energy storage systems in future solar thermal

power plants in order to enlarge the solar capacity of mid-load or near base-load plantswith solar shares up to 100 % on an annual average.

4.2 Roads to the Market of Central Receiver Systems

Central receiver systems will proceed by the following main items on their road to the market: Projection on the success of current central receiver experience and on the low-risk

approach to advance the state of the central receiver technology by several steps duringthe next decades, in order to reach the necessary synergy of technology developmentand market awareness/expansion/acceptance

Hybrid ISCCS plants using current central receiver technology; hybrid plant design

optimization and optimized linkage to conventional power plants or to co-generationplants and to bio-mass plants

Heliostat field and receiver improvements by better optical and thermal properties, lighter

mirrors and optimized heliostat structures, better heliostat/field controls

Proof of solar system performance and reliability during representative operating times Process improvements by further advances in selected heat transfer media and receiver

concepts for commercial power generation (European technology of volumetric airreceiver, U.S. technology of advanced molten salt-in-tube receiver)

Improvements in the system integration by reduced parasitic loads, optimized start-up

procedures, better control strategies, automatic heliostat field control

Development and application of low-cost/very efficient energy storage systems in future

central receiver power plants in order to enlarge the solar capacity of mid-load or nearbase-load plants with solar shares up to 100% on an annual average.

4.3 Roads to the Market of Parabolic Dish Systems

Parabolic dish systems will proceed by the following main items on their road to the market: Improvements of dish reflector and receiver, including better optical properties of the

mirrors; lighter mirrors and structures, better system control characteristics; developmentof an automatic control system for remote operation and for long-distance control

太阳能热利用 热发电 光伏发电 论文

System improvements using Stirling and Brayton (gas turbine) engines adapted to solar

processes with advanced heat-pipe and volumetric air receivers

Proof-of-reliable operation of advanced Stirling engine/receiver units over the long run

Improvements in system integration by reduction of parasitic loads, optimization of start-

up procedures, better control strategies and hybrid operation of Stirling or Braytonengines.

Literature

Becker, M. and Meinecke, W. (ed.) (1992). Solar Thermal Technologies, Comparative

Study of Central Receiver, Parabolic Trough, Parabolic Dish and Solar Chimney PowerPlants (in German). Springer Publishing House, Berlin, 1992

Becker, M. and Klimas, P. (ed.); Chavez, J. M., Kolb, G. J. and Meinecke, W. (authors)

(1993).Second Generation Central Receiver Technologies, A Status Report. PublishingHouse C. F. Müller, Karlsruhe, 1993

Becker, M. and Gupta, B. (ed.); Meinecke, W. and Bohn, M. (authors) (1995): Solar

Energy Concentrating Systems, Applications and Technologies. DLR. C. F. MuellerPublishing House, Heidelberg, 1995

Becker, M. and Böhmer, M. (ed.) (1999). Proceedings of the 8th SolarPACES International

Symposium on Solar Thermal Concentrating Technologies, Köln, October 6 – 11, 1996.Publishing House C. F. Müller, Heidelberg, 1996

Cohen, G. E., Kearney D. W. and Kolb G. J. (1999). Final Report on the Operation and

Maintenance Improvement Program for Concentrating Solar Power Plants. SANDIAReport SAND99-1290, June 1999

Enermodal Engineering Ltd. (1999). Cost Reduction Study for Solar Thermal Power

Plants. Final Report. Prepared by Enermodal Engineering Ltd. In association with MarbekResource Consultants Ltd., by contract of World Bank/GEF, Washington D.C., May 5,1999

Flamant, G, Ferriere, A. and Pharabod, F. (ed.) (1999). Proceedings of the 9th

SolarPACES International Symposium on Solar Thermal Concentrating Technologies,Font-Romeu, June 22 – 26, 1998. Journal de Physique IV, Vol. 9. EDP-Science, France,1999

Geyer, M. and Klaiß, H. (1998). 194 MWe Solar Electricity from Trough Collector Plants

(in German). BWK Journal, Vol. 6, pp. 288 – 295, 1998

Geyer, M., Holländer, A., Aringhoff, R. and Nava, P. (1998). 7,000 GWh Solar Electricity

from Parabolic Trough Power Plants, Half of World-wide Produced Solar Electricity (inGerman). SONNENERGIE, Vol. 3, June 1998

Klaiss H. and Staiss, F. (ed.) (1992). Solar Thermal Power Plants for the Mediterranean

Region (in German), Vol. I and II. Springer Publishing House, Berlin, 1992

Pilkington Solar International (ed.) (1996). Solar Thermal Power – Now, A Proposal for

Rapid Market Introduction of Solar Thermal Technology. Co-operative Position Paper ofPikington Solar, Kramer Junction Co., SOLEL, DLR, Plataforma Solar de Almeria,CIEMAT, Bechtel, Fichtner and Schott Rohrglas, 1996

Stine, W. B. and Diver, R. B. (1994). A Compendium of Solar Dish/Stirling Technology.

SANDIA Report SAND93-7026 UC-236, January 1994

Trieb, F. (1998). Competitive Solar Thermal Power Stations until 2010, The Challenge of

Market Introduction (SYNTHESIS Programme). In Proceedings of the 9th SolarPACESInternational Symposium on Solar Thermal Concentrating Technologies, Font-Romeu,June 22 – 26, 1998. Journal de Physique IV, Vol. 9. EDP-Science, France, 1999

Tyner, C., Kolb, G. J., Meinecke, W. and Trieb, F. (1999). Concentrating Solar Power in

1999, An IEA-SolarPACES Summary and Future Prospects. SolarPACES Task I: ElectricPower Systems. SolarPACES, January 1999

太阳能热利用 热发电 光伏发电 论文

List of Abbreviations

CESA 1

Colon Solar

DIAPR

DISS

DISTAL

EuroDish

EuroTrough

ISCCS

KfW

LEC

LS-3

PHOEBUS-TSA

PS 10

REFOS

SEGS

SIREC

SOLAIR

SOLASYS

SOLAR ONE

SOLAR TWO

SOLGAS

THESEUS1 MWe Central Electrosolar Uno at the PSA, Tabernas, SpainCo-generation project using central receiver technology at Colon, SpainDirectly irradiated annular pressurised receiverDirect Solar Steam ProjectDish/Stirling Almeria, R&D project at the Plataforma Solar de Almeria,SpainEuropean dish/Stirling R&D programmeEuropean parabolic trough R&D programmeIntegrated solar combined cycle systemKreditanstalt für Wiederaufbau, GermanyLevelized electricity costsLUZ System, parabolic trough system model No.3 of LUZPHOEBUS technology programme solar air receiver10 MWe central receiver power plant project Planta Solar 10 nearSevilla, SpainModular pressurised volumetric air receiver, R&D project for solarpreheating of combustion air of fossil-fired gas turbines and combinedcycle power plantsSolar electric generating systemsSistemas de receptor central (systems for central receiver) project,involving CIEMAT and IAER for heliostat and receiver development,SpainAdvanced solar volumetric air receiver for commercial solar tower powerplants, European R&D projectNovel solar assisted fuel driven power system10 MWe central receiver power plant No. 1, Barstow, CA., USA10 MWe central receiver power plant No. 2, Barstow, CA., USASolar/gas-fired hybrid co-generation plant project using central receivertechnology in Andalusia, Spain50 MWe parabolic trough power plant project, Frangocastello on Crete,

Greece

太阳能热利用 热发电 光伏发电 论文

Figure 1: Schematic diagrams of the three main concepts of concentrating solar thermal

electricity generation:

a) Parabolic trough, b) Central receiver (tower), c) Parabolic dish

(Source: DLR-Köln)

Figure 2: The parabolic trough field arrays of five SEGS plants at Kramer Junction, CA./USA

(Source: Pilkington Solar International, Germany)

Figure 3: The direct solar steam generation test facility using LS-3 trough collectors on the

Plataforma Solar de Almería

(Source: PSA, Spain)