Trends in Linear Solar Concentrators

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1 Trends in Linear Solar Concentrators Eduardo Zarza CIEMAT-Plataforma Solar de Almería, P. Box 22, Tabernas, E Almería, Spain Slide: 1

2 Trends in Linear Solar Concentrators Index Present status of technologies current trends Conclusions Slide: 2

3 Trends in Linear Solar Concentrators Index Present status of technologies current trends Conclusions Slide: 3

4 Linear Solar Concentrators Typical parabolic trough collector Supporting structure Parabolic trough concentrator Receiver pipe Slide: 4

5 Linear Solar Concentrators Typical Linear Fresnel collector Receiver Long linear reflectors Supporting structure Fresnel linear collector in Liddell (Australia) Slide: 5

6 Present status of technologies (I) Solar reflectors: - back-silvered thick-glass reflectors (annealed or tempered) are used for big PTCs, while back-silvered annealed thin-glass reflectors are used for LFCs. Metallic flexible aluminium reflectors are only used for small parabolic troughs. Receiver pipes: - parabolic troughs use evacuated receiver pipes for most applications. Non-evacuated pipes are used only for temperatures < 300ºC and small plants. - evacuated receivers are used only for small linear Fresnel collectors (in IPH applications), while non-evacuated receivers composed of either a single pipe or several parallel pipes are used for large units. Working fluids: Thermal oil is the working fluid used in parabolic trough plants for T>250ºC, while water is the fluid used in Fresnel linear collectors Slide: 6

7 Present status of technologies (II) Supporting structures: - Though there exist several designs for large parabolic trough collectors their size is similar (parabola width of 5-5,7 m and total length of m). Smaller designs only used for small plants (IPH mainly). There are two concepts available: a) with torque box, or b) with torque tube - Concerning linear Fresnel concentrators, every industrial group involved in this technology has its own design, with small differences among them. EuroTrough Solargenix SenerTrough AlbiasaTrough Slide: 7

8 Trends in Linear Solar Concentrators Index Present status of technologies current trends Conclusions Slide: 8

9 Solar reflectors Current Trends for Parabolic Troughs Though back-silvered thick-glass curved mirrors have a very good durability they are expensive (20% of solar field cost) and new cheaper options are being developed: Option 1: acrylic substrates with a silver layer: this type of solar reflector will be a very good option if good durability is guaranteed for real outdoor O&M conditions Option 2: aluminum or silver reflective layer deposited on a flexible aluminum sheet: outdoor durability is the main constraint at present to gain the confidence of the customers Option 3: aluminum sheet reflector glued to a rigid glass-fiber substrate or polymer: geometrical accuracy and outdoor durability are significant constraints of this option Current back-silvered glass mirrors are likely to remain the best option in short and medium terms. Commercial deployment of any other option at large scale will depend on its cost/durability ratio Slide: 9

10 Current Trends for Parabolic Troughs Receiver tubes: Partially-evacuated receiver pipes without glass-to-metal welding Glass-to-metal welding will be replaced by a mechanical seal. The main benefit of these receiver tubes is their superior durability and reliability at a price similar to evacuated receivers Evacuated receiver tubes for higher temperatures (T>500ºC) New selective coatings with better thermal durability (T>500ºC) and lower emissivity (ε<0,12 at 500ºC) have already been developed in laboratories and the industrial process for mass production is underway Receiver tubes for T>500ºC will very soon be available at the market and the number of suppliers will increase, thus reducing the prices. The glass-to-metal welding will likely be replaced by other ways of sealing in a medium term. Slide: 10

11 Current Trends for Parabolic Troughs Supporting structures: New designs with reduced installation cost Development of new designs compatible with LS-3 mirrors and receiver tubes are underway with the aim of significantly reducing the on-site installation cost, thus reducing the overall solar field investment New designs with bigger collecting surface per unit Several designs of parabolic troughs with a parabola width of about 7 meters are underway. Though new receiver tubes and mirrors will have to be developed to meet the new dimensions, a cost reduction is expected due to a smaller number of drive units and ball-joint for the same solar field power output New designs using composite materials Innovative designs where usual steel elements are replaced by composite materials are underway. The higher cost of composite material versus steel is their main constraint Cheaper collector designs will be available very soon, because of either bigger collecting surface per unit or cheaper assembly procedures. However, the long-term mechanical behavior of bigger collectors must be carefully analyzed to assure a good intercept factor during the whole life time of the solar field. Slide: 11

12 Current Trends for Parabolic Troughs Working Fluids: Thermal oil currently used in parabolic trough collectors has major disadvantages: limited maximum steam temperature ( 380ºC) pollution and fire hazards Three new working fluids are being investigated to replace thermal oil and thus overcome its limitations: molten salts direct steam generation (the so-called DSG process) pressurized gas Slide: 12

13 Current Trends for Parabolic Troughs New working fluids for parabolic-trough collectors Fluid Molten salts Advantages over thermal oil - More efficient heat storage - Higher working temperature - No pollution or fire hazards Disadvantages compared to thermal oil -Higher thermal losses overnight -More complex solar field design -Higher electricity consumption Direct Steam Generation - Simple plant design - Higher working temperature - No pollution or fire hazards -Lack of suitable storage system -More complex solar field control -Solar field higher pressure Gas - Higher steam temperature - Thermal storage enhancement - No pollution or fire hazards -Poor heat transfer in the receiver tubes -More complex solar field control -Solar field higher pressure Slide: 13

14 Current Trends for Parabolic Troughs New working fluids for parabolic-trough collectors (State-of-the-art) Molten salts Technical feasibility has been proven by ENEA (Italy) in a small experimental facility (350 kwt) installed near Rome (Casaccia). A 5 MWe pre-commercial plant is being installed in Priolo (Italy) to experimentally check the feasibility and commercial viability of large plants Slide: 14

15 Current Trends for Parabolic Troughs New working fluids for parabolic-trough collectors (State-of-the-art) Molten salts Technical feasibility has been proven by ENEA (Italy) in a small experimental facility (350 kwt) installed near Rome (Casaccia). A 5 MWe pre-commercial plant is being installed in Siracusa (Italy) to check the feasibility and commercial viability of large plants Direct Steam Generation Technical feasibility has been proven at the PSA in a single-row test facility (2,45 MWt). A 3 MWe precommercial plant will be installed in Puertollano (Spain) to check the technical and commercial feasibility of large plants Slide: 15

16 Current Trends for Parabolic Troughs The DSG test facility implemented at the PSA Aerial view of the facility Row of collectors B.O.P. building Solar field (from south) Slide: 16

17 Current Trends for Parabolic Troughs New working fluids for parabolic-trough collectors (State-of-the-art) Molten salts Technical feasibility has been proven by ENEA (Italy) in a small experimental facility (350 kwt) installed near Rome (Casaccia). O&M experience with a small pre-commercial plant (i.e., 3-5 MWe) is required to check the feasibility and commercial viability of large plants Direct Steam Generation Technical feasibility has been proven at the PSA in a single-row test facility (2,45 MWt). O&M experience with a small pre-commercial plant (i.e., 3-5 MWe) is still required to check the technical and commercial feasibility of large plants Pressurized Gas A 350 kwt test facility has been installed and successfully operated at the PSA at 400ºC to prove the feasibility of this concept and it will be operated at 520ºC in Slide: 17

18 Current Trends for Parabolic Troughs The PSA test facility for PTCs with pressurized gas Overall view of the facility Solar field in operation Slide: 18

19 Solar reflectors Current Trends for Linear Fresnel Concentrators Since back-silvered thin-glass mirrors currently used are cheap and durable, so significant change is expected. Current R+D activities are related to the assembly process and design to assure a good rigidity without increasing the costs Receiver tubes: A significant effort is currently devoted to improve the thermal stability in hot air, durability and good optical performance of the receiver assembly. The result will be a better efficiency and durability at a similar cost. Supporting structures: The more significant improvements are expected in the elements associated to the Sun tracking system to guarantee a good intercept factor with moderate wind speeds. Working Fluids: Water will be the working fluid within a short term. Molten salts or pressurized gas could be used if their technical feasibility is successfully analyzed and experimentally evaluated. Slide: 19

20 Trends in Linear Solar Concentrators Index Present status of technologies current trends Conclusions Slide: 20

21 Trends in Linear Solar Concentrators Conclusions Though current cost of thermal energy produced by Linear Solar Concentrators is still high, there is a large potential for cost reduction in a medium to long term A lot of money is currently invested to develop improvements and innovations that could achieve a significant cost reduction, thus making reduction of public subsidies and large commercial deployment possible Parabolic trough collectors are likely to experience significant technology improvements mainly related to the working fluid, collector designs and receiver pipes. Slide: 21

22 Trends in Linear Solar Concentrators End of Presentation! Many thanks for your attention Slide: 22

23 Linear Fresnel Concentrators Non-evacuated receiver pipes Thermal insulation Secondary concentrator Absorber pipe Thermal insulation Flat glass window Single-pipe design Multi-pipe design Absorber pipes Slide: 23

24 Evacuated Receivers for PTCs Glass pin to evacuate the air Vacuum between the glass cover and the steel pipe Glass-to-Metal weld Steel pipe with selective coating Glass cover 'Getter' to keep and maintain the vacuum Expansion bellows Solel s design Schott sdesign Archimedes Solar s design Slide: 24

25 Parabolic trough collectors Recent commercial plants IBERSOL plant in Ciudad Real (Spain) ANDASOL-I plant in Granada (Spain) Slide: 25