CSP Today Sevilla 2015 Sevilla 12 th November 2015 The reflectance of the solar field in CSP plants Aránzazu Fernández-García arantxa.fernandez@psa.es
Contents 1. Introduction 2. Soiling 3. Cleaning 4. Reflectance measurements
Introduction PT: 0.58 1.02 ha of reflective surface per MW e 3
Introduction Performance overall K P th, loss P solar ρ P solar γ τ α P th,loss 4
Introduction Reflectance decrease mechanisms Absorption Scattering/beam spread Both mechanisms are produced by these sources Soiling deposition: soiling reduction & cleaning Aging due to environment: increased durability 5
Soiling Soiling rate depends on the reflector type and the location Water availability Closeness to coast, industrial areas, cities Weather Particles (dust and sand) concentration and type 6
Soiling prevention Nightly stow positions of heliostats and troughs avoid settling of dirt Paved roads, not dirt roads in power plants Vegetation, location, etc 7
Soiling prevention Wind fences: Natural or artificial To reduce wind and/or to filter it 8
Soiling prevention Anti-soiling coatings Self-cleaning effect and dust repellent properties Optical properties must be kept Titania (TiO2) is used to obtain a self-cleaning effect due to its hydrophilic effect Hydrophobic coatings are also applied (Schwarberg, 2012) 9
Soiling prevention Anti-soiling coatings (Schwarberg, 2012) 10
Cleaning: natural cleaning Rain (and snow) will clean mirrors only above a certain intensity Light rains can have the opposite effect Light rain washes out the suspended particles in the atmosphere and deposits them on the mirror surface If rain is heavy enough less dirt will stay on the mirrors Dew can wash the mirrors in some cases Dew can also glue smallest particles to surfaces 11
Cleaning: natural cleaning Normalized Monochromatic Specular Reflectance (-) 1,00 0,95 0,90 0,85 0,80 0,75 0,70 0,65 0,60 0,55 0,50 0,45 0,40 0,35 0,30 0,25 0,20 0,15 Reflectance by cleaning method (Unwashed) Structure 4 Rainfall 03/08/2011 21/09/2011 02/11/2011 14/12/2011 25/01/2012 07/03/2012 18/04/2012 11/07/2012 05/09/2012 Time (Date) 31/10/2012 12/12/2012 23/01/2013 06/03/2013 22/04/2013 12/06/2013 (Fernández-García et al., 2014) 12
Cleaning methods: water based Pressurized water systems 13
Cleaning methods: water based Brush cleaning systems 14
Cleaning methods: water based Brush cleaning systems 15
Cleaning: water based Optimization of the water-based cleaning method Spray distance, number of passes, etc. Using some additives (mainly detergents) Applying a brush, a foam, a tissue, steam, etc. 1.00 0.98 Reflectance by cleaning method (Fernández-García et al., 2014) Normalized Monochromatic Specular Reflectance (-) 0.96 0.94 0.92 0.90 0.88 0.86 0.84 0.82 0.80 Period 1 04/08/2011 22/09/2011 03/11/2011 Period 2 Period 3 15/12/2011 26/01/2012 08/03/2012 23/04/2012 12/07/2012 Period 4 Period 5 Period 6 06/09/2012 18/10/2012 29/11/2012 10/01/2013 22/02/2013 09/04/2013 30/05/2013 Time (Date) Structure 1 Structure 2 Structure 3 Rainfall 16
Cleaning: water based Optimization of the water-based cleaning method Washing parameters optimization Reflectance as a result of washing water temperature and pressure combination Combining the temperature and pressure 93,90 Reflectance [% ] 93,75 93,60 200 150 30 40 50 T emperature[ºc] 60 50 100 Pressure [bar] (Fernández-García et al., 2010) Innovative methods with low water consumption WASCOP Project: Tekniker and DLR devices Collect and reuse!!!! 17
Cleaning methods: Dry cleaning It is not a suitable option in humid ambient (particle adhesion) Dry cleaning with a pad was studied in ANU. Combination of pressure against the reflector, number of wipes and velocity (Worsman and Lovegrove, 1996) 18
Reflectance measurements When to clean? Economic losses due to dirtiness higher than the cleaning cost Selection of the cleaning methods Effectiveness of the cleaning methods Predictive algorithms Durability checking 19
Reflectance measurements METHODOLOGY How many measurements? Where to measure?
Reflectance measurements The proper optical parameter to evaluate the quality of reflectors is the solar-weighted specular reflectance, ρ s (SW,θ,φ) λ: whole solar spectrum θ: depends on tech and site φ: depends on tech On-site measurements: Portable Reduced weight High automony Easy to use and handle Data storage system Adaptable to curvature and different thickness 21
Reflectance measurements Reflectometers Monochromatic Specular Reflectance 15R-USB, D&S θ = 15º φ = {3.5,7.5,12.5,23.0} mrad λ = [635,685] nm; 660 nm Source: LED Resolution: 0.001 Spot size: 10 mm Optical aligment Curvature and thinkness Time consuming Cost: 16000 22
Reflectance measurements Reflectometers Monochromatic Specular Reflectance 15R-RGB (MWR), D&S θ = 15º φ = {2.3,3.5,7.5,12.5,23.0} mrad λ = {460,550,650,720} nm Source: white light + filters Resolution: 0.001 Spot size: 10 mm Optical alignment Curvature and thickness Cost: 18000 23
Reflectance measurements Reflectometers Monochromatic Specular Reflectance Condor, Abengoa θ = n/a φ = 204 mrad λ = {435,525,650,780,940,1050}nm Source: LED Resolution: 0.001 Spot size: 1 mm No optical alignment Easy to handle Cost: 22000 24
Reflectance measurements Reflectometers Monochromatic Hemispherical and Diffuse Reflectance SOC 410 Solar, Surface Optics θ = 20º φ = 52.4 mrad λ = 7 bands; 330-2500 nm Source: Tungsten Resolution: n/a Spot size: 6.35 mm No optical alignment Cost: 20000 25
Reflectance measurements Reflectometers Spectral Hemispherical and Diffuse Reflectance CM 700-d, Konica Minolta θ = 8º φ 50 mrad λ = [400-700] nm Source: Xenon Resolution: 0.0001 Spot size: 8 mm No optical alignment No curvature Cost: 10000 26
Reflectance measurements Reflectometers Monochromatic Specular Reflectance µscan, SMS θ = 25º φ = n/a λ = 670 nm Source: Laser Resolution: 0.001 Spot size: 1 mm No optical alignment Small repeatability Cost: 14000 27
Reflectance measurements 1.1 New instruments: Automatic device TraCS Automatic real time measurement of a test mirror with sun spectrum High time resolution allows for identification of weather influences on soiling Validated with hand measurement devices TraCS cleanliness 1.0 0.9 0.8 0.7 0.6 0.5 0.5 0.6 0.7 0.8 0.9 1.0 Reference cleanliness 1.0 cleanliness factor 0.9 0.8 0.7 0.6 16-Jun-12 17-Jun-12 18-Jun-12 19-Jun-12 20-Jun-12 21-Jun-12 22-Jun-12 23-Jun-12 (Wolfertstetter, 2012)
Reflectance measurements New instruments: soiling sensor A transparent substrate is exposed to the same environmental conditions as the concentrator mirror Based on the scattering of a modulated infrared beam directed to the dust or dirt from the bottom of the substrate The measurement provides real time (seconds) percentage of soil, relative to a predefined 100% criteria Low-cost and high-sensitivity: distributed system of measurement in real time
Reflectance measurements New instruments: Pflex App for mobile phone Communication via bluetooth Data storage on phone Stray light suppression, robustness LED light source (red, on demand blue, green or white mixed LED) No cable Reference mirror needed for absolute values Fast measurements
Reflectance standardization STAGE-STE PROJECT : WP 11. Linear focusing STE technologies (CIEMAT) Task 11.2.2 Reflectance/soiling on site (CIEMAT) Commercial plant: Sener R+D facility: Abengoa Evaluators: CIEMAT: D&S 15R Cranfield University: Condor ISE Fraunhofer: PFlex Tekniker: share information about MAINBOT 31
Thank you for your attention!!!!! arantxa.fernandez@psa.es 32