DLR.de Chart 1 Solar tower plant modelling: needs and current practices Stefano Giuliano DLR, Institute for Solar Research DNICast workshop 02.12.15, Oberpfaffenhofen
DLR.de Chart 2 Content Introduction Heliostat field calculation and optimization Current practice to consider atmospheric attenuation losses Example Summary and Outlook
DLR.de Chart 3 Solar Tower Systems Solar Tower, Crescent Dunes, 100MW e Heliostat Field Receiver with Tower Thermal storage Power Block Total power of CSP power plant: P sys, el DNI A SF SF Rec TES PB Most often systems are economically optimized (LCOE minimum) LCOE annual cost [ EUR / kwh] annual energy yields
Elevationswinkel (Sonnenstandswinkel) DLR.de Chart 4 2005 Maßong Verlag www.karena.de Loss Mechanism of Heliostat Fields PS10 Abengoa Solar 90 80 70 60 50 9 h Vormittag 10 h 11 h Sonnenbahndiagramm jeweils 21. Tag eines Monats Mittag 12 h Jun Mai/Jul Apr/Aug Mär/Sep 13 h Objekt: hier Objektnamen eingeben Standort: hier Standort eingeben Breitengrad: 35 nördlicher Breite Nachmittag 14 h 15 h 40 30 20 6 h 7 h 8 h 9 h 10 h 11 h 10 8 h 16 h 5 h 19 h 0 60 90 120 150 180 210 240 270 300 Ost Süd West Feb/Okt Jan/Nov Dez 13 h 14 h Azimuthwinkel (entspricht Kompassrose) 15 h 16 h 17 h 18 h Losses: cosine loss reflectivity <100% shading and blocking atmospheric attenuation Intercept losses (non-perfect focussing) P inc _ Hel ( x, y, t ) DNI ( t ) A Mir refl SF_ Hel cos( x, y, t) atmo( x, y, t) b& s ( x, y, t) inc ( x, y, t) 2 beamerror 2 sun 2 beamquality
DLR.de Chart 5 Specific modelling approach for solar tower systems solar field performance calculation DNI, sun position, sun shape, extitintion given Number, size, position und optical quality of heliostat given Size and position of tower given Chracteristics, size and position of receiver given PS10 Abengoa Solar Calculation of heliostat field performance (with Raytracing Tools like Mirval, STRAL, Spray etc.) solar field layout optimization Charakteristic data of Heliostats and position tower receiver Are varied to improve annual yields or to reduce generation cost PS10 Abengoa Solar Optimization of heliostat field: improve annual yield or reduce LCOE (with tools like HFLCAL, University of Houston Code, DELSOL, etc.)
DLR.de Chart 6 Field Layout Optimization: Example from HFLCAL
DLR.de Chart 7 Atmospheric Attenuation losses Atmospheric Attenuation of the reflected radiation looks impressive. PSA, Source: Gerhard Weinrebe but is a loss! PS10 / Abengoa Solar
DLR.de Chart 8 Atmospheric Attenuation in Heliostat Fields DNI data already consider a atmospheric attenuation through the atmosphere For solar tower important: Atmospheric attenuation of reflected radiation between heliostat and receiver due to absorption and scattering processes in the atmosphere Distance between heliostat and receiver (slant range) is up to more than 1 km Important atmospheric profile is ~0 300m (tower height) Atmospheric attenuation varies strongly with time and location (as the DNI!) Atmospheric attenuation has a significant influence of the yield of a solar tower plant (as the DNI!) Currently only few data for atmospheric attenuation for different sites are available PS10 Abengoa Solar Tower height Slant range DNI Measurement
DLR.de Chart 9 Current practice to consider atmospheric attenuation Current ray-tracing & field layout codes use simplified models for atmospheric attenuation Data basis goes back to a few activities in the eighties (e.g. Vittitoe and Biggs, 1978) Only standard atmospheres are used, no local conditions are considered Most tools allow the decision between 2 different extinction levels: clear day and hazy day. Annual mean values are used for all time steps! Example of DELSOL: atmospheric transmittance for a clear day in Τ a = 0.99326-0.1046 SLR + 0.017 SLR 2-0.002845 SLR 3 where SLR is the slant range from heliostat to receiver in kilometers
DLR.de Chart 10 Case Study Analysis of influence from atmospheric attenuation for solar tower heliostat fields for the heat generation cost Different power sizes were analyzed The calculations and optimization were done with the code HFLCAL Only field layout is considered, not the full power plant! 2 different extinction levels were considered: clear day (23km visibilty) (little) hazy day (12km visibilty) Annual mean values for atmospheric attenuation are used for all time steps Gefördert durch: aufgrund eines Beschlusses des deutschen Bundestages
DLR.de Chart 11 Case Study - Results For large scale power levels the heat generation cost differ up to 8% Optimal power scale for solar towers in hazy atmospheric conditions are becoming smaller For a individual solar tower project reliable and accurate data for the atmospheric attenuation are necessary If not available incorrect planning can occur with a financial risk. After the field layout is fixed and the field erected, it is not possible to correct. Gefördert durch: aufgrund eines Beschlusses des deutschen Bundestages
DLR.de Chart 12 Summary Atmospheric attenuation of reflected radiation between heliostat and receiver is important for solar towers Important atmospheric profile is ~0 300m Atmospheric attenuation is strongly varying with time and for the specific site Current ray-tracing and field layout codes use simplified models considering only standard atmospheres The codes use only two extreme conditions: clear or hazy. And only annual mean values! Atmospheric attenuation can be a relevant loss for a solar tower at certain sites. The annual yields can be overestimated by up to 10% if the wrong data base is used. Currently only few data for atmospheric attenuation for different sites are available. Therefore incorrect planning can occur with a financial risk. At sites with different meteorological conditions a site specific design is an important task for the planning of the solar tower plant.
DLR.de Chart 13 Outlook A meteo data set (measured or from satellite data) should include information about atmospheric attenuation like DNI, temperature etc. The question is with what kind of definition: transmittance as f(slr),,? Beside a DNI world map a map for atmospheric attenuation (with high resolution) is required We need to know more about the dependency of the vertical profile for the relevant height <300m Is the micro local dependence really neglectable for very large scale towers? We need much more data for different sites (measured or from satellite data) With the collected data a useful model needs to be implemented in ray-tracing and field layout codes. These models will then be used for a site specific optimization approach for heliostat fields and shall improve the annual yield assessment and shall allow to minimize the LCOE of solar towers
DLR.de Chart 14 Thank you for your attention!