Luis Martín PomaresIrSOLaVCalle Santiago Grisolia nº2, 28760 Tres Cantos (Madrid)firstname.lastname@example.org / www.solarexplorer.info
Introduction Solar resources evaluation is a necessary first step for the study of any energy system. The objective is the determination of the solar radiation collected in a specific site, for its use in a specific solar technology. As inputs, it is necessary to have information related to the source and to the technology. The methodologies can be classified as: classical evaluation (from measurements), and evaluation from satellite images.
Procedure proposed Time series Hourly, monthlyWhat do I need? Global, DNI Maps For what: Report, modeling No Satellite information Measurements? Any other approach Yes Ok? Solar resource knowledge
Solar radiation characteristics Solar energy reaches the earth in a discontinuous form, showing cycles or periods: Daily cycle: accounts for 50% of the total availability of daily hours. Another effect of the daily cycle is the modulation of the received energy throughout the day. Seasonal cycle: modulation of the received energy throughout the year.
Solar constant and solar geometry Is the amount of solar energy incident in 1 m2 of surface perpendicularly exposed to the solar rays and placed at 1 AU of distance. Changes slightly with time, but can be considered as constant Ion = 1367 W/m2.(WRC). Solar geometry is well knownWe can estimate with high accuracy the solar irradiation at the topof the atmosphere at every moment and every place
Interaction of solar radiation withthe atmosphere Radiation at the top of atmosphere Absorption (ca. 1%) Ozone.……….….... Rayleigh scattering and absorption (ca. 15%) Air molecules..…… Scatter and Absorption (ca. 15%, max. 100%) Aerosol…….………..…...…… Clouds………….……….. Reflection, Scatter, Absorption (max. 100%) Water Vapor…….……...……… Absorption (ca. 15%) Direct normal irradiance at ground
Solar Geometry The position of the Sun can be calculated suing the following trigonometric equations: ZENITH Cenital angle (θz) or its SOLTRAYECTORIA SOLAR complementary solar angle (α) (+) MAÑANA W 1 (-) ESTE θz z z cos sin sin cos cos cos -ψ α ψS N 0 +ψ Azimutal angle (ψ): PROYECCION DE LA 1 TRAYECTORIA SOLAR sin cos sin / sin z E
Solar radiation components RADIATION REFLECTED BY CLOUDS GROUND ALBEDO ABSORPTION SCATTERING DIRECT NORMAL RADIATION DIFUSE RADIATION
Ley of Beer In I 0 e( k L) I 0 e( m) I0 T In In d I 0 e( k L) d ISC e m Clear sky models or transmitance models Bn I CS (TRToTgTwTa 0.013) Yang C Bn ICS exp[ 0.8662 TLAM 2 mp R ] ESRA
The concept of optical massAproximation to plane- parallel 1 m cos Karsten equation 1.253 1 m (sin 0.15( 3.885) )
Air mass: variability 35 30 25 Masa relativa de aire 20 15 10 5 0 4 6 8 10 12 14 16 18 20
Sensibility of ESRA model to TL Influence of TLINKE and altitude above sea level on DNI for clear sky Dia juliano=200, z=500, Lat=37º N Long=-2º E TL=4, dia juliano=200, Lat=37º N Long=-2º E 1200 1000 TL=2 z=0 m TL=4 900 z=500 m 1000 TL=6 z=1000 m 800 700 800DNI (Wh m-2) 600 DNI (Wh m-2) 600 500 400 400 300 200 200 100 0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 0 5 10 15 20 25 Hora Hora
Components and non-dimensioanl indexes Components of solar radiation in horizontal surface IG IB cos ID Clear sky or transparency index IG kt I0 Difuse radiation fraction ID kd IG Beam radiation transmitance IB kb I0
Estimation of beam solar radaition Correlations to estimate difuse radiation fraction G (1 kd ) Ib 1.0 0.09kt kt 0.22 sen( ) kd 0.9511 1.1604kt 0.165 kt 0.8 4.388kt 2 16.638kt 3 12.336kt 4 0.22 kt 0.8 Correlations to estimate beam transmitance Ib kb I o kb 0.002 0.059kt 0.994kt 2 5.205kt 3 15.307kt 4 10.627kt 5
Measuring Solar Radiation:Pyrheliometers EKO MS-54 Measures direct beam irradiance Typically used for calibration transfers Middleton DN5 Normally defined with an opening angle of 5 If used in conjunction with pyranometers, the optical flat protecting entrance should match the optical material of the pyranometer domes Relatively easy to characterize 4 major manufacturers: EKO Instruments (Japan) Eppley Instruments (USA) Kipp & Zonen (Netherlands) Middleton Solar [Carter Scott Design] (Australia) Normally mounted on passive or active solar tracking systems
Measuring Solar Radiation: Pyranometers Tilted Irradiance Most pyranometers use a thermopile as means of converting solar irradiance into an electrical signal. Silicon cell pyranometers are also available, but are not recommended by WMO. Advantage of the thermopile is that it is spectrally neutral across the entire solar spectrum (domes may have spectral dependencies). Disadvantage is that the output is temperature dependent and the instruments must ‘create’ a cold junction.
Measuring Solar Radiation: Silicon Pyranometers Instrument’s spectral response is non-linear and does not match solar spectrum. General calibrations are through comparison with pyranometers, therefore there are spectral mismatch problems. LiCor is the primary instrument manufacturer and recognizes these problems: “The spectral response of the LI-200 does not include the entire solar spectrum, so it must be used in the same lighting conditions as those under which it was calibrated.” –Pyranometer sensors are calibrated against an Eppley Precision Spectral Pyranometer (PSP) under natural daylight conditions. Typical error under these conditions is ±5%. (LiCor) –Similar problems arise when using sensors calibrated in one climate regime and used in a different regime.
Rotating Shadowband Radiometer RSR2 LI-COR Terrestrial Radiation Sensors Irradiance Inc. (www.irradiance.com) LI-200 Pyranometer is a silicon photodiode calibrated from LI-COR ±5% RSR2 Head unit includes a moving shadowband that momentarily casts a shadow over a LI-200 pyranometer Motor controller contains circuit to control the exact movement of shadowband LI-200 Pyranometer Correction provided by Algorithm Measurement: Global Horizontal Irradiance Diffuse Horizontal Irradiance Calculation: Direct Normal Irradiance RSR2 Headunit RSR2 Motor Controller
Measuring Solar Radiation:Typical BSRN-like stations
Measurement recomendations • Know exactly what temporal reference of the masurements you are using (TSV, GMT, Local etc) • Register with enough temporal resolution, almost 10 minutes to register the dinamic of cloud transients. • Follow BSRN recomendation for maintenance of instruments. Cleaning every day radiometers, calibrate once per year each instrument,… • Secure the relation G=B cos θ + D. Some solar trackers have embeded this filter in its program to activetes realtime alarms when measurement is worng.
Satellite classificationAccording to the type of orbit :Polar satellites: placed in polar orbits, modifying its perspective and distance to the earth. The resolutions of these satellites are around 1m to 1km.Geostationary satellites: placed in the geostationary orbit that is, the place in the space where the earths attraction force is null. It is an unique circumference where all the geostationary satellites are situated in order to cover the whole earths surface. The resolutions of these satellites are higher in the sub satellite point on the equator, and go decreasing in all directions.
Meteosat Satellite coverage Meteosat Prime Meteosat East Spatial resolution 2.5 km at sub satellite, eg. About 3x4 km in Europe Temporal resolution 1h. Current Coverage: Meteosat Prime up to 1991-2005, Meteosat East 1999 - 2006
Solar radiation derived from satellite imagesSatellite to irradiance: general procedure Meteosat – Goes - Mtsat 60’, 30’ or 15’ images in the visible position assessement geometric corrections – pixels averaging model to obtain global irradiance
AOD (Aerosol Optical Depth estimations) Estimations from MODIS (Moderate Resolution Imaging spectroradiometer) on NASA’s Terra satellite http://earthobservatory.nasa.gov/ AOD and water vapor vertical content estimations from satellite
Radiometric Databases • Baseline Surface Radiation Network (BSRN) • World radiation data centre (WRDC) • Meteonorm
SSERadiometric Databases: SSE from NASAhttp://eosweb.larc.nasa.gov/sse / • Surface Meteorology and • Solar Energy (SSE) Datasets • And Web interface • Monthly data • Free upon registrationGrowing over the last 7 years to nearly 14,000 • 1ºx1º (120x120users, nearly 6.4 million hits and 1.25 milliondata downloads km) resolution
Solar radiation derived from satellite imagesSWERA ProjectThe SWERA project provides easy access to high quality renewable energy resource informationand data to users all around the world. Its goal is to help facilitate renewable energy policy andinvestment by making high quality information freely available to key user groups. SWERAproducts include Geographic Information Systems (GIS) and time series data
Comercial data from satellite• Irsolav• Solemi (DLR)• 3Tier• Solargis• ….
IrSOLaV activities Ciemat promoted a spin-off company for solar resource characterization services (www.irsolav.com). Thus IrSOLaV interacts with the industry needs and supply data and consulting services on solar resource and also collaborates with Ciemat in R&D. IrSOLaV and Ciemat develops R&D programs in the solar resource field and collaborates with international scientific groups (DLR, NREL, NASA, JRC, CENER, Universities…) through European projects (COST project) or other initiatives (Task 46 SHC/IEA) Within Spain IrSOLaV and CIEMAT collaborates with universities (UAL, UJA, UPN) and support the industry through agreements for doing specific research on solar resource knowledge (forecasting, model improvements, atmospheric physics, etc)