Meteorological Measurements for Solar Energy

Energy Meteorology Symposium, Wageningen, 11.5.2017 Stefan Wilbert, Fabian Wolfertstetter, Natalie Hanrieder, Bijan Nouri, Pascal Kuhn, Florian Sutter, Florian Wiesinger DLR – German Aerospace Center Institute of Solar Research Qualification Solar Energy Meteorology

• Introduction: • Solar energy options • Solar energy meteorology and its relevance for solar

power plants

• Presentation of meteorological parameters that help solar power and their measurement

Overview Meteorological measurements for solar energy

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Photovoltaic (PV) power plant options

• Different cell types • Fixed tilt, 1 or 2 axes tracker • Concentrating PV (CPV)

CPV images: Hirsch, T., N. Martin, L. Gonzalez, M. Biencinto, S. Wilbert, M. Schroedter-Homscheidt, F Chenlo, and J.F. Feldhoff. 2014. Technical report on the functional requirements for the nowcasting method. Report D2.1, FP7 project DNICast, Grant Agreement No. 608623.: DLR, CIEMAT.

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Power Tower Central Receiver

Dish Stirling

Concentrating Solar Power (CSP) technology options

Parabolic Trough & Linear Fresnel

• Electricity and/or heat

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Other solar energy technologies

• Flat plate collectors for heating and cooling • Collectors for solar water treatment • …

Images: CIEMAT, psa.es

Solar energy meteorology

Ground measurements

Prediction of plant yield

Satellite

data Modelled data

Application: • Site selection • Site specific plant layout • Optimal decisions during

plant operation

- long term yield of future plant - behavior & yield of existing plant

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Meteorological parameters relevant for solar plants Parameters - GTI (Global Tilted Irradiance)

and/or DNI (Direct normal irradiance) - Circumsolar radiation - Spectrally resolved

- Wind speed, direction and gust - Temperature, humidity, pressure - Soiling rate, dew, snow, rain - Extinction between heliostats and receiver - UV, salt concentration, abrasion Historical and live meteo data & forecasting required for bigger plants

Meteo data collection not a burden, but a chance for energy cost reduction - Low data uncertainties reduce financial risk and financing costs! - Cost reductions due to smart site specific design - Cost reductions due to optimized operation (live data, forecasting → yield ↑)

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Solar radiation measurements

Operational since 2010 -2013 Planned

Solar radiation measurements

Satellite derived data and ground measurements are required for MW+ plant projects - to reach the required accuracy for historic long term data - & for the plant operation.

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x

Direct normal irradiation per year [kWh/m²]

• Robust instrument used for solar resource assessment at remote sites

• Characterization, further improvements & calibration

Global horizontal irradiance (GHI)

Diffuse horizontal Irradiance (DHI)

DNI (Direct Normal Irradiance)

Principle of operation 1. Pyranometer measures global irradiance 2. Shadowband rotates once per minute 3. During rotation: measure the diffuse irradiance → DNI is calculated → GTI calculated

Solar radiation measurements Rotating Shadowband Irradiometers

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Instrument calibration and characterization

-Calibration is the greatest uncertainty source of common radiometers -Enhancement of calibration techniques -Evaluation of systematic errors and accuracy -Correction functions for systematic errors -Calibration of Si-sensors & RSI

Solar spectra

-Measurements with spectroradiometers -Simulations with radiative transfer codes based on measurements (aerosol properties, broadband DNI & GHI, temp., rel. hum., press., …)

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Relevant for: -efficiency -selection of PV type

Spectral effects on solar technologies and radiometers

-spectral effects on PV and Si pyranometers must be considered for yield analysis

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DNI GHI

- Measurement of aerosol properties

- e.g. NASA’s AERONET - reference for satellite based aerosol measurements

Sun photometers DLR.de • Chart 14

PSA

α

• Circumsolar radiation is forward scattered solar radiation

• Concentrating collectors use: nearly the complete disk radiation

+ a smaller fraction of the circumsolar

radiation

disk radiation

Circumsolar radiation

Relevant for: -operation and plant output -design of plants (field size) -selection of solar technology

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- SAM (Sun & Aureole Measurement), software (+ optional sun photometer) - camera based system @ 670nm - broadband radiation needed for CSP, spectral radiation for CPV

- master-system running at PSA

- 2 replicas: CNRS/Odeillo (France), Masdar Institute (United Arab Emirates)

SAM sun photometer

Measurement of circumsolar radiation – SFERA system DLR.de • Chart 16

Circumsolar Radiation Sensor using pyrheliometers

1

2

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Black Photon Instruments

Circumsolar radiation measurement with RSIs DLR.de • Chart 18

Circumsolar radiation measurement with RSIs

Shadow on pyranometer

DHI partly blocked by band

Circumsolar contribution from 1° to 3.2°

measured with an RSI

disk radiation

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- Algorithm analyses measurement during rotation - No additional hardware required

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Variability of irradiance & forecasting

Andasol parabolic trough plants

Variability of irradiance & forecasting

Forecasting and temporal and intra-plant-spatial variability are relevant for: -PV production ramp rate control -PV back up system control (diesel generator) -CSP&PV plant yield optimization (e.g. market participation) -CSP & PV plant design (storage size) -selection of solar technology depending -grid operation

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Point like

10 m

100 m

1 km

10 km

100 km

1 m

in

30 m

in

45 m

in

6 h

All sky imagers Satellite Global NWP Limited area NWP

Spat

ial r

esol

utio

n (l

og-s

cale

)

Forecast lead time (log-scale) 60 m

in

0.1

min

5 m

in

Imag

e: A

RM

INES

, SM

HI,

DLR

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Irradiance nowcasting

• Spatially resolved DNI, GTI, GHI maps with high temporal resolutions • Combination with NWP (numerical weather prediction) and satellite nowcasts

All sky imager (ASI) based irradiance nowcasting

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Example ASI image

Working principle of ASI based nowcasting systems

ASI cameras film clouds

Clouds are segmented

Clouds are geolocated

Shadow map is estimated

Sensors provide irradiance data

Irradiance map is created

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Track cloud position and extrapolate

User interface of a nowcasting system (WOBAS) DLR.de • Chart 25

Radiometer and ShadowCam-system Ground-filming cameras provide irradiance maps

6x

sunny + shaded reference image

6x

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radiometers

4 Q24 ASI (All Sky Imager) 6 M25 ShadowCams 20 Si-pyranometers Pyrheliometers + pyranometers Ceilometer

2.0km

Radiometer and ShadowCam-system

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Soiling

Soiling

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Soiling measurements for PV modules and reference cells

CSP-specific soiling measurements with TraCS or handheld reflectometers

Relevant for: -operation and plant output

-When do we have to clean? -plant design, site selection

HVS Grimm

Optical systems, e.g.:

• Scatterometer type

Gravimetrical system

• Filter in air flow

Soiling modelling based on simple measurements Dust sampling

Zagora meteo station

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Beam attenuation between heliostat and receiver

Beam attenuation in tower plants

Relevant for: -design of tower plants (field size) -selection of solar technology -operation and plant output

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Vaisala FS11 scatterometer

Optec LPV-4 transmissometer

Beam attenuation in tower plants

Before ABC

ABC improves coincidence between both sensors!

Commercially available instruments applicable for CSP if ABC correction is applied!

ABC - Absorption and Broadband Correction

After ABC

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Compare clear sky DNI measurement with modelled DNI for aerosol free atmosphere + Assumption about aerosol height profile Calculate extinction

coefficient close to ground

1km Constant aerosol extinction coefficient

Extinction modelling based on DNI measurement

Validated for PSA

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Parameters affecting durability

Radiation

Temperature

Wind

Aerosols

Sandstorms Humidity • Air humidity, dew, rain •Chemical reactions •Soiling

• Abrasion

• Salt, dust, industrial emissions • Soiling • Chemical reactions, especially on hot surfaces

• Mechanical loads • Soiling • especially UV-A, UV-B

•Chemical reactions

• Diurnal changes • frost • Mechanical stress

Relevant for: -cheaper components & longer lifetime

Parameters influencing durability

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• Durability tests of new products by outdoor exposure take too long

• Accelerated aging tests in the laboratory are used • Analysis of wind speed and flying sand concentration

analyses • Operation parameters for laboratory tests

Sandstorm chamber

Abrasion due to sandstorms

Sandstorm chamber

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Meteorological Measurements for Solar Energy Summary and conclusion Solar irradiance is the most relevant parameter, but several other parameters also have to be measured Meteo data collection & application = chance for energy cost reduction -Low data uncertainties reduce financial risk and hence financing costs -Cost reductions due to smart site specific design -Cost reductions due to optimized operation: live meteo data, nowcasting, forecasting required

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Thank you for your attention and for the invitation! Questions?

Contact:

Dr. rer. nat. Stefan Wilbert

Team Leader ‘Solar Energy Meteorology’

Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)

German Aerospace Center Institute of Solar Research - Qualification

Plataforma Solar de Almería, Carretera de Senés s/n, km 5, 04200 Tabernas, Spain

Tel. 0034-950277619 | Fax 0034-950260315 | stefan.wilbert@dlr.de

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