The Solar Resource

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The Solar Resource

• Solar Energy Workshop
• Colorado School of Mines
• Steve Wilcox
• National Renewable Energy Laboratory
• June 21, 2007

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Outline

• A Primer on Solar Radiation Data from Shining On
• What are solar radiation measurements?
• Why do we need solar radiation data?
• What influences the amount of solar radiation?
• How do we use solar radiation data?
• How accurate do the data need to be?
• How are we meeting our solar radiation data
  needs?
• Where can you obtain solar radiation data?

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The SunA Constant Source of Energy?
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Measuring and Using Solar Radiation at the
Earths Surface

• Energy from the Sun at the Earths Surface
• Different parts of the sky
• Change with time (minutes, hours)
• Change with time (seasons, years, decades)
• Change with location

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What are Solar Radiation Measurements?

• Light from the sky dome
• Direct from the sun
• Everywhere but the sun
• Entire sky
• We call it
• Direct (beam)
• Diffuse (sky)
• Global (total)
• Global is the sum of direct and diffuse

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What are Solar Radiation Measurements?
Direct Normal Measured by a Pyrheliometer on a
sun-following tracker
Global Horizontal Measured by a Pyranometer with
a horizontal sensor
Diffuse Measured by a shaded Pyranometer under a
tracking ball
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Solar Irradiance Components

• Global Direct Normal Cos(Z) Diffuse

18 dots 8 dots
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Clear Sky
Direct (Beam)
Global (Total)
Diffuse (Sky)
http//www.nrel.gov/srrl
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Partly Cloudy Sky
Direct (Beam)
Global (Total)
Diffuse (Sky)
http//www.nrel.gov/srrl
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Units of Solar Radiation

• Watts per square meter (W/m2)
• Watt hours per square meter (Wh/m2)
• Joules per square meter
• BTU per square foot
• Langleys
• Calories per square centimeter

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Units of Power and Energy

• Work Force x distance (newton meter)
• An activity involving force and movement in the
  direction of the force
• Power Work per unit time (Nm/s, watt)
• A rate of doing work how quickly work can be
  accomplished can be instantaneous
• Energy Sustained power (joule, watt sec or
  more commonly, watt hours)
• The capacity to do work the currency of work
  how much work can be done is not instantaneous

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Power and Energy

• With automobiles
• You buy power at the car dealer
• You buy energy at the filling station
• When you pay your electric bill, which are you
  paying for?
• a) Power
• b) Energy

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Power and Energy

• With automobiles
• You buy power at the car dealer
• You buy energy at the filling station
• When you pay your electric bill, which are you
  paying for?
• a) Power
• b) Energy
• c) Work

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Aesop on Power and Energy

• The Tortoise and the Hare
• The hare leaps forward to an early lead, then
  rests half way through the course.
• The tortoise moves ahead at a steady pace and
  crosses the finish line before the hare awakens.
• Slow and steady wins the race means what in the
  context of power and energy?

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Units of Solar Radiation

• Which is Power which is Energy?
• Watts per square meter (W/m2)
• Watt hours per square meter (Wh/m2)

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Spectral Distribution of Solar Radiation
Broadband Solar Radiation 280 nm - 3,000 nm
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Spectral Irradiance

• Basic Solar Spectral Regions
• Ultraviolet..200 - 400 nm
• Visible....400 - 700 nm
• Infrared..700 - 3000 nm

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Follow the Photons!
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Photovoltaic Responses
ASTM Standard AM 1.5 Global _at_ 37.5º Tilt
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Simple Model for Atmospheric Radiative Transfer
of SunshineSMARTS
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Thermopile Detectors
How do the radiometers work? Thermo-electric
detectors Two metals Heat
Electrical Potential
The Eppley Laboratory, Inc.
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Photoelectric Detectors
Fast, Low-Cost, with Reduced Spectral Response
www.kippzonen.com
www.licor.com
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Changes with Time Location Annual Cycle
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Changes with Time Inter-annual
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Changes with Time Inter-annual
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Why Do We Need Solar Radiation Data?

• Agriculture Photosynthesis
• Astronomy Solar Output Variation
• Atmospheric Science Numerical Weather Prediction
• Climate Change Energy Balance
• Health UV effects on skin
• Hydrology Evaporation
• Materials Degradation
• Oceanography Energy Balance
• Photobiology Light and Life
• Renewable Energy Sustainability

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Why Do We Need Solar Radiation Data?Renewable
Energy

• The amount of solar energy reaching the earths
  land areas
• in 1 hour is enough to supply the U.S. energy
  needs for
• 1 year (100 Quads/yr)
• Photovoltaics
• Solar Heat-thermal
• Solar Heat-electric
• Solar Fuel-biomass
• Passive Solar Lighting
• Building HVAC
• Solar Detoxification

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What Influencesthe Amount of Solar Radiation?

• Solar output 11 year solar cycle
• Earth-Sun distance 3.5 annual variation
• Clouds Dominant factor
• Water vapor Selective absorber
• Air pollution 40 less direct
• Smoke from forest fires Natural or man-made
• Volcanic ash Global effect for years
• Location
• Time of day Solar position
• Season

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What Influencesthe Amount of Solar Radiation?

• Earths Orbit
• Earth-Sun distance
• Relative tilt
• Time of day

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Solar Constant
World Radiation Center, Davos, Switzerland
http//www.pmodwrc.ch/
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What Influences the Amount of Solar Radiation?
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How Do We Use Solar Radiation Data?

• Technology Selection
• Siting
• System Design
• Performance Monitoring

Flat Plate and Concentrating Collectors
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How Accurate Do the Data Need to Be?

• What are the Cost/Benefit and risks?
• Illuminated through Resource Assessment of solar
  resource
• Higher value project (risk?) may demand higher
  accuracy
• What is the application?
• Residential (solar water preheat)
• Commercial (daylighting building thermal
  performance)
• Industrial (concentrating collector solar power
  plant)
• What is the period of interest?
• Instantaneous, daily, seasonal, annual? Longer
  averaging intervals can remove random errors
• Recent data more accurate than historical records
  (climate trends and technology advancements)

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How Accurate Do the Data Need to Be?

• What is possible?
• Measurement Uncertainty Estimates

Instantaneous data intervals
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How Will We Meet Our Solar Radiation Data Needs?

• Research Activities
• Solar Radiation Research Laboratory
• Metrology
• Optics
• Electronics
• Data Acquisition
• Photovoltaic Program
• Radiometric Measurements
• Climate Change
• Broadband Radiometer Mentor
• Collaborations
• WMO, UNEP, NCAR, NOAA, state local govt,
  academia

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Solar Radiation Research Lab

• Baseline Measurements
• Radiometer Calibrations
• Instrument Development
• Station Operator Training

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NSRDB Update 1991-2005Released in May 2007

• NSRDB Gridded SUNY Data
• Includes hourly satellite modeled solar data for
  years 1998-2005 on 10km grid
• Hourly solar for any location can be combined
  with hourly met data for PV and CSP simulation.

• NSRDB Station Data
• Contains hourly solar and meteorological data for
  1454 ground locations, 1991-2005
• Distributed by National Climatic Data Center and
  NREL via web

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Southwest Solar ResourcesUnfiltered Data
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Southwest Solar ResourcesTransmission Overlay
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Southwest Solar ResourcesSolar Resource gt 6.75
kWh/m2/day
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Southwest Solar ResourcesPrevious plus
environmental Land Use Exclusions
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Southwest Solar ResourcesPrevious plus slope lt 3
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Where Can You Obtain solar Radiation Data?

• Shining On Primer
• http//rredc.nrel.gov/solar/pubs/shining/
• Renewable Resource Data Center (Includes NSRDB)
• http//rredc.nrel.gov
• Measurement Instrumentation Data Center
  (Real-time data)
• http//www.nrel.gov/midc
• NREL Map Server (Maps and interactive products)
• http//www.nrel.gov/maps
• World Radiation Data Center (International solar
  data)
• http//wrdc-mgo.nrel.gov
• National Climatic Data Center (Meteorological
  data)
• http//www.ncdc.noaa.gov
• DOE Atmospheric Radiation Measurement Program
  (Research)
• http//www.arm.gov
• NOAA Surface Radiation Research Branch (Research)
• http//www.srrb.noaa.gov
• NOAA Earth Systems Research Laboratory (Research)
• http//www.esrl.noaa.gov/gmd/

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Key Points

• Accurate information is important for policy
  decisions, technology selection, siting,
  designing,and monitoring the performance of solar
  energy conversion systems
• Accurate measurements are important for model
  development
• The work we do to improve solar measurements
• Calibration
• Instrument characterization
• Measurement techniques (operations and
  maintenance, radiometer selection, installation
  considerations, etc.)
• Data Quality Assessment
• Training
• Data distribution to meet user needs (MIDC,
  RReDC, NSRDB)

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The Solar Resource

• Thank you!
• Questions?