Dissecting the Differences Between Pyranometer and Reference Cell Irradiance Measurements
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Transcript of Dissecting the Differences Between Pyranometer and Reference Cell Irradiance Measurements
Dissecting the Differences between Pyranometer and Reference Cell
Irradiance Measurements
Anton DriessePV Performance Labs, Freiburg, Germany
October 24, 2016
ηη
ηη
Acknowledgements
European Joint Research Center (JRC)
Sandia National Laboratories (Sandia)
National Renewable Energy Laboratory (NREL)
Fraunhofer Institute for Solar Energy Systems (ISE)
ηη Introduction
Output: ± 1% or better Input: ± 3% or worse
ηη Introduction
Output: ± 1% or better
± 0.5%
Input: ± 3% or worse
± 5.0%
ηη 42 Sensors
1. Secondary standard thermopile pyranometers
2. Second class thermopile pyranometers
3. Photodiode pyranometers
4. Reference cells
ηη Test Facilities
ηη 42 Sensors
ηη 42 Irradiances
ηη “Recalibration” at AM1.5
ηη Similarities
Pyranometer
• output signal mainly proportional to irradiance
Reference cell
• output signal mainly proportional to irradiance
ηη Differences
Pyranometer
• circular
• dome (usually)
• thermoelectric principle
Reference cell
• square
• flat (usually)
• photovoltaic principle
ηη Angular Response
ηη Spectral Response
ηη Temperature Response
ηη Today’s Question
• How much do each of these effects contribute to differences in reported irradiance (and by extension to reported PV system performance)?
Procedure• Using measured spectra, component irradiances and
other weather parameters, for one year, calculate the expected output signal of each type of sensor.
• Calculate and illustrate the differences from a reference value both in absolute and relative terms.
ηη Locations Details
• Irradiance measurements from NREL-Solar Radiation Research Laboratory
– DNI, GHI, DHI, global tilted at 40°
– ambient temperature
• Spectral measurements from NREL Outdoor Test Facility
– Eko MS-700
– global tilted at 40°
• “Latitude tilt”, therefore high irradiance levels in winter as well as summer
ηη Results
ηη Daily Profile for a Reference Cell
ηη Daily Profile for a Reference Cell
ηη Daily Profile for a Pyranometer
ηη Daily Profile for a Pyranometer
ηη Annual Profile for a Reference Cell
ηη Annual Profile for a Reference Cell
ηη Annual Profile for a Pyranometer
ηη Annual Profile for a Pyranometer
ηη Reference Cell vs Pyranometer
ηη Additional Factors
Pyranometer
• delayed response
• thermal offsets
• alignment accuracy
• non-linearity
Reference cell
• spectral resp. vs temperture
• spectral resp. vs. angle
• alignment accuracy
• non-linearity
ηη Conclusions
• Understanding of the systematic difference between sensor types gives insight into when and why different instruments readings are obtained
• Precise quantification of those systematic differences allows instrument readings to be corrected, or adapted to the analysis needs
• Temperature and angular effects can be measured and processed with reasonable effort
• Spectral effects are challenging because spectral measurements have limited wavelength range
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