Dissecting the Differences Between Pyranometer and Reference Cell Irradiance Measurements

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Dissecting the Differences between Pyranometer and Reference Cell Irradiance Measurements Anton Driesse PV Performance Labs, Freiburg, Germany October 24, 2016 η η

Transcript of Dissecting the Differences Between Pyranometer and Reference Cell Irradiance Measurements

Page 1: 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

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Acknowledgements

European Joint Research Center (JRC)

Sandia National Laboratories (Sandia)

National Renewable Energy Laboratory (NREL)

Fraunhofer Institute for Solar Energy Systems (ISE)

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ηη Introduction

Output: ± 1% or better Input: ± 3% or worse

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ηη Introduction

Output: ± 1% or better

± 0.5%

Input: ± 3% or worse

± 5.0%

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ηη 42 Sensors

1. Secondary standard thermopile pyranometers

2. Second class thermopile pyranometers

3. Photodiode pyranometers

4. Reference cells

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ηη Test Facilities

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ηη 42 Sensors

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ηη 42 Irradiances

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ηη “Recalibration” at AM1.5

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ηη Similarities

Pyranometer

• output signal mainly proportional to irradiance

Reference cell

• output signal mainly proportional to irradiance

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ηη Differences

Pyranometer

• circular

• dome (usually)

• thermoelectric principle

Reference cell

• square

• flat (usually)

• photovoltaic principle

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ηη Angular Response

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ηη Spectral Response

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ηη Temperature Response

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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.

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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

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ηη Results

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ηη Daily Profile for a Reference Cell

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ηη Daily Profile for a Reference Cell

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ηη Daily Profile for a Pyranometer

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ηη Daily Profile for a Pyranometer

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ηη Annual Profile for a Reference Cell

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ηη Annual Profile for a Reference Cell

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ηη Annual Profile for a Pyranometer

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ηη Annual Profile for a Pyranometer

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ηη Reference Cell vs Pyranometer

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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

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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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