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

  • Acknowledgements

    European Joint Research Center (JRC)

    Sandia National Laboratories (Sandia)

    National Renewable Energy Laboratory (NREL)

    Fraunhofer Institute for Solar Energy Systems (ISE)

  • Introduction

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

  • Introduction

    Output: 1% or better

    0.5%

    Input: 3% or worse

    5.0%

  • 42 Sensors

    1. Secondary standard thermopile pyranometers

    2. Second class thermopile pyranometers

    3. Photodiode pyranometers

    4. Reference cells

  • Test Facilities

  • 42 Sensors

  • 42 Irradiances

  • Recalibration at AM1.5

  • Similarities

    Pyranometer

    output signal mainly proportional to irradiance

    Reference cell

    output signal mainly proportional to irradiance

  • Differences

    Pyranometer

    circular

    dome (usually)

    thermoelectric principle

    Reference cell

    square

    flat (usually)

    photovoltaic principle

  • Angular Response

  • Spectral Response

  • Temperature Response

  • Todays 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.

  • 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

  • Results

  • Daily Profile for a Reference Cell

  • Daily Profile for a Reference Cell

  • Daily Profile for a Pyranometer

  • Daily Profile for a Pyranometer

  • Annual Profile for a Reference Cell

  • Annual Profile for a Reference Cell

  • Annual Profile for a Pyranometer

  • Annual Profile for a Pyranometer

  • Reference Cell vs Pyranometer

  • 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

  • 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