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State of the art of indoor calibration of pyranometers and pyrheliometers

State of the art of indoor calibration of pyranometers and pyrheliometers. Main points. Most field pyranometers are calibrated indoors Many procedures for indoor calibration Not all well connected to ISO 98-3 GUM Industry requires straightforward approach. Industry.

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State of the art of indoor calibration of pyranometers and pyrheliometers

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  1. State of the art of indoor calibration of pyranometers and pyrheliometers

  2. Main points • Most field pyranometers are calibrated indoors • Many procedures for indoor calibration • Not all well connected to ISO 98-3 GUM • Industry requires straightforward approach

  3. Industry • Meteorology - Solar renewable energy • Site assessment • Installation performance • Professionalisation / IEC

  4. Conclusion • Points for discussion • Normal incidence calibration is preferred (diffuse dome not) • Uncertainty & accuracy of reference can be optimised • Pyrheliometer indoor calibration must be added

  5. Myself • Kees VAN DEN BOS • Engineer Physics • Director / owner Hukseflux Thermal Sensors • Last 20 years sensor design

  6. Hukseflux 2010

  7. Hukseflux international

  8. Founded 1993 Thermal sensors 15 employees 5 radiometry compensation pyrheliometer Hukseflux DR01 pyrheliometer

  9. Hukseflux solar concentrator sensors

  10. Background • Most pyranometers and pyrheliometers have indoor calibration • Exception: highest accuracy (BSRN, outdoor) • Exception: Japan, China (outdoor) • Cost, time, weather; outdoor calibration is unacceptable to industry

  11. Present status (excerpt) • Eppley, US Weather Bureau: indoor integrating diffuse source • Kipp, Hukseflux: indoor normal incidence • EKO, JMA: outdoor tracker with collimation tube (changes) • China: outdoor

  12. ISO 9060

  13. ISO 9060

  14. Background • Measurement uncertianty is a function of: • Characterisation / class • Calibration • Measurement & maintenance conditions • Environmental conditions

  15. Background • Indoor calibration covered by ISO 9847 • Present ASME: “Indoor Transfer of Calibration from Reference to Field Pyranometers”

  16. Indoor calibration

  17. ISO 9846

  18. ISO 9847 also indoor

  19. ISO 98-3 GUM

  20. Hierarchy of Traceability • A: Reference calibration (uncertainty) • B: Correction of reference to indoor conditions (uncertainty) • C: Indoor calibration of field instrument (uncertainty) • Indoor calibration uncertainty estimate (A+B+C) • Field measurement uncertainty estimate

  21. Hierarchy of Traceability • A: Reference calibration (uncertainty) • B: Correction of reference to indoor conditions (uncertainty) • C: Indoor calibration of field instrument (uncertainty) • Indoor calibration uncertainty estimate (A+B+C)

  22. ISO 98-3 GUM

  23. Hierarchy of traceability

  24. ISO 98-3 GUM

  25. Hierarchy of Traceability • KNMI TR 235 "uncertainty in pyranometer and pyrheliometer measurements at KNMI in De Bilt".

  26. ISO 98-3 GUM

  27. Hierarchy of Traceability • A: Reference calibration (uncertainty) (conditions and class) • B: Correction of reference to indoor conditions (uncertainty) • C: Indoor calibration of field instrument (uncertainty) • Indoor calibration uncertainty estimate (A+B+C) • Field measurement uncertainty estimate (conditions & class)

  28. Strange… • Errors in reference calibration re-appear in measurement errors • Counted double • At least systematic errors (Zero offset A and directional errors) can be avoided.

  29. One step back • Present approach works well if calibrated instruments are used: • Outdoor / unventilated • Without applying GUM analysis • At same latitude

  30. One step back • Present approach does not work well calibrated if instruments are used: • As indoor reference • Applying GUM analysis • At other latitudes • Ventilated

  31. Typical calibration • Irradiance 800 W/m2 • 40 to 60 degrees angle of incidence, + / - 30 degrees azimuth • Zero offset A: -9 +/- 3 W/m2 (larger than ISO9060) • Directional: +/- 10 W/m2 @ 1000 W/m2 , now estimated +/- 5 W/m2

  32. Typical calibration • PMOD specified uncertainty +/- 1.3% • Systematic error -1%? Type B.

  33. Improved approach • Zero offset A: -9 +/- 3 W/m2 (larger than ISO9060) • Directional: +/- 10 W/m2 • Solution 1: ventilation • Solution 2: single angle of incidence

  34. For consideration • Japanese collimated tube with tilt correction and ventilation

  35. Diffuse sphere source • Uniformity of sphere top-edge (experimental -13%) • Weighing for non uniform source requires weighing of reference with source • Diffuse sphere: weighing requires weiging of field instrument with source. Complicated! • Normal incidence: weighing of field instrument is not necessary

  36. Conclusion • Indoor calibration offers only acceptable solution for manufacturers and solar industry • “Normal incidence” calibration fits within ISO 98-3 GUM

  37. Conclusion • Indoor normal incidence calibration is preferred (diffuse dome not) • Accuracy and precision of reference can be optimised (single angle, ventilated) • Pyrheliometer indoor calibration must be added

  38. P.S. • Memo available via server

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