The latest on DNI and Diffuse measurement options

Riaan MeyerMD, GeoSUN Africa

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Contents• Terminology• Background• History• What is new?

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The latest on DNI and Diffuse measurement options

DNI and GHIDirect Normal Irradiance and Global Horizontal

Irradiance

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Global Horizontal Irradiance (GHI) Direct Normal Irradiance (DNI)

GHI applies to PV and SWH DNI applies to CSP and CPV

Factor 1.2 Factor 3

Solar Resource - Reducing uncertainty

DNI: ±3.5%

GHI: ±2.5%

Best achievable uncertainty

0

2

4

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0 12 24 36 48

Ach

ieva

ble

unce

rtain

ty (%

)

Period of ground measurements (months)

DNI P99.5

DNI P90

GHI P99.5

GHI P90

Running a ground-monitoring campaign and combining measurements with satellite derived data is the way to obtain low uncertainties.

Values are indicative and represent long term annual averages.

Source: SolarGIS

• All CSP developers deploy on-site solar (and meteorological) measurements

• Mandated by RE-IPPPP (CSP) and required by banks• Due to higher uncertainties of satellite derived data• In established markets PV plants can rely on satellite derived data

only (no ground measurements) for GHI. In new markets (mainly developing countries) ground measurements are required.

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Solar Resource – Ground Measurements

History

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History

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History

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DNI

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Alternatives – Small trackers

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Alternatives - RSR

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Alternatives - RSR

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Alternatives – SPN1

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Summary

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Option InstrumentDNI

uncertainty (daily)

Instrument + tracker (if required)

With additional equipment to

obtain Modbus output

1 SPN1 ~ 5 – 6 % R 65 000 R 80 0002 RSR 4 % R 100 000 R 125 000

3 Pyrheliometer (Second Class*) on small tracker 2 % R 130 000 R 130 000

4Pyrheliometer(First Class*) on conventional tracker

1 % R 220 000 R 235 000

*ISO 9060 classification

17 http://globalsolaratlas.info

Thank you for your attentionContact DetailsMr Riaan Meyer, 084 876 4816, Unit 1, CS Africa building, 1 Meson Street Techno Park, Stellenbosch, 7600, South Africa, riaan.meyer@geosun.co.zawww.geosun.co.za

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