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Satellite-based estimates of the Influence of Solar Spectrum

Variations on PV Performance

Thomas Huld1, Ana Gracia Amillo1, Jörg Trentmann2 1European Commission, Joint Research Centre, Ispra

2Deutscher Wetterdienst, Offenbach, Germany

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4th PV Performance Modelling and Monitoring Workshop Köln, Germany, 22-23 October 2015

Overview of presentation

1. Calculation of the influence of spectral variations of PV power

2. Estimates of spectrally resolved solar irradiance from geostationary satellite data, methods and input data

3. Results and discussion, lots of maps

4. Conclusions

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Calculating the influence of spectrum

Given the spectral response of a subcell l of a PV device (SR), the

short-circuit current can be written as:

𝐼𝑠𝑐,𝑙 = 𝑘 𝑆𝑅𝑙(𝜆)𝐺𝜆𝑑𝜆

where k is a proportionality factor and Gλ is the spectrally resolved

irradiance.

At each point in time we define a spectral correction factor: Cs,l for

subcell l:

𝐶𝑠,𝑙 = 𝑆𝑅𝑙(𝜆)𝐺𝜆𝑑𝜆

𝑆𝑅𝑙(𝜆)𝐺𝜆,𝑆𝑇𝐶𝑑𝜆

𝐺𝜆,𝑆𝑇𝐶𝑑𝜆

𝐺𝜆𝑑𝜆

Here, Gλ,STC is the STC spectrally resolved irradiance.

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Calculating the influence of spectrum

The overall spectral mismatch of the device can then be

𝑀𝑀 = 𝐶𝑠,𝑙𝐺𝑗𝑁𝑗=1

𝐺𝑗𝑁𝑗=1

In this calculation Cs,l is the spectral correction

factor for the subcell that is current-limiting at

hour j.

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Spectral response curves

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Normalized spectral response curves for 5 different modules, measured at the ESTI laboratory


Satellite-based spectral irradiance

Spectrally resolved irradiance data have been calculated using the SPECMAGIC algorithm developed by Deutscher Wetterdienst and the University of Oldenburg.

Cloud effects are calculated from METEOSAT images using

a Heliosat-type method. This is then used by SPECMAGIC together with data on aerosols, water vapour and ozone to calculate global and direct irradiance in 24 spectral bands between 300nm and 2200nm.

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Satellite-based spectral irradiance

SPECMAGIC has been used to process 30 years of METEOSAT data to generate the CMSAF SARAH data set. Hourly global and direct irradiance values are freely available through the CM SAF web site:

www.cmsaf.eu

SARAH version 2 will feature various improvements and also provide spectrally resolved irradiance data

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4th PV Performance Modelling and Monitoring Workshop, 22-23 October 2015

http://www.cmsaf.eu/

Data sources

• Spectral irradiation data calculated from satellite by the CMSAF collaboration (www.cmsaf.eu) and JRC Ispra

• Hourly time resolution

• Spatial resolution around 3-5km

• Temperature and wind speed data from ECMWF (www.ecmwf.int) operational forecast data • 3-hourly time resolution, linear interpolation to hourly values

• Spatial resolution 0.125° latitude/longitude

• Module power measurements mainly by the ESTI Laboratory

All calculations shown use one year of data, with modules

at 20°inclination (equator-facing).

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http://www.ecmwf.int/





Annual global in-plane irradiation

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Total for 2011, kWh/m2


Module performance ratio

The Module Performance Ratio (MPR) is the ratio of actual module energy output to the output if the module always had the efficiency measured under Standard Test Conditions. It can be expressed as:

Here Htot is the total in-plane irradiation (kWh/m2) and Etot is the total module energy output during the same period (kWh)

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)/(1000 totstctot HPEMPR


Overall MPR, c-Si modules

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Annual average MPR, c-Si module, including AOI, spectral effects, temperature and wind speed


Spectral effects, c-Si module

Annual percentage

change in MPR

due to spectral

effects, c-Si

modules

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Low H2O?

Spectral effects, CdTe module

Annual percentage

change in MPR

due to spectral

effects, CdTe

modules

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Multi-junction PV technologies

Multi-junction PV cells/modules have a more complicated response

to spectral variations since the current of the whole cell/module is

determined by the junction or subcell with the lowest current.

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Multijunction response curves

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Under STC, top cell is

current-limiting, ratio of

Isc is 0.87:1

Under STC, middle cell is

current-limiting, ratio of

Isc is 0.87:0.83:1

Tandem a-Si module Triple-junction III-V cell

Spectral effects, tandem a-Si

Annual percentage

change in MPR

due to spectral

effects, tandem a-

Si modules

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Top cell is practically always limiting

Note different scale

Spectral effects, III-V concentrator cell

Annual percentage

change in MPR

due to spectral

effects, III-V

concentrator cell

under DNI

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Spectral effects, III-V concentrator cell

Percentage of

energy delivered

when top cell is

limiting

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Conclusions

• Satellite-derived spectral irradiance data can be used to

estimate the spectral effects on PV performance over large

geographical regions

• Results in some extreme climates have not been properly

validated, in particular the cold dry climates at high elevation

• PV technologies with narrow blue-dominated SR have the

highest positive spectral effect in tropical regions with high

diffuse content

• The spectral effects of multi-junction cells seem to depend

strongly on which subcell tends to be current-limiting. More

studies are under way.

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Thank you for your patience!

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References Müller R., Behrendt T., Hammer A., Kemper A. A new Algorithm for the

Satellite-based Retrieval of Solar Surface Irradiance in Spectral Bands.

Remote Sensing, 4, 622-647 (2012)

[2] Gracia Amillo A., Huld T., Vourlioti P., Müller R., Norton M. Application of

Satellite-Based Spectrally-Resolved Solar Radiation Data to PV

Performance Studies. Energies, 8, 3455-3488 (2015)

[3] Müller R., Pfeifroth U., Träger-Chatterjee C., Trentmann J., Cremer R.

Digging the METEOSAT treasure – 3 decades of solar surface radiation.

Remote Sensing, 7, 8067-8101 (2015)

[4] Vourlioti P., Huld T., Gracia Amillo A., Norton M. Geospatial mapping of

spectral mismatch of multi-junction photovoltaic modules using satellite-

retreived spectral irradiance data. Proc. 31st EUPVSEC, Hamburg,

Germany (2015)

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