Department of Electrical Engineering and Automation

Metro-PV (2020-2023)

Metrology Research Institute was involved in project Metro-PV - "Metrology for Emerging PV applications" financed by the European Metrology Programme for Innovation and Research (EMPIR) that ended in November 2023.

The project

The project co-ordinated by Dr. Stefan Winter of PTB (Physicalisch-Technische Bundesanstallt, Germany) developed metrological infrastructure, techniques, and guidance to accelerate time-to-market for emerging photovoltaics (PV) technologies, such as Perovskite, amorphous silicon, and organic solar cells. The new cell technologies are being developed and taken into use to reduce the cost of photovoltaic energy, the most important energy source in the future, but the technologies pose challenges to measurements.

Emerging PV technologies, such as Perovskite Tandem on Silicon, are the next generation of solar devices with higher conversion efficiency compared to conventional single junction silicon solar cells. In the field of Industry 4.0 applications, the use of Indoor-PV is gaining momentum. The project also addressed measurement capabilities for indoor solar cells. 

The objectives of the project can be summarised as reduction of the reference solar cell calibration uncertainty, development of international standards, including measurement procedures for emerging PV technologies, reduction of the uncertainty of the PV calibration chain, and in a wider perspective, reduction of the financial uncertainty of investments.

Official web pages of the project https://www.metro-pv.ptb.de/home/

Co-ordination of intercomparisons

In the project, Metrology Research Institute co-ordinated three round robin comparisons of solar cell measurements:

1. Adapted reference cells for emerging technologies,

2. Solar cells and modules based on emerging technologies,

3. Indoor solar cells.

The comparisons revealed challenges that were not expected. Despite all the efforts carried out for developing and standardising the measurements, results deviated more than their estimated uncertainties imply. The perovskite cells and modules used are nonlinear, have hysteresis, and the measurement results depend on the history of their lighting conditions. The agreement among the participants was at the level of 3 – 5 % in maximum power, when uncertainties were of the order of 2 %. With reference cells, the agreement in short-circuit current was better, indicating that the discrepancies were caused by the cell properties.

With indoor cells, the discrepancies were even bigger, of the order of 50 % in short-circuit currents, uncertainties being of the order of 0.5 – 4 %. The discrepancies seem to be associated with illuminance measurements of LED-based large-area solar simulators, a challenge totally unforeseen, needing further studies and standardisation.

Bifacial solar cell being measured
Fig 1. A solar cell being measured for its differential spectral responsivity (DSR) at Aalto. Aalto used DSR to calculate responsivities that the cells would have for various light sources specified for comparisons. [1, 2]

Indoor solar cells and internet of things

Aalto also carried out research on using solar cells in indoor applications. Most existing methodologies for characterizing solar cells are for outdoor use. When used indoors, the spectra of light sources will be significantly different from standardized sources such as AM1.5. The research carried out included measuring lighting conditions in a modern office building, Väre, and measuring efficacies of solar cells illuminated with LED luminaires.  

Figure 2 shows the measurement setup used at Väre - a spectroradiometer, a luxmeter, and a reference solar cell. [3] The colour temperature of the measuring site ranged from 5120 to 5770 K as seen in Fig. 3. The lowest illuminance measured was 1020 lx and the maximum was 3090 lx. The measurements were used to analyse luminous efficacies of various cell types, including gallium arsenide, amorphous silicon, mono-crystal silicon, poly-crystal silicon, and indium gallium arsenide.

Various setups were developed and tested in the measurements. Solar cells were characterised in the photometric bench using newly standardised CIE LED L41 (B3) as the light source. Other sources needed for characterisations included CIE Standard Illuminant A, and a small self-made solar simulator based on a Xe-lamp replicating reference spectrum AM1.5.

Standardisation

The project developed standardisation where Aalto also took part. Work on correlations that already started with earlier projects was finished within Metro-PV. [4] We were engaged in a round-robin intercomparison of energy rating calculation methods for solar panels. [5,6]

Measuring equipment at the measuring site.
Fig 2. Measuring equipment at the modern office building, Väre. Power produced by a solar cell depends on lighting level, but also on the spectral composition of the light that should be considered in accurate characterisation of indoor cells.
Colour temperatures calculated from the spectral spectrum and measured illumination intensity over the period 19-20 August 2021
Fig 3. Colour temperatures calculated from the spectra and measured illumination intensity over the period 19-20 August, 2021.

Contact person: Petri Kärhä

Publications and references

1. Petri Kärhä, Hans Baumgartner, Janne Askola, Kasperi Kylmänen, Benjamin Oksanen, Kinza Maham, Vo Huynh, and Erkki Ikonen, “Measurement setup for differential spectral responsivity of solar cells,” Opt. Rev. 27, 195–204 (2020). https://doi.org/10.1007/s10043-020-00584-x

2. A. Eghbali Yeldagermani, E. Ikonen, and P. Kärhä, “Differential Spectral Responsivity of Solar Cells Measured with an LED Based Experimental Setup,” in proceedings of 2023 Middle East and North Africa Solar Conference (MENA-SC), Dubai, United Arab Emirates, 2023, pp. 1-6. DOI: 10.1109/MENA-SC54044.2023.10374492.

3. Iikka Huttu, Power output of solar cells in an LED-lit office building from the point of view of internet of things, BSc. thesis, Aalto University, 34 p, 2021 (in Finnish). http://urn.fi/URN:NBN:fi:aalto-202201251390

4. Kinza Maham, Petri Kärhä, and Erkki Ikonen, “Spectral mismatch uncertainty estimation in solar cell calibration using Monte Carlo simulation,” IEEE Journal of Photovoltaics 13, 899 – 904 (2023). DOI: 10.1109/JPHOTOV.2023.3311890

5. Malte Ruben Vogt, Stefan Riechelmann, Ana Maria Gracia-Amillo, Anton Driesse, Alexander Kokka, Kinza Maham, Petri Kärhä, Robert Kenny, Carsten Schinke, Karsten Bothe, James C. Blakesley, Esma Music, Fabian Plag, Gabi Friesen, Gianluca Corbellini, Nicholas Riedel-Lyngskær, Roland Valckenborg, Markus Schweiger, and Werner Herrmann, ”PV Module Energy Rating Standard IEC 61853-3 Intercomparison and Best Practice Guidelines for Implementation and Validation,” IEEE Journal of Photovoltaics 12, 844-852 (2022). DOI: 10.1109/JPHOTOV.2021.3135258

6. Data from PV module energy rating standard IEC 61853-3 intercomparison, Friesen, G. (Contributor), Kokka, A. (Contributor), Riechelmann, S. (Contributor), Valckenborg, R. (Contributor), Plag (Contributor), Schinke, C. (Contributor), Kenny, R. (Contributor), Corbellini, G. (Contributor), Schweiger, M. (Contributor), Bothe, K. (Contributor), Herrmann, W. (Contributor), Gracia-Amillo, A. M. (Contributor), Driesse, A. (Contributor), Riedel-Lyngskær, N. (Contributor), Vogt, M. R. (Contributor), Music, E. (Contributor), Maham, K. (Contributor), Kärhä, P. (Contributor) & Blakesley, J. C. (Contributor), Zenodo, 18 Dec 2021 (Dataset). DOI: 10.5281/zenodo.5750185, https://zenodo.org/record/5750185

 Petri Kärhä

Petri Kärhä

Principal University Lecturer
T410 Dept. Electrical Engineering and Automation
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