Progress beyond the state of the art and results

This project will improve the accuracy of the measurements needed for the calibration of reference solar cells, by using the limitations of existing standards as a starting point in order to further reduce the lowest uncertainty in the world. Also, procedures for the evaluation of uncertainties will be established, i.e. brought to standardisation bodies. Furthermore, a metric will be developed to rate the shading sensitivity of PV modules. To improve the use of indoor-PV for the energy supply of IoT devices, the results of this project will contribute to international standardisation. As standardisation has thus far focused on outdoor applications, the development of new calibration facilities for indoor-PV with irradiance levels 100 to 1000 times lower than under standard outdoor conditions goes beyond the state of the art.

Validation of suitable reference devices and measurement procedures
The most accurate primary calibrations of WPVS type reference solar cells are performed by PTB. The “world record” lowest uncertainty is 0.4 %, using PTB’s Laser-DSR facility. As these calibrated solar cells act as references and thus as the starting point of the traceability chain for the performance rating of the solar cells and solar modules manufactured by industry, a reduction of this important quantity is crucial.
This project aims to reduce the expanded uncertainty to a value down to 0.35 %, or even below, to successively affect all following calibrations and performance measurements in the traceability chain. In addition, there is a rising demand for calibrations of emerging PV devices (e.g. for perovskite solar cells). Due to their properties (e.g. response time) it is challenging to measure and calibrate these devices with low uncertainties. The uncertainties will be reduced from 3 % to 2 %. The activities within this project will also allow a reduction of the lowest available uncertainty of emerging PV devices.

Evaluation of uncertainty sources related to the output power and energy of PV modules
The standards concerning measurement issues (the IEC 60904 standard series) describe procedures for the determination of I-V curves and of the spectral responsivity of PV devices, but they regularly lack documentation for determination of the uncertainty of the measurements. This determination of the uncertainty is often requested by the users of the standards.
The project will remedy the deficiency of the IEC 60904 standard series by writing technical reports on how to calculate the measurement uncertainties.

Definition of a quality metric for the sensitivity of PV modules power output in shady locations
State of the art energy rating procedures are currently not applicable to the emerging technologies (e.g. perovskite-on-silicon tandem). The existing methods and calculations do not consider the non-uniformity of irradiance in shady urban areas.
In this project a metric will be developed to rate the shading sensitivity of PV modules. This metric will improve the accuracy of energy yield determination.

Characterisation and classification of PV-based energy-harvesting devices for Internet of Things (IoT) applications
In the area of indoor-PV, standardisation has just started recently. Indoor PV is used for autarkic energy supply of energy harvesting Internet of Things applications, e.g. for communication and sensor issues. No standards are currently available, although they are important for Industry 4.0 applications.
The research activities within this project will contribute significantly to the ongoing standardisation processes by providing input to the standardisation.