Scientific and technical objectives

The JRP addresses the following scientific and technical objectives:

  • A metric (energy based) for PV efficiency will be developed and its uncertainty budget will be assessed. Standardised environmental data-sets will be defined for Europe and beyond.
  • Robust and improved characterisation methods with an accuracy sufficient for the parameters necessary for the new metric (e.g. spectrally resolved angular dependency of the responsivity, low light performance, and temperature dependency) will be developed. This will include solving metrological challenges for new PV technologies.
  • The measurement uncertainty for the absolute measurement of the natural and simulator irradiation conditions, spectrally and angularly resolved, will be reduced. The upper limit of the measured wavelength will be extended from 1050 nm to 2000 nm.
  • The spectrally and angularly resolved measurements of solar devices will be validated by comparison with integral measurements. Primary traceability and harmonisation of indoor/outdoor characterisation methods will be established through a NMI level intercomparison.
  • New reference devices will be developed for an accurate SI traceable calibration process from the cell to the solar park. In addition, procedures for their application will be developed.



Expected results and potential impact

A metric (energy based) for PV efficiency

Developing a metric for PV efficiency based on energy output under European climate conditions (objective 1), with added uncertainty evaluations, will allow a risk assessment to be undertaken based on these predictions, which is currently not possible. This will enable system planners and financial institutions to optimise their services. Current decisions on how to invest public (government) and private (industry/consumers) money on PVs are being made based on power efficiency numbers that do not correlate with energy output under operational conditions and give no indication of the risks involved.

In the last six months, a data set of climatic conditions has been created to represent typical European climatic zones. Using this data, upcoming results of the characterisations of PV devices will be used to test the calculation of energy rating. A comparison of the spectral irradiance scale of JRC and PTB has been performed to enable future improvements of the data sets.

Robust and improved characterisation methods for the new metric

Metrological challenges for new PV technologies will be solved, thus improving the availability of methods for the determination of efficiency and energy output of solar devices with reduced measurement uncertainty; and consequently with reduced financial uncertainty.

The Centre for Renewable Energy Systems Technology (CREST) is a prominent research centre associated with the Energy theme and aims to advance renewable energy technology to provide substantial and benign energy options for present and future generations. The polychromatic method for determining spectral response has been used at CREST on four different PV technologies. At the mini-module scale, earlier difficulties in the measurement of spectral irradiance have largely been addressed and the current effort is now focused on the filter selection, particularly to increase the spectral variability from one filter to another in the non-visible region. For two small-area PV technologies, comparison of the results showed an acceptable level of agreement between the different measurement systems and indicated this can be done directly with the hardware of the full-scale system systems. The next steps are to verify this with measurements of larger sized devices. The overall process is still undergoing development, mainly in the improvement of spectral irradiance measurements, and the model is being used to represent spectral response and algorithm selection for parameter optimisation. It is not yet clear how to combine the various sources of measurement and fitting stability uncertainties and so the overall uncertainty model is still being formulated.

The wavelength scale of the Fourier-Transform Spectroradiometer has been validated against an external HeNe-laser by PTB; and the wavelength uncertainty was estimated to be <0.01 nm (k=2). Performing a radiometric calibration of two different entrance optics and internal detectors of the Fourier-Transform spectroradiometer, using a halogen standard lamp traceable to the SI, radiometric correction functions and assigned uncertainties were derived and the radiometric calibration was validated by measuring the spectrum of a sun simulator. FTS can now be utilised for traceable calibration of the array spectroradiometer wavelength scale to the HeNe frequency using the laser-based DSR facility. Implementing an Avantes Array spectroradiometer system into the Laser-DSR facility at PTB has also led to a total standard uncertainty for the centre wavelength determination of u(λ) < 0.10 nm.

Reduced measurement uncertainty for absolute measurement of natural and simulator irradiation conditions

This objective will provide the ability to develop a precise and realistic energy based metric. The first step in reducing the main measurement uncertainty component has been done by more accurately determining the distance between the light source and the detector by implantation of an optical confocal displacement sensor.

Validation of spectrally and angularly resolved measurements of solar devices

The current state-of-the-art reference cells used to calibrate various PV device technologies are based on crystalline silicon material. However, silicon material has a limited spectral response (about 300 nm to 1100 nm), which results in spectral mismatch when used to calibrate PV devices made from different materials with extended spectral responses beyond that of silicon. Spectral properties, linearity and device stability depend not only on the material used, but also on the cell technology and structure, which has a major impact on these properties. The limitations of such reference devices for the indoor calibration of PV devices contribute further to the resulting uncertainty in the device efficiency determination.

The total uncertainty, especially of non-Si solar cells, has been reduced by the implementation of a Fourier-Transform-Spectroradiometer (FTS) for the most accurate traceability of the wavelength of the radiation behind a monochromator. A reduction of the wavelength uncertainty from 0.3 nm to less than 0.05 nm was obtained, even if the bandwidth of the monochromator is more than 10 nm. To take the direction of the (direct and diffuse) light into account, now the PV devices can be measured angular dependent. This is important if an indoor calibrated solar cell is to be used outdoor, because neglecting the angular dependency can cause errors of up to 1 % due to the diffuse blue light from all directions. On cloudy days this effect can increase the error to up to 10 % if no correction is performed. PTB could extend its portfolio by offering the measurement of the angular dependence of solar cells. There has been already two official calibrations for a customer outside of the EMRP project.


New reference devices for accurate SI traceable calibration

The spectral adaption and stability of the existing and new World Photovoltaic Scale (WPVS) reference cells will be improved. The new version will be made commercially available and will improve precision in many of the steps in the traceability chain.

So far, a questionnaire about the needs of the end users concerning reference solar cells has been performed and evaluated; and a literature review has been undertaken to summarise the current status of energy-yield models.


Currently PTB is the only European NMI qualified as a WPVS laboratory and it is aimed to broaden this metrological basis to more European NMIs or DIs. This will lead to a more local certification of PV efficiency. Extending the number of WPVS qualified laboratories in Europe will support innovation and will accelerate the deployment of new PV technologies to provide faster and more reliable calibration and certification of European PV products.

PTB also aims to significantly extend its calibration service portfolio to the end user community by covering primary calibration of the short circuit current of 6” reference solar cells and reference mini-modules, with an uncertainty of <0.8 %. This will enable industry to improve the optimisation of their products.


Good metrology practice and novel PV measurement methodologies will be disseminated to European industries via the project website and paper–copies will be distributed at workshops and conferences.

NPL has designed and develop a new compressed sensing method for the spatial characterisation of PV (fast current mapping) using micro-electrical-mechanical system (MEMS) digital mirror arrays. Initial results of projecting both orthogonal illumination patterns and random intensity patterns and showed that in both cases a feature map can be recovered using less measurements than is necessary through conventional raster scanning. NPL intends to develop the technique further by improving both resolution and measurement speed and obtaining direct comparison results between standard measurement processes. This new technique will allow defects to be identified at considerably higher speeds than using conventional raster scanning techniques. The application of the method in the area of PV by Loughborough University led to a Best Paper Prize at the 11th Photovoltaic Science Application and Technology (PVSAT-11) conference and the Best Student Award during 31th European PV Solar Energy Conference and Exhibition (31th EU PVSEC).

The project website ( was launched in June 2014, with a public area for updates on the project progress. Since the beginning of the project, the partners have presented at 17 scientific conferences, including five presentations at the European PV Solar Energy Conference and Exhibition (EU PVSEC) 2014 and 2015.  

Two further standard meetings have been attended by project partners during the last six months. In September 2015, PTB and TÜV Rheinland presented the project activities to the German National Standards committee DKE; and in November 2015, JRC, REG(LU) and PTB contributed to the International Electrotechnical Commission (IEC) TC82 (Solar photovoltaic energy systems) WG2 draft documentary standard.

A draft of the 61853-2 energy rating standard was sent by the standardisation project leader REG(LU) to the convenor of IEC TC82 WG2. By this step one of the great objectives towards an energy-based parameter for photovoltaic classification were fulfilled.


Follow-up project (16ENG02 PV-Enerate)

The EMPIR project Opens external link in new window16ENG02 PV-Enerate deals with emerging aspects of energy rating.