The photocurrent produced by a multijunction III-V cell is limited by the component cell of the union which yields the lowest photocurrent. The induced energy losses are quantified by the Energy Matching Factor (EMF),... more
The photocurrent produced by a multijunction III-V cell is limited by the component cell of the union which yields the lowest photocurrent. The induced energy losses are quantified by the Energy Matching Factor (EMF), defined as the ratio between the energy produced by a III -V multijunction cell and the energy that could be produced if the subcells were current matched at any moment. Accurate EMF estimations generally require accurate measurement of solar spectrum. An alternative method is to measure the spectrum using three “isotype” cells, or single-junction cells that have the same spectral response as each of the three component cells in the multi-junction stack. That method is validated against photocurrents calculated from spectral measurements (by spectroradiometer) and broadband direct beam measurements (by pyrheliometer). Those comparisons show agreement in the results above 98% under clear-sky conditions. The difference between the two independent EMF calculations is within 1% margin. That method enables to characterize the photocurrent produced by a Concentrating Photovoltaics (CPV) module with a sufficient accuracy for CPV applications, on the sole basis of measurements of the direct beam radiation by a pyrheliometer and three photocurrents by three isotype cells. The application of this method to the spectral measurements achieved in Madrid in 2009 leads to estimate annual current spectral mismatching losses of some 5-10%.
The photocurrent produced by a multijunction III-V cell is limited by the component cell of the union which yields the lowest photocurrent. The induced energy losses are quantified by the Spectral Radiation Matching Factor (SRMF),... more
The photocurrent produced by a multijunction III-V cell is limited by the component cell of the union which yields the lowest photocurrent. The induced energy losses are quantified by the Spectral Radiation Matching Factor (SRMF), defined as the ratio between the energy produced by a III-V multijunction cell and the energy that could be produced if the subcells were current matched at any moment. Accurate SRMF estimations generally require accurate measurement of solar spectrum. Another method is to measure the spectrum using three ``isotype'' cells, or single-junction cells that have the same spectral response as each of the three component cells in the multi-junction stack. That method is validated against photocurrents calculated from spectral measurements (by spectroradiometer) and broadband direct beam measurements (by pyrheliometer). Those comparisons show agreement in the results above 98% under clear-sky conditions. The difference between the two independent SRMF calculations is within 1% margin. The application of this method to the spectral measurements realized in Madrid in 2009 leads to estimate an annual current spectral mismatching of around 7%.
