A simple optical setup for current mapping of small area PV devices using different sampling strategies

An optical setup for current mapping of photovoltaic devices is presented. It is based on a digital micro-mirror device (DMD) and a small number of additional optical elements making the implementation simple and cost effective. The specific properties of the DMD chip enable the application of two different sampling methods; point by point sampling and compressive sampling. Both sampling strategies are compared and cases when each one of them performs better are investigated. It is shown that compressive sampling can significantly enhance weak current signals and provide current maps in the cases when the point by point current signal is below the noise threshold

Compressed sensing current mapping of PV devices using a DLP projector

A commercial Digital Light Processing (DLP) projector has been utilised for compressed sensing current mapping of photovoltaic (PV) devices. Through the projector, the necessary patterns are projected to apply compressive sampling for measurement acquisition. The reconstruction of the current map is achieved by an optimisation algorithm. The main advantage of this method is that measurement time is significantly reduced, compared to conventional LBIC measurement systems. This is achieved mainly by acquiring fewer measurements than a raster scan would need. Initial current maps of cells and modules have been acquired, showing the feasibility of the method. The issues of such a system have been investigated and its potential for fast and simple current mapping of PV modules is demonstrated

Towards current mapping of photovoltaic devices by compressed imaging

A new photovoltaic (PV) device current mapping method has been developed, utilizing the recently introduced compressed sensing sampling theory. The aim is to significantly reduce measurement time of Light Beam Induced Current measurements. A prototype setup has been built at National Physics Laboratory (NPL) to implement the method. Initial results are presented and illustrate the feasibility of the method

Compressed sensing current mapping methods for PV characterisation

The Compressed Sensing (CS) sampling theory has been combined with the Light Beam Induced Current (LBIC) method, to produce an alternative current mapping technique for photovoltaic (PV) devices. Compressive sampling of photocurrent is experimentally implemented using a Digital Micro-mirror Device (DMD). The main advantage of this new method for current mapping is that measurement time can be significantly reduced compared to conventional LBIC measurement systems. This is achieved mainly by acquiring fewer measurements than a raster scan would need and by utilizing the fast response of the micro-mirror array. Two different experimental layouts are considered in this work. The first is a small area optical set-up based on a single wavelength laser source. The second layout utilizes a commercial Digital Light Processing (DLP) projector through which compressive sampling is applied. Experimental results with both experimental schemes demonstrate that current maps can be produced with less than 50% of the measurements a standard LBIC system would need. The ability to acquire current maps of individual cells in encapsulated modules is also highlighted. The advantages and drawbacks of the method are presented and its potential to significantly reduce measurement time of current mapping of PV cells and modules is indicated

Fast current mapping of photovoltaic devices using compressive sampling

Light Beam Induced Current (LBIC) measurements are a useful tool in photovoltaic (PV) device characterisation for accessing the local electrical properties of PV devices. The main disadvantage of a typical LBIC system is measurement time, as a raster scan of a typical silicon solar cell can last several hours. The focus of this paper is the reduction of LBIC measurement time by means of compressed sensing (CS). The CS-LBIC system described in this paper can theoretically reduce measurement time to less than 25% of that required for a standard LBIC raster scan. Measurement simulations of a CS-LBIC system are presented as well as a practical demonstration using a digital micro-mirror array, which further reduces the measurement time by an order of magnitude. Instead of a raster scan, the PV device under measurement is sampled by a series of patterns and the current map is reconstructed using an optimization algorithm. Simulations of CS-LBIC measurements using the 2D spatially-resolved PV-Oriented Nodal Analysis (PVONA) model developed at CREST are used as a tool to explore the capabilities and verify the accuracy of this measurement technique as well as its ability to detect specific defects, such as cracks and shunts. Simulation results confirm that the CS sampling theory can be applied as an effective method for significantly reducing measurement time of current mapping of PV devices. An initial CS-LBIC system prototype has been built at the National Physical Laboratory (NPL) and measurements of small area devices (1cm x 0.8cm) using this system are given. The current maps are created using a Digital Micromirror Device (DMD) kit as a pattern generator. The response time of the micro mirror array is less than 20μs. This is another factor in the reduction of measurement time, as the movement time of an x-y translation stage is considerably slower. Initial measurement results show that current maps of PV cells can be acquired with 75% fewer measurements which, combined with the fast response of the pattern generator, can reduce LBIC measurement time by an order of magnitude

Compressed sensing current mapping spatial characterization of photovoltaic devices

A new photovoltaic (PV) device current mapping method has been developed, combining the recently introduced Compressed Sensing (CS) sampling theory with Light Beam Induced Current (LBIC) measurements. Instead of a raster scan, compressive sampling is applied using a Digital Micro-mirror Device (DMD). The aim is to significantly reduce the time required to produce a current map, compared to conventional LBIC measurements. This is achieved by acquiring fewer measurements than a full raster scan and by utilizing the fast response of the micro-mirror device to modulate measurement conditions. The method has been implemented on an optical current mapping setup built at the National Physical Laboratory (NPL) in the UK. Measurements with two different PV cells are presented in this work and an analytical description for realisation of an optimised CS current mapping system is provided. The experimental results illustrate the feasibility of the method and its potential to significantly reduce measurement time of current mapping of PV devices

Compressed sensing current mapping methods for PV characterisation

The Compressed Sensing (CS) sampling theory has been combined with the Light Beam Induced Current (LBIC) method, to produce an alternative current mapping technique for photovoltaic (PV) devices. Compressive sampling of photocurrent is experimentally implemented using a Digital Micro-mirror Device (DMD). The main advantage of this new method for current mapping is that measurement time can be significantly reduced compared to conventional LBIC measurement systems. This is achieved mainly by acquiring fewer measurements than a raster scan would need and by utilizing the fast response of the micro-mirror array. Two different experimental layouts are considered in this work. The first is a small area optical set-up based on a single wavelength laser source. The second layout utilizes a commercial Digital Light Processing (DLP) projector through which compressive sampling is applied. Experimental results with both experimental schemes demonstrate that current maps can be produced with less than 50% of the measurements a standard LBIC system would need. The ability to acquire current maps of individual cells in encapsulated modules is also highlighted. The advantages and drawbacks of the method are presented and its potential to significantly reduce measurement time of current mapping of PV cells and modules is indicated