Reassessment of cell to module gains and losses: Accounting for the current boost specific to cells located on the edges

The power produced by a photovoltaic module is not simply the sum of the powers of its constituents cells. The difference stems from a number of so-called “cell-to-module” (CTM) gain or loss mechanisms. These are getting more and more attention as improvements in cell efficiency are becoming harder to achieve. This work focuses on two CTM mechanisms: the gain due to the recapture of light hitting the apparent backsheet in the “empty” spaces around the cells and the loss from the serial connection of “mismatched” cells i.e. with different maximum power points. In general, for insulation purposes, the spaces on the edges of modules are larger than the spacing between cells. This study reveals that, when reflective backsheets are used, these “edge spaces” provide an additional current boost to the cells placed at the edges that can lead to a 0.5% gain in the output power of modules (with 60 or 72 cells). This location-dependent current boost adds to the usual variations in cell characteristics dictated by the binning size and results in larger “cell-to-cell mismatch losses”. However, the simulations reveal that for short-circuit current bin size smaller than 5%, this additional mismatch loss is lower than 0.05%. All considered, this study demonstrates that the spaces at the edges of PV modules have a significant impact on the cell to module ratios (≈+0.5%abs or ≈16% of the CTM gains) when reflective backsheets are used

Field test and electrode optimization of electrodynamic cleaning systems for solar panels

Soiling is the major cause of power loss of photovoltaics (PV) and concentrated solar power (CSP) in desert areas. Electrodynamic cleaning system (EDS) is an automatic and water-free integrated cleaning system for mirrors or solar panels, which uses pulsed electric fields to remove dust off their surface. The first EDS field test over a long period on PV modules is reported here and shows a clear effect on soiling reduction in real conditions in Saudi Arabia. A total of 458 days of measurements is analyzed, and depending on the considered periods, performance losses due to soiling (soiling rate) can vary from -0.06%/day to -0.41%/day for a reference module, while the relative soiling rate reduction using an EDS can be up to 95.7% with an average of 32.1%. Cost calculations demonstrate an added value of the modules equipped with the EDS between 2.6 and 5.2 & xa2;/Wp compared with usual cleaning system, which is nearly between 10% and 20% of the module price. In addition, extended indoor tests of various electrode designs of EDS for heliostat dedicated to CSP or PV applications show a high cleaning efficiency of up to 98% with front glass thickness of more than 1 mm. A good specular reflectivity, only 4% lower than the bare reference mirror, is obtained with patterned sputtered silver in a spiral electrode design. High reliability of two types of electrode deposition is demonstrated after 200 cycles between -40 degrees C and +85 degrees C

Performance of Hybrid Micro-Concentrator Module with Integrated Planar Tracking and Diffuse Light Collection

The Swiss start-up Insolight aims to be the first company to commercialize a high-efficiency III-V based low profile micro-CPV product that uses planar micro-tracking to eliminate the need for a tilting solar tracker, allowing rooftop mounting using typical flat-plate hardware, as well diffuse light capture using low cost Si solar cells which cover the area of the back plane not taken up by III-V solar cells. The IES-UPM has made an initial performance evaluation of a 0.1m2 prototype. We show that the integrated planar tracking can reach 55° AOI, show CSTC efficiency near to 30% for III-V output, and demonstrate the diffuse capture and planar tracking capability in a multi-week test campaign at our test site in Madrid

Performance of Hybrid Micro-Concentrator Module with Integrated Planar Tracking and Diffuse Light Collection

The Swiss start-up Insolight aims to be the first company to commercialize a high-efficiency III-V based low profile micro-CPV product that uses planar micro-tracking to eliminate the need for a tilting solar tracker, allowing rooftop mounting using typical flat-plate hardware, as well diffuse light capture using low cost Si solar cells which cover the area of the back plane not taken up by III-V solar cells. The IES-UPM has made an initial performance evaluation of a 0.1m2 prototype. We show that the integrated planar tracking can reach 55° AOI, show CSTC efficiency near to 30% for III-V output, and demonstrate the diffuse capture and planar tracking capability in a multi-week test campaign at our test site in Madrid

Towards industrialization of planar microtracking photovoltaic panels

Planar micro-tracking concentrator photovoltaic modules hold great promises, as they enable the combination of efficiencies greater than 30% with the form factor of conventional rooftop panels operating at fixed tilt. Over the past three years, Insolight has been developing a fixed-tilt system, combining a biconvex silicone lens array, high efficiency multi-junction cells and integrated micro-tracking. A first prototype built in 2016 was validated with a peak conversion efficiency of 36.4 %. On the path towards industrialization of the systems, we present the evolution from the first lab prototype to fully automated panels featuring several thousands cells, installed on a rooftop pilot site. Continuous operation and data logging of the outdoor installation over a year enable us to validate a simple and robust integrated micro-tracking scheme. Recent measurements showed a module efficiency of 29% at concentrated standard test conditions. Different hybrid PV-CPV architectures are under evaluation for the capture of global irradiance

The impact of silicon solar cell architecture and cell interconnection on energy yield in hot & sunny climates

Extensive knowledge of the dependence of solar cell and module performance on temperature and irradiance is essential for their optimal application in the field. Here we study such dependencies in the most common high-efficiency silicon solar cell architectures, including so-called Aluminum back-surface-field (BSF), passivated emitter and rear cell (PERC), passivated emitter rear totally diffused (PERT), and silicon heterojunction (SHJ) solar cells. We compare measured temperature coefficients (TC) of the different electrical parameters with values collected from commercial module data sheets. While similar TC values of the open-circuit voltage and the short circuit current density are obtained for cells and modules of a given technology, we systematically find that the TC under maximum power-point (MPP) conditions is lower in the modules. We attribute this discrepancy to additional series resistance in the modules from solar cell interconnections. This detrimental effect can be reduced by using a cell design that exhibits a high characteristic load resistance (defined by its voltage-over-current ratio at MPP), such as the SHJ architecture. We calculate the energy yield for moderate and hot climate conditions for each cell architecture, taking into account ohmic cell-to-module losses caused by cell interconnections. Our calculations allow us to conclude that maximizing energy production in hot and sunny environments requires not only a high open-circuit voltage, but also a minimal series-to-load-resistance ratio

Compositional differences between infant and adult human corneal basement membranes

PURPOSE. Adult human corneal epithelial basement membrane ( EBM) and Descemet's membrane ( DM) components exhibit heterogeneous distribution. The purpose of the study was to identify changes of these components during postnatal corneal development. METHODS. Thirty healthy adult corneas and 10 corneas from 12-day- to 3-year-old children were studied by immunofluorescence with antibodies against BM components. RESULTS. Type IV collagen composition of infant corneal central EBM over Bowman's layer changed from alpha 1-alpha 2 to alpha 3-alpha 4 chains after 3 years of life; in the adult, alpha 1-alpha 2 chains were retained only in the limbal BM. Laminin alpha 2 and beta 2 chains were present in the adult limbal BM where epithelial stem cells are located. By 3 years of age, beta 2 chain appeared in the limbal BM. In all corneas, limbal BM contained laminin gamma 3 chain. In the infant DM, type IV collagen alpha 1-alpha 6 chains, perlecan, nidogen-1, nidogen-2, and netrin-4 were found on both faces, but they remained only on the endothelial face of the adult DM. The stromal face of the infant but not the adult DM was positive for tenascin-C, fibrillin-1, SPARC, and laminin-332. Type VIII collagen shifted from the endothelial face of infant DM to its stromal face in the adult. Matrilin-4 largely disappeared after the age of 3 years. CONCLUSIONS. The distribution of laminin gamma 3 chain, nidogen-2, netrin-4, matrilin-2, and matrilin-4 is described in the cornea for the first time. The observed differences between adult and infant corneal BMs may relate to changes in their mechanical strength, corneal cell adhesion and differentiation in the process of postnatal corneal maturation

Compositional differences between infant and adult human corneal basement membranes

PURPOSE. Adult human corneal epithelial basement membrane ( EBM) and Descemet's membrane ( DM) components exhibit heterogeneous distribution. The purpose of the study was to identify changes of these components during postnatal corneal development. METHODS. Thirty healthy adult corneas and 10 corneas from 12-day- to 3-year-old children were studied by immunofluorescence with antibodies against BM components. RESULTS. Type IV collagen composition of infant corneal central EBM over Bowman's layer changed from alpha 1-alpha 2 to alpha 3-alpha 4 chains after 3 years of life; in the adult, alpha 1-alpha 2 chains were retained only in the limbal BM. Laminin alpha 2 and beta 2 chains were present in the adult limbal BM where epithelial stem cells are located. By 3 years of age, beta 2 chain appeared in the limbal BM. In all corneas, limbal BM contained laminin gamma 3 chain. In the infant DM, type IV collagen alpha 1-alpha 6 chains, perlecan, nidogen-1, nidogen-2, and netrin-4 were found on both faces, but they remained only on the endothelial face of the adult DM. The stromal face of the infant but not the adult DM was positive for tenascin-C, fibrillin-1, SPARC, and laminin-332. Type VIII collagen shifted from the endothelial face of infant DM to its stromal face in the adult. Matrilin-4 largely disappeared after the age of 3 years. CONCLUSIONS. The distribution of laminin gamma 3 chain, nidogen-2, netrin-4, matrilin-2, and matrilin-4 is described in the cornea for the first time. The observed differences between adult and infant corneal BMs may relate to changes in their mechanical strength, corneal cell adhesion and differentiation in the process of postnatal corneal maturation