Bifacial photovoltaics present a clean and cheaper alternative to diesel generators for high-latitude remote communities; however, solar cells are tested at air mass 1.5, while average air mass increases with increasing latitude. For example, Cambridge Bay (69ºN) has an irradiance-weighted average air mass of 3.1. We demonstrate improved efficiency of bifacial silicon heterojunction modules under high air mass spectra due to reduced incident UV light. We implement air mass correction in our bifacial PV modelling software, and we quantify the impact of air mass on energy yield for fixed-tilt and tracked systems in high latitude locations.
Bifacial photovoltaics present a clean and cheaper alternative to diesel generators for high-latitude remote communities; however, solar cells are typically tested at 0° angle of incidence, 25°C, and AM1.5, from which high-latitude conditions vary greatly. A bifacial silicon photovoltaic cell optimized for high-latitude conditions will improve energy yield for these systems. We integrate experimentally-derived cell parameters with a systems-level model capable of fixed-tilt and tracked energy yield predictions. We optimize to find the most efficient cell design for high-latitude environments in Sentaurus and SunSolve and determine the resulting improvement in energy yield for an entire panel in MATLAB.
One of the challenges associated with forecasting and evaluating concentrating photovoltaic system (CPV) performance in diverse locations is the lack of high-quality spectral solar resource data. Various local atmospheric conditions such as air mass, aerosols, and atmospheric gases affect daily CPV module operation. A multi-channel filter radiometer (MFCR) can be used to quantify these effects at relatively low cost. The proposed method of selectively sampling the solar spectrum at specific wavelength channels to spectrally reconstruct incident irradiance is described and extensively analyzed. Field spectroradiometer (FSR) measurements at the University of Ottawa's CPV testing facility (45.42°N, 75.68°W) are fed into our model to mimic the outputs from the MCFR. The analysis is performed over a two year period (2011-2012), using 46,564 spectra. A recommendation is made to use four aerosols channels at 420, 500, 780, and 1050 nm, one ozone channel at 610 nm and one water vapour channel at 940 nm, all of which can be measured with ubiquitous Si photodiodes. A simulation of this MFCR channel configuration produces an RMS error under 1.5% over 96% of the 350-1830 nm range, when compared with the FSR, for the 2012 data set in Ottawa.
Matthew Wilkins, Richard Beal, Joan Haysom, Jeffrey Wheeldon, Philippe Mulet, Graeme Jamieson, Nashed Youssef, Dhan Balachandreswaran, Jennifer Fan, Trevor Hall, Stefan Myrskog, Karin Hinzer
An on-sun Concentrating Photovoltaic (CPV) test site with a multiplexed current-voltage measurement capability has
been installed at the University of Ottawa. Herein, we present details of the instrumentation, which is designed to
provide in-situ I-V measurements of individual solar cells within a functioning, series connected, string. A 4-wire
multiplexing system enables current-voltage measurements of individual cells. Where other multi-cell test systems have
left cells at open-circuit or connected to a fixed resistor when not selected by the multiplexer, in this system each test
cell operates within a string of cells controlled by a maximum power point tracker. This allows us to maintain the test
cells at realistic operating conditions for all irradiance conditions. Using the current-voltage data, a range of parameters
of interest can be monitored over time, including the solar cell temperature, photovoltaic efficiency and optical
efficiency. This information is correlated with time-synchronized spectrometer and pyrheliometer data, allowing
automated collection of performance data from several strings of optic/solar cell assemblies. The test site includes two
20m2, dual-axis, ring mounted solar trackers and is being used to test new CPV systems which incorporate novel lightguiding
optics designed and manufactured by Morgan Solar Inc.
A technique, based on quantum well (QW) intermixing, has been developed for the post growth, spatially selective tuning of the QW bandgap in a semiconductor laser structure. High energy (MeV) ion implementation is used to create a large number of vacancies and interstitials in the device. During high temperature processing (rapid thermal annealing), these defects simultaneously enhance the intermixing of the QW and the barrier materials, producing a blue shift of the quantum well bandgap, and are annealed out. Increases in the bandgap energy of greater than 100 nm at 1.55 (mu) m in InGaAs/InGaAsP/InP structures can be achieved, while absorption losses are unaffected or reduced. Absorption spectroscopy in the waveguide geometry is used to quantify any excess loss in the structure. Using a simple masking scheme to spatially modify the defect concentration, different regions of a wafer can be blue shifted by different amounts. This allows the integration of many different devices such as lasers, detectors, modulators, amplifiers and waveguides on a single wafer using only a single, post-growth processing step. The performance of both passive (waveguide) and active (laser and amplifier) devices produced using this technique will be described, as well as the practicality of this technique in the production of photonic integrated circuits.
Selective area CW Nd:YAG laser annealing of GaInAsP/InP quantum well (QW) structures has been investigated as a possible route towards the fabrication of monolithically integrated photonic circuits. Laser irradiation of a 5 QW laser structure, originally designed to yield lasers emitting at 1.5 micrometers , yielded material having a continuously changing band-gap ranging from 1.5 to 1.38 micrometers over the distance of about 3 mm. Bars with arrays of broad area lasers, having lengths from 300 to 600 micrometers , were fabricated form the processed materials. An individual bar comprised lasers operating typically between 1.4 and 1.5 micrometers . The lasers showed stable threshold current density and quantum efficiency as function of the operating wavelength. This demonstration indicates that the applied technology has the potential to realize the cost-effective fabrication of advanced photonic devices and photonic integrated circuits.
Selective area quantum well intermixing is used to create buried heterostructure narrow waveguides, which are shown to be effective waveguides for a narrow range of wavelengths near the lasing wavelength of the structure. Measurements on as-grown and uniformly intermixed slab waveguide are used to determine the refractive index of the two regions, and the net refractive index difference is used to predict modal behavior of the buried waveguides.
N. Sylvain Charbonneau, Andre Delage, Joan Haysom, Fang Yang, Philip Poole, Geof Aers, Jian Jun He, Emil Koteles, Paul Piva, Todd Simpson, Ian Mitchell
A technique, base don quantum well (QW) intermixing, has been developed for the post growth, spatially selective tuning of the QW bandgap in a semiconductor laser structure. High energy ion implantation is used to create a large number of vacancies and interstitials in the device. During high temperature processing, these defects enhance the intermixing of the QW and the barrier materials while being annealed out, producing a blue shift of the QW bandgap. Increases in bandgap energy of greater than 10 nm at 1.55 micrometers in InGaAs/InGaAsP/InP structures can be achieved. Absorption spectroscopy in the waveguide geometry is used to quantify the losses in the structure. Using a simple masking scheme to spatially modify the defect concentration, different regions of a wafer can be blue shifted by different amounts. This allows the integration of many different devices such as lasers, detectors, modulators, amplifiers and waveguides on a single wafer using only a single, post-growth processing step. The performance of both passive and active devices produced using this technique will be described, as well as the practicality of this technique in the production of photonic integrated circuits.
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