LED-based solar simulator for terrestrial solar spectra and orientations

The star map has the characteristics of large amount of data and wide angle of view. The star points are displayed as limited pixels on the image and easy to get disturbed by noise, so it is difficult to build a feature model to obtain the complete star map. In this paper, we have revised the OTSU algorithm and extracted the star points accurately according to the characteristics of star point pixels. We are inspired by the idea of compressed perception to break the local spatial relationship of stars, construct the aggregated star group model of relative relationship of local stars, realize the matching and construct the extended model to realize the stitching of wide angle star images. In order to meet the requirements of efficient transmission and storage in the air or on the ground, we have proposed the algorithm of star point storage and mapping. We set up a database with 600 frames of real star images from CCD camera and 600 frames of simulated star images, and the experiments show that our algorithm can compress the data and realize the star image stitching.

The image stitching algorithm based on aggregated star groups

This thesis presents the simulated optical design of a fully LED-based solar simulator.
The work focuses on the spectral mismatch, the spatial uniformity acquired
with direct light and the spectral uniformity. The proposed LED solar simulator has
an illuminated area of 32cm x 32cm and can characterise medium size photovoltaic
devices under variable light intensities and variable output spectra. The spectral
range covered is between 350nm and 1300nm which offers the capability of characterising
various different PV technologies. The spectral match classification is A+
for the 400nm-1100nm spectral range and B for the 350nm-1300nm spectral range.
The spatial non-uniformity of irradiance is also A+ across the illuminated area. The
temporal stability of LEDs can easily reach class A as proven by previous work in
the group and is not examined here.
An automated LED selection methodology that optimises the spectral mismatch
was developed to replace the trial and error method usually employed. The algorithm
created accommodates a more accurate selection of the most appropriate LED
wavelengths in order to represent the solar spectrum even more closely than before
and improve the uncertainties caused by the spectral mismatch. A genetic algorithm
and the chi-squared error criterion were used to create the automated methodology
applying a minimisation technique. This technique helps the user choose from a
wide variety of LEDs available on the market, determine the wavelengths and the
number of LEDs per wavelength needed to accurately represent the AM1.5G solar
spectrum and other spectra and provides a cost-effective and straightforward solution.
The solution chosen for this project involves 24 different wavelengths.
A direct beam approach was followed regarding the collimation of light to account
for the measurement errors introduced by the frequent overestimation of the
current due to the unpredicted reflections caused by diffuse light. Extended simulations
of different optics were performed to determine the best layout that offers
good directionality and satisfactory non-uniformity of irradiance and light collection
efficiency. Total internal reflectors of 13.5mm diameter proved to be the most
appropriate primary optics with the highest collection efficiency. An imaging homogeniser
was chosen as secondary optics for its capability to mix the light and
achieve low levels of non-uniformity of irradiance. The spatial non-uniformity of
irradiance achieved with 612 LEDs is 0.29% across the 32cm x 32cm illuminated
area and the irradiance is equal to 1316 W/m2 assuming 1W LEDs.
The hexagonal placement set-up was used for the placement of the LEDs since
it results in the lowest non-uniformity and it is the best option for keeping the lamp
size compact. An optical engineering software called FRED was used for ray-tracing
individual optics. Due to the time and computational demands of the simulations a
different approach needed to be found for overlaying the irradiance profiles of hundreds
or even thousands optical elements. An algorithm was developed in Matlab
that takes into consideration the geometry of each case and calculates the final irradiance
profile.
A placement methodology that accounts for the spectral uniformity on the illuminated
target was also developed. It was shown that placing the LEDs randomly
does not offer enough spectral mixing and is therefore problematic as it introduces
an unexpected source of measurement uncertainty. The influence of spectral non-uniformity
varies for different photovoltaic technologies due to their variable spectral
responses. Thus, a placement methodology using a genetic algorithm was developed
to optimise the positioning of the LEDs. As a result the highest spectral non-uniformity
drops from almost 5% to 1.46% and the measurement uncertainty is
reduced significantly since an improvement of up to 1.8% is noted in the current
density non-uniformity.

Optical design of a fully LED-based solar simulator

Design of Static Star Simulator and Proposes A Technique of Correction Method for the Position of Star

Fabricating nanoparticulate organic thin film transistor (OTFT) and organic photovoltaic (OPV) devices using inkjet printing

In order to carry out on site calibration and accuracy test of a high accuracy star sensor, a type of compact very high accuracy star simulator system is needed, and its accuracy should be less than 02″ Firstly, we should study on the
optical system with high imaging precision Then, put a high-precision and large size star board on the star display system, in a static form to simulate dynamic star map Finally, we should design the structure for star simulator according
to parameters of optical system, to ensure installation accuracy and reliability of lens The result shows that all of design
indexes meet the requirement, and accuracy better than 02″, so star simulator proposed in this paper is satisfied for on
site calibration and accuracy test of the high accuracy star sensor

Compact star simulator with very high accuracy

In order to improve simulation precision of solar simulator, this paper researched general design scheme of optical
system. First of all, this paper discussed optimization techniques for focusing system, optical integrator, collimating
system, and which aberrations influenced the uniformity of optical integrator; Secondly, analysis of defocus effect for
integrator projector lens and put forward optimal defocus distance formula, then using ZEMAX to design collimating
optical system, and simulated the system in LightTools; Finally, tested solar simulator, the results show that: it can
simulated one solar constant, irradiation range reached Φ200mm, working distance is 1000mm, irradiation non
uniformity in 60mm range is less than ±1%, and in (60-200) mm is less than ± 2%, instability is better than ± 1%/h.

Technique for solar simulator

To solve the bottleneck caused by the fact that solar simulators are unable to simulate a solar collimation angle of 32′ and an irradiance of one solar constant at the same time, we designed a new type of optical system for solar simulators. Five major design aspects of the optical system are addressed: the hybrid condenser, collimation lens, field stop, optimization of the optical integrator and the effects on the non-uniformity when the projector lens is defocused. The results show that the solar simulator described in this paper can realize a solar angle of 32′ and an irradiance of one solar constant. Meanwhile, the non-uniformity is less than ±1.34% when the irradiation area has a diameter that is no more than 100 mm and in the 100–300 mm diameter range is less than ±3.8%.

Yujun Gao

Papers

Compact star simulator with very high accuracy

Technique for solar simulator

Design of an optical system for a solar simulator with high collimation degree and high irradiance