Review of physical vapor deposited (PVD) spectrally selective coatings for mid- and high-temperature solar thermal applications

improved solar collectors (40) comprising glass tubing (42) attached to bellows (44) by airtight seals (56) enclose solar absorber tubes (50) inside an annular evacuated space (54;. The exterior surfaces of the solar absorber tubes (50) are coated with improved solar selective coatings {48} which provide higher absorbance, lower emittance and resistance to atmospheric oxidation at elevated temperatures. The coatings arc multilayered structures comprising solar absorbent layers (26) applied to the metal surface of the absorber tubes (50), typically stainless steel, topped wiih antireflective Savers (28) comprising at least two layers (30. 32) of refractory metal or metalloid oxides (such as titania and silica) with substantially differing indices of refraction in adjacent layers. Optionally, at least one layer of a noble metal such as platinum can be included between some of the layers. The absorbent layers cars include cermet materials comprising particles of metal compounds is a matrix, which can contain oxides of refractory metals or metalloids such as silicon. Reflective layers within the coating layers can comprise refractory metal silicides and related compounds characterized by the formulas TiSi. Ti3SiC2, TiAlSi, TiAN and similar compounds for Zr and Hf. The titania can be characterized by the formulas TiO2, Ti3O5. TiOx or TiOxN1-x with x 0 to 1. The silica can be at least one of SiO2, SiO2x or SiO2xN1-x with x = 0 to 1.

High temperature solar selective coatings

A review of high-temperature selective absorbing coatings for solar thermal applications

This invention pertains to coated polymer sheets which are useful as visibly transparent heat reflective thermal control films and which are suitable for use in glazing applications. The coated polymer sheets are characterized by a high transmission of visible radiation (i.e., visibly transparent) and a high reflectance at one or more near infrared radiation center wavelengths (i.e., heat reflective), and rely primarily on the interference effects of the dielectric layers to achieve these results. More specifically, the present invention pertains to thermal control films comprising (a) a thin flexible polymeric sheet having a first face and an opposite second face and a thickness of from 0.1 to 100 mils; and, (b) a multilayer coating adhered to said first face, said coating comprising two or more contiguous alternating layers of high and low index of refraction inorganic dielectric material of optical thickness approximately equal to one quarter of an infrared center wavelength, λ 0 , between 750 and 2000 nm; said thermal control film characterized by an average transmittance of visible radiation of wavelength 380 to 750 nm at 0° incidence of at least 50%; said thermal control film further characterized an average reflectance of infrared radiation in an infrared radiation band which is at least 100 nm wide and falls within the wavelength band 750 to 2000 nm, at 0° incidence, of at least 50%.

Thermal control films suitable for use in glazing

Novel Mo-Si3N4 based selective coating for high temperature concentrating solar power applications

Solar energy absorptive coatings that comprise single cermet layers with a homogeneous metal volume fraction exhibit an absorptance of about 0.8, which is not high enough for practical solar applications. To achieve absorptance greater than 0.9, graded composite films have been developed, but they give rise to higher thermal emittance due to the absorption edge not being sharp enough. This leads to increased thermal emittance at high operating temperatures, in the range of 300° C. to 500° C. There is now disclosed a novel solar selective surface coating which is composed of two cermet layers, with different metal volume fractions in each layer. The two cermet layers have different thicknesses, and the layers have thicknesses and volume fractions such that solar radiation is absorbed by internal absorbing and phase cancellation interference, but the cermet layers are substantially transparent in the thermal infrared region.

Thin film solar selective surface coating

We develop new visualization and diagnostics techniques for the analysis of the mechanical causes of second-order scattered light, applying these to the stray-light analysis of the MONS space telescope, whose scientific aim is the measurement of low-amplitude photometric oscillations in stars. The telescope is designed to detect amplitudes of 1 part per million, requiring a high stray-light rejection factor, and is thus an ideal subject for this work. The analysis involved determining stray-light cases and then using an innovative approach to efficient high-order ray tracing to produce detailed predictions of the stray-light flux distributions. In addition to demonstrating the utility of the approaches developed here, the results of the analysis show that the MONS space telescope design meets the stray-light rejection requirements.

MONS space telescope, part 2: analysis of very high stray-light rejection

The i-INSPIRE satellite is the result of a collaborative project at the University of Sydney, across the science
and engineering faculties The satellite is a compact tube-shaped pico-satellite with a mass of less than 075 kg
i-INSPIRE carries three science instruments - a photonic spectrograph, a radiation counter and an imaging
camera, and will be launched to a 310km polar orbit in late 2012 or early 2013 Here we describe the satellite
and its subsystems (including the science instruments and the communication system) as well as the ground
station, pre-launch tests, and the proposed launch itself i-INSPIRE will be Australia's first fully university
operated pico-satellite

The i-INSPIRE satellite: a university pico-satellite project

Instrumentation of the i-INSPIRE satellite

i-INSPIRE (initial-INtegrated SPectrograph, Imager and Radiation Explorer)is a collaborative project of School of Aerospace, Mechanical andMechatronic Engineering and the School of Physics within the University ofSydney. It aims to verify the ability of a 1 kg tube-satellite tocarry advanced space and astronomical payloads (a radiation counter,photonic sprectrograph, and a CMOS imager). As the first nanoSat to befully constructed by one Australian university and to be launched intospace, the i-INSPIRE project will be a prototype for future morecomplex nano-satellite platforms. The satellite platform distributes thepower, communication and control subsystems into three individual PCBboards, respectively. Observational data from payloads will be collectedand stored in external memory, which is connected to the microcontrollerby an SPI interface. A FM transceiver, the main part of communicationsubsystem, will work in the UHF band and initially be in receivingmode. After obtaining a confirmation signal from the groundstation, the microcontroller will transmit house-keeping and payloaddata to the ground station at the University of Sydney. The additionof a nano IMU (Inertial Measurement Unit) is being considered todetermine the current attitude of i-INSPIRE, in order to complementand confirm the pointing inferred from the imaging camera.

Anthony Monger

Papers

Thin film solar selective surface coating

MONS space telescope, part 2: analysis of very high stray-light rejection

The i-INSPIRE satellite: a university pico-satellite project

Instrumentation of the i-INSPIRE satellite

i-INSPIRE Tube-Satellite Bus Design