Труды Всемирного конгресса Международного общества солнечной энергии

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Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

542

structure-property relationships.

2. EXPERIMENTAL

2.1 Material Preparation

For the systematic investigation 2 different UV-curing

resins (resins A and B) and 2 thermotropic additives

(additives 1 and 2) exhibiting switching temperatures

between 45 and 55°C were selected (see Table 1).

Thermotropic layers were produced under variation of

additive concentration between 2, 5 and 7 wt%. For the

production of thermotropic layers, a dissolution of the

thermotropic additive in the resins was filled into an

intervening space located between two glass panes, which

were sealed around the edge. Afterwards the mixture was

cured by UV-radiation (Ultra Vitalux, Osram GmbH,

München, GER) for 5 minutes. Film thickness was 800µm.

As to the nomenclature A-1-5 indicates a film based on

resin A containing 5w% of additive 1, for example.

TABLE 1: ADDITIVES USED

ADDITIVE SWITCHING TEMPERATURE [°C]

1 55

2 46

2.2 Material Characterization

The switching behaviour of the thermotropic layer is

determined by thermal transitions of the additives. Thus a

comprehensive thermal characterization of the additives

was done by Differential Scanning Calorimetry (DSC).

Thermograms were recorded under static air on a Mettler

Toledo DSC823e (Schwarzenbach, CH) in a temperature

range between 0°C and 130°C applying a heating rate of

10K/min. The sample mass was 10mg. Melting point and

melting enthalpy were evaluated according to ISO 11357-3.

In addition specific focus has been directed towards

temperature differences between melting and crystallization

(i.e. hysteresis effects).

The additive contents of the produced thermotropic layers

were determined by DSC operating in Temperature

Modulation mode (TM-DSC). TM-DSC was performed

under static air from 0°C to 130°C at a heating rate of

1K/min, a modulation amplitude of ±0.5°C and a

modulation period of 75s. Weighting the transition enthalpy

of the thermotropic layer by the heat of fusion of the pure

additive allowed for the evaluation of the films additive

content.

The thermotropic materials were analyzed as to solar

optical properties, switching temperature, switching

process and residual transmittance in the opaque state

applying UV/Vis/NIR spectroscopy. To investigate the

switching behavior a conventional UV/Vis/NIR

spectrophotometer (Lambda 950, Perkin Elmer Instruments

GmbH, Überlingen, GER) equipped with an

Ulbricht-sphere (diameter 150 mm) was adapted by a

heating stage allowing for controlling the sample

temperature from ambient to 100°C. Prior to the

measurements the sample was maintained at the selected

temperature for 10 minutes. Due to restrictions in the

measurement set-up, which are currently improved, it was

only possible to record direct transmittance spectra within a

wavelength range between 250 and 2500 nm. Integral solar

optical transmittance values were determined by weighting

the measured spectral data in steps of 5 nm by the AM 1.5

Global solar irradiance source function, given in [4].

3. RESULTS AND DISCUSSION

In Figs. 1 and 2 representative thermograms of the

investigated additives 1 and 2 are shown, respectively.

Besides the melting peak in the temperature range between

50 and 60°C material 1 shows an endothermic effect at

lower temperatures. This peak can be attributed to a phase

transition in the crystalline structure. Whereas no

significant differences in transition temperature range can

be observed between the additives, the temperature shift

between melting and crystallization is higher for additive 2.

The additive contents of the film types determined by

TM-DSC measurements are compared in Table 2.

Significant deviations from the theoretical concentration

are observable especially for the resins formulated with

additive 1. This is an indication for enhanced compatibility

between additive 2 and the matrix materials.

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

543

Fig. 1: Thermogram of additive type 1.

Fig. 2: Thermogram of additive type 2.

TABLE 2: ADDITIVE CONTENT OF THE THERMO-

TROPIC LAYERS

ADDITIVE CONTENT

[wt%]

THERMO-TR

OPIC

LAYER

theoretical results of TM-DSC

A-1-2 2 0.2

A-1-5 5 1.6

A-1-7 7 5.5

A-2-2 2 1.7

A-2-5 5 4.8

A-2-7 7 7.0

B-1-2 2 0.9

B-1-5 5 1.3

B-1-7 7 2.1

B-2-2 2 0.8

B-2-5 5 4.8

B-2-7 7 6.9

In Fig. 3 a representative thermotropic resin (layer B-2-5)

in transparent and light diffusing state is shown. It is

observable that the film shows a hazy appearance above the

switching temperature.

Fig. 3: Thermotropic layer in clear (top left) and opaque

state (bottom right).

Direct transmittance spectra of film type A-1-5 and of film

type B-2-5 in the clear and the scattering state are plotted in

Fig. 4. In general the layers show a stronger decrease of

transmission in the region between 300 and 1500 nm than

at longer wavelengths. This is an indication for increasing

differences in refractive index with decreasing wavelength.

Also scattering domains with dimensions well below 1500

nm may be predominantly active in these layers.

Comprehensive investigations as to scattering domain size

applying phase imaging Atomic Force Microscopy (AFM)

are currently carried out. However, the decrease of direct

transmittance is more pronounced for film types formulated

with additive 2 than for materials containing additive 1.

The influence of the additive type on the scattering

behaviour is emphasized by integral solar optical properties

of selected layers determined over the solar spectral

intensity AM 1.5 summarized in Table 3.

The film types show direct solar transparencies between 64

and 83% in the clear state. No significant differences

between film types formulated with the various additives

are observable, although additive concentrations differ

significantly. This further underlines the higher

compatibility of additive 2 with the matrix material. The

increased light scattering of film types formulated with

additive 2 in the cloudy state may be attributed to the

higher additive content and thus to the increased number of

scattering domains. However, considering layers exhibiting

nearly the same additive concentrations (A-1-7 vs. B-2-5),

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

544

direct transmittance [-]

wavelength [nm]

direct transmittance [-]

wavelength [nm]

Fig. 4: Direct transmittance spectra of selected thermotropic

layers in clear and scattering state; top: layer A-1-5;

bottom: layer B-2-5.

TABLE 3: DIRECT SOLAR TRANSMITTANCE VALUES

OF SELECTED THERMOTROPIC LAYERS

DIRECT SOLAR

TRANSMITTANCE [%]

THERMOTROPIC

LAYER

CLEAR CLOUDY

A-1-2 83 80

A-1-5 73 49

A-1-7 66 31

B-2-2 81 68

B-2-5 79 35

B-2-7 64 27

a more pronounced decrease of direct solar transmittance

above the switching temperature is observable for films

formulated with additive type 1. This can be ascribed to a

more distinct change in refractive index of additive type 1

compared to additive type 2. In the cloudy state the direct

solar transmittance decreases to values between 27 and

80%. In general an increasing additive concentration causes

a decrease of solar transmittance in the clear state on the

one hand, but improves the light shielding property

significantly on the other hand.

In Fig. 5 direct solar transmittance values of layer A-1-5 are

plotted as a function of temperature. In general the

thermotropic material is characterized by a steep and rapid

switching process. The comparison of the switching of the

film with the additives thermal transition reveals a good

correlation. This indicates that the switching temperature of

the layer can be set accurately by selecting adequate

additives.

Fig. 5: Relationships between thermal transition of additive

1 and switching of thermotropic layer A-1-5.

4. SUMMARY AND CONCLUSIONS

For the present investigation various thermotropic resins

were produced under variation of resin base and additive

type and concentration. The materials were characterized

as to additive content, optical properties, switching

temperature, switching process and residual transmittance

in opaque state. TM-DSC measurements revealed

significant deviations in additive content from theoretical

values, especially for additive 1.The different film types

show a direct solar transparency between 64 and 83% in the

clear state. The direct solar transmittance decreases to

values of about 27% to 80% above the switching

temperature. Considering additive concentration the

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

545

differences between clear and cloudy state are more

pronounced for film types formulated with additive 1. This

may be attributed to more distinct differences in the

refractive index between the matrix materials and additive

type 1. In general the thermotropic resins are characterized

by a steep and rapid switching process. The switching

temperature can be set by varying the different additives.

The comparison of films thermal transitions with the

switching performance revealed a good correlation. This

enables the production of thermotropic materials exhibiting

tailor-made properties by selecting adequate additives.

5. ACKNOWLEDGMENTS

The research work of this paper was performed at the

Polymer Competence Center Leoben GmbH within the

framework of the K

plus

Program of the Austrian Ministry of

Traffic, Innovation and Technology with the contibutions

by the University of Leoben, Graz University of

Technology, Johannes Kepler University Linz,

JOANNEUM RESEARCH ForschungsgmbH and Upper

Austrian Research GmbH. The PCCL is funded by the

Austrian Government and the State Governments of Styria

and Upper Austria.

This work is funded by the State Government of Styria,

Department Zukunftsfonds Steiermark.

The authors wish to express their acknowledgements to

Cytec Surface Specialties (Drogenbos, BEL), Sasol

Germany GmbH (Hamburg, GER) and Chemson Polymer

Additive AG (Arnoldstein, AUT) for providing the

materials.

6. REFERENCES

(1) R. Hausner, G.M. Wallner, K. Resch, 2007, “All

polymeric flat-plate collector – potential of

thermotropic layers to prevent overheating”, in

Proceedings of ISES SWC 2007, September 18-21, in

press.

(2) G.M. Wallner, K. Resch, R. Hausner, 2006,

“Solarthermische Kunststoffkollektoren mit integriertem

Überhitzungsschutz“, in Procedings of Gleisdorf Solar

2006, September 6-8, p. 105-114.

(3) P. Nitz and H. Hartwig, 2005, “Solar control with

thermotropic layers”, Solar Energy 79, p. 573-582.

(4) R.E. Bird, R.L. Hulstrom, 1983, “Terrestrial solar

spectral data sets”, Solar Energy 30, p. 563-573.

THERMAL PERFORMANCE ANALYSIS OF A SOLAR HEATING AND

NOCTURNAL RADIANT COOLING SYSTEM

Wang Yiping

School of Chemical Engineering and Technology,

Tianjin University

Weijin road No.92, Nankai district

Tianjin 300072, China

Cui Yong

School of Chemical Engineering and Technology,

Tianjin University

Weijin road No.92, Nankai district

Tianjin 300072, China

yolanda207@163.com

Zhu Li

School of Architecture, Tianjin University

Weijin road No.92, Nankai district

Tianjin 300072, China

zly_tj@163.com

Kong Jianguo

Tianjin Cuipinghu Science Park

Tianjin 301908, China

ABSTRACT

The solar heating and nocturnal radiant cooling techniques

are united to produce a novel heating and cooling system.

The HCPs (heating and cooling panels) can be used as

structure materials for building envelope, which realizes the

real building integration. Its thermal performance, namely

heat-collecting capacity, heat-collecting efficiency and

cooling capacity are analyzed after a systematic description

of the whole system. HCPs thermal performances are

compared among different coatings .The results show that

the system has good heating and cooling functions, which

can supply domestic hot water, space heating and space

cooling loads. With two sorts of coating materials, which

are acrylic resin coating, sprayed on HCPs, the daily

average heat-collecting efficiency are respectively about

32% and 20% with the maximum points of 50% and 30%,

while at night the cooling capacity are about 20W/m

and

40W/m

in Tianjin, China in November.

1. INTRODUCTION

Under the situation of increasingly severe energy and

environment problems in the world, solar energy utilization

technologies, especially solar water heating and solar

air-conditioning technologies are being widely used and

attract more and more people studying on them. However,

from the long term viewpoint, problems of higher cost and

difficulty to be integrated with buildings will hinder their

future large-scale development. Nocturnal radiant cooling

technology with the advantages of energy saving and simple

usage is one type of passive cooling technique utilizing the

transmittance of the earth’s atmosphere for thermal radiation

through the two atmospheric windows (8μm~13μm and

13.5μm~16μm) to the sky, since the sky temperature is lower

than the temperature of most of the objects on the earth.

Considerable researches have been carried out to study the

radiant cooling technology under different climate

conditions. Evyatar Erell and Yair Etzion [1] have set up a

radiant cooling system whose cooling capacity output was

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

547

80W/m

in the arid area and presented an equation for

predicting the cooling output. Maal and Kodah [2] have

built another radiant cooling system whose cooling

capacity output was 13MJ/(m

·night) in Jordan and present

a mathematical model. A building model utilizing radiant

cooling technology for preserving vegetable has been built

in Japan, and the cooling capacity is 40-60W/m

[3].

Aubrey Jaffer and others [4-7] have studied the radiant

cooling coating materials, energy conservation and

environmental-protection effects of such a radiant cooling

technology, and developed a great variety of coating

materials such as silicon, cadmium telluride and TiO

The Patents CN 1529018A and 200610013044.3 [8, 9]

present a sort of solar collector that can be used as the

component of building envelop, which realizes the perfect

combination of solar energy equipments with the building.

In this paper, the nocturnal radiant cooling technology was

coupled with the solar collector mentioned in the Patents to

produce the perfect building integrated solar heating and

cooling system. Experimental apparatus were set up for

detailed study on its performance.

2. SYSTEM DESCRIPTION

2.1 Experiment Set

Fig.1 is the flow diagram of the novel solar heating and

nocturnal radiant cooling system. The arrows show the

working fluid flow way and direction. The solid line

represents the heating cycle between the HCP and the

heat-storage tank, and the dashed line demonstrates the

cooling cycle between the HCP and the cool-storage tank.

The HCP can use as collector to absorb solar radiation to

heat the working fluid in daytime and radiator to cool the

working fluid at night. The back of HCP is insulated with

polystyrene board with 90mm thickness and conductivity

of 0.043W/(m·K). The volume of the two storage tanks are

both 30L, and the outside surfaces of the tanks and

circulating pipes are all insulated by the rubber-plastic

insulation board with 30mm thickness and conductivity of

0.034W/(m·K).

When it is the heating cycle, the pump2, rotameter2 and

valve2 are closed, and the pump1, rotameter1 and valve1

are turned on. The working fluid in the bottom of

heat-storage tank is drew out by pump1, and heated by

solar radiation irradiating on HCP. Then the working fluid

goes back to the heat-storage tank. When it comes to the

cooling cycle, valves and pumps are set in reverse. The

working fluid in the top of cool-storage tank is drew out by

pump2, and cooled by means of radiation, maybe also the

convection way. Then the working fluid goes back to the

cool-storage tank. The rotameter has the functions of valve

and regulating flux of the working fluid.

pump1

ro ta meter 1

valve1

rota m ete r2

pump2

valve2

heat-

stora g e

tan k

cool-

storage

tan k

Fig. 1: Flow chart of the HCP testing system.

Fig. 2 is the sectional profile of HCP whose area is 2m

Six copper tubes with 8mm outside diameter and 200mm

long are arranged in distance of 150mm to be attached with

the aluminum plate by a type of heat-conducted adhesive

with the conductivity of 3.12W/(m·K) made by ourselves,

and then the copper tube is fixed by aluminum sections

with groove. So the copper tube could be integrated with

the aluminum plate tightly, which make the plate and tube

be unit to reduce the heat transfer resistance.

Fig. 2: Structure of the HCP.

2.2 Measurement

Solar radiation is measured by a solar cell whose output

signal was proportional to the solar radiation and is put on a

horizon unscreened plane 1m away from the system. All of

the temperatures are measured by thermoresistances, which

include the inlet and outlet temperature, the temperature

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

548

points in the tanks, the temperature distribution points in

both width and axial directions on HCP, and also the

environmental data. The thermoresistance for environment

temperature is put in the thermometer shelter away 1m

away from the system. The signals then are all linked with

an automatic digital processing and display instrument

using a computer to obtain the real-time collecting data.

3. RESULTS AND DISCUSSION

3.1 Thermal Performance

Fig. 3 shows the complete analysis process based on the

measured climate conditions and temperature data with

coating material of 0.7absorptivity, 0.92~0.96emissivity

and 0.3reflectivity [10]. Operation status can be changed

between the heating cycle and the cooling cycle through

the forced circulation way with a mass flow rate of 0.04

kg/s. Fig.3a at first demonstrates solar radiation reaches

the maximum of about 350W/m

at 12:00pm, and the

highest environment temperature is about 17ć at

14:30pm in November 2006. Because of the shelter from

cloud, solar radiation could decrease suddenly at 11:00am

and at 12:30pm. Fig.3b further shows the inlet and outlet

temperature of the system. The vertical line is the turning

point between the heating cycle and cooling cycle. The

magenta line represents the outlet temperature during the

heating cycle and inlet temperature during the cooling

cycle. And the cyan line is in reverse. Fig.3c demonstrates

the heat-collecting capacity of the system. When solar

radiation incident onto HCP decreases, the heat-collecting

capacity would reduce accordingly. The heat-colleting

capacity would be less than zero after 15:00pm, because

the change of incident angle makes the decrease of solar

radiation incident on HCP, and then results in heat loss

from HCP. The maximum heat-collecting capacity is

about 150W/m

. Fig.3d shows the heat-collecting

efficiency of the system from 8:30am to 14:30pm. T he

heat-collecting efficiency increases at 11:30am and at

12:30pm, because the thermal capacity of the fluid is big,

and the heat-collecting efficiency would increase. The

daily average heat-collecting efficiency is 32% with the

maximum point is 50%. Fig. 3e shows the cooling

capacity curve at night, and the average cooling capacity

is about 20W/m

Fig. 3: Performance curves of system.

3.2 Influence of Coating Materials

Fig. 4a demonstrates the current weather condition. The

solar radiation gets to the maximum of nearly 350W/m

3 SOLAR COLLECTOR TECHNOLOGIES AND SYSTEMS

549

TABLE 1: PROPER TIES OF THE COATING MATERIALS [10]

material A material B

Absorptivity 0.7 0.4

emissivity 0.92~0.96 0.92~0.96

reflectivity 0.3 0.6

12:00pm, and environment temperature could be the

maximum of about 17 at 1ć 4:30pm, which lags about 2.5

hours behind the maximum solar radiation. Fig.4b shows

the inlet and outlet temperature of the system with two

coating materials. The vertical line is the turning point

between the heating cycle and cooling cycle. The magenta

and cyan lines are the inlet and outlet temperature with

coating materials A, and purple and green lines are the inlet

and outlet temperature with coating materials B. The intake

and outlet of the working fluid are in reverse between the

heating cycle and cooling cycle. Due to higher absorptivity

and lower reflectivity of coating material A than coating

material B, the inlet and outlet temperature with coating

material A are higher than those with coating material B

during the heating cycle. Fig.4c compares the

heat-collecting capacity of the system with two coating

materials. Because the absorptivity of coating material A is

higher than that of coating material B, the heat-collecting

capacity of the system with coating material A is always

larger than that with coating material B during the heating

cycle. The heat-collecting capacity firstly increases and

then declines. The heat-collecting capacity gets to the

maximum of about 150W/m

with coating material A and

about 90W/m

with coating material B. Fig.4d shows the

comparison curves of heat-collecting efficiency with two

kinds of different coating materials from 8:30am to

14:30pm. There are several abrupt rises at the

heat-collecting efficiency curves, which reason is that in

these periods, because of the cloud cover or other reasons,

solar radiation decreases suddenly, the heat-collecting

efficiency of that time would increase due to the bigger

heat capacity of the working fluid. After 14:40pm, solar

radiation reduces and solar incidence angle changes, the

heat-collecting capacity decreases accordingly, so the

heat-collecting efficiency would be less. The daily average

heat-collecting efficiency is 32% with the maximum

efficiency of 50% with coating material A, and the daily

average heat-collecting efficiency is 20% with the

maximum point of 30% with coating material B. Fig.4e shows

Fig. 4: Performance comparison with different coating

materials.

the comparison curves of cooling capacity. At the

beginning of the cooling cycle, performance of the system

are greatly affected by the solar radiation and environment

temperature, the cooling capacity would be negative value.

Proceedings of ISES Solar World Congress 2007: Solar Energy and Human Settlement

550

During the cooling cycle, the cooling capacity of the

system with coating material A is lower than that with

coating material B. The average cooling capacity of the

system are 20W/m

with coating material A and 40 W/m

with coating material B, respectively in Tianjin, China in

November.

4. CONCLUSION

Solar heating and nocturnal radiant cooling techniques are

united to produce the novel heating and cooling system.

The HCP with both heating and cooling functions can be

used as structure materials for the building envelope, which

realizes the true building integration with solar energy and

natural energy. With two sorts of coating materials sprayed

on HCP, the daily average heat-collecting efficiency are

respectively about 32% and 20% with the maximum points

of 50% and 30%, while at night the cooling capacity are

about 20W/m

and 40W/m

5. REFERENCES

(1) .E. Erell, Y. Etzion, “Heating experiments with a

radiative cooling system”, Building and Environment,

31(6):509-517, 1996.

(2) M. A. A. Nlmr, Z. Kodah, B. Nassar, “A theoretical

and experimental investigation of a radiative cooling

system”, Solar Energy, 63(6): 367-373, 1998.

(3) “Effects of the Passive Use of Nocturnal Radiative

Cooling in Fresh Vegetable Cooling”, 2001.

(4) A. Jaffer, “Radiative cooling in hot humid climates”,

1-22, 2006.

(5) L. Z. Cun, C. Hui, L. J. Hong, “Microstructure and

optical properties of Silicon Nitride thin films as

radiative cooling materials”, Acta Energiae Solaris

Sinaca, July 302-305, 2001.

(6) M. Benlattar, E. M. Oualim, “Harmouchi. Radiative

properties of cadmium telluride thin film as radiative

cooling materials”, Optics Communications, 256:10-15,

2005.

(7) C. F. Li, L. X. Guo, “A kind of doped transparent film

with spectral selectivity for radiative cooling”,

Functional Material, 28 (6):658-650, 1997.

(8) W. Y. Ping, Y. Bing, Z. J. Li, “The Solar Collector

Wall”, China, CN 1529018A, 2003.

(9) Z. Li, W. Y. Ping, C. Yong, Y. Z. Yong, “A Type of

Solar Collector Wall”, China, 200610013044.3, 2006.

(10) G. S. Yan, N. H. Yue, “Thermal radiation property and

measurement”, Science and Technique Press, 1989.

THE INVESTIGATION OF CARBON NANOPARTICLES EMBEDDED IN ZnO

And NiO AS SELECTIVE SOLAR ABSORBER SURFACES

G. Katumba

Physics Department, University of Zimbabwe, P. O. Box MP

167, Mt. Pleasant, Harare, Zimbabwe.

katumba@science.uz.ac.zw

A. Forbes

Council for Scientific and Industrial Research, National

Laser Centre, P. O. Box 395, Pretoria 0001, South Africa and

School of Physics, University of KwaZulu-Natal, Private

Bag X54001, Durban 4000, South Africa.

B. Mwakikunga

Council for Scientific and Industrial Research, National

Centre for Nanostructured Materials,

P. O. Box 395, Pretoria 0001, South Africa, and

School of Physics, University of the Witwatersrand, Private

Bag X3, P O Wits 2050, Johannesburg,

Gauteng, South Africa.

E. Wäckelgård

Division of Solid State Physics, Department of Engineering

Sciences, Uppsala University, P. O. Box 534, Uppsala

SE-751 21, Sweden.

J. Lu

Division of Electron Microscopy, and Nanoengineering,

Department of Engineering Sciences, Uppsala University

P O Box 534, SE-751 21 Uppsala, Sweden.

L. Olumekor, G. Makiwa

Physics Department, University of Zimbabwe, P. O. Box MP

167, Mt. Pleasant, Harare, Zimbabwe.

ABSTRACT

Selective solar absorber coatings of carbon nanoparticles

embedded in ZnO and NiO matrices on rolled aluminium

substrates have been fabricated by a low cost acetate

sol-gel technique. Spectrophotometry was used to

determine the solar absorptance and the thermal emittance

at 100 °C of the composite coatings in the wavelength

range 0.3 to 20 μm. The surface morphology of the

samples was studied by scanning electron microscopy

(SEM). Cross-sectional high resolution transmission

electron microscopy (X-HRTEM) was used to study the

fine structure of the samples. Samples were subjected to an

accelerated ageing test in a climate chamber with 95%

relative humidity and a temperature of 45 °C. The SEM

studies showed that C-NiO surface was smooth while that

of the C-ZnO sample had micro roughness. The X-HRTEM

investigations revealed a nanocrystalline nature of C-NiO

sample and a layered structure for the C-ZnO samples.

The thermal emittances of the samples were 6% for the

C-ZnO and 4% for the C-NiO matrix materials. The solar

absorptances were 71% and 84% for the C-ZnO and C-NiO

samples, respectively. The accelerated ageing tests

produced performance criterion (PC) values of 0.04 and

0.007 at 95 hours for the C-ZnO and C-NiO samples,

respectively. Based on these results, C-NiO matrix sample

proved to have better solar selectivity behaviour than the

C-ZnO counterpart.

1. INTRODUCTION

With energy supply and demand constraints an ever-present

concern, there is renewed interest in low cost, efficient and

environmental-friendly energy alternatives based on

thermal solar power[1-5]. Efficient thermal solar collectors

Труды Всемирного конгресса Международного общества солнечной энергии - 2007. Том 2

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