VISIBLE AND INFRARED ABSORPTION SPECTRA OF COVERING MATERIALS FOR SOLAR COLLECTORS

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1 AGRICULTURAL ENGINEERING VISIBLE AND INFRARED ABSORPTION SPECTRA OF COVERING MATERIALS FOR SOLAR COLLECTORS Ltvi University of Agriulture E-mil: Astrt Use of solr energy inreses every yer. In Ltvi, solr energy is use minly y solr olletors. The min prt of the solr olletor is the sorer, ut not less importnt is the overing mteril whih protets the sorer from the ooling impt of the win. This over must e trnsprent for solr rition, ut opque for therml rition of the sorer, whih is t greter wvelengths. Therefore it is importnt to mesure sorption spetr of possile overing mterils t visile n infrre wvelength rnges. Asorption spetr hve een mesure for severl mterils: glss, polythene, Plexigls, n ells Plexigls. Asorption spetr for ll these mterils re mesure in three rnges: ultrviolet visile (UV VIS): 5 nm; ner infrre (NIR): 7 nm; infrre (IR): 8 nm. UV-VIS spetr with the Oen Optis evie HR- hve een mesure, ut NIR n IR with Bruker Furje spetrometer EQUINOX 55. Evlution of sorption spetr showe tht the most suitle mteril (from the onsiere) for overing of solr olletors is Plexigls. Key wors: solr olletor, therml rition, sorption spetr. Introution Besies other environment-frienly renewle energy soures, solr energy is wiely use in the worl. Also in Ltvi solr olletors re use (Ziemelis et l., ; Knevi et l., 6). The energy reeive of the solr olletor n e lulte (Pelee et l., 7). However, importnt is lso energy loss euse of re-rition. The min prt of the solr olletor is the sorer, ut not less importnt is the overing mteril whih protets the sorer from the ooling impt of the win. This over must e trnsprent for solr rition, ut opque for therml rition of the sorer, whih is t greter wvelengths. Some uthors (Muresn et l., 6; Mtouk Khoukhi et l., 6) spek out sorption of solr rition t the over, ut not ny ws foun pying ttention to therml rition of the sorer. Therefore it is importnt to mesure sorption spetr of possile overing mterils t visile n infrre wvelength rnges. Suh spetr hve not een foun in the literture. Mterils n methos Solr energy n e use in two wys: solr ells, whih trnsform solr energy into eletril energy, n solr olletors, where solr energy is use for heting of wter. In Ltvi, solr olletors re more populr euse of their superior effiieny ompre to solr ells (BSI, 5). A tritionl flt-plte solr olletor (Fig. ) onsists of sorer (lk, well soring mteril), het rrier (usully pipes in whih wter irultes), het insultion, n over (Ziemelis et l., ; Knevi et l., 6). Min funtion of the over is to protet the sorer from the ooling impt of the win. This over must e, of ourse, trnsprent for solr rition. But the sorer sme, s wrm oy, irrites therml rition. Therml rition n e esrie y suh well-known formule: rition power of lk oy per unit of re, unit of soli ngle, n unit of frequeny is given y

2 where h u(, T) = h exp ν frequeny, Hz; k T B T temperture, K; h Plnk s onstnt, J s; spee of light, m s - ; k B Boltzmnn onstnt, J K -., () Fig.. Struture of the solr olletor: sorer, het rrier, insultion, over. Integrting the ove eqution over ν the power output given y the Stefn Boltzmnn lw is otine W = AT, () where σ Stefn-Boltzmnn onstnt, W m - K - ; A re of the riting surfe, m - ; T temperture, K. The wvelength λ, for whih the emission intensity is highest, is given y Wien s Lw: =, mx T where Wien s isplement onstnt, m K; T temperture, K. Solr rition spetrum is shown in Fig. (Rottmn, 6). () Irrine, W m - nm -.. Top of Atmosphere Surfe 5 5 Fig.. Solr rition spetrum t the top of the tmosphere n t the se level.

3 Mximl irrine is t 55 nm. Integrl power t the top of the tmosphere is equl to the solr onstnt S = 67 W m -. Men temperture of the sorer of the solr olletor usully is pproximtely 6 ºC. The spetrum of the therml rition of lk oy with suh temperture is shown in Fig...8 Irrine, W m - nm Wvelength, µm Fig.. Therml rition of lk oy t the temperture of 6 ºC. Mximl irrine is t wvelength of μm. Integrl irrine is pproximtely 67 W m -. Sine rel ojets, inluing lk-oloure solr olletor, re not solutely lk, the integrl irrine n e even hlf of tht, ut still is omprle with the inoming solr rition. The over mteril of the solr olletor must e trnsprent for the mximum rition of the sun (t wvelengths smller thn μm), ut opque for the mximum rition of the sorer (t wvelengths greter thn pproximtely 5 μm). Therefore it is importnt to know the sorption spetr of these mterils. Asorption spetr hve een mesure for severl mterils: glss, polythene, Plexigls, n ells Plexigls. Asorption spetr for ll these mterils re mesure in three rnges: ultrviolet visile (UV VIS): 5 nm; ner infrre (NIR): 7 nm; infrre (IR): 8 nm. UV-VIS spetr with the Oen Optis evie HR- hve een mesure, ut NIR n IR with Bruker Furje spetrometer EQUINOX 55. Results n isussion At the visile rnge ( to 7 nm), the most trnsprent is glss (Fig. ), ut, if lso ultrviolet rnge is onsiere, in whih the sun lso irrites, more trnsprent is Plexigls (Fig. ). Cells Plexigls (Fig. ) is less trnsprent t oth visile n ultrviolet rnges. Polythene (Fig. ) is more trnsprent thn glss n Plexigls t the ultrviolet rnge, ut less trnsprent t the visile rnge. At the ner infrre rnge (7 to nm), more trnsprent is Plexigls (Fig. 5 ). Vlues of sorption of glss n polythene (Fig. 5 n resp.) re similr to eh other n greter thn tht of Plexigls. Lest trnsprent is ells Plexigls (Fig. 5 ). At the infrre rnge ( to nm), where solr rition is wek, ut therml rition of the sorer is onsierle, etter for overing is more opque mteril. Gretest sorption t this rnge is tht of Plexigls n ells Plexigls (Fig. 6 n resp). For glss (Fig. 6 ) n polythene (Fig. 6 ), sorption t this wvelength rnge is weker. Evlution of sorption spetr showe tht the most suitle mteril (from the onsiere) for overing of solr olletors is Plexigls. Of ourse, in orer to hoose the mteril for overing of the solr olletor, the sorption is not the only riteri. Importnt re lso osts n, espeilly if the solr olletor is not flt, possiility to shpe it. Polythene n Plexigls re more mllele thn glss n ells Plexigls. Importnt is lso urility. Plexigls n ells Plexigls re more urle thn glss n polythene.

4 Fig.. Asorption spetrum of glss (), Plexigls (), ells Plexigls (), n polythene () t visile n ultrviolet rnge. 5

5 Fig. 5. Ner infrre sorption spetr of glss (), Plexigls (), ells Plexigls (), n polythene (). 6

6 Fig. 6. Infrre sorption spetr of glss (), Plexigls (), ells Plexigls (), n polythene (). Consequently, from ll viewpoints together, the est mteril for overing of solr olletors is Plexigls. Investigtions re lso require on the stility of those optil hrteristis in outoor onitions. 7

7 Conlusions.. Energy loss of the solr olletor vi therml rition is onsierle.. If only optil qulities of mterils re onsiere, the est mteril for overing of solr olletors is Plexigls. Aknowlegement Thnks to Jnis Kleperis n Georgy Chikvize for ssistne in mesuring of spetr. Referenes. Bunesvern Solrinustrie. Knevi L., Nviks J., Ziemelis E., Ziemelis I. (6) Inrese of the Effiieny of Solr Colletors. Seon Interntionl Sientifi Conferene: Biometris n Informtion Tehnologies in Agriulture: Reserh n Development.- Lithuni, Kuns, 89-9 pp.. Mtouk Khoukhi, Shigeno Mruym, Atsuki Komij, Msu Behni. (6) Flt-Plte Solr Colletor Performne with Cote n Unote Glss Cover. Het Trnsfer Engineering, 7(), pp Muresn C., Menezo C., Benner R., Villon R.(6) Numeril Simultion of Vertil Solr Colletor Integrte in Builing Frme: Rition n Turulent Nturl Convetion Coupling. Het Trnsfer Engineering, 7(), pp Pelee I., Iljins U., Ziemelis I., Ziemelis E. (7) Theoretil lultions of energy reeive y solr olletors. Proeeings of the 6 th Interntionl Sientifi Conferene Engineering for rurl evelopment, Jelgv, pp Rottmn G. (6) Mesurement of totl n spetrl solr irrine. Spe Siene Reviews, 5, pp Ziemelis I., Iljins U., Nviks J. () Eonomil Comprison of Some Prmeters of Flt-Plte Solr Colletors. Interntionl Reserh Conferene: The Role of Chemistry n Physis in the Development of Agriulturl Tehnologies.- Lithuni, Kuns, pp. 5. 8