Influence of Dust in Solar Cells Used for Measuring Solar Radiation

INFLUENCE OF DUST IN SOLAR CELLS USED FOR MEASURING SOLAR RADIATION Lillo, I; A oyo, A.M.; Sil a, M; Ba ea J.M. Escuela Supe io de Ingenie os de Se illa A enida de los Descub imien os, s/n 41092. Se ille (SPAIN) e-mail: isido olill[email p o ec ed] ABSTRACT: The pho o ol aic cells (PV) a e commonly used as global adia ion measu emen de ice, e en hough when i has been p o ed ha he e a e signi ican di e ences wi h espec o using py anome e s. The di deposi ed on he su ace o he PV is one o he mos in luen ial ac o s in he measu emen o he sola adia ion. In his wo k we ha e made expe imen al measu emen s wi h ou iden ical cells, wo cleans and wo di ies wi h di e en soil densi y (0.2 g/m2, 0.4 g/m2, 0.8 g/m2, 1.2 g/m2 and 1.5 g/m2) and di e en size pa icles (< 125 μm) compa ing he esul s and ob aining a co ela ion be ween he densi y o he dus and he di e ence be ween he measu ed i adiance o clean and di y cells o each pa icle size. Keywo ds: Sola adia ion, sola cell, py anome e . 1 INTRODUCTION Py anome e s a e nowadays he mos accu a e senso o measu e he sola global adia ion due o hey co e all sola adia ion spec um. Howe e , PV cells, ha only co e a ac ion o he sola adia ion spec um depending on he echnology, a e also used as a measu emen de ice o sola global adia ion. The e a e di e ences be ween bo h kind o de ices, py anome e s and PV cells, and he alues gi en by PV cells a e usually lowe han hose gi en by py anome e s [1]. On he o he hand, PV cells a e cheape han py anome e s and when i is needed o e alua e he pe o mance o a PV plan , he ac ual a ailable global adia ion is mo e p ecisely gi en by a cell (made o he same echnology han he plan ) han by a py anome e , because he incidence angle and spec um losses o he plan a e accoun ed on he cell measu emen s bu hey a e no on he py anome e measu emen s. The di e ence be ween he measu emen s om PV cells and py anome e s is de e mined by mul iple a iables as he cell echnology, he cell empe a u e, he spec al esponse o he cell (cha ac e ized by he humidi y and he cloudiness index) and, ob iously, he di le el o he cell and o he py anome e . A e nine mon hs o measu emen s i has been p o en ha he highe he humidi y and he cloudiness he lowe he di e ences be ween he PV cell and he py anome e a e, while he highe he incidence angle he highe hese di e ences a e. A ele an ac o ha a ec s o he measu emen s om PV cells is he dus le el. In gene al e ms, he di deposi ed on a su ace a ec s, among o he s, o he ansmi ance. In a sola cell, as he p o ec i e su ace ansmi ance is a ec ed (usually glass), he cell esponse is in luenced. This e ec on he asmi ance has been ex ensi ely s udied o se e al ma e ial and di e en wea he condi ions [2,3]. The e ec o he dus on a PV de ice has been also analyzed and i has being de e mined he in luence o he dus on he pe o mance o a PV module. The s udies ha e been based on he wea he condi ions o he si e (dese a eas, humidi y, and wind speed), he o ien a ion and he il o he module o sola cell and he cha ac e iza ion o he dus , especially om he size, he densi y and he geome y o he pa icles. [4,5]. The e a e e en s udies ha ha e aking in o accoun he in luence o he di on PV modules as a unc ion o he cell echnology [6]. As a summa y, in e e y case he ollowing e ec s ha e been obse ed: On one hand he highe he di on he cell he lowe he sho -ci cui in ensi y and he ou powe a e, ela ion ha can be app oxima ed by a leas squa es i . On he o he hand, he open ci cui ol age does no depend on he di [7]. In addi ion he sola cell deg ada ion is mo e signi ican o ine pa icles han o coa se pa icles [4]. The PV cell e iciency dec eases wi h a much highe slope o dus densi y lowe han 1.5g/m2. F om his alue, he pa icles begin o be deposi ed one abo e he o he , and hen hey do no co e mo e e ec i e a ea o he [7]. The sola cell il di ec ly a ec s o he dus accumula ion. So, de ices wi h li le inclina ion show a highe end o he accumula ion o dus . Mo eo e , he ansmi ance dec eases as he il angle is dec easing [3]. The in luence o he cosine ac o is decisi e on he eliabili y o a sola cell esponse. In his sense, o incidence angles highe han 20º, he cell e lec ance inc eases apidly and his esponse is ou o eliable alues [8]. Wi h espec o he ai mass, he s udies show ha his ac o is signi ican o sola ele a ions up o 30º [8]. The Bonne and Saps o d s udy [1] p oposes wo calib a ions cons an o co ec he adia ion da a eco ded by a silicon cell: one o clea sky and he o he o o e cas sky. Co ela ions ha e been de eloped o compensa e he de ia ion on he esponse ha a sola cell expe imen due o empe a u e changes and he sola spec um [9]. The esponse imp o es signi ican ly when i is co ec ed by sola spec um. Anyway, di use adia ion esul s show a highe de ia ion han di ec ones. The a iables ha in luence on he dus quan i y ha i is deposi ed on a su ace is qui e s udied opic. Dus induced deg ada ion o py anome e sensi i i y. All hese conside a ions show he mul i ude o a iables, 28 h Eu opean Pho o ol aic Sola Ene gy Con e ence and Exhibi ion 3567 besides dus , ha in luence on he pe o mance o a PV cell as a sola adia ion measu emen de ice. 2 OBJECTIVE The pu pose o he wo k is o analyze and p o e expe imen ally he in luence o dus in he measu e o he sola adia ion wi h pho o ol aic cells depending on he densi y and size o he dus and in he le el o i adiance. I has been ca ied ou by he expe imen al compa ison be ween clean and di y iden ical cells. 3 HYPOTHESES AND METHODOLOGY This pape answe s his ques ion unde he ollowing assump ions: Two iden ical calib a ed py anome e s ha e been used (PL and PS) and ou iden ical calib a ed monoc is aline silicon PV cells. The cells a e encapsula ed by pai s, wo o wo. One o his pai s (CL1 and CL2) has been kep always clean (cleaned dia y), while he o he pai (CS1 and CS2) has been di ied using di e en soil densi ies (0.4; 0.8; 1.2 and 1.5 g/m2) and di e en pa icle size o clay and sil (be ween 0 μm and 65 μm o clay and be ween 0.65 μm and 150 μm o sil ). In he same way one o he py anome e s has been kep always clean (PL) and he o he has been di ied in di e en le els (PS). E e y de ice has been placed on a ho izon al su ace. The da a ha e been eco ded e e y i e seconds and he mean alue o bo h he clean and he di y cells ha e been de e mined. As a p e ious s ep i was p o ed ha he maximum e o in he adia ion measu es was less han 0.1% o he ou cells and less han 0.05% o he wo py anome e s. 4 THEORETICAL BACKGROUND In Figu e 1 he absolu e di e ence be ween he measu emen s om he clean cells and he di y ones is shown as a unc ion o he mean alue measu es by he clean cells. This i s igu e is o clay pa icles (be ween 0 μm and 65 μm) and o di e en di y densi y alues (0.2, 0.4, 0.8, 1.2 and 1.5 g/m2). I can be obse ed ha he highe he densi y and he i adiance, he highe he absolu e di e ence be ween he clean and he di y cells is. The maximum alue o he di e ence is a ound 20 W/m2 o a densi y o 1.5 g/m2. Figu e 1. Absolu e i adiance di e ence be ween clean and di y cells o i e di e en di densi ies as a unc ion o i adiance. Clay Simila ly, in Figu e 2 he absolu e di e ence be ween he measu emen s om he clean cells and he di y ones is shown as a unc ion o he mean alue measu es by he clean cells, bu o sil pa icles in his case (be ween 65 μm and 125 μm) and o di e en di y densi y alues (0.2, 0.4, 0.8, 1.2 and 1.5 g/m2). Again, he di e ence inc eases wi h he di densi y and also wi h he i adiance. Fo low densi ies, lowe han 0.4 g /m2, Figu e 1 and Figu e 2 a e e y simila bu hey a e no so simila o highe densi ies han 0.4 g /m2 ( o sil he maximum di e ence be ween clean and di y cells is a ound 40 W/m2). In any case he absolu e di e ence depends mainly on he i adiance mo e han on he cell empe a u e, he incidence angle o he sola spec um. Figu e 2. Absolu e i adiance di e ence be ween clean and di y cells o i e di e en di densi ies as a unc ion o i adiance. Figu es 3 and 4 show he same in o ma ion bu in pe cen age e ms. Figu e 3. Pe cen age i adiance di e ence be ween clean and di y cells o i e di e en di densi ies as a unc ion o i adiance. Clay Figu e 4. Pe cen age i adiance di e ence be ween clean and di y cells o i e di e en di densi ies as a unc ion o i adiance. 28 h Eu opean Pho o ol aic Sola Ene gy Con e ence and Exhibi ion 3568 I is no ed ha he e o in he measu emen inc eases as he le el o i adiance inc eases in absolu e e ms bu emains almos cons an in pe cen age e ms o i adiance le els abo e 300 W/m2 and medium-low di le els (<0.4g/m2), especially o clay, while o high le els o con amina ion, he di e ence dec eases as he le el o i adiance inc eases, eaching a maximum a 200 W/m2. The esul s show he in luence o he dus le el in he measu emen o he sola adia ion wi h a PV s a ing ha he e o s, when exp essed in pe cen age, a e p ac ically cons an o each densi y le el depending on he dus pa icle size. This conclusion can be ex apola ed o he p oduc ion o a pho o ol aic plan . 6 CONCLUSIONS The absolu e e o be ween he measu emen s om a clean and a di y cell depends mainly on he i adiance le el and he pa icle size mo e han on he cell empe a u e, he incidence angle o he sola spec um. A di y monoc is aline PV cell makes a bigge absolu e e o when he i adiance and he pa icle size a e highe . The maximum alue o he e o is a ound 40 W/m2 o 1000 W/m2, o a pa icle size o 125 µm and o a di densi y o 1.5 g/m2. In he same condi ions bu o pa icles up o 65 µm, he maximum e o is a ound 20 W/m2. A di y monoc is aline PV cell makes a pe cen age e o ha p ac ically only depends on he di densi y o pa icle sizes up o 65 μm. The same e ec can be obse ed o pa icles up o 125 μm and densi ies up o 0.4 g/m2. Fo highe densi ies han 0.4 g/m2, he pe cen age e o in he sola adia ion measu emen depends also on he i adiance le el. 7 REFERENCES [1] Bonne , M. G. & Saps o d, C. M. 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