COMPUTER PROGRAM FOR CLIMATOLOGICAL PARAMETERS CALCULATION AND RADIATION SIMULATION

Transcription

1 COMPUTER PROGRAM FOR CLIMATOLOGICAL PARAMETERS CALCULATION AND RADIATION SIMULATION L. COSTE E. EFTIMIE Abstrct: The pper presents softwre developed for the determintion of the bsic input dt used to design renewble solr energy system. The computer progrm clcultes the ngles tht describe the pprent movement of the Sun in the sky. It llows the user n interctive selection of both the site nd the period of time desired, s well s the clcultion of vrious elements, such s: solr ngles, ir mss, Linke turbidity fctor, nd solr rdition received on horizontl or tilted surfce. The computer progrm lso permits grphicl disply of the vrition in solr elevtion nd zimuth ngles during equinoxes nd solstices, s well s of the sunchrt digrms. Key words: Linke turbidity fctor, ir mss, opticl depth, direct rdition.. Introduction In good design of renewble energy systems, the objectives tht must be reched re the minimistion of the overll cost nd the mximistion of the energy performnce of the system. In order to clculte the performnce of n existing system or one tht is being designed, pproprite nd ccurte wether nd climtologicl dt must be collected nd nlysed for the specific geogrphic re. This tsk requires the hndling nd processing of significnt volume of dt. In this respect, both n nlysis of the influence of the mesurement intervl of solr rdition nd wind speed, s well s good fit for the dt mesured in typicl hybrid energy system re of prmount importnce, not only with regrd to technicl relibility, but lso in the minimistion of the system s totl costs (i.e. power consumption). Nture offers vriety of freely vilble options for producing energy. It is minly question of how to convert sun rdition, wind, biomss or wter into electricity, het or power s efficiently, sustinbly nd cost-effectively s possible. On verge, the energy of the sunshine tht reches the Erth is bout one kilowtt per squre meter worldwide. According to the Reserch Assocition for Solr Power, the power is gushing from renewble energy sources t rte of times more energy thn is needed in the world tody. In one dy, the sun rdition which reches the Erth produces enough energy to stisfy the world s current power requirements for eight yers. Even though only percentge of tht potentil is techniclly ccessible, this is still enough to provide just under six times more power Dept. of Product Design nd Robotics, Trnsilvni University of Brşov.

2 34 Bulletin of the Trnsilvni University of Brşov Vol. 2 (5) Series I thn the world currently requires. To meet the necessities nd requirements of the renewble energy systems designer, numerous softwre progrms hve been developed, with prticulr or lrge pplicbility. The softwre developed by the uthors ws progrmmed in Visul FoxPro to obtin the bsic input dt used by the solr energy systems designers: solr ngles, climtologicl prmeters, simultion of the solr rdition on horizontl or tilted surfce nd the sun chrt. The computer progrm provides friendly interfce, from which the user cn choose the dt to be displyed, llows of the tbulr nd grphicl disply of the clculted climtologicl prmeters (the opticl ir mss, the opticl Ryleigh depth, Linke turbidity fctor, nd the simulted globl, diffuse nd direct rditions, on both horizontl nd tilted surfce). Further on, the direct link between the climtologicl prmeters nd the quntity of solr rdition received by horizontl or tilted surfce will be discussed. 2. Computer Progrm s Objectives The computer progrm designed tkes into considertion the following objectives [3]: the use of n dvnced softwre tht permits the processing of lrge volume of dt; the progrm must disply high degree of generlity nd pplicbility; the progrm s structure must llow of further development; the modelling of the climtologicl prmeters for more sites in Romni using defult list, but lso for ny other loction, for which the ltitude or geogrphicl coordintes must be typed in; the computer progrm should llow of both numericl (tbulr dt presenttion) nd grphicl disply; the progrm should clculte the following elements: solr ngles, Linke turbidity fctor, solr rdition received on horizontl or tilted surfce, ir mss, opticl depth nd sunchrt for selected site. The computer progrm uses originl procedures developed for dtbse computer modelling. The progrm is run nd the simultion performed for Brşov re, but due to its flexible structure, it cn lso be used for ny desired site. 3. Computer Progrm s Theoreticl Bsis for Climtologicl Prmeters The correct determintion of solr energy tht specific site cn receive in cler sky condition is importnt for studies nd reserch to find the chrcteristic climtologicl prmeters of the re. There is direct dependence between the solr rdition tht reches the Erth s surfce nd the climtologicl prmeters, minly through Linke turbidity fctor, the reltive opticl ir mss nd Ryleigh opticl depth. 3.. Linke Turbidity Fctor (T L ) Solr rdition pssing through the tmosphere is scttered nd bsorbed by molecules nd prticles. It lso intercts with lrger prticles such s wter droplets nd dust when these re present in the ir []. Informtion bout the quntity nd the properties of these prticles is needed to ccurtely estimte the rdition in cler sky conditions. Linke turbidity fctor T L helps to quntify this informtion. The turbidity fctor represents the number of cler dry tmospheres necessry to produce the observed ttenution. Severl tmospheric turbidity coefficients hve been introduced during the pst decdes in order to quntify the influence of tmospheric erosol content on direct rdition received t the Erth s surfce.

3 Coste, L., et l.: Computer Progrm for Climtologicl Prmeters Clcultion 35 Some of these re: Linke turbidity fctor, T L (Linke, 922), Ångström turbidity prmeters, α nd β (Ångström, 929), Shϋepp coefficient, B (Shϋepp, 949), Unsworth-Monteith turbidity fctor, T U (Unsworth nd Monteith, 972) nd horizontl visibility. Of ll them, Linke turbidity fctor is most commonly used. The computer progrm designed proposes different vlues of Linke turbidity fctor clculted for Brşov urbn re (for n ir mss equl to 2). Linke turbidity is very convenient pproximtion to model the tmospheric bsorption nd scttering of solr rdition under cler sky conditions. This fctor denotes the trnsprency of the cloudless tmosphere: TL = δ m r E0 ε ln, () B where: δ r - opticl thickness of wter- nd erosol-free tmosphere (cler nd dry tmosphere); m - ir mss; B - norml incidence direct irrdince nd E 0 ε - solr constnt (367 W/m 2 ) corrected by the eccentricity fctor: 2πdy _ no ε = cos (2) A typicl vlue of Linke turbidity for Europe is 3 []. However, this vlue exhibits strong fluctutions in spce nd time, depending on the geogrphicl nd climtic conditions. Linke turbidity fctor represents key input to severl models ssessing the rdition modelling under cler skies. The computer progrm clcultes ll the climtolgicl prmeters under cler sky conditions. Considering the bove-mentioned fcts, it is very importnt to determine Linke turbidity fctor with respect to the rel conditions of prticulr site (Figure ). It hs been determined using two models: A. The first model is bsed on Ksten nd Young formul for the opticl ir mss (989) nd the improved Ksten formul for Ryleigh opticl depth (996) [4]. B. The second model is bsed on Remund- Pge corrections (2002) for the reltive opticl ir mss nd Ryleigh opticl depth [5]. The expressions of bem nd diffuse rditions re dependnt on turbidity fctor vrition. Thus, considering the studies conducted with view to determining Linke turbidity for Brşov re, the present simultions will use the dily mens vrition of the turbidity fctor corresponding to the vrition presented in Figure Reltive Opticl Air Mss (m ) nd Ryleigh Opticl Depth (δ r ) Fig.. Linke turbidity fctor In order to clculte the turbidity fctor vlues (T L ) with eqution (), the vlues of ir mss (m ) nd Ryleigh opticl thickness in clen dry tmosphere (δ r ) must be known. The reltive opticl ir mss is the length of the opticl pthwy long which solr rdition trvels through the Erth s tmosphere.

4 36 Bulletin of the Trnsilvni University of Brşov Vol. 2 (5) Series I Fig. 2. Dily mens of Linke turbidity fctor for Brşov re The computer progrm does the clcultion of reltive opticl ir mss nd Ryleigh depth using two modelling reltions, respectively. The first one proposes the clssicl formul - reltions (3) nd (4) - for reltive ir mss (m ) nd opticl depth. The second modelling reltions suggest, for reltive ir mss, the use of two reltions depending on the solr elevtion ngle; for solr elevtion ngles α > 25 o, ir mss is clculted with reltion (3), while for solr elevtion ngles α < 25 o, reltion (5) is used. Ryleigh opticl depth (δ r ) is clculted with reltion (6): m =, (3) sin α δ r =. (4) m These second modelling reltions use the equtions developed by F. Ksten nd A. Young [4]: sin α sin α m =, (5) 3 2 sin α sin α sin α δ r =. (6) m 0.202m m m Solr Rditions on Horizontl or Tilted Surfce In the brnch literture there re numerous models tht simulte solr rdition on horizontl or tilted surfce, long with its components: bem solr rdition (or direct solr rdition) (B), diffuse solr rdition (D) nd globl solr rdition (G), under cler sky or norml conditions. The quntity of solr rdition received on horizontl or tilted surfce is conditioned by vrious fctors, such s: seson (dy of the yer, declintion, ltitude), hour (hour ngle), time of dy, climtologicl conditions nd prmeters (clouds, rin, the tmosphere s turbidity, reltive opticl ir mss, opticl

5 Coste, L., et l.: Computer Progrm for Climtologicl Prmeters Clcultion 37 thickness), geogrphicl coordintes, relief configurtion, nd degree of pollution. Thus, model tht simultes solr rdition nd its components must include ll these fctors nd the interdependence estblished mong them. In order to simulte globl, direct (bem), nd diffuse rditions on horizontl surfce, the computer progrm uses the formuls proposed by Bson []: B = E 0 ε sin α exp( T L m δ r ), (7) D ( 49.04T L 42.32)[ exp(0.t α)], (8) = L where T L, m nd δ r formuls hve been presented in subchpters 3. nd 3.2 bove. Globl solr rdition on horizontl surfce is clculted s the sum of its components (diffuse rdition nd bem rdition). In order to simulte globl, direct (bem), nd diffuse rditions on tilted surfce, the following equtions re used [2]: cos θ Bβ = B, (9) cos θ z where θ nd θ z represent the incidence ngle of the solr bem on tilted nd horizontl surfce, respectively, nd re expressed by the following reltions: cos θ = cos( ϕ β) cos δcos ω + + sin( ϕ β)sin δ, (0) cos θ z = cos ϕcos δcos ω+ () + sin ϕsin δ, where φ - site ltitude; δ - declintion ngle; ω - hour ngle. The diffuse component on tilted surfce is given by reltion: D β = D ( + cos β), (2) 2 where β - inclintion ngle of the surfce. Reltions (9) nd (2) re used to clculte solr rdition when plne-surfce, non-trcking solr systems re employed. These re south oriented nd set t n optimum ngle towrds horizon (β), for the given site nd the working period during yer. 4. Computer Progrm s Interfce On the user-friendly progrm interfce, the dilog between progrm nd user is crried out through input dt fields, res 2, 3, 4, 5, nd 6 (Figure 3). The defult list, re, contins predefined cities in Romni for which the progrm runs implicitly. By clicking one of the buttons 7 to 5, the corresponding required dt will be displyed in re 6 (Figure 4). The progrm s interfce enbles the user to choose the type of dt needed (e.g. solr ngles, tilted ngle, solr rdition or climtologicl prmeters) s well s to select the mnner in which the output dt will be displyed (either in tbulr or grphicl fshion). If the loction required by the user is in the defult list, the progrm clcultes the ltitude nd longitude tht cn be seen in res 3 nd 4; otherwise, the ltitude of the site cn be typed in the Enter ltitude field (re 5). The user cn lso choose the time intervl (re 6) for which the progrm will clculte the selected dt. By clicking button 7, set of bsic input dt for designing solr energy system will be shown in tbulr form in the output dt disply re, see Figure 4.

6 38 Bulletin of the Trnsilvni University of Brşov Vol. 2 (5) Series I Fig. 3. User-computer progrm interfce 5 Fig. 4. Bsic dt - tbulr disply By clicking button 9, the solr rdition on horizontl surfce cn be shown in either tbulr or grphicl form, see Figure 5. The verge per dy vlues of solr rdition on horizontl surfce hve been clculted (the uthors hve opted for n verge-per-dy pproch, s more suggestive nd representtive grphicl disply cn be obtined in this fshion, see Figure 5). By clicking button 0, the solr rdition on tilted surfce cn be shown in tbulr or grphicl disply (Figure 6). It should be mentioned tht ll dt displyed cn be exported nd sved in file for lter use (e.g. comprtive nlysis or different grphs displying).

7 Coste, L., et l.: Computer Progrm for Climtologicl Prmeters Clcultion 39 Fig. 5. Solr rdition on horizontl surfce - grphicl disply surfce is smller s compred to tht gthered by horizontl surfce, but through correct orienttion of solr system, the direct solr rdition received cn be mximised. By selecting button, Linke turbidity fctor cn be shown in the output dt re; for tbulr disply, see Figure ; for grphicl disply, see Figure 2. By selecting button 2, both opticl ir mss nd Ryleigh opticl depth re displyed in the output dt re, see Figure 8. ) Fig. 6. Solr rdition on tilted surfce - grphicl disply In order to view the difference between the solr rdition on horizontl nd tilted surfce, grph hs been plotted for direct rdition received in both cses, see Figure 7 (dt exported from two files hs been used). b) Fig. 8. Opticl ir mss nd Ryleigh opticl depth: ) tbulr disply; b) grphicl disply 5. Conclusions Fig. 7. Direct solr rdition It cn be noticed tht, during the summer, the direct solr rdition received by tilted The progrm presented in this pper is very importnt tool for the determintion of mjor climtologicl prmeters used in the design of renewble energy systems. Due to the comprtive nlysis of solr rdition vilble on both horizontl nd

8 40 Bulletin of the Trnsilvni University of Brşov Vol. 2 (5) Series I tilted surfces, the progrm mkes it possible to determine the optimum inclintion ngle of the solr energy system (with respect to horizontl surfce). Thus, ccording to the necessities of solr rdition during yer, the inclintion ngle cn be determined. It is ssumed tht by using tilted surfces the vilble rdition on them cn be either mximised or minimised (for instnce, during the summer the necessities of solr rdition cn decrese). The uthors intend to conduct further reserch in order to enhnce this softwre s verstility, by using the current models, such s: Adnot, Hurwitz nd Ksten formuls for globl rdition, Bugler formul for diffuse rdition nd Hottel formul for direct rdition. Another model we hve in mind is the Europen Solr Rdition Atls (ESRA). We lso intend to develop more ccurte rdition models for Brşov urbn re. To chieve this, it is essentil to tke into considertion the geogrphicl nd climtologicl prmeters, s well s ny other conditions specific to n urbn re (especilly ir pollution). Acknowledgements This pper is supported by the Sectorl Opertionl Progrmme Humn Resources Development (SOP HRD), finnced by the Europen Socil Fund nd Romnin Government, under the contrct number POSDRU/6/.5/S/6". References. Bson, F.: Diffuse Solr Irrdince nd Atmospheric Turbidity. In: EuroSun 2004 Conference Proceeding, Freiburg, Germny, June Avilble t: Accessed: Bostn, I.: Conversion Systems of Renewble Energy. Chişinău. Technic- Info Publishing, Coste, L., Butuc, B.: Progrmme for the Sun-Erth Angles Determintion. In: Annls of the Orde University, 2009, p Ksten, F., Young, A.T.: Revised Opticl Air Mss Tbles nd Approximtion Formul. In: Applied Optics 28 (989) No. 22, p Remund, J., Wld, L., Lefèvre, M., Rnchin, T.: Worldwide Linke Turbidity Informtion. In: Proceedings of ISES Solr World Congress, 6-9 June 2003, Göteborg, Sweden. Avilble t: Accessed: