For floating PV (FPV), the operating temperature of the PV modules has been a major source of uncertainty. As the operating temperature of PV modules affects their efficiency, knowledge of this parameter is critical in order to perform accurate energy yield assessment (EYA). This uncertainty is reflected in the scientific literature but has also hampered the bankability and realization of commercial FPV projects. Our work proposes a model that computes both the efficiency of heat loss to the environment for a given FPV technology and the operational cell temperature, needed to compute the module efficiency. The suggested model is applicable to different FPV technologies. We show that PV modules that are not in direct thermal contact with water have similar heat loss behavior as land-based PV. We thereafter investigate a specific technology in which the modules are mounted on a membrane resting directly on the water body. The model is validated against actual production and weather data from deployed FPV systems. Our results show that the water temperature impacts both FPV technologies, however to a smaller degree for the air-cooled system, where the wind is of greater influence. When in direct thermal contact with water, the water body provides superior cooling, and the resulting U-value of about 86.5 W/m 2 K is significantly larger than typical values reported for land-based modules.
Num erica l Heat Tr an sfer , Par t A, 35:155 ± 172, 1999 Cop yrigh t Q 1999 Taylor & Fr an cis 1040 ± 7782 r r r r r Ê A th ree-dimension al math ematical model is presen ted that is tailor made for calculation of the non stationary temperatu re field in rectan gu lar stocks of steel heated in a reh eating furn ace. Discretization of th e gov ernin g equation is done by means of a finite element m ethod wh ere the time integration is perform ed by an expon ential transform ation of the heat equation combined with an altern ating-direction-implicit method. The bou ndary conditions are assu med time dependent. The temperature uniform ity of the heated stock is of great importan ce for th e su bsequ ent rollin g. Nonun iform ity of the stock disch arge temperature m ay cause un acceptable thickn ess v ariation s du ring the rollin g and thu s influences the qu ality of the final produ ct. The proposed model is v alidated with respect to an analytical solu tion, to a nu merical solu tion, as well as to fu ll-scale experim ental data. It is concluded that th e three-dim ension al finite element code is capable of takin g into account n onu n iform heating of the stocks caused by radiation sh adowing of the skid pipes, the contact between the wearer bars an d the stocks, baffles in the fu rnace, an d end effects in the stocks. INTRODUCTIONStrict de mands are re quire d on the te mpe rature uniformity of ste e ls that are discharge d from re he ating furnaces for the subseque nt rolling. If the nonuniformity in the tem pe rature fie ld of the stock is too large , it m ay cause unacce ptable thickne ss variations during the rolling. Re ducing the tem pe rature gradie nts in the stocks will re sult in better quality of the final products and incre ase the ste e l production.As the stocks are transfe rred through various zone s in the furnace , the y are typically he ate d from above and from be low by side , front, and roof burne rs. Nonuniform he ating of the stocks m ay be caused by baffle s in the furnace , the locations of the burne rs, as we ll as air le akage into the furnace . In top and bottom fire d furnace s the stocks are resting on ridge s conne cte d to a water-coole d skid system. Physical contact be twe e n the ridge s and the stocks, as we ll as radiation Receive d 24 May 1998; accepte d 27 July 1998. The authors would like to acknowle dge E dvin Nitte be rg at the Institute for Ene rgy Te chnology, È and Ke nt O ste rgard and Tor Rundstrom at SSA B O xelosund AB, who have all contribute d to the Ê È È proje ct. Addre ss corre sponde nce to Dag Lindholm , Institute for Ene rgy Te chnology, P.O . Box 40, 2007 Kje lle r, Norway. 155 Downloaded by [The University of Manchester Library] at 11:35 26 November 2014 D. LINDHOLM AND B. LEDEN 156 NOMENCLATURE A me an gas absorptivity for radiation e e missivity of the CO flue gas g m g, C O 2 2 s . s . from stock and walls, Eq. 13 compone nt, E q. 10 a A gas absorptivity for radiation from e e missivity of the H O flue gas g s g, H 2 O 2 s . s . the stock, E q. 9 c...
Polysilicon production costs contribute approximately to 25-33% of the overall cost of the solar panels and a similar fraction of the total energy invested in their fabrication. Understanding the energy losses and the behaviour of process temperature is an essential requirement as one moves forward to design and build large scale polysilicon manufacturing plants. In this paper we present thermal models for two processes for poly production, viz., the Siemens process using trichlorosilane (TCS) as precursor and the fluid bed process using silane (monosilane, MS). We validate the models with some experimental measurements on prototype laboratory reactors relating the temperature profiles to product quality. A model sensitivity analysis is also performed, and the effects of some key parameters such as reactor wall emissivity, gas distributor temperature, etc., on temperature distribution and product quality are examined. The information presented in this paper is useful for further understanding of the strengths and weaknesses of both deposition technologies, and will help in optimal temperature profiling of these systems aiming at lowering production costs without compromising the solar cell quality.
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