On the methodology of energy yield assessment for one-Sun tandem solar
Haohui Liu a ,c ,?,Armin G.Aberle a ,c ,Tonio Buonassisi b ,d ,Ian Marius Peters b
Solar Energy Research Institute of Singapore (SERIS),National University of Singapore,7Engineering Drive 1,117574,Singapore b
Massachusetts Institute of Technology,77Massachusetts Avenue,Cambridge,MA 02139,USA c
NUS Graduate School for Integrative Sciences &Engineering (NGS),National University of Singapore,28Medical Drive,117456,Singapore d
Singapore-MIT Alliance for Research and Technology (SMART),1CREATE Way,138602,Singapore
a r t i c l e i n f o Article history:
Received 26February 2016
Received in revised form 6June 2016Accepted 10June 2016
Energy yield calculation Spectrum
Si based tandem solar cells
a b s t r a c t
In this paper we compare different energy yield calculation methods for non-concentrating (i.e.,1-Sun)tandem solar cells,which are believed to be a viable next-generation high-ef?ciency photovoltaic (PV)concept.The yield calculation methods use illumination inputs with different levels of detail and accu-racy.Through this exercise,we show how subtleties in the temporal resolution and accuracy of the illu-mination input affect the calculated energy yield in the theoretical analysis of the expected outdoor performance of 1-Sun tandem solar cells.The algorithm which we use to compute the energy yield is computationally ef?cient and is based on the average photon energy of a given optical spectrum.This approach involves device simulation,which is particularly relevant for solar cells and modules at the research and development stages.Energy yield calculations using this approach are performed for differ-ent time scales and are compared to results from a reference calculation.For short-term yield calcula-tions,a detailed input of illumination conditions with high temporal resolution is necessary for obtaining accurate results.For long-term yield calculations,it is less important to capture rapid ?uctua-tions.It is found that using simulated spectra to evaluate spectral effects,as is routinely done for concen-trating PV devices,is not accurate enough for 1-Sun tandem solar cells,as it can underestimate the losses in the performance ratio by as much as 60%.Our analysis also indicates that the availability of detailed and realistic illumination conditions is important for the design of 1-Sun tandem solar cells.
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In solar cell design and ratings,the conversion ef?ciency under standard testing conditions (STC)has always been the main ?gure of merit.However,realistic outdoor operating conditions may deviate to a substantial degree from standard testing conditions.These deviations concern the irradiance level (i.e.,light intensity),spectral composition,device temperature and other effects.These deviations can have a pronounced impact on the power generation of solar cells,especially tandem solar cells which are well known to be more sensitive to spectral variations due to current mismatch losses (Faine et al.,1991;Philipps et al.,2010).In addition,as the top cell ?lters the incoming irradiance,the bottom cell will receive less power than a single-junction 1-Sun solar cell.As a result,low irradiance losses may become more pronounced when tandem
solar cells are used in non-concentrating applications.As solar cells are usually designed for optimum performance under STC,power generation under deviating conditions can be reduced signi?-cantly.For large-scale PV applications,the most important mea-sure is the energy yield,which in this paper refers to the total electricity generated in a certain time period (see Appendix A ),in a given time period (say 12months),for which the STC cell ef?-ciency is only a ?rst approximation.A somewhat equivalent mea-sure of actual outdoor performance is the performance ratio (PR),which is the ratio between the actual energy yield of a PV system and the expected energy yield of the PV system based on the STC ef?ciency of the solar cell (see IEC 61724,1998and Appendix A ).When developing a novel tandem solar cell,it is important to determine its realistic energy yield and potential PR as early as possible.Currently,tandem solar cells are only used in space or concentrator PV (CPV)applications.However,with the advent of c-Si based tandem solar cells,particularly III–V or perovskite on Si tandem cells (Bailie et al.,2015;Werner et al.,2015;Essig et al.,2015;Derendorf et al.,2013;Taguchi et al.,2003),tandem
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?Corresponding author at:Solar Energy Research Institute of Singapore (SERIS),National University of Singapore,7Engineering Drive 1,117574,Singapore.
E-mail address:liu.haohui@http://m.wendangku.net/doc/46fe6f12ba0d4a7302763af3.html (H.Liu).