Recovery of LeTID by low intensity illumination: Reaction kinetics, completeness and threshold temperature

Axel Herguth, Christian Derricks, Philipp Keller, Barbara Terheiden
2017 Energy Procedia  
District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand
more » ... door temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract Light (and elevated Temperature) Induced Degradation (LeTID) can seriously limit the efficiency of mc-Si PERC solar cells if no countermeasures are taken. Within this paper, the subsequent regeneration reaction, also induced by light at elevated temperatures, is investigated systematically in the low intensity regime (up to 4 suns) as a possible countermeasure. As might be expectable, degradation and regeneration reaction are found to speed up with increasing treatment temperature; however, completeness of regeneration is also found to be noticeably reduced at high temperatures (up to 380°C). This enforces the introduction of reverse reactions and gives rise to a 3-state reaction model for LeTID explaining the observed threshold temperature above which LeTID elimination does not work anymore. Furthermore, it is found that a treatment at high temperatures not only fails to eliminate LeTID, but also slows down the regeneration in a later low temperature treatment. Abstract Light (and elevated Temperature) Induced Degradation (LeTID) can seriously limit the efficiency of mc-Si PERC solar cells if no countermeasures are taken. Within this paper, the subsequent regeneration reaction, also induced by light at elevated temperatures, is investigated systematically in the low intensity regime (up to 4 suns) as a possible countermeasure. As might be expectable, degradation and regeneration reaction are found to speed up with increasing treatment temperature; however, completeness of regeneration is also found to be noticeably reduced at high temperatures (up to 380°C). This enforces the introduction of reverse reactions and gives rise to a 3-state reaction model for LeTID explaining the observed threshold temperature above which LeTID elimination does not work anymore. Furthermore, it is found that a treatment at high temperatures not only fails to eliminate LeTID, but also slows down the regeneration in a later low temperature treatment.
doi:10.1016/j.egypro.2017.09.090 fatcat:rekxezdg7rhd5mc4whh74j42qq