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Abstract Organic photovoltaics (OPV) has improved significantly in recent years and power conversion efficiencies are getting close to those of hybrid and inorganic thin film PV technologies. In this work, we demonstrate high performance inverted organic photovoltaic cells from electrospun nanofiber based electron transport layers, which outperform their thin-film counterpart. FTO/ZnOfilm/ZnOnanofibers/PTB7:PC70BM/MoO3/Ag devices were designed with different ZnO nanofiber based electron transporting layers (ETL) varying the nanofiber width and thickness, using a conventional electrospinning technique for the nanofiber ETL fabrication. We demonstrate that 35 nm thick films of electrospun ZnO nanofibers results in an improvement of the short-circuit current density (Jsc) and fill factor (FF) in the cells, leading to power conversion efficiency of up to 7.6%. The improvement is assigned to an improved charge collection efficiency, due to realization of direct and continuous pathway for electron extraction inside the solar cell structure. The results highlight the application of one-dimensional nanofiber based charge extraction layers as a promising route for development of high performance OPV devices in the future.

We investigate rapid thermal processing (RTP) as alternative to the prolonged thermal annealing process used to form tunnel-oxide passivating contacts for silicon solar cells. The thermal treatment is generally followed by hydrogenation to passivate defects at the Si/SiOx interface. Whereas industrial manufacturing generally uses Cz wafers, research is often carried out with FZ wafers. Both types of wafers are prone to the formation of thermal defects in the bulk. To disentangle effects of the interface and the bulk, we assess the lifetime at different steps of the process sequence for both wafer types. We find that the initial bulk lifetime of our p-type FZ material is maintained for RTP up to temperatures of about 450°C, followed by a severe decay and eventually a moderate extent of recovery at temperatures above 800°C. Compared to FZ material, the initial bulk lifetimes in our p-type Cz material are slightly lower, but they are maintained on that level up to about 600°C. Beyond that temperature, the lifetimes also decay, but to a lesser extent than in the FZ material, and there is no curing at higher temperatures. Hydrogenation can partially passivate the bulk defects in FZ material, but the initial state is not recovered. In Cz material, it appears that RTP creates two different types of defects; for those created up to 800°C the initial state can be recovered by hydrogenation whereas those created at higher temperature cannot be passivated by hydrogenation. We also investigate the formation of n-type passivating contacts by RTP, and we fabricate solar cell precursors with a single RTP step and the same hydrogenation for both contact polarities. After sputtering a transparent conducting ITO layer on the full area and an Ag metallization, we achieve solar cells efficiencies up to 20.5%.

100 cm2 molten carbonate fuel cells (MCFC) was used for testing the fuel and oxidant composition influence on MCFC performance as a temperature function. The fuel composition varies over the cell surface, and throughout the stack, because inlet fuel is rich in H2 (and CO2), while the exhaust stream is depleted. The cell performance is usually not uniform over the entire surface. It is thus necessary to examine the cell performance as a function of fuel utilization. In a laboratory-sized cell, this is usually difficult to do. An alternative approach is to investigate performance as a fuel composition function. Based on the obtained experimental data for different compositions, the MCFC mathematical model was calibrated. The new approach for modeling the voltage was used. Electrochemical, thermal, electrical and flow parameters are collected in the 0-D mathematical model. A validation process for various experimental data was made and adequate results are shown.

Abstract Ongoing concerns about electrical grid stability and existing economic interests create unattractive conditions for grid-injection of renewable energy produced in building integrated photovoltaic systems (BIPV). As a result, BIPV often fails to use the full potential of the building envelope and site. An effective approach to increase BIPV size is maximizing self-consumption of the generated renewable energy through building demand flexibility and energy storage. Unfortunately, in cooling dominated office buildings with BIPV, shading by passing clouds can increase grid demand as the building maintains its energy demand in a moment when BIPV output is reduced. This paper analyses the effectiveness of turning off the heating ventilation and air conditioning system (HVAC) to offset temporary reductions in BIPV output due to passing clouds. Analysis of cloud duration in different climates shows that, on average, clouds last 20 min and occur predominately in the afternoon. When HVAC is off due to cloud shading, the building thermal mass limits indoor temperature increase to 2 °C in the first 50 min. Simulation based analysis of HVAC control-based energy flexibility shows that it is possible to maintain acceptable thermal comfort while reducing HVAC grid energy demand by 60% during the cooling season.

A model to obtain the optimal allocation and timing of renewable distributed generation under uncertainty is proposed as part of distribution expansion planning. The problem is formulated using a stochastic two-stage multiperiod mixed-integer linear programming (MILP) model, where investment decisions are done in the first stage and scenario-dependent operation variables are solved in the second stage. The model aims to minimize renewable distributed generation (photovoltaic and wind) investment costs, substation expansion investment cost, operation and maintenance costs, energy losses cost, and the cost of the power purchased from the transmission system. Active and reactive power flow equations are linearized and constraints include voltage limits, substation and feeders capacities, renewable generation limits, and investment constraints. The model is tested on a 34-bus system and conclusions are duly drawn.

Abstract This paper presents theoretical investigations into a hybrid ejector and CO2 vapour compression (VC) system for road transport cooling. The purpose is to utilise the waste heat from exhaust gas and the VC sub-system to drive the ejector system, whose cooling effect will be employed to subcool the VC sub-system. Exploitation of the energy consumption ratio between ejector sub-system and CO2 VC sub-system indicated that the more energy obtained from exhausted gas, the better system performance could be achieved for CO2 VC sub-system, and hence higher cooling capacity of the VC sub-system at the same compression power. Thermodynamic simulations of two sub-systems and the hybrid system were presented. The results indicated that, at boiler temperature of 120 °C, evaporator temperature of 10 °C, a COP of 0.584 was achieved for hybrid system, with 22% improvement over a single ejector cycle. Preliminary experimental studies were carried out on a single ejector cycle, with boiler temperatures between 115 °C and 130 °C, and evaporator temperatures between 5 °C and 10 °C. The effects of various operation conditions on the overall ejector operation were coherently analysed. The COP of the ejector sub-system from experimental results was approximately 85% compared with simulation results, which showed a good agreement between theoretical analysis and experimental results.

Abstract Solar energy is key factor in the demand for clean energy development and management. In particular, global horizontal irradiance (GHI) and direct normal irradiance (DNI) are the foremost important solar resource components that need to be well characterized in order to seek an efficient operation of photovoltaic and concentrated solar power plants, respectively. The objective of the present work is to assess the quality of short-term (24 h) forecasts from a global Numerical Weather Prediction (NWP) model regarding the GHI and DNI components for solar energy applications. Forecast accuracy for the Integrated Forecasting System (IFS), the global model of the European Centre for Medium-Range Weather Forecasts (ECMWF), was verified through the comparison of the predicted hourly values with the corresponding ground-based measurements in southern Portugal. In this study, results from one year of IFS data are analysed, yielding a general good agreement between model and four ground-based measuring stations. High correlations occur particularly for GHI whilst DNI simulations are predominantly hindered by cloud and aerosol representation (i.e. the radiative effects of clouds tend to be underestimated by the model and the radiative effects of the aerosols are overestimated by the model under very clear atmospheric conditions), being closely linked to the parameterization of absorption and scattering phenomena as function of cloud and aerosol type and dimension. Relative differences of annual availabilities for GHI are found between ∼0.16% to ∼2.12% whilst for DNI values ranging from ∼7% to ∼12% are found. The respective correlations coefficients are around 0.95 for GHI and between 0.65 and 0.77 for DNI. Regional irradiation maps of GHI and DNI are presented, showing that NWP predictions are an important tool for the operation of electricity generation systems based on solar energy.