Experimental analysis of the energy performance of a passive attached sunspace

During the studies carried out at the Institute for Building Technology of the National Research Council (ICITE), a method has been developed to analyse the energy performance of passive solar components in the building industry by using test cells that simulate a conventional dwelling environment. The paper describes the tested components, the experimental analysis of energy performance that has been carried out, the complementary analysis performed, and the obtained results.     

Environmental and economic cost analysis of housing in temperate climate using an innovative lightweight partitioning system

This paper presents an economic and environmental cost analysis of a representative Portuguese housing dwelling unit using an innovative lightweight adjustable membrane partitioning system, developed within a research project. The environmental and economic costs of this system, both on the construction and occupancy phases, were compared with the Portuguese conventional dividing wall solution, in hollow brick, simulated on the same reference dwelling, using the same layout and remaining constructive elements. The occupancy phase costs were evaluated by computer simulation, which allowed determining how the occupancy schedule of daytime and night time occupied areas may influence the cooling and heating needs for different solar orientations.     

发射极掺杂工艺对产业化IBC太阳电池性能的影响

主要对n型IBC太阳电池结构的发射极硼掺杂工艺进行优化设计,并通过ENDA2模拟软件对实验结果进行验证分析,通过复合损失分析,研究不同发射极硼扩工艺对产业化IBC太阳电池电性能的影响.实验结果表明,采用较高推进温度的硼扩散工艺,获得发射极方阻98Ω/sq,该发射极具有最低的表面浓度1.68×1019 cm-3和最深结深...     

Numerical simulation of underground Seasonal Solar Thermal Energy Storage (SSTES) for a single family dwelling using TRNSYS

A system for capturing and storing solar energy during the summer for use during the following winter has been simulated. Specifically, flat plate solar thermal collectors attached to the roof of a single family dwelling were used to collect solar thermal energy year round. The thermal energy was then stored in an underground fabricated Seasonal Solar Thermal Energy Storage (SSTES) bed. The SSTES bed allowed for the collected energy to supplement or replace fossil fuel supplied space heat in typical single family homes in Richmond, Virginia, USA. TRNSYS was used to model and simulate the winter thermal load of a typical Richmond home. The simulated heating load was found to be comparable to reported loads for various home designs. TRNSYS was then used to simulate the energy gain from solar thermal collectors and stored in an underground, insulated, vapor proof SSTES bed filled with sand. Combining the simulation of the winter heat demand of typical homes and the SSTES system showed reductions in fossil fuel supplied space heating in excess of 64%. The optimization of the SSTES scheme showed that a 15 m³ bed volume, 90% of the south facing roof, and a flow rate of 11.356 lpm through the solar collectors were optimal parameters. The overall efficiency of the system ranged from 50% to 70% when compared to the total useful energy gain of the solar collectors. The overall efficiency was between 6.1% and 7.6% when compared to the total amount of solar radiation incident upon the solar collectors.     

A method of simulation of solar processes and its application

TRNSYS, a program for simulating the dynamic thermal behavior of transient systems, is a general program for solving sets of differential and algebraic equations which describe solar energy systems. It is based on a modular approach which enables the user to readily simulate a wide variety of systems. The program consists of component models (for collectors, controls, storage tanks, heat exchangers, furnaces, building loads, integrators, recorders, etc.) and an executive routine.The designer selects both his components and the design parameters describing the components and specifies, in a simple fashion, the way in which the components are interconnected. The whole process is analogous to specifying an experimental system. The designer also selects the information he wants from the simulation, again in a manner analogous to a physical experiment, and includes the appropriate instrument components in his simulation.The use of the program is illustrated by a comparison of methods of operating a solar heating system.     

Prediction of global solar irradiance based on time series analysis: Application to solar thermal power plants energy production planning

Due to strong increase of solar power generation, the predictions of incoming solar energy are acquiring more importance. Photovoltaic and solar thermal are the main sources of electricity generation from solar energy. In the case of solar thermal energy plants with storage energy system, its management and operation need reliable predictions of solar irradiance with the same temporal resolution as the temporal capacity of the back-up system. These plants can work like a conventional power plant and compete in the energy stock market avoiding intermittence in electricity production.This work presents a comparisons of statistical models based on time series applied to predict half daily values of global solar irradiance with a temporal horizon of 3 days. Half daily values consist of accumulated hourly global solar irradiance from solar raise to solar noon and from noon until dawn for each day. The dataset of ground solar radiation used belongs to stations of Spanish National Weather Service (AEMet). The models tested are autoregressive, neural networks and fuzzy logic models. Due to the fact that half daily solar irradiance time series is non-stationary, it has been necessary to transform it to two new stationary variables (clearness index and lost component) which are used as input of the predictive models. Improvement in terms of RMSD of the models essayed is compared against the model based on persistence. The validation process shows that all models essayed improve persistence. The best approach to forecast half daily values of solar irradiance is neural network models with lost component as input, except Lerida station where models based on clearness index have less uncertainty because this magnitude has a linear behaviour and it is easier to simulate by models.     

Improvement in long-term stability of dye-sensitized solar cell for outdoor use

To improve the intrinsic stability of the component of dye-sensitized solar cells (DSCs), we have fabricated the unit cell using solvent-free ionic liquid electrolyte. The degradation in the continuous 1 sun light soaking test at 60 °C over 15,000 h was effectively suppressed, compared with the cell using γ-butyrolactone electrolyte. The lifetime for outdoor use was estimated over 15 years from acceleration factor based on the outdoor exposure test. To confirm the stability of the DSC under practical outdoor use, we fabricated the solar light using the DSC modules, rechargeable batteries and bright light emitting diode (LED). The solar lights have been emitting a bright white light at night using the electricity from batteries charged by the DSC modules during the daytime in any weather condition for a half year.     

A linear model for passive solar evaluation

A simple algebraic model for the evaluation of the average performance of passive solar dwelling units is presented. The model is based on a first order representation for the mass effect of walls and thermal energy balances for a dwelling unit, during the day and the night. The model requires as climatological input the mean temperature during the day and the night and the daily solar irradiation for each month. The model is capable of predicting the performance of both direct gain and storage wall systems and can be used to evaluate the effect of design parameter such as mass, internal or external insulation, temperature difference between day and night.     

UV solar radiation on a tilted and horizontal plane: Analysis and comparison of 4 years of measurements

In the global wavelength range (300–3000 nm), it is known that a plane with a slope equal to the latitude of the location, receives more annual energy than the horizontal plane, mainly due to the increase in direct irradiation on the interest plane. The UV (280–400 nm) spectra at the earth surface, has a larger component of diffuse and a minor component of direct solar radiation compared to the global wavelength range, therefore the increase in annual energy due to plane inclination should also be different. This work, analyzes 4 years of solar UV radiation measurements performed on tilted and horizontal planes located at the Plataforma Solar de Almería, Spain. The monthly mean ratio of tilted/horizontal solar UV irradiation varies with the time of the year, reaching values of 1.25 and 0.95 for winter and summer, respectively. The same ratio in the solar global spectra rises up to 1.70 and 0.85 for the same months. The annual UV solar energy increase on a plane tilted 37° and oriented towards the equator is around 3–4%, whereas is around 10% in the global spectra. In this way UV annual energy increase due to inclination and orientation of the plane is much lower than that for global radiation. Determination of a unique method to assess all possible inclinations and orientations, require simultaneous measurement of diffuse and direct UV radiation performed with radiometers of identical spectral response. Given the worldwide scarcity of these type of data, an empirical correlation that relates horizontal UV irradiation to that on a 37° inclined plane was determined. Monthly and annual tendencies of solar UV irradiation have been analyzed and compared with the solar global irradiation.     

Heat flux sensors: Calorimeters or radiometers?

Different methods may be used for measurement of very high solar irradiance on large areas, all of them are based on one or several heat flux sensors. The most common gages used for this purpose are the Gardon type, which are usually calibrated using a black body at a certain temperature as the radiant source. An alternative way to calibrate these sensors based on a thermal balance is presented in this article.The agreement between both methodologies confirms the validity of the black body calibration procedure and the potential of the calorimetry to calibrate heat flux sensors. However, with the proposed method, the uncertainty in estimating the calibration constant of these sensors is reduced from 3% to less than 2%. This procedure calibrates these sensors to measure properly under concentrated solar radiation.     

Hybrid solar heating and ventilation: The monymusk housing project

The paper reports on recent research at Aberdeen University to predict, with the aid of transient systems simulation, the performance of a new hybrid solar sheltered housing development in Monymusk, Scotland. The proposed dwelling units embody several unique design concepts, including an entirely traditional exterior appearance indistinguishable from the local vernacular, a new optimised omni-directional solar roof collector system which combines both heating and ventilation functions, and the ability to automatically switch between a range of heating and/or ventilation modes when required.     

Investigations into the functioning of a supply air window in relation to solar energy as determined by experiment and simulation

‘Supply air windows’ under optimum flow conditions function as an efficient heat reclaim device. Heat escaping from the room, through the inner glass pane, is entrained in the air flow between the inner and outer sashes and returned to the room. A low-E coating to the inner glass acts as a barrier to radiation heat loss across the window so very low U-values can be achieved. These same characteristics enable the window to function as a passive solar component. Its efficiency is inferior to that of a dedicated passive solar device due to its transparency, but even so at modest levels of incident solar gain a worthwhile proportion is entrained into the air flow and supplied to the rooms as pre-heated ventilation air supply. These characteristics have been established by laboratory, test cell investigations, and simulations using computational fluid dynamics and ESP-r, a whole building dynamic thermal modelling tool.     

Improvement of PV module optical properties for PV-thermal hybrid collector application

Photovoltaic-thermal collectors (or PV-T collector) are hybrid collectors where PV modules are integrated as an absorber of a thermal collector in order to convert solar energy into electricity and usable heat at the same time. In most of the cases, the hybrid collectors are made by the superposition of a PV module on the thermal absorber of a solar collector. In this paper, the approach is different and is to analyze thermal and optical properties related to both PV and solar thermal functions in order to identify an optimum combination leading to a maximum overall efficiency. Indeed, although these two functions do not exploit the same range of radiation wavelengths, thermal and PV functions are not so complementary due to photo-conversion thermal dependency. In this context, an alternative PV cell lamination has been developed with increased optical and thermal performance. The improvements were evaluated around 2 mA/cm² in terms of current density in comparison to a standard module encapsulation. Based on this technique, a real size PV-T module has been built and tested at Fraunhofer solar test facilities. The results show a global efficiency of the PV-T collector above 87% (79% thermal efficiency plus 8.7% electrical efficiency, based on the absorber area).     

New contact frame design for minimizing losses due to edge recombination and grid-induced shading

Edge recombination and grid shading are two loss mechanisms which decrease solar cell efficiency. We introduce a new way for decreasing both significantly by a novel contact frame design which runs along the edge on the surface of a solar cell. No additional processing is necessary for preparing the contact frame. For a 100 cm² commercial c-Silicon (Si) solar cell the efficiency increased from 16.18% to 16.83% at 1 Sun (AM 1.5) as estimated by careful device simulation.     

New methodologies to estimate the hourly global solar radiation; Comparisons with existing models

This paper describes two new friendly and reliable approaches to estimate hourly global solar radiation on a horizontal surface even with a pocket calculator.Such fast and reliable predictions for the hourly solar radiation are necessary for the real-time management of both the solar energy sources, like a PV generator output in the one hand and the power loads, on the other.The predicted global solar hourly radiation values are compared with estimates from two existing packages and the recorded solar radiation for the two biggest cities of Greece.The two methodologies presented in this paper can be applied to any other site.     

Industrially feasible multi-crystalline metal wrap through (MWT) silicon solar cells exceeding 16% efficiency

On the way to higher efficiencies, back contact solar cells seem to be a promising alternative to the conventional screen-printed solar cells. Especially, the metal wrap through (MWT) solar cell concept with only two additional process steps is appropriate for a fast transfer to industry. Hence, an industrially feasible process based on a new contact design was developed and tested at the pilot-line of the Photovoltaic Technology Evaluations Center (PV-TEC). A maximum cell efficiency of 16% is achieved. Compared with conventionally processed cells made of the same mc Si-block, an efficiency gain of 0.5% absolute is observed. Due to a cell interconnection on the back the serial resistance losses in the tabs decrease. Therefore, a fill factor of almost 77% and an efficiency of 15% for a MWT module prototype (16 MWT cells) is reached.     

A detailed study of H2 plasma passivation effects on GaAs/Si solar cell

The hydrogen plasma passivation effects of MOCVD-grown GaAs solar cell on Si substrate have been studied in detail. To get a more reproducible increase of conversion efficiency and test the thermal stability of the plasma-exposed GaAs/Si solar cell, both the plasma exposure and post-passivation annealing conditions were optimized. Annealing the H₂ plasma passivated GaAs/Si solar cell at 450°C in AsH₃/H₂ ambient seems a very essential parameter to restore the carrier concentration, especially, without losing the beneficial effects of H incorporation into GaAs on Si. For the H₂ plasma passivated GaAs/Si solar cell, a highest conversion efficiency of 18.3% was obtained compared with that of the as-grown cell (16.6%) due to the H passivation effects on nonradiative recombination centers, which increased the minority carrier lifetime.     

Separation of solar cell current into its constituent parallel currents under illumination

A method is presented which suggests the sharing out of total cell short circuit current among the constituent parallel branches of the equivalent circuit, allowing for the identification of their contributions to the total current–voltage (I–V) characteristics under illumination in solar cells described through two parallel diodes. The method is based on the fact that all parallel branches are always under the same voltage; in particular, the open circuit voltage is the same for the cell as a whole as well as for each of the two diodes. With the help of the parameters of each diode and its share in the cell short circuit current, its light I–V characteristic can be drawn, and its individual fill factor calculated. Furthermore, the method suggests a way to estimate the cell fill factor with the help of the individual fill factors. The application of the method is carried out on experimental data of a ZnO/CdS/CuGaSe₂ single crystal solar cell.     

Internal quantum efficiency for solar cells

The total internal quantum efficiency (IQE) of a flat-band p–n homojunction silicon solar cell and contributions of the three regions to it are numerically evaluated. It is found that both the spatial widths of the cell and the surface recombination velocities have significant impacts on the IQEs. By a linear transformation and a proper approximation, the differential equation of the minority carrier density in a textured cell becomes the same form as for the flat cell. What makes differences is that texturization slightly enhances the IQEs for photons with longer wavelengths while notably increasing external quantum efficiency. Hence it plays a good role for getting a better performance of a solar cell. It is considered that the results in the present are of universal technical importance both in designing solar cells and their surface structures.     

Integrated solar heating systems: From initial sizing procedure to dynamic simulation

The sizing of the solar installation of an individual dwelling is a problem which can be solved in many ways. The approach described in this paper is a simplified procedure of considerable interest. It requires only a small quantity of data and can be computed in a short time. The performance of this procedure was evaluated by a more complex sizing method based on detailed simulation. The simplified procedure was applied to the case of an individual dwelling using a solar collector field to produce domestic hot water and space heating. The building and the solar installation have then been modelled with the software TRNSYS 16 and their behaviour was simulated during a whole year. The results obtained are particularly close to the ones expected by the simplified sizing procedure.