CdTe PV Modules Research Articles

Analysis of the Performance of mc-Si and CdTe Modules Under Soiling Conditions

In this work, we study the soiling impact on the performance of two PV technologies installed in the south of Spain. For this purpose, we include electrical measurements as well as spectral aspects such as dust transmittance, quantum efficiency and the local solar spectrum to analyse their response. The studied technologies were multicrystalline silicon (mc-Si) and cadmium telluride (CdTe) PV modules. The solar spectra representative for clear sky, clean glass cover and soiled glass as well as the spectral response of the PV modules were used for the calculation of the photogenerated current density and spectral mismatch factor. Two cloudless days were chosen for analysis. In terms of the solar resource, these days did not exhibit large differences. Nevertheless, soiling was present to a different extent. When comparing the corresponding power output of the technologies on day 1 and day 2, the power losses at 12 UTC were 3 times larger for mc-Si and nearly the same for CdTe. This result shows that the soiling impacts differently on PV modules having different spectral responses.

Comparative study of dynamic thermal performance of photovoltaic double skin façades influenced by glass transmittance and natural ventilation

As a promising facade technology for building energy efficiency, the overall performance of double skin façade integrated with semi-transparent photovoltaic glass (STPV-DSF) was affected by multiple factors. The combined effects of two important factors, namely glass transmittance (τ) and natural ventilation, on the dynamic thermophysical behaviors of STPV-DSF were investigated in detail. Three parallel DSF cells, including two STPV-DSFs (τ = 20% and τ = 40%) and one clear glass DSF, combined with three ventilation modes (i.e. non-ventilation, external circulation and noontime external-internal circulation) were adopted for in-situ experiments on a test rig in both summer and winter. Results showed that both factors would affect the solar heat transmission through DSFs and the influence of natural ventilation was not as significant as that of glass transmittance in summer daytime. The influence of natural ventilation on thermal transmittance became more significant during nighttime, causing lower U-values. The lowest SHGC was achieved by τ = 20% STPV-DSF under external circulation in summer of merely 0.053 and the highest was for the clear glass DSF with non-ventilation in winter of 0.534. By employing the external-internal circulation only around noontime in winter, fresh air was preheated through the cavity to a temperature of 22–27 °C, which can be introduced indoors without increasing the heating load. Impact of lowered operation temperature of CdTe PV modules by natural ventilation on the improvement of power output efficiency was found insignificant. The energy efficiency potential of STPV-DSF may be weakened with the decrease of glass transmittance regarding the accentuated imbalance of the reduced cooling load and the increased heating load between the two seasons compared with that of the clear glass DSF.

Efficiency Assessment of Five Types of Photovoltaic Modules Installed on a Fixed and on a Dual-Axis Solar-Tracked Platform

A solution to increase the electrical output of the photovoltaic systems relies on solar tracking mechanisms that increase the amount of received solar energy. The experimental results obtained during a monitoring period of one year are comparatively presented in the paper for five types of photovoltaic modules installed on a fixed platform (as reference) and on a dual-axis solar tracking platform in the Renewable Energy Systems and Recycling R&D Centre of the Transilvania University of Brasov, Romania. The influence of the solar-tracking mechanism and the meteorological conditions specific to the four seasons during the monitoring period on the output of the analysed photovoltaic technologies are discussed in the paper. The solar tracking increases by 28% the amount of the yearly received solar energy and by 29.6% the electrical energy output of the entire PV platform. The solar conversion efficiency of the tracked PV platform is slightly increased (14.34%) when compared with the fixed one (14.17%). When assessing the influence of solar tracking on each type of PV, the results show that the CIGS PV module has the highest relative energy gain (34%) followed by CIS (30.8%), m-Si (30.6%), p-Si (27.3%) and CdTe (23.4%) PV modules.

Study of the second-generation of CdTe and CIGS thin film PV modules under natural sunlight conditions

There is a significant amount of research in the literature concerning the performance of solar panels operating during outdoor exposure, but the full topic is not yet exhausted. One of the reasons is that the photovoltaic cell technology is constantly evolving. In this paper, a comparison of two types of CdTe and CIGS modules operated with a nominal power of 80 W and 140 W, respectively is studied. The module tests were performed under external conditions during autumn, winter, spring, and summer from October 2019 to July 2020 in the temperate climate of Miękinia, South Poland. The photovoltaic panels were connected to the electric grid via microinverters. During the tests, the temperature of the panels was monitored. To determine the influence of solar radiation on the energy conversion efficiency of photovoltaic panels, a pyranometer installed in the plane of the panels was used. Based on the monitoring of the atmospheric conditions and the measurement of instantaneous power, the efficiency of the modules is determined.

Comparison of different simplistic prediction models for forecasting PV power output: Assessment with experimental measurements

This paper tested the energy outputs of different types of PV modules and evaluated the accuracies of different simplistic PV module power prediction models. A test rig was developed in Hong Kong to assess the PV power outputs of ten PV modules. The solar radiation, ambient temperature and power generation are recorded. The evaluated models include simple efficiency model, temperature correction model and one-diode model. The results show that the mono-Si PV module is the highest in terms of the annual energy outputs per unit area, and a-Si PV modules is the lowest. The simple efficiency model overestimates the power output of all types of PV modules for more than 10% except for a CdTe PV module. The one-diode model demonstrated the highest accuracy for mono-Si and poly-Si PV modules. The accuracies of the evaluated models are low for thin-film PV technologies. Although the mean bias error of the one-diode model is larger than 10% for the thin-film PV modules (expect for one CdTe PV module), the one-diode model has the highest accuracy among the three models. Further studies should be conducted to investigate the energy performance of thin-film PV modules and then improve their prediction accuracy.

Performance Evaluation of a Building Integrated PV (BIPV) at Heriot-Watt University Malaysia

Building Integrated Photovoltaics (BIPV) is a promising technology that combines the generation of energy into the building structure where the modules act as building material or blend completely with architectural design. This study analyses the performance characteristics of a proposed BIPV system for Heriot-Watt University Malaysia building, the system is designed with aim to utilize the curved roof area of the building. The available roof area of 7725 m2 is curved with varying tilt angles from 1.5° to 26°. The environmental plugin Ladybug integrated within Grasshopper was used to visualize and estimate the energy potential from the roof surface in Rhinoceros 3D modeling software. Additionally, detailed system simulations are conducted with PVSyst software. Eight proposed system variants of different PV technologies and modules types are studied with capacities of 411.8 kW to 1085.6 kW. The recommended system has a size of 1085.5 kW and utilizes Thin-film CdTe PV modules. The system generates 1415 MWh annually with a performance ratio of 84.9%, which saves 62.8% of the electricity bill and has an estimated cost of 901 thousand USD. Installation of the proposed system should preserve the aesthetical value of the building’s roof and satisfy BIPV rules.

Sputter-Deposited Oxides for Interface Passivation of CdTe Photovoltaics

Commercial CdTe PV modules have polycrystalline thin films deposited on glass, and devices made in this format have exceeded 22% efficiency. Devices made by the authors with a magnesium zinc oxide window layer and tellurium back contact have achieved efficiency over 18%, but these cells still suffer from an open-circuit voltage far below ideal values. Oxide passivation layers made by sputter deposition have the potential to increase voltage by reducing interface recombination. CdTe devices with these passivation layers were studied with photoluminescence (PL) emission spectroscopy and time-resolved photoluminescence (TRPL) to detect an increase in minority carrier lifetime. Because these oxide materials exhibit barriers to carrier collection, micropatterning was used to expose small point contacts while still allowing interface passivation. TRPL decay lifetimes have been greatly enhanced for thin polycrystalline absorber films with interface passivation. Device performance was measured and current collection was mapped spatially by light-beam-induced current.

Cadmium telluride leaching behavior: Discussion of

Zeng et al. (2015) evaluate the leaching behavior and surface chemistry of II–VI semiconductor materials, CdTe and CdSe, in response to pH and O2. Under agitation in acidic and aerobic conditions, the authors found approximately 3.6%–6.4% (w/w) solubility of Cd content in CdTe in the Toxicity Characteristic Leaching Procedure (TCLP), Waste Extraction Test (WET), and dissolution test, with lower solubility (0.56–0.58%) under agitation in acidic and anoxic conditions. This range is comparable with prior long-term transformation and dissolution testing and bio-elution testing of CdTe (2.3%–4.1% w/w solubility of Cd content in CdTe). The implications for potential leaching behavior of CdTe-containing devices require further data. Since CdTe PV modules contain approximately 0.05% Cd content by mass, the starting Cd content in the evaluation of CdTe-containing devices would be lower by three orders of magnitude than the starting Cd content in the authors’ study, and leaching potential would be further limited by the monolithic glass-adhesive laminate-glass structure of the device that encapsulates the semiconductor material. Experimental evaluation of leaching potential of CdTe PV modules crushed by landfill compactor has been conducted, with results of TCLP and WET tests on the crushed material below regulatory limits for Cd. CdTe PV recycling technology has been in commercial operation since 2005 with high yields for semiconductor (95%) and glass (90%) recovery.

Uncertainty in PV Module Measurement---Part II: Verification of Rated Power and Stability Problems

Standard testing condition power of PV modules, especially thin-film modules, is not a constant value. Exposure to irradiance and temperature, as well as electrical bias and dark storage, cause changes in STC power, which complicate the interpretation of quality assurance measurements and tests. This paper presents a literature review and summarizes current knowledge of metastability and stability problems of PV modules with focus on their influence on quality assurance, especially the verification of rated module power. Three groups of thin-film PV technologies are addressed: amorphous silicon, cadmium telluride (CdTe), and chalcopyrite technologies (CIGS). Amorphous silicon is affected mostly by light-induced degradation and seasonal annealing, whereas sensitivity to dark storage is the most relevant effect for CdTe and CIGS PV modules. In conclusion, it is not possible to quantify the impact of specific (meta)stability effects on measured STC power for all modules of one technology in general, as there is a strong sensitivity to the exact composure and processing of the modules. With regard to the total uncertainty inherent in the verification of rated power of new modules, this paper introduces the concept of differentiating between measurement-related and module-stability-related uncertainty and suggests a procedure for its determination.

Tellurium, its resourcefulness and recovery

Although it looks similar to tin, tellurium is a metalloid chemical element which is used in a variety of industries, primarily in the form of an additive to an assortment of compounds and alloys. As solar cell technology has improved the cadmium telluride (CdTe) PV modules have become among the lowest-cost producers of solar electricity. Consequently, interest has recently been focused on tellurium recovery. In this paper, tellurium’s availability and its distribution in general metallurgical processing is summarized and analyzed. Because tellurium is the scarcest of all the byproducts and mainly recovered from copper sulfides, hydrometallurgical recovery of tellurium from electrolytic copper anode slimes is described.

Scale-up issues of CIGS thin film PV modules

Photovoltaics cost has been declining following a 70% learning curve. Now the challenge is to bring down the cost of solar electricity to make it competitive with conventional sources within the next decade. In the long run, the module efficiencies tend to reach 80% of the champion cell efficiencies. Using a semiempirical methodology, it has been shown earlier that while the triple junction a-Si:H thin film technology is competitive, CIGS and CdTe thin film module technologies are highly competitive and presently offer the best approach for significantly exceeding the cost/performance levels of standard and non-standard crystalline Si PV technologies. Since 2006, the production of thin film solar cell in the U.S. has surpassed that of c-Si. At present, the production of CIGS PV modules lags considerably behind that of CdTe PV modules. This is mainly because of its complexity. Scale-up issues related to various CIGS preparation technologies such as co-evaporation, metallic precursor deposition by magnetron sputtering and non-vacuum techniques such as ink-jet printing, electroplating or doctor-blade technology followed by their selenization/sulfurization are discussed so as to assist the CIGS technology to attain its full potential. Besides the welcome announcements of large volume production, it is essential to achieve the production cost below $1/Wp in the near term and attain production speeds comparable to CdTe production speeds. Comparable production speeds are expected to be achieved within the next decade. This will enable reduction of CIGS module production costs to ∼65¢/Wp that would be comparable to the CdTe module projected production cost. Additionally CIGS will have a higher efficiency premium.

Life-cycle analyses of very-large scale PV systems using six types of PV modules

The authors have been studied the life-cycle analysis of the VLS-PV systems installed in desert area using sc-Si, mc-Si, a-Si/sc-Si, a-Si/μc-Si, CdTe, and CIS PV modules. The sc-Si and a-Si/sc-Si, a-Si/μc-Si are new items from the last studies [1]. It is assumed 1 GW system in Gobi desert including transmission lines. We estimated energy requirement, energy pay-back time, CO 2 emissions, and CO 2 emissions rate. Concerning the energy requirement, the CIS is the smallest, and biggest energy requirement is the sc-Si. The mc-Si, a-Si/sc-Si, thin-film Si and CdTe are average. The energy pay-back time of the CIS’s VLS-PV system is approximately 1.8 years, and sc-Si is 2.5 years. The others are approximately 2.0–2.3 years. Characteristics of the CO 2 emissions rate are almost same as energy pay-back time. The CO 2 emissions rate is 43–54 g-CO 2/kW h. The mc-Si, a-Si/sc-Si, and CIS shows lower CO 2 emissions rate.

CdTe photovoltaics: Life cycle environmental profile and comparisons

We discuss the emissions of cadmium throughout all the life stages of CdTe PV modules, from extracting, refining, and purifying the raw materials to producing, using, and disposing or recycling of the modules. Then, we compare these emissions with those in the life cycle of three different types of crystalline Si PV modules. The energy requirement and energy pay back times (EPBT) of CdTe PV modules are considerably shorter than that of crystalline Si modules, although the latter exhibit higher efficiencies. This difference is primarily due to the energy used to process silicon, a fraction of which is derived from fossil fuels, inevitably producing Cd and many other heavy-metal emissions. The lower energy requirement of CdTe PV results in lower emissions of all pollutants, including cadmium.

High efficiency ultra-thin sputtered CdTe solar cells

Abstract Large scale manufacturing of CdTe PV modules at the GW/yr level may be constrained due to the limited availability of the relatively rare (Te) element and the volume of potentially hazardous (Cd) material being used in the typically 3–8 μm thick CdTe absorber layer. However, we find that it is possible to reduce the CdTe layer thickness without much compromise in efficiency. The CdS/CdTe solar cells were fabricated using magnetron sputtering with ultra-thin CdTe layers in the range of 0.5–1.28 μm. The ultra-thin films and cells were characterized using X-ray diffraction (XRD), optical transmission, scanning electron microscopy (SEM), current–voltage and quantum efficiency measurements. These results were compared with those of standard 2.3 μm thick CdTe sputtered cells. Different post-deposition processing parameters were required for cells with ultra-thin and standard CdTe thicknesses to achieve high efficiency. Ultra-thin CdTe cells showed crystallographic texture and CdTe1−xSx alloy formation after CdCl2 treatment very similar to standard CdTe cells. Optimization of the post-deposition CdCl2 treatment and back-contact processing yielded cells of 11.2% efficiency with 0.7 μm CdTe compared to 13.0% obtained with standard 2.3 μm CdTe cells.

Extraction and separation of Cd and Te from cadmium telluride photovoltaic manufacturing scrap

The extraction and separation of cadmium, tellurium, and copper from CdTe PV module scrap was investigated. Several leaching technologies were assessed and the extraction of CdTe from samples of PV modules was optimized for maximum efficiency and minimum cost. A dilute aqueous solution of hydrogen peroxide and sulfuric acid was sufficient to completely leach out cadmium and tellurium from these samples. The same method successfully removed cadmium and tellurium from actual manufacturing scrap; copper was partially extracted. Subsequently, cation-exchange resins were used to separate cadmium and copper from tellurium. Complete separation (i.e., 99·99%) of Cd from Te was accomplished. The estimated costs of these processes for 10 MW/year processing are about 2 cents per W. Copyright © 2006 John Wiley & Sons, Ltd.

Energy Use and Greenhouse Gas Emissions in the Life Cycle of CdTe Photovoltaics

AbstractThe life cycle of the thin film CdTe PV modules in the U.S. have been investigated based on materials and energy inventories for a commercial 25 MW/yr production plant. The energy payback times (EPBT) of these modules are 0.75 years and the GHG emissions are 18 gCO2-eq/kWh for average U.S. solar irradiation conditions. Adding the impact of an optimized ground-level balance of system (BOS), result in a total EPBT of 1.2 years and total life-cycle GHG emissions of 24 gCO2-eq/kWh.