High Concentration Photovoltaic Research Articles

Performance analysis of high-concentrated multi-junction solar cells in hot climate

ABSTRACTMulti-junction concentrator solar cells are a promising technology as they can fulfill the increasing energy demand with renewable sources. Focusing sunlight upon the aperture of multi-junction photovoltaic (PV) cells can generate much greater power densities than conventional PV cells. So, concentrated PV multi-junction solar cells offer a promising way towards achieving minimum cost per kilowatt-hour. However, these cells have many aspects that must be fixed to be feasible for large-scale energy generation. In this work, a model is developed to analyze the impact of various atmospheric factors on concentrator PV performance. A single-diode equivalent circuit model is developed to examine multi-junction cells performance in hot weather conditions, considering the impacts of both temperature and concentration ratio. The impacts of spectral variations of irradiance on annual performance of various high-concentrated photovoltaic (HCPV) panels are examined, adapting spectra simulations using the SMARTS model. Also, the diode shunt resistance neglected in the existing models is considered in the present model. The present results are efficiently validated against measurements from published data to within 2% accuracy. Present predictions show that the single-diode model considering the shunt resistance gives accurate and reliable results. Also, aerosol optical depth (AOD) and air mass are most important atmospheric parameters having a significant impact on HCPV cell performance. In addition, the electrical efficiency (η) is noticed to increase with concentration to a certain concentration degree after which it decreases. Finally, based on the model predictions, let us conclude that the present model could be adapted properly to examine HCPV cells' performance over a broad range of operating conditions.

Analysis of the Spatiotemporal Characteristics of High Concentrator Photovoltaics Energy Yield and Performance Ratio

The evaluation of the high concentrator photovoltaics (HCPV) power output at regional scale is required to demonstrate the benefits of HCPV systems for utility-scale electricity production. In this context, the spatial and temporal variability of the systems’ energy yield is important. However, assessment methods of the HCPV energy output of complete systems operated under real atmospheric conditions have started to surface only recently. We present the results of an evaluation study of the spatially distributed energy yield of a typical HCPV system in peninsular Spain for the period 2003–2012, using one of such models developed in Southern Spain. Overall, the annual energy yield is relatively homogeneous (≍1800 kWh/kWp), and its standard deviation over the evaluation period and throughout the vast majority of the study region is below 7%. The overall system losses by deviations from the spectrum and cell temperature reference conditions are ≍2.5% and smaller than ≍4%, respectively, on an annual basis. Finally, the use of a single bulk value of performance ratio to evaluate the energy output of HCPV systems from the DNI alone has proven good to within ±2% in Spain, as long as its value is reliable and sufficiently representative of the long-term regional average conditions.

A worldwide assessment of economic feasibility of HCPV power plants: Profitability and competitiveness

Numerous exhaustive analyses of the economic assessment of conventional PV systems are available in the literature. However, there is a lack of these studies concerning High Concentrator Photovoltaic (HCPV) technology. Besides, future owners and potential investors on HCPV plant demand information relating to the economic feasibility of their investment. In this work the profitability and competitiveness of HCPV plants in several countries are analysed. To analyse the profitability the internal rate of return (IRR) criterion has been used, while the competitiveness has been analysed based on estimating the so-called HCPV generation parity. As a result of the economic profitability analysis conducted the group of countries where the investment in HCPV could be interesting has been identified. The results obtained could be also useful for researchers to identify the weaknesses of the HCPV technology and take actions at making it more competitive. From the competitiveness analysis carried out in several Eurozone countries and USA for two possible scenarios 2015 and 2020, the results show that HCPV could be competitive in some locations in 2020. Therefore, government organizations of the studied countries, which participate in the design or the selection of support mechanisms for HCPV, can be guided by the results obtained.

Assessment of the Carbon Footprint, Social Benefit of Carbon Reduction, and Energy Payback Time of a High-Concentration Photovoltaic System

Depleting fossil fuel sources and worsening global warming are two of the most serious world problems. Many renewable energy technologies are continuously being developed to overcome these challenges. Among these technologies, high-concentration photovoltaics (HCPV) is a promising technology that reduces the use of expensive photovoltaic materials to achieve highly efficient energy conversion. This reduction process is achieved by adopting concentrating and tracking technologies. This study intends to understand and assess the carbon footprint and energy payback time (EPBT) of HCPV modules during their entire life cycles. The social benefit of carbon reduction is also evaluated as another indicator to assess the energy alternatives. An HCPV module and a tracker from the Institute of Nuclear Energy Research (INER) were applied, and SimaPro 8.0.2 was used for the assessment. The functional unit used in this study was 1 kWh, which is produced by HCPV, and inventory data was sourced from Ecoinvent 3.0 and the Taiwan carbon footprint calculation database. The carbon footprint, EPBT, and social benefit of carbon reduction were evaluated as 107.69 g CO2eq/kWh, 2.61 years, and 0.022 USD/kWh, respectively. Direct normal irradiation (DNI), life expectancy, and the degradation rate of HCPV system were subjected to sensitivity analysis. Results show that the influence of lifetime assumption under a low DNI value is greater than those under high DNI values. Degradation rate is also another important factor when assessing the carbon footprint of HCPV under a low DNI value and a long lifetime assumption. The findings of this study can provide several insights for the development of the Taiwanese solar industry.

Porous Nanomaterials for Ultrabroadband Omnidirectional Anti‐Reflection Surfaces with Applications in High Concentration Photovoltaics

Materials for nanoporous coatings that exploit optimized chemistries and self‐assembly processes offer capabilities to reach ≈98% transmission efficiency and negligible scattering losses over the broad wavelength range of the solar spectrum from 350 nm to 1.5 µm, on both flat and curved glass substrates. These nanomaterial anti‐reflection coatings also offer wide acceptance angles, up to ±40°, for both s‐ and p‐polarization states of incident light. Carefully controlled bilayer films have allowed for the fabrication of dual‐sided, gradient index profiles on plano‐convex lens elements. In concentration photovoltaics platforms, the resultant enhancements in the photovoltaics efficiencies are ≈8%, as defined by experimental measurements on systems that use microscale triple‐junction solar cells. These materials and their applications in technologies that require control over interface reflections have the potential for broad utility in imaging systems, photolithography, light‐emitting diodes, and display technologies.

A worldwide assessment of levelised cost of electricity of HCPV systems

Numerous works of exhaustive analysis of the economic assessment of PV systems are available in the literature. However, there is a lack of this kind of studies concerning High Concentrator Photovoltaic (HCPV) technology. In this work, a worldwide economic feasibility analysis of HCPV systems is performed through the LCOE estimation, since it is a commonly method to assess and compare energy generation systems of different technologies. The LCOE of HCPV grid-connected systems is estimated and analysed for 133 countries. The analysis and detection of the optimal zones for HCPV technology is conducted in terms of the LCOE, and in addition, an innovative global map of the LCOE of HCPV is presented. Moreover, the grid parity in the domestic market segment for the year 2014 is analysed and found to be a reality for several developed countries. Finally, a prospective scenario comparing the LCOE of HCPV and conventional PV systems for the year 2020 is analysed and plotted in a global map, in which many countries have found to be preferable for the HCPV technology in terms of the LCOE. As an important result, although the Annual Final Yield, Yf, and LCOE are apparently inversely proportional, when comparing both parameters, Yf and LCOE, on one hand, it is obtained that some countries with relative high Yf values are also of relative high LCOE values (e.g. Iran and Sudan), and, on the other hand, some other countries with relative low Yf values are also of relative low LCOE values (e.g. Canada and France).

Ultrahigh Efficiency HCPV Modules and Systems

Semprius manufactures high-concentration photovoltaic (HCPV) modules and systems. Module characterization and quality control methods are described in this paper. Module efficiency distribution for thousands of modules is presented, currently showing an increase in average efficiency from 33% in 2013 to 35%. Data from modules and systems in the field are presented showing consistent performance over all seasons and no apparent degradation after 3 years. Finally, the effect of ambient temperature and wind speed on performance was studied.

Comparative study of methods for the extraction of concentrator photovoltaic module parameters

The modelling and outdoor evaluation of high concentrator photovoltaic (HCPV) systems is complex due to the use of multi-junction solar cells and optical devices. At the same time, the single exponential model (SEM) is widely used for predicting the IV characteristics of PV systems. In this paper, several conventional analytical methods for extracting the five parameters of the SEM model of non-concentrating PV devices are applied and evaluated for the electrical characterization of a HCPV module for the first time. Among the different approaches, three simple analytical methods have been selected with the aim of offering rapid and easy solutions for the characterization of HCPV systems. The selected methods are: the method of Phang et al., the method of Blas et al. and the method of Khan et al. In addition, these methods are compared with a numerical extraction method previously introduced by the authors. Results show that all the methods investigated can be valid for predicting the IV curve of a HCPV module except the method of Khan et al., which tends to underestimate the IV curve and maximum power of the module. The dependence of the extracted SEM model parameters with the input irradiance is also discussed.

Enhancement of the electrical response in high concentrating photovoltaic systems by antireflective coatings based on silica nanoparticles

Silicon dioxide (SiO2) nanoparticles, obtained by sol-gel technique, were used to create an antireflective coating (ARC) for the use in a high concentrating photovoltaic (HCPV) device. These ARCs have shown a transmission increase from 92% up to 99% when deposited on glass substrate.The introduction of these same ARCs, with different optical paths, in the HCPV system has shown an overall power increase with strong dependence of the HCPV module performance (based on triple junction solar cells) upon the different ARC transmission spectra.Optimal ARC spectral shape was thus determined. A net additional power generation of 4.3% of the HCPV was measured, indicating almost complete elimination of Fresnel reflection losses in the system.

Experimental demonstration of high‐concentration photovoltaics on a parabolic trough using tracking secondary optics

AbstractA new approach to high‐concentration photovoltaics (HCPV) based on a parabolic trough primary concentrator is presented. The design diverges from the standard HCPV arrangement of a two‐axis tracking point‐focus concentrator, and rather employs a simpler parabolic trough primary concentrator to reduce cost. To break the 2D limit of concentration, and bring the system into the realm of HCPV, the system employs an array of rotating secondary concentrators is arranged along the focal line of the parabolic trough. The resulting line‐to‐point (LTP) focus geometry allows the system to achieve a geometric concentration of 590×, yet still maintains the advantages of having a linear trough primary concentrator, namely manufacturability, economy, and scalability. A full‐scale prototype of the system was constructed in Biasca, Switzerland. During on‐sun tests a flux concentration of 364 suns was measured at the exit of the secondary concentrator, the highest reported concentration for any parabolic‐trough‐based system. Moreover, the system reached a peak efficiency of 20.2%, the highest measured solar‐to‐DC efficiency for a parabolic trough‐based solar collector. Long‐term performance is estimated by means of a coupled optical‐electrical model validated vis‐à‐vis the experimental results. This work serves as an experimental proof‐of‐concept for high‐concentration trough‐based collectors, thereby opening new avenues for reducing the cost of HCPV systems. Copyright © 2016 John Wiley & Sons, Ltd.

Cascade closed-loop control of solar trackers applied to HCPV systems

High concentration photovoltaic (HCPV) modules require a high precision tracking system for reaching their highest conversion efficiency. One way to accomplish this goal is by using a closed-loop mechanism and a sun sensor to track the sunlight. This paper proposes a cascade control algorithm capable of achieving a sun tracking error of 1′ for its application in high concentration photovoltaic systems. The algorithm follows an inner loop-outer loop topology. The inner loop employs a Nonlinear Proportional-Proportional Integral (NP-PI) controller and the outer loop resorts on a Proportional Integral (PI) controller. A tuning procedure for setting up the cascade controller is also described. Experiments on a laboratory prototype compare the performance of the proposed cascade controller with a PI controller not resorting on an inner loop. These outcomes show that the proposed control law provides improved tracking accuracy with less actuator wear.

Performance, limits and economic perspectives for passive cooling of High Concentrator Photovoltaics

This paper provides an analysis of the benefits of passive cooling for High Concentrator Photovoltaic (HCPV) systems in terms of costs and kWh annual energy yields. For the first time, the performance of the heat sinks has been related to the calculated energy yield of a standard triple-junction GaInP/GaAs/Ge HCPV cell in a system deployed at several suitable locations across the globe. Copper and aluminium heat sinks have been considered and their merits have been compared. The finite element analysis software package COMSOL was employed to gain insights regarding a simple flat plate heat sink. The cell temperature was found to have a linear dependence on the geometric concentration with a characteristic slope that increases with cell size (ranging from 10 to 0.25mm). The results show the advantages of miniaturisation, and that the cooling of smaller cells can be accomplished using flat heat sinks. Within the considered range of geometric concentration ratios (up to 1000×), aluminium heat sinks are, in general, found to be preferred over copper, because of their lower densities and costs for the same thermal management. Closed-form thermal models based on the Least-Material (LM) approach have been utilised to design more complex finned heat sinks (operated under natural convection) that yield the best compromise between thermal performance and weight. For a 60°C cell operating temperature, a greater kWh output is obtained, but an LM heat sink designed for a cell temperature of 80°C has a material cost per unit energy that is between 50% and 70% less than the one designed for 60°C. Heat sink costs between $0.1 and 0.9 per Wp were estimated for a geometric concentration above 500suns, depending on the cell׳s temperature and size. There are strong reductions in HCPV installation costs by limiting the dimensions of the cooling system at high concentrations.

Determination of the current–voltage characteristics of concentrator systems by using different adapted conventional techniques

The modelling of the current–voltage characteristics of HCPV (high concentrator photovoltaic) modules is fundamental for the design, monitoring and energy prediction of HCPV systems and power plants. However, the modelling of these devices is inherently different and more complex than that of conventional PV (photovoltaic) modules. Because of this, considerable efforts have been done to develop models tailored to the specific features of this technology. However, there is still a lack of studies and techniques concerning the modelling of the whole I–V curve of HCPV modules. In the present work, the possibility of obtaining the I–V curve of a HCPV module by applying common methods exploited in conventional PV technology by using the effective irradiance and cell temperature is analysed. In particular, the studied methods are: the single exponential model, the Blasser's method and the bilinear interpolation method. Every method has been adapted to be entirely function of the effective irradiance and cell temperature of the concentrator. Results show that all the methods present a good performance in the estimation of the I–V curve of a concentrator, with an average RMSE (root mean square error) ranging from 1.15% to 5.23%, and an average MBE (mean bias error) close to 0%.

Performance Analysis of a Grid-connected High Concentrating Photovoltaic System under Practical Operation Conditions

High concentrating photovoltaic (HCPV) is a promising technique for the practical commercial utilization of solar energy. However, the performance of a HCPV system is significantly influenced by environmental parameters such as solar direct normal irradiance (DNI) level and environmental temperature. This paper analyzes the performance of a 9 kWp grid-connected HCPV system in Kunming (Yunnan, China), during practical field operations over an entire year, and discusses how the environmental parameters influence the performance from both the energy conversion and power inversion perspective. Large variations in the performance of the HCPV system have been observed for different months, due to the respective changes in the environmental parameters. The DNI level has been found to be a dominant parameter that mainly determines the amount of energy production as well as the performance ratio of the HCPV system. The environmental temperature and wind velocity have less influence on the system performance ratio than expected. Based on the performance of the present HCPV system, a quantified correlation between the output power and the direct normal irradiance has been derived, which provides guidelines for both the cogent application and the modeling of HCPV techniques for grid-connected power generation.

A performance evaluation model of a high concentration photovoltaic module with a fractional open circuit voltage-based maximum power point tracking algorithm

High concentration photovoltaic (HCPV) modules employing high-efficiency III–V solar cells promise greater system-level efficiency than conventional photovoltaic (PV) systems. Nevertheless, the output power of an HCPV system is very sensitive to rapidly fluctuating tracking errors and weather patterns. The fractional open circuit voltage (FOCV) based maximum power point (MPP) tracking technique benefits from simplified processing circuits with speed response. To investigate the feasibility of using the FOCV technique for MPP estimation on HCPV modules, a theoretical model and simulation are presented in this study. A MATLAB-based MJSC circuit model of an HCPV module with buck-type converter and load is proposed and validated. In addition, the magnitude of the optical loss caused by Fresnel lens shape deformation and air mass (AM) ratio is modeled and quantized. The FOCV technique is then employed and compared with the conventional perturb and observe (P&O) method on the HCPV module under varying irradiance and temperature conditions to study its effectiveness. The results suggest that the FOCV technique could help an HCPV module to attain greater power efficiency.

Performance and optimization research of triple-junction solar cell along the optical axis direction on \text{the HCPV module}

High concentrating photovoltaic (HCPV) technology plays a more and more important role in solar power generation due to its extremely high efficiency. However, the efficiency of the HCPV module can be reduced by many factors. Especially, there are not enough researches and knowledge on the light intensity distribution and non-uniform illumination of different wavelengths of light concentrated by Fresnel lens. It is generally considered that the maximum power of multi-junction solar cell is achieved when the cell is placed on the focal plane of Fresnel lens. But it is proved to be incorrect by our research. When light beams of different wavelengths go through the Fresnel lens, their light spot distributions on the optical axis are not the same as those when they have different refractive indexes in Fresnel lens. At the same time, the triple-junction solar cell consists of three sub-cells which absorb light beams of different wavelengths respectively. Therefore, the performance of triple-junction cells would be influenced by the light distribution along the optical axis, this is exactly what we want to study in this work. The method of simulating the light tracing is used to calculate and analyze the light intensity distribution and non-uniform characteristics of different wavelengths of light concentrated by Fresnel lens. Combined with them from the circuit network model of a triple-junction solar cell, the electrical performances of triple-junction solar cell at different positions along the optical axis are studied. It is found from the simulation that the performance of cell does not reach the best state when cell is placed on the focal plane. The power of cell on the focal plane reaches only 0.41 W while the maximum point arrives at 0.69 W. The high non-uniformity of light on cell surface when cell is placed on the focal plane causes the decline of power. And an outdoor HCPV testing system with the ability to change the distance between Fresnel lens and the cell is conducted. The experimental results and the simulation results match well, therefore our simulation approach is verified. It shows that the module achieves the maximum power on either side of the focal plane, and the output power can increase more than 20% after optimization. It is a result after equilibrium between light intensity and uniformity on cell surface.

Experiment and Simulation Study on Silicon Oil Immersion Cooling Densely-Packed Solar Cells Under High Concentration Ratio

In order to solve the heat dissipation problem of densely-packed solar cells in high concentration photovoltaic (HCPV) system, a new cooling method of using silicon oil directly immerse the solar cells was proposed. The heat transfer performance of silicon oil immersion cooling the densely-packed solar cells with and without fin structure was investigated through experiment and simulation methods. The results of heat transfer performance of solar cells without fin structure showed that the simulated data was consistent well with data of experiment and the temperature could be lowered down in the operation range of solar cell. Furthermore, the heat transfer performance of solar cells with fin structure was researched using the model under different silicon oil inlet temperatures, inlet flow rates and the flow pressure drop was measured. The results indicated that the solar cells temperature declined and distributed well with silicon oil inlet flow rate increasing but the solar cells temperature raised linearly with silicon oil inlet temperature increasing. The optimized parameters of cooling receiver with fin structure were that: height of fin was 14 mm, number of fin was 50 and the thickness of substrate was 1.5 mm, with which the large amount of heat of densely-packed solar cells under high concentration ratio could be well controlled and make sure the power generation of HCPV system was high efficient.

A Microchip Integrated Sensor for the Monitoring of High Concentration Photo-voltaic Solar Modules

A CMOS sensor fabricated in 0.35μm technology, specifically designed for the monitoring of High Concentration Photo-Voltaic (HCPV) modules, is presented. The microchip was designed to monitor temperature and illumination of each solar cell in a module. Temperature is measured by monitoring the base-emitter voltage of two coupled, diode connected, bipolar transistors, while the illumination sensor is an integrated p-n junction photodiode. A custom communication protocol is implemented in the chip to allow the sharing of a two-wire communication resource among the cells.

Comparative assessment of the spectral impact on the energy yield of high concentrator and conventional photovoltaic technology

Photovoltaic materials are spectrally selected and their electrical output is affected by the spectral distribution of the incident irradiance. The performance of high concentrator photovoltaic (HCPV) systems is more influenced by the spectral changes than conventional single-junction photovoltaic (PV) systems due to the use of multi-junction (MJ) solar cells and optical devices. Despite this, the detailed comparison of the spectral impact on the electrical output of HCPV and PV technology under the same atmospheric conditions has not been addressed yet. Because of this, this paper aims to compare the spectral impact on the energy yield of both type of devices at a monthly and annual time scale at several locations with disparate climate conditions. The spectral dependence of both technologies is quantified by using the spectral factor (SF) index in conjunction with the Simple Model of Atmospheric Radiative Transfer of Sunshine (SMARTS) at five locations of the Aerosol Robotic Network (AERONET) database. The present paper shows that the current HCPV systems present annual spectral losses of around 5% with respect to PV systems at representative locations.

Global Annual Final AC Yield Comparison between HCPV and c-Si PV

A worldwide comparison of the annual yield between conventional c-Si photovoltaic (PV) technology and high concentrated photovoltaic (HCPV) technology is presented. The idea of this paper is to find the most appropriate locations for HCPV systems in terms of the annual energy produced when comparing to fixed tilt PV systems and two-axis oriented PY systems. For estimating the annual energy generation, the method of the Performance Ratio is used. For some locations with high annual direct normal irradiation values, which are distributed around the world, HCPV systems are found to be more advantageous than fixed tilt PV systems. World maps showing this comparison are presented.