High Concentration Photovoltaic System Research Articles

A Hybrid Electric and Thermal Solar Receiver

Summary Solar energy offers a promising renewable energy source; however, it is expensive to store electricity from photovoltaics (PV), the most widely deployed solar electricity technology. Solar thermal energy technologies can be paired with inexpensive thermal storage, but are more expensive overall. We have developed a solar receiver that combines PV and solar thermal systems to efficiently convert solar radiation to electricity (to be used immediately) and thermal energy (to be stored and converted to electricity on demand). This paper describes the Hybrid Electric And Thermal Solar (HEATS) receiver and models its performance. An idealized model predicts high solar-to-electricity efficiency (35.2%) with high dispatchability (44.2% of electricity from thermal energy) at an operating temperature of 775 K. Modeling using measured performance values for HEATS subcomponents predicts 26.8% efficiency and 81% dispatchability with silicon PV and 28.5% efficiency and 76% dispatchability with gallium arsenide PV, both operating at 700 K.

Experimental and numerical optimization of direct-contact liquid film cooling in high concentration photovoltaic system

Thermal management is a critical issue for normal operation of dense-array solar cells in high concentration photovoltaic system. A cooling method of direct-contact liquid film was experimentally and numerically investigated. In the experiments, deionized water was adopted as coolant and an electric heating plate was optimal designed to simulate dense-array solar cells. A two-dimension model was derived to present the temperature distribution on the surface of the simulated solar cells and flow characteristic of liquid film. The effect of various inlet parameters such as water temperature, inlet width and velocity had been numerical studied. The experiment results suggest that the surface temperature is well controlled under 120 °C at corresponding conditions, with concentration ratios ranging from 300 to 500X. The numerical results show that inlet width has a crucial effect on the liquid film thickness. The subcooled boiling state is a necessary condition to ensure cooling effect. High water inlet temperature is preferable for better heat transfer performance and temperature uniformity. The best optimizing inlet velocity, width and temperature are 1.06 m/s, 0.75 mm and 75 °C, respectively.

Characterization of the Spectral Matching Ratio and the Z-Parameter From Atmospheric Variables for CPV Spectral Evaluation

The spectral matching ratio (SMR) and the Z -parameter are indexes used to assess the direct solar spectrum and its coupling to the multijunction solar cells employed in high-concentrator photovoltaic systems. An experimental campaign based on component cell sensors equivalent to a lattice-matched GaInP/GaInAs/Ge solar cell was carried out in Jaen, South of Spain, in order to measure the spectral data required to obtain these indexes. The main atmospheric parameters influencing the solar spectrum were simultaneously registered. An analysis of the data was carried out to characterize the spectral indexes by simple expressions as a function of air mass, aerosol optical depth, and precipitable water. As a result, the indexes are approximated with root mean square errors between 5.18% and 6.49%. The expressions for the SMR between the top and middle subcells and between the middle and bottom subcells were compared to other expressions proposed in the literature. The SMR between the top and bottom subcells and the Z -parameter were characterized from atmospheric variables for the first time. This study is an alternative method for the spectral evaluation of high-concentrator photovoltaic systems without using any relatively expensive measuring equipment, given that a meteorological database is available for a particular location worldwide.

A dish-type high-concentration photovoltaic system with spectral beam-splitting for crop growth

Photovoltaic (PV) systems are playing a more and more important role as a renewable energy supplier. However, their large-scale applications is still limited by low conversion efficiency and high land-use requirement, especially for those areas where land and solar energy resources are more important for agriculture. In this paper, we suggest a dish-type high-concentration photovoltaic system, with which the competition between sunlight for crops' growth and PV application is solved by beam-splitting techniques. A purposely-designed beam filter acts as a solar spectrum splitter, and the most effective bands of solar spectrum for plant growth are transmitted down to plants while the other parts are all directed to the solar cell receiver. The spectral and spatial distribution of radiant intensity is investigated by ray tracing method, and the quantitative evaluation of the beam splitting effect on crop growth and PV power generation is provided in detail. The results show that, on one hand, the proposed system is superior to other natural and artificial light sources at driving the photosynthetic process (thus promoting crop growth); on the other hand, it generates PV power with high efficiency. Furthermore, the design can be optimized for certain kinds of plants and PV generation, both or independently. This spectral splitting scheme opens a promising future for PV applications in cooperation with precision farming.

Study on the uniformity of high concentration photovoltaic system with array algorithm

The uniformity of the receiver surface energy flux density in the reflective high-power concentration photovoltaic system can affect the photoelectric conversion efficiency of the photovoltaic cell, and even cause the “hot spot” to damage it. In this paper, the plane mirror array algorithm is used to design a reflective high-power condenser, and TRACEPRO is used to numerical simulation study the uniformity of receiver surface energy flux density. The results show that the uniformity is greater than 99%, the experimental result (96.907%) is in agreement with the simulation results. In addition, the relationships of the effective area of the photoelectric conversion, the average irradiance, the maximum irradiance and the focal length are studied, and in the case of theoretical concentration ratio C is unchanged, the effective area of the photoelectric conversion is unchanged, the relationship of the maximum irradiance Emax with the focal length f is Emax=a+b ln(f-c), and the relationship of the average irradiance Eave with focal length f is also Eave=a+b ln(f-c).

Note: Photoluminescence measurement system for multi-junction solar cells.

We describe a photoluminescence spectroscopy system developed for studying phenomena of optical coupling in multiple-junction solar cells and processed/unprocessed wafers, under the high solar concentration levels typical of HCPV (High Concentration PhotoVoltaic) systems. The instrument operates at room temperature over two spectral ranges: 475 nm-1100 nm and 950 nm-1650 nm. Power densities exceeding 10 000 suns can be obtained on the sample. The system can host up to four compact focusable solid state laser sources, presently only three are mounted and operated at 450 nm, 520 nm, and 785 nm; they provide overlapped beams on the sample surface and can shine simultaneously the sample to study possible mutual interaction between the different junctions.

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.

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.

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%.

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.

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.

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.

A new procedure for estimating the cell temperature of a high concentrator photovoltaic grid connected system based on atmospheric parameters

The working cell temperature of high concentrator photovoltaic systems is a crucial parameter when analysing their performance and reliability. At the same time, due to the special features of this technology, the direct measurement of the cell temperature is very complex and is usually obtained by using different indirect methods. High concentrator photovoltaic modules in a system are operating at maximum power since they are connected to an inverter. So that, their cell temperature is lower than the cell temperature of a module at open-circuit voltage since an important part of the light power density is converted into electricity. In this paper, a procedure for indirectly estimating the cell temperature of a high concentrator photovoltaic system from atmospheric parameters is addressed. Therefore, this new procedure has the advantage that is valid for estimating the cell temperature of a system at any location of interest if the atmospheric parameters are available. To achieve this goal, two different methods are proposed: one based on simple mathematical relationships and another based on artificial intelligent techniques. Results show that both methods predicts the cell temperature of a module connected to an inverter with a low margin of error with a normalised root mean square error lower or equal than 3.3%, an absolute root mean square error lower or equal than 2°C, a mean absolute error lower or equal then 1.5°C, and a mean bias error and a mean relative error almost equal to 0%.

A high-efficiency hybrid high-concentration photovoltaic system

Photovoltaic power generation is a growing renewable primary energy source, expected to assume a major role as we strive toward fossil fuel free energy production. However, the photovoltaic efficiencies limit the conversion of solar radiation into useful power output. Hybrid systems extend the functionality of concentrating photovoltaics (CPV) from simply generating electricity, to providing simultaneously electricity and heat. The utilization of otherwise wasted heat significantly enhances the overall system efficiency and boosts the economic value of the generated power output. The current system consists of a scalable hybrid photovoltaic–thermal receiver package, cooled with an integrated high performance microchannel heat sink. The package can be operated at elevated temperatures due to its overall low thermal resistance between solar cell and coolant. The effect of the harvested elevated coolant temperature on the photovoltaic efficiency is investigated. The higher-level available heat can be suitable for sophisticated thermal applications such as space heating, desalination or cooling (polygeneration approaches). A total hybrid conversion efficiency of solar radiation into useful power of 60% has been realized. The exergy content of the overall output power was increased by 50% through the exergy content of the extracted heat. An analysis based on the economic value of heat illustrates that the reused heat can double the economic value of such a system.

Model for estimating the energy yield of a high concentrator photovoltaic system

The prediction of the energy yield of HCPV (high concentrator photovoltaic) systems is crucial to evaluate the potential and promote the market expansion of HCPV technology. Currently, there is a lack of experience in the modelling of these kinds of systems due to the special features of such technology. In this work, a practical model based on simple mathematical expressions and atmospheric parameters is introduced. The proposed model takes into account the main important parameters which influence the output of a HCPV system such as cell temperature, spectrum and efficiency of the inverter and other losses of the BOS (balance of system). The results obtained are validated using the data of a HCPV installation located at the University of Jaen in southern Spain and monitored daily every minute since 2011. The model accurately predicts the monthly energy yield with a deviation ranging from 4.07% to −0.47% and the annual final energy yield with a deviation of 0.9%.