Concentrated Photovoltaic Solar Cells Research Articles

Cost‐effective energy harvesting at ultra‐high concentration with duplicated concentrated photovoltaic solar cells

AbstractConcentrated photovoltaic (CPV) systems are one of the few technologies that can provide cost reduction while offering efficiency improvement. In this respect, the resistive losses are some of the main limiting factors, which restrict the efficiency improvement and the cost reduction at ultrahigh concentrations (UHCs). In this work, we propose and investigate new designs consisting of duplicated junction solar cells. The approach can resolve the issues related to the resistive losses. Simulation results, based on Shockley‐Queisser limit, demonstrate that the detrimental effects of series resistance losses in the degradation of efficiency at UHC factor can be mitigated with this strategy. The modeled structures are composed of multiple junctions of materials (GaInP, GaAs, and Ge), which are lattice‐matched to Ge or GaAs. These results illustrate the potential of duplicated junction designs for enhancing efficiency of III‐V solar cells under high concentrations, exceeding 1000 suns (under AM1.5D solar spectrum at 300 K). Finally, a relative cost calculation indicates that more than 30% of cost reduction can be achieved using these designs at UHCs.

Integrative passive and active cooling system using PCM and nanofluid for thermal regulation of concentrated photovoltaic solar cells

An integration of passive and active cooling systems for thermal regulation of concentrated photovoltaic (CPV) solar system has been developed and modeled. A heat storage battery of phase change material (PCM) is combined with a closed loop water cooling system in the developed design. A two dimensional model has been developed for the simulation of the CPV layers with the integrated cooling system. Results have been investigated to evaluate the thermal and electrical performances of the system components and the entire system. Further investigations have been conducted to study the effects of different arrangements of the PCM plates in the water tank on the system performances. Enhancing the system performance by using nanofluid as heat transfer fluid (HTF) was also evaluated. Results showed that the proposed system achieves 60% reduction in the CPV average temperature compared to the conventional direct PCM-PV and water-cooling individual systems. At 10 concentration ratio (CR) and 0.01 m/s HTF velocity, the cell temperature does not exceed 78 °C. Moreover, the PCM maximum temperature is kept below the degradation temperature limit. The effect of the PCM plates’ arrangements in the water tank on the system performance is negligible. Using nanofluid as HTF enhancer increases the CPV efficiency by 2.7% and reduces the PV maximum temperature and the PCM melting time by 4 °C and 12%, respectively.

Investigation of water cooled aluminium foam heat sink for concentrated photovoltaic solar cell

Concentrated photovoltaic cell (CPV) is a popular renewable source nowadays. It has high efficient yet cost effective energy harvesting system available in the market. The performance of the CPV depends strongly on the temperature of the solar cell. The efficiency reduces as the surface temperature of the CPV increases. It is crucial to reduce the temperature of the CPV and maintains a small temperature variation along the surface of the CPV. Metal foam is an ideal solution for a CPV thermal management system. It helps to enhance the mixing of coolant due to its porous characteristics and lead to higher heat transfer rate and reduce the overall average temperature of a CPV. The main objective of this study is to enhance the heat removal rate along of the CPV. Aluminium foam is used as a heat sink to removal the heat generated. The effects of porosities and pores density (PPI) of the aluminium foam are measured against the thermal performance. Computational thermal fluid dynamics is conducted to study the thermal performance of aluminium foam heat sink. The parameters required for the simulations are extracted from literature. The results suggested that aluminum foam is able to enhance the heat removal and maintains better temperature uniformity of the CPV. 10PPI aluminum foam with porosity 0.682 provides the most optimum results with average temperature of 55.1 ˚C and temperature different of 7.4 °C at flow rate of 40 g/s. This approach is suitable to promote the efficiency of the CPV and prolong the cycle life.

Numerical study of the geometrically graded metal foam for concentrated photovoltaic solar cell cooling

Abstract Concentrated photovoltaic cell (CPV) had gained much attention recently due to high efficiency at a competitive cost. However, efficiency of CPV is inversely proportional to the temperature. Hence, it is important to reduce the maximum temperature and variation of temperature across the CPV. Metal foam with its high specific surface area, thermal conductivity and tortuous flow path to promote mixing is an ideal candidate for thermal management for CPV. However, the thermal performance of the metal foam may drop from upstream to downstream and lead to poor cooling performance near the outlet. In this study, functionally graded metal foam is attached on the CPV to extract the heat generated. Functionally graded aluminum foam with gradual variation porosity are modelled to investigate the thermal performance and flow field using computational thermal fluid dynamics analysis. Heat transfer correlation, permeability and resistance loss coefficient are extracted from the literature and used in the simulation. The results showed that functionally graded metal foam with gradual reducing porosity offered a better temperature uniformity for the CPV. Therefore, this approach will further extend the cycle life as well as improve the overall efficiency of the CPV.

Thermal Management of Concentrated Multi-Junction Solar Cells with Graphene-Enhanced Thermal Interface Materials

We report results of experimental investigation of temperature rise in concentrated multi-junction photovoltaic solar cells with graphene-enhanced thermal interface materials. Graphene and few-layer graphene fillers, produced by a scalable environmentally-friendly liquid-phase exfoliation technique, were incorporated into conventional thermal interface materials. Graphene-enhanced thermal interface materials have been applied between a solar cell and heat sink to improve heat dissipation. The performance of the multi-junction solar cells has been tested using an industry-standard solar simulator under a light concentration of up to 2000 suns. It was found that the application of graphene-enhanced thermal interface materials allows one to reduce the solar cell temperature and increase the open-circuit voltage. We demonstrated that the use of graphene helps in recovering a significant amount of the power loss due to solar cell overheating. The obtained results are important for the development of new technologies for thermal management of concentrated photovoltaic solar cells.

Pushing the limits of concentrated photovoltaic solar cell tunnel junctions in novel high‐efficiency GaAs phototransducers based on a vertical epitaxial heterostructure architecture

AbstractA monolithic compound semiconductor phototransducer optimized for narrow‐band light sources was designed for achieving conversion efficiencies exceeding 50%. The III‐V heterostructure was grown by metal‐organic chemical vapor deposition, based on the vertical stacking of 5 partially absorbing GaAs n/p junctions connected in series with tunnel junctions. The thicknesses of the p‐type base layers of the diodes were engineered for optimal absorption and current matching for an optical input with wavelengths centered near 830 nm. Devices with active areas of ~3.4 mm2 were fabricated and tested with different emitter gridline spacings. The open circuit voltage (Voc) of the electrical output is five times or more than that of a single GaAs n/p junction under similar illumination. The device architecture allows for improved Voc generation in the individual base segments because of efficient carrier extraction while simultaneously maintaining a complete absorption of the input photons with no needs for complicated fabrication processes or reflecting layers. With illumination powers in the range of a few 100 mW, the measured fill factor (FF) varied between 88 and 89%, and the Voc reached over 5.75 V. The data also demonstrated that a proper combination of highly doped emitter and window layers without gridlines is adequate for sustaining such FF values for optical input powers of several hundred milliwatts. As the optical input power is further increased and approaches 2 W (intensities ~58 W/cm2), the multiple tunnel junctions sequentially exceed their peak current densities in the case for which typical (n++)GaInP/ (p++)AlGaAs concentrated photovoltaic tunnel junctions are used. Lower bandgap tunnel junctions designed with improved peak current densities result in phototransducer devices having high FF and conversion efficiencies for up to 5 W optical input powers (intensities ~144 W/cm2). Measurements at different temperatures revealed a Voc reduction of −6 mV/°C at ~59 W/cm2. Copyright © 2015 John Wiley & Sons, Ltd.

Effect of placing GaAs solar cells on the optical rod prism of a concentrated photovoltaic

In a concentrated photovoltaic (CPV) solar cell system, placing an additional solar cell on an optical rod prism with parallel connection to the original cell generated more than 12.1 mA output current and 15.6% output power under the same illumination conditions. This mechanism provided a simple method to enhance the utility rate of CPV solar cells. Such a concept can be further applied to the aerospace industry and to the development of CPV solar energy.