Terrestrial Photovoltaics Research Articles

Review of Recent Offshore Floating Photovoltaic Systems

Photovoltaic (PV) power generation is a form of clean, renewable, and distributed energy that has become a hot topic in the global energy field. Compared to terrestrial solar PV systems, floating photovoltaic (FPV) systems have gained great interest due to their advantages in conserving land resources, optimizing light utilization, and slowing water evaporation. This paper provides a comprehensive overview of recent advancements in the research and application of FPV systems. First, the main components of FPV systems and their advantages as well as disadvantages are analyzed in detail. Furthermore, the research and practical applications of offshore FPV systems, including rigid floating structures and flexible floating structures, are discussed. Finally, the challenges of offshore FPV systems are analyzed in terms of their stability and economic performance. By summarizing current research on FPV systems, this overview aims to serve as a valuable resource for the development of offshore FPV systems.

Floating photovoltaics performance simulation approach

Floating photovoltaics (FPVs) provide various benefits especially where land is scarce (e.g., reducing land occupancy, water evaporation and environment control…), or when they are combined with hydropower plants (enhanced capacity factor and green energy generation). Software such as PV∗SOL, SAM and PVSyst® are commonly used for the design and simulation of land-based photovoltaic (PV) systems. However, when it comes to the simulation of photovoltaics installed on water surface, such software does not offer the option to directly simulate FPV systems.In this work, a new approach combining MATLAB and Rhino/Grasshopper environments is proposed for the assessment of FPV systems performance. The approach is divided into various steps considering major influencing parameters such as temperature, irradiance, albedo, PV modelling, panel rows spacing, tilt angle, as well as the benefits of including a tracking mechanism. The proposed approach was validated against PV∗SOL simulations for land-based PV systems with a small deviation of less than 2.4%. FPVs simulations considering climatic conditions of Štěchovice, Czechia, showed an increase of the performance in the range of 3% compared to terrestrial PVs. This result is in accordance with some published studies based on real FPVs installations. Finally, the developed approach was applied in the simulations of two large-scale FPV systems with different designs (fixed and with a tracking mechanism) including economical aspects.

Prospects of light management in perovskite/silicon tandem solar cells

Abstract Perovskite/silicon tandem solar cells are regarded as a promising candidate to surpass current efficiency limits in terrestrial photovoltaics. Tandem solar cell efficiencies meanwhile reach more than 29%. However, present high-end perovskite/silicon tandem solar cells still suffer from optical losses. We review recent numerical and experimental perovskite/silicon tandem solar cell studies and analyse the applied measures for light management. Literature indicates that highest experimental efficiencies are obtained using fully planar perovskite top cells, being in contradiction to the outcome of optical simulations calling for textured interfaces. The reason is that the preferred perovskite top cell solution-processing is often incompatible with usual micropyramidal textures of silicon bottom cells. Based on the literature survey, we propose a certain gentle nanotexture as an example to reduce optical losses in perovskite/silicon tandem solar cells. Optical simulations using the finite-element method reveal that an intermediate texture between top and bottom cell does not yield an optical benefit when compared with optimized planar designs. A double-side textured top-cell design is found to be necessary to reduce reflectance losses by the current density equivalent of 1 mA/cm2. The presented results illustrate a way to push perovskite/silicon tandem solar cell efficiencies beyond 30% by improved light management.

Multijunction solar arrays for space and terrestrial applications

Photovoltaic conversion of the solar energy is the most prospective direction of the renewable power engineering. Solar arrays ensure power supply of spacecrafts and are gaining increasingly more application on the Earth. In the majority of developed countries, laws on state support of the green power engineering assisted in a substantial increase of power of the solar photovoltaic systems have been adopted. The main barrier to increasing the terrestrial solar photovoltaics development rates is a relatively high cost of the solar electric power. The ways for reducing the cost are the rise of the efficiency of power systems and the reduction of the material consumption for arrays based on multijunction solar cells. Results of multijunction solar cells and modules developments for space and terrestrial solar arrays are discussed in the article. In the last years, a significant experience on creation of multijunction solar cells was accumulated. Cascade solar cells and solar photovoltaic installations on their base with sunlight concentrators have been developed. At present, the terrestrial cascade solar cell efficiency exceeds 45%, which is substantially higher than that in conventional Si and thin-film solar arrays. The cascade solar cell efficiency increase has been achieved at the expense of splitting the sunlight spectrum into several intervals by the solar cell semiconductor structure fulfilling more effective photon energy conversion of each of these intervals in a definite parts of this structure. It is shown that multijunction solar cells provide the highest efficiency and they are the basic components of space arrays. Multijunction solar cells provide the highest conversion efficiency of concentrated sunlight as well. It opens prospects for decreasing the solar cell area and cost proportionally to the sunlight concentration. Developed concentrated photovoltaic installations are promising for wide applications in the high scale terrestrial solar photovoltaic energetics.

III-V-Based Optoelectronics with Low-Cost Dynamic Hydride Vapor Phase Epitaxy

Silicon is the dominant semiconductor in many semiconductor device applications for a variety of reasons, including both performance and cost. III-V materials exhibit improved performance compared to silicon, but currently, they are relegated to applications in high-value or niche markets, due to the absence of a low-cost, high-quality production technique. Here we present an advance in III-V materials synthesis, using a hydride vapor phase epitaxy process that has the potential to lower III-V semiconductor deposition costs, while maintaining the requisite optoelectronic material quality that enables III-V-based technologies to outperform Si. We demonstrate the impacts of this advance by addressing the use of III-Vs in terrestrial photovoltaics, a highly cost-constrained market.

III-V Nanomembranes for High Performance, Cost-Competitive Photovoltaics

ABSTRACTDue to their highly favorable materials properties such as direct bandgap, appropriate bandgap energy against solar spectrum, and ability to form multiple junctions, epitaxially grown III-V compound semiconductors such as gallium arsenide have provided unmatched performance over silicon in solar energy harvesting. However, their large-scale deployment in terrestrial photovoltaics remains as a daunting challenge mainly due to the high cost of growing device-quality epitaxial materials. In this regard, releasable multilayer epitaxial growth in conjunction with printing-based deterministic materials assemblies represents a promising approach that can overcome this challenge but also create novel engineering designs and device functionalities, each with significant practical values in photovoltaic technologies. This article will provide an overview of recent advances in materials design, fabrication concept, and nanophotonic light management of multilayer-grown nanomembrane-based GaAs solar cells aiming for high performance, cost-efficient platforms of III-V photovoltaics.

Multilayer-Grown Ultrathin Nanostructured GaAs Solar Cells as a Cost-Competitive Materials Platform for III–V Photovoltaics

Large-scale deployment of GaAs solar cells in terrestrial photovoltaics demands significant cost reduction for preparing device-quality epitaxial materials. Although multilayer epitaxial growth in conjunction with printing-based materials assemblies has been proposed as a promising route to achieve this goal, their practical implementation remains challenging owing to the degradation of materials properties and resulting nonuniform device performance between solar cells grown in different sequences. Here we report an alternative approach to circumvent these limitations and enable multilayer-grown GaAs solar cells with uniform photovoltaic performance. Ultrathin single-junction GaAs solar cells having a 300-nm-thick absorber (i.e., emitter and base) are epitaxially grown in triple-stack releasable multilayer assemblies by molecular beam epitaxy using beryllium as a p-type impurity. Microscale (∼500 × 500 μm2) GaAs solar cells fabricated from respective device layers exhibit excellent uniformity (<3% relative) of photovoltaic performance and contact properties owing to the suppressed diffusion of p-type dopant as well as substantially reduced time of epitaxial growth associated with ultrathin device configuration. Bifacial photon management employing hexagonally periodic TiO2 nanoposts and a vertical p-type metal contact serving as a metallic back-surface reflector together with specialized epitaxial design to minimize parasitic optical losses for efficient light trapping synergistically enable significantly enhanced photovoltaic performance of such ultrathin absorbers, where ∼17.2% solar-to-electric power conversion efficiency under simulated AM1.5G illumination is demonstrated from 420-nm-thick single-junction GaAs solar cells grown in triple-stack epitaxial assemblies.

High Performance Ultrathin GaAs Solar Cells Enabled with Heterogeneously Integrated Dielectric Periodic Nanostructures.

Due to their favorable materials properties including direct bandgap and high electron mobilities, epitaxially grown III-V compound semiconductors such as gallium arsenide (GaAs) provide unmatched performance over silicon in solar energy harvesting. Nonetheless, their large-scale deployment in terrestrial photovoltaics remains challenging mainly due to the high cost of growing device quality epitaxial materials. In this regard, reducing the thickness of constituent active materials under appropriate light management schemes is a conceptually viable option to lower the cost of GaAs solar cells. Here, we present a type of high efficiency, ultrathin GaAs solar cell that incorporates bifacial photon management enabled by techniques of transfer printing to maximize the absorption and photovoltaic performance without compromising the optimized electronic configuration of planar devices. Nanoimprint lithography and dry etching of titanium dioxide (TiO2) deposited directly on the window layer of GaAs solar cells formed hexagonal arrays of nanoscale posts that serve as lossless photonic nanostructures for antireflection, diffraction, and light trapping in conjunction with a co-integrated rear-surface reflector. Systematic studies on optical and electrical properties and photovoltaic performance in experiments, as well as numerical modeling, quantitatively describe the optimal design rules for ultrathin, nanostructured GaAs solar cells and their integrated modules.

A direct thin-film path towards low-cost large-area III-V photovoltaics

III-V photovoltaics (PVs) have demonstrated the highest power conversion efficiencies for both single- and multi-junction cells. However, expensive epitaxial growth substrates, low precursor utilization rates, long growth times, and large equipment investments restrict applications to concentrated and space photovoltaics (PVs). Here, we demonstrate the first vapor-liquid-solid (VLS) growth of high-quality III-V thin-films on metal foils as a promising platform for large-area terrestrial PVs overcoming the above obstacles. We demonstrate 1–3 μm thick InP thin-films on Mo foils with ultra-large grain size up to 100 μm, which is ~100 times larger than those obtained by conventional growth processes. The films exhibit electron mobilities as high as 500 cm2/V-s and minority carrier lifetimes as long as 2.5 ns. Furthermore, under 1-sun equivalent illumination, photoluminescence efficiency measurements indicate that an open circuit voltage of up to 930 mV can be achieved, only 40 mV lower than measured on a single crystal reference wafer.

Making Solar Cells a Reality in Every Home: Opportunities and Challenges for Photovoltaic Device Design

Globally, the cumulative installed photovoltaic (PV) capacity has topped the 100-gigawatt (GW) milestone and is expected to reach 200 GW by the year 2015. More than 90% of the installed PV capacity employs bulk-silicon solar cells. Engineering problems that include thermal and optical challenges have not permitted the large-scale commercialization of concentration PV systems, lack of functional reliability-and the concomitant lack of economic bankability-being a major barrier. For increasing the efficiency of single-junction cells beyond the Shockley-Queisser limit, several approaches based on concepts such as multiple exciton generation, carrier multiplication, hot-carrier extraction, etc., have been proposed; however, these do not seem to be commercially viable. Since both bulk-silicon and thin-film (amorphous silicon, cadmium telluride, and copper indium gallium selenide) solar cells remain as the only two commercially viable options for terrestrial PV applications, a multi-terminal multi-junction architecture appears promising for inexpensive PV electricity generation with efficiency exceeding the currently feasible 25%. The architecture exploits the present commercial silicon solar cells along with abundant and ultra-low-cost materials such as Cu2O. With the availability of well-controlled manufacturing processes at the sub 2-nm length scale, it will become possible to manufacture ultra-high efficiency and ultra-low cost PV electricity generation modules based on silicon.

Materials challenges for terrestrial thin-film photovoltaics

The terrestrial photovoltaics market has been dominated from the beginning by crystalline silicon and by cast multicrystalline silicon. Continuing improvements in materials quality and innovative designs are responsible for keeping silicon solar cells at a market share of about 85%. However, in the past two years, thin-film solar modules based on amorphous silicon, cadmium telluride, and copper indium gallium diselenide have gained a strong foothold in the market, particularly in the United States and Europe. This article will briefly review the status of silicon solar cells and then discuss developments, opportunities, and materials challenges in thin-film solar cells.

Transparent Conducting Oxides for Photovoltaics

AbstractTransparent conducting oxides (TCOs) are an increasingly important component of photovoltaic (PV) devices, where they act as electrode elements, structural templates, and diffusion barriers, and their work function controls the open-circuit device voltage. They are employed in applications that range from crystalline-Si heterojunction with intrinsic thin layer (HIT) cells to organic PV polymer solar cells. The desirable characteristics of TCO materials that are common to all PV technologies are similar to the requirements for TCOs for flat-panel display applications and include high optical transmissivity across a wide spectrum and low resistivity. Additionally, TCOs for terrestrial PV applications must use low-cost materials, and some may require device-technology-specific properties. We review the fundamentals of TCOs and the matrix of TCO properties and processing as they apply to current and future PV technologies.

Towards highly efficient 4-terminal mechanical photovoltaic stacks

At present renewable energy sources consist mainly of hydro power and wind energy, with the latter becoming increasingly important. However, the number of solar cells being produced yearly (in terms of watts produced by these solar cells under a standardized spectrum) has been growing consistently over the last 10 years, with growth rates between 25 and 70%/year; for 2005 solar cell production reached 1.7GW. This terrestrial photovoltaic (PV) market is currently dominated by flat plate modules incorporating Si solar cells. However, to sustain the present growth rate of terrestrial PV, the use of expensive semiconductor material must be minimized, necessitating the development of new technologies.

Triple-Junction III–V Based Concentrator Solar Cells: Perspectives and Challenges

This paper gives a review of the work performed in the framework of the EC-funded project FULLSPECTRUM aiming for higher photovoltaic (PV) conversion efficiencies by investigating GaInP∕GaInAs∕Ge triple-junction concentrator solar cells. Lattice mismatched structures reached efficiencies beyond 35% at 600 sun concentration level. These cells are now ready to enter the terrestrial PV market. The perspectives and challenges associated with the market introduction of these cells are addressed. Specifically issues of reliability and on-wafer characterization are discussed. A new characterization tool MAPCON was developed and is presented.

Space and terrestrial photovoltaics: synergy and diversity

AbstractA historical view of the research and development in photovoltaics from the perspective of both the terrestrial and the space communities is presented from the early days through the 1970s and 1980s, 1990s and beyond. The synergy of both communities, both at the beginning and in the present, and hopefully in the future, are highlighted, with examples of the important features in each program. The space community which was impressed by the light weight and reliability of photovoltaics drove much of the early development. Even today, nearly every satellite and other scientific space probe that has been launched has included some solar power. However, since the cost of these power systems was only a small fraction of the satellite and launch cost, the use of much of this technology in the terrestrial marketplace was not feasible. It was clear that the focus of the terrestrial community would be best served by reducing costs. This would include addressing a variety of manufacturing issues and raising the rate of production. Success in these programs and a resulting globalization of effort resulted in major strides in the reduction of PV module costs and increased production. Although, the space community derived benefit from some of these advances, its focus was on pushing the envelope with regard to cell efficiency. The gap between theoretical efficiencies and experimental efficiencies for silicon, gallium arsenide and indium phosphide became almost nonexistent. Recent work by both communities have focused on the development thin‐film cells of amorphous silicon, CuInSe2 and CdTe. These cells hold the promise of lower costs for the terrestrial community as well as possible flexible substrates, better radiation resistance, and higher specific power for the space community. It is predicted that future trends in both communities will be directed toward advances through the application of nanotechnology. A picture is emerging in which the space and terrestrial solar cell communities shall once again share many common goals and, in fact, companies may manufacture both space and terrestrial solar cells in III–V materials and thin‐film materials. Basic photovoltaics research, including these current trends in nanotechnology, provides a valuable service for both worlds in that fundamental understanding of cell processes is still vitally important, particularly with new materials or new cell structures. It is entirely possible that one day we might have one solar array design that will meet the criteria for success in both space and on the Earth or perhaps the Moon or Mars. Published in 2002 by John Wiley &amp; Sons, Ltd.

Terrestrial photovoltaic technologies update

A description of terrestrial photovoltaics (PV), what it is and what it accomplishes, and a very brief historical perspective of its development are presented. Today's leading technologies are identified and discussed. Current areas for improvement and suggestions for future R&D focus are presented. Information is provided on the latest developments in terms of efficiencies, cost, industry output and prospects. The most suited applications are also addressed.

Third generation photovoltaics: Ultra‐high conversion efficiency at low cost

AbstractSince the early days of terrestrial photovoltaics, a common perception has been that ‘first generation’ silicon wafer‐based solar cells eventually would be replaced by a ‘second generation’ of lower cost thin‐film technology, probably also involving a different semiconductor. Historically, cadmium sulphide, amorphous silicon, copper indium diselenide, cadmium telluride and now thin‐film polycrystalline silicon have been regarded as key thin‐film candidates. Any mature solar cell technology seems likely to evolve to the stage where costs are dominated by those of the constituent materials, be they silicon wafers or glass sheet. It is argued, therefore, that photovoltaics is likely to evolve, in its most mature form, to a ‘third generation’ of high‐efficiency thin‐film technology. By high efficiency, what is meant is energy conversion values double or triple the 15–20% range presently targeted, closer to the thermodynamic limit of 93%. Tandem cells are the best known of such high‐efficiency approaches, where efficiency can be increased merely by adding more cells of different bandgap to a cell stack, at the expense of increased complexity and spectral sensitivity. However, a range of other more ‘paralleled’ approaches offer similar efficiency to an infinite stack of tandem cells. These options are reviewed together with possible approaches for practical implementation, likely to become more feasible with the evolution of materials technology over the next two decades. Copyright © 2001 John Wiley &amp; Sons, Ltd.

The U. S. PV program: Now and the year 2000

There will be a vigorous U.S. Photovoltaic (PV) program in 2000, despite the current turmoil and debate over the size and legitimate role of nearly every aspect of the Federal government. There are two fundamental reasons why there will still be an active Federal role in PV development in the 21st century. First, as the program and technology have progressed, the environmental and job creation potential of the PV industry are increasingly recognized as important to the nation's future. Second, Federal investment in research and development is necessary to counteract the private sector's tendency to under-invest in research and development. What will change is the emphasis and role of the Federal PV program, because the PV industry is changing. The U.S. government is no longer the principal customer of the PV industry, and research and development is more of an equal partnership between government and industry compared to 1974, when the terrestrial PV research program began. Today, industry revenues and markets are continuing to grow, while Federal R&D investments will remain relatively stable or contract between then and now. From 1994 to 1995 PV sales increased over 21 percent, from 70 MW to 84 MW, and are expected to continue along this trend. In contrast, from FY95 to FY96, the U.S. PV research budget dropped by roughly 31%. In spite of changes in the relative size of government and industry resources, the PV Program's strategic focus on technology validation, market conditioning, and joint ventures will continue into the year 2000 and beyond, but the relative share of resources and leadership in key areas will continue to shift toward industry.

Photovoltaic Efficiency Measurements

A variety of performance indicators have been employed by the photovoltaic (PV) community to rate the performance of PV cells, modules, and arrays. The PV power conversion efficiency under a set of standard reporting conditions serves as a basis for meaningful comparisons of PV performance, within and among PV technologies. PV efficiency is defined as 100 times the maximum PV electrical power density produced divided by the incident light power at a reference PV temperature, total irradiance, and spectral irradiance. Standard reporting conditions commonly used by the PV community are summarized in Table I.The direct and global reference spectra were generated by a comprehensive Monte-Carlo computer model and actually integrate to 768 W m−2 and 964 W m−2. The terrestrial PV community has arbitrarily assigned a 1-sun total irradiance of 1,000 W m−2 for the global and direct reference spectra. The term “direct” in Table I refers to the direct-normal (5° field of view about the sun) component of the global spectral irradiance distribution. The term “global” in Table I refers to the spectral irradiance distribution on a 37-tilted south-facing surface with a solar zenith angle of 48.2° (AM1.5). The terms AM1 or AM1.5 are often used to refer to standard spectra, but the relative optical air mass (AM) is a geometrical quantity and can be obtained by taking the secant of the angle between the sun and the zenith.

The first forty years: A brief history of the modern photovoltaic age

AbstractThis brief history of the modern photovoltaic (PV) age is divided into four major periods: the beginning in 1953‐1954; the next steps, 1954‐1956; the space PV period, 1956‐1970; and the terrestrial PV period, 1970 onwards. the author began his participation in photovoltaics in 1953 and has been a participant in, or a witness to, the events that he describes.