Solar cells with one-day energy payback for the factories of the future

Benzodithiophene-Based Small-Molecule Donors for Next-Generation All-Small-Molecule Organic Photovoltaics

Due to the intermittent nature of sunlight, practical solar energy utilization systems demand both efficient solar energy conversion and inexpensive large scale energy storage. We will first discuss the rational design and demonstration of efficient photoelectrochemical hydrogen generation systems using efficient semiconductors and earth-abundant catalyst materials. We have further developed novel hybrid solar-charged storage devices that integrate regenerative photoelectrochemical solar cells and redox flow batteries (RFBs) that share the same pair of redox couples. In these integrated solar flow batteries (SFBs), solar energy is absorbed by semiconductor electrodes and photoexcited caries are collected at the semiconductor-liquid electrolyte interface and used to convert the redox couples in the RFB to fully charge up the battery. When electricity is needed, the charged up redox couples will be discharged on carbon electrodes to generate the electricity as in a RFB. We have demonstrated that such SFB devices can be charged under solar light without external electric bias and deliver a high discharge capacity comparable with state-of-the-art RFBs over many cycles. After developing silicon solar cells and high performance solar cells, carefully matching them with various organic or inorganic redox couples, and optimizing several generations of SFB device designs, we have recently achieved integrated SFB device with an overall direct solar-to-output electricity efficiency (SOEE) of 14%. These high performance SFBs can serve as distributed and standalone solar energy conversion and storage systems in remote locations and enable practical off-gird electrification.

Clean and low-carbon energy sources and technologies have emerged as a critical driver in delivering the energy transition and achieving net zero-carbon emissions. All energy sources and power systems produce greenhouse gases (GHGs) and hence they contribute to anthropogenic greenhouse gas emissions and resultant climate change besides contributing to other negative environmental impacts. Energy sustainability remains a major challenge globally due to current heavy reliance on depletable and polluting fossil fuels for most of global energy needs. This study examines the energy transition strategies and proposes a roadmap for sustainable energy transition for sustainable energy planning and grid electricity generation and supply in wake of commitments made by the world community to the Paris Agreement aimed at reducing greenhouse gas emissions and limiting the rise in global average temperature to 2oC and preferably 1.5oC above the preindustrial level and realisation of the sustainable development goal of the United Nations. The sustainable transition strategies typically consist of three major technological changes namely, energy savings on the demand side, generation efficiency at production level and fossil fuel substitution by various renewable energy sources and low carbon non-renewable sources like nuclear power and carbon emission reduction strategies like carbon capture and sequestration and a conversion from high carbon fossil fuels like coal and oil to natural gas which remains the cleanest fossil fuel. The study demonstrated that decentralised generation with application of both demand side management and behind the meter management (BTM) strategies are effective measures to increase the use of renewable energy resources which are often locally available leading to higher uptake of renewable energy sources and conversion of consumers to prosumers making the transition economically sustainable. Waste to energy options have a significant potential to contribute to the energy transition e.g. use of biowaste for biogas production, slaughterhouse waste biodigestion for biogas and electricity generation and waste treatment and disposal, waste heat recovery from used geothermal for extra power generation and reinjection to improve the reservoir sustainability and use of bagasse and sugarcane trash for grid-based power production in sugar factories. Therefore, domestic, and industrial scale waste to energy conversion can enhance the economic sustainability of waste management process by offering useful energy substitutes for fossil fuels and enhanced energy security through decentralisation of generation. Whereas sustainable development has social, economic, and environmental pillars, energy sustainability is best analysed by five-dimensional approach consisting of environmental, economic, social, technical, and institutional/political sustainability to determine energy resource sustainability. The study recommends the adoption of sustainability-based planning for energy development and optimisation of electricity generation and supply where energy sources are analysed and ranked based on the five dimensions of energy sustainability instead of Least Cost Development Planning (LCDP) often applied by many countries. On this basis, the sustainable energy transition and optimisation of power generation will rely on both renewable and non-renewable energy since both have an important role in the realisation of the energy transition plans even though the desire is to shift entirely to renewable energy sources by the year 2050. The sustainability of various energy sources was assessed with hydrogen, wind, solar, sugarcane bagasse and cane trash, biogas and ocean energy technologies proving to be among the most sustainable renewable energy and sustainable sources. The study also examined various power plants and energy conversion systems for electricity generation in terms of their specific role and potential in grid-based power generation with hydro power plants, geothermal, nuclear, fuel cells, raking high on performance indicators like load and capacity factors making them ideal for base load power supply. Diesel engines and gas turbines using cogeneration and dual cycle systems powered by cleaner fuels like natural gas, hydrogen and biomethane will play an important role in supplying intermediate and peak load power. The study highlighted enabling technologies and concepts in the energy transition which include decentralisation of generation, cogeneration and trigeneration, demand side and behind the meter management microgrids and smart grid technologies, energy and generation planning and optimisation models, energy storage, electrification of transport and use of electric cars as decentralised electricity sources through the V2X technologies like the G2V and V2G, and carbon capture and sequestration for emissions reduction in fossil fuel power plants making them more sustainable. The study classifies electric vehicles as distributed power plants and variable loads with extensive use of energy storage while sugar cane bagasse is noted as a sustainable energy resource for power generation by cane sugar factories by application of more efficient grid connected cogeneration power plants. The study identified long project gestation period as the main factor limiting nuclear and geothermal energy deployment and recommends the adoption of modularised wellhead generators and small modular nuclear reactors (SMRs) as a solution to enhance exploitation of these sustainable energy and technologies through faster deployment with high degree of flexibility. Biogas and biomethane demonstrated significant potential as renewable energy sources for power generation and substitute fuels in all applications of fossil natural gas. The study recommends sustainability-based planning for the energy sector and power generation and use of both renewable and non-renewable but sustainable sources of energy, adoption of smart energy concept by all sectors and investment in energy technology and infrastructure development for hydrogen and other promising energy sources like ocean thermal, wave and tidal energy and the conversion of the transition from the traditional to smart grid systems and a shift from centralised to decentralised power generation. Since the transport sector accounts for a significant portion of the global greenhouse gas emissions, electrification of the transport sector and coupling with the power sector is a key strategy recommended for the transition with the smart grid and microgrids playing an enabling role. Since energy sources and generation technologies have associated emissions occurring at different sections of the lifecycle, the use of lifecycle costs and emissions are helpful in long term energy and generation planning which demonstrate that renewable sources and nuclear are the most sustainable when analysed within the five dimensions of energy sustainability, but with the non-renewable sources playing a critical role as dispatchable sources for sustainable grid power generation, while the smart grids and use of energy storage can increase the uptake of variable renewables to as high as 95% to 100% up from a low of 20-25% uptake of variable renewables with the traditional grid. This will significantly help the world in achieving the global emissions and climate targets as. stipulated in the Paris Agreement as well as the sustainable development goals (SDGs). Graphical Abstract The overall objective of the study was to provide solutions to build global energy systems based on renewable and sustainable energy resources and optimise power generation and consumption by use of sustainable energy resources and generation technologies based on the five dimensions of energy sustainability. A sustainable energy system should intergrade electricity and other sectors through smart electricity grids, smart gas grids and smart heat grids as demonstrated below.

Increasing the global energy demand as well as the carbon dioxide (CO2) level in the atmosphere caused by burning fossil fuel as the main source of energy motivate the development of green energy technologies. However, the real activity improvement for these technologies is mainly impeded by intermittent nature of renewable energy technologies. One smart approach to overcome this issue is to store energy into the chemical bonds1–6 using inexpensive and efficient energy conversion and storage technologies. In these systems, energy can be converted or stored into chemical bonds as a form of fuels or electricity using renewable energy sources, e.g., solar and wind energy7–9. Despite recent progress, the development of these systems is advanced far more slowly due to the expensive and less efficient materials employed in these technologies. Here, I will present my aim to design, synthesis, and characterization of inexpensive earth-abundant transition metal dichalcogenide class of materials suitable for energy conversion and storage systems. I have tested the performance of this class of catalysts for the carbon dioxide (CO2) reduction reaction, oxygen reduction, oxygen evolution reactions. The results indicate (i) 100 times higher turn over frequency- per atom activity- far exceeding the performance of state-of-the-art catalysts for CO2 reduction reaction, and (ii) a highly efficient bi-functional catalyst for oxygen reduction and evolution reactions in the aprotic media compared to conventional noble metal catalysts used for the same application (e.g., Platinum and Gold). I also tested the performance of molybdenum disulfide nanoflakes (MoS2 NFs) -a versatile member of TMDCs- in lithium-air batteries known as a promising alternative to the conventional lithium-ion batteries. The results indicate that MoS2 NFs in the ionic liquid EMIM-BF4 electrolyte performs remarkably well in the actual air environment with a small discharge/charge potential gap as well as good stability and cyclability up to 550 cycles without any evidence of failure. I will discuss these and other results including the potential of our recent discovery to open a new route towards energy efficient, highly active and cost-effective energy storage and conversion systems to replace fossil fuels.

Net energy analysis for concentrated solar power plants in northern Chile

Life cycle analysis for future photovoltaic systems using hybrid solar cells

Surface passivation and optical design of silicon heterojunction solar cells

The Chilean Energy Policy calls for 15 percent of new power generation capacity to come from renewable energy sources from 2006 to 2010, and then a 5% of electric energy generated from renewable energy sources with gradual increases in order to reach 10% by 2024. Concentrated solar power is an interesting alternative to help achieving those objectives, as it is estimated that northern Chile has high radiation levels, coupled with high values of the local clearness index and availability of flat terrain. The present report investigates the net energy attributes of parabolic trough plants installed in the Atacama Desert. Monthly means of solar radiation are used in order to estimate the solar fraction for a 100 MW plant at three different locations. Our analysis considers three cases: operation during sunlight hours only, with and without fossil fuel back-up, and continuous operation during 24 hours a day. The net energy analysis for concentrated solar power (CSP) plants is then performed, considering the energy costs of manufacturing, transport, installation, operation and decommissioning. The results indicate that the CSP plants are a net energy source when operating in sunlight-only mode and that the energy payback time is a linear function of the total operation time when utilizing fossil fuel back-up. In the continuous operation mode, the CSP plants become fossil fuel plants with solar assistance, and therefore all locations display negative net energy. Based on this result, the back-up fraction required for the plants to be net energy sources is estimated from the EROEI as function of the back-up fraction. It is estimated that the net energy analysis is a useful tool for determining under which conditions a CSP plant becomes a net energy source, and thus can be utilized in order to define geographical locations and operation conditions where they can be considered renewable energy sources.

The favorable bandgap and natural abundance of Si, combined with the large expertise base for semiconductor wafer processing, have led to the use of wafer-based crystalline Si in the vast majority of photovoltaic cells and modules produced worldwide. However the high cost of purifying, crystallizing, and sawing Si wafers has inhibited these photovoltaic energy sources from approaching cost parity with fossil fuels. Crystalline Si microwires, grown by the catalytic vapor-liquid-solid (VLS) chemical vapor deposition process, have recently emerged as promising candidate materials for thin-film photovoltaics--combining low-cost Si deposition techniques with mechanically flexible, high-performance device geometries. This thesis presents several achievements that have helped to establish the viability of high-performance Si microwire photovoltaics. We begin by developing a comprehensive numerical model of Si microwire-array solar cells, combining finite-element device physics simulations with time-domain optical methods to predict that these devices can exceed 17% solar energy conversion efficiency. We then turn our attention to the optical properties of Si microwire arrays, concerned that the sparsely packed wires might not absorb enough sunlight. However our experiments reveal that simple light-trapping techniques can dramatically improve their absorption, not only permitting them to effectively absorb sunlight using 1/100th as much Si as a wafer, but also leading to an unexpected and fundamentally advantageous absorption enhancement over classical light trapping in planar materials. Techniques are then presented to characterize the material quality of VLS-grown Si wires. Although the growth of these wires is catalyzed by notoriously undesirable metal impurities for crystalline Si (e.g., Au, Ni, and Cu), we find it is nonetheless possible to synthesize high-quality material with remarkable diffusion lengths. By combining these materials with effective surface-passivation and a novel junction-fabrication technique, we realize single-wire solar cells that achieve open-circuit voltages of ~600 mV and with fill factors exceeding 80%. These observations suggest that Si microwires may offer a promising alternative to wafers for cost-effective crystalline Si photovoltaics.

Solar cell has gained Wide Attention in the last decade or so due to the fact that solar cell has the potential to tap the worlds current energy demand of 15TW besides this solar cell is renewable and cleaner source of energy unlike fossil fuel . The primary problem currently with the solar cell is that it has relatively low efficiency and expensive installation and very long energy payback time. Lot of research and development is going on to make solar cells affordable recently polymer solar cell gained wide attention worldwide as it belongs to the category of direct band gap semiconductors which helps in decreasing the thinness of photo-voltaic up to a level of few micrometer also the polymer solar cell has an inherit advantage of flexibility, very low thickness but has incorporated with an disadvantage of low efficiency which is around 11% but tandem solar cell which is comprised of two layers of different active material which enables the cell to cover broad spectrum and overall increase in efficiency. Tandem solar cell has a huge potential due to utilization of energy extracted from two active layers in a single solar cell that’s the reason there is noticeable addition in the performance, efficiency and other parameters of the solar cell. This article tends to provide an overview how tandem solar cell works, the polymer material that is being used in tandem solar cell which is divided into two categories high energy band gap polymers and low energy band gap polymers then discussing different types and use of interconnecting layer in polymer tandem solar cell.

Rapid escalation in energy demand and pressure over finite fossil fuels reserves with augmenting urbanization and industrialization points towards adoption of cleaner, sustainable and eco-friendly sources to be employed. Solar cell devices known for efficient conversion of solar energy to electrical energy have been attracting scientific community due to their remarkable conformity with the principles of green chemistry. The future candidacy of solar cells is expressed by their efficient conversion. Such a great potential associated with solar cells has instigated research since many decades leading to the emergence of a wide myriad of solar cells devices with novel constituent materials, designs and architecture reflected in form of three generations of the solar cells. Considering the cleaner and sustainability aspects of the solar energy, current review has systematically compiled different generations of solar cells signifying the advancements in terms of architecture and compositional parameters. In addition to the chronological progression of solar cells, current review has also focused on the innovations done in improvement of solar cells. In terms of efficiency and stability, photovoltaic community is eager to achieve augmented efficiencies and stabilities for using solar cells as an alternative to the conventional fossil fuels.

The photoelectrochemical (PEC) production of hydrogen offers a direct pathway for the conversion of solar energy into an energy dense and transportable fuel. In an integrated PEC device, solar radiation is absorbed by photoactive components which provide the necessary potential for water electrolysis to take place in the integrated proton exchange membrane electrolysis cell (PEMEC). The produced current density in the photovoltaic component (PV) increases with increasing solar irradiation, i.e. concentration. This results in higher hydrogen production rates for a PEMEC with small overpotentials, i.e. good ohmic conductors and efficient catalysts, compared to non-concentrating systems. We also expect further reduction in energy and material requirements of a concentrated PEC (CPEC) device and its fabrication and, consequently, its energy payback time (EPBT). We compared the EPBT of PEC and CPEC devices for water electrolysis. For the latter, we compared existing concentrating technologies - lenses, mirrors, and Cassegrain reflectors - and a novel integrated CPEC device using a self-tracking wave-guide concentrator.We developed a model that assesses the energy requirements of the different component (concentrator, electrolysis cell, photovoltaic cell, external components) by coupling the energy and material inventory of devices to a detailed performance model under different concentrations. The model uses the Shockley-Queisser limit to assess the performance of the multijunction photovoltaic cell, and an equivalent circuit model was used to assess the performance of the electrolysis cell, including kinetic overpotentials via Butler-Volmer expressions, ohmic resistances via Ohm’s law, and mass transport overpotentials [1].The results show that the EPBT of all concentrating technologies are in the same order of magnitude (5-10 years). However, the integrated self-tracking concentrator design shows a lower EPBT than Fresnel lenses-based concentrating systems due to a lower primary energy demand of the former (1600 MJ/m² for integrated, self-tracking concentrator, and 2800 MJ/m² for external Fresnel concentrator coupled to PV-electrolyzer). A sensitivity analysis showed that the most influential parameters for the reduction of the EPBT are the yearly solar irradiation, the primary and operating energy demand of the concentrator, the performance of the concentrator, the exchange current density of the catalysts, and the fill factor of the photovoltaic cell. The EPBT could be reduced by at least 6% with a variation of 10% of one of these parameters for all the technologies studied. This developed model provides a useful tool for device design to compare and optimize the energy requirements of integrated PEC and CPEC devices[1] P. K. Das, X. Li, and Z.-S. Liu, “Analytical approach to polymer electrolyte membrane fuel cell performance and optimization,” J. Electroanal. Chem., vol. 604, no. 2, pp. 72–90, Jun. 2007.

An overview on basics of organic and dye sensitized solar cells, their mechanism and recent improvements

The first chapter of this study describes modeling and design of the heterostructure cascaded solar cells with potential efficiency of 28–29%. Presence of few intrinsic layers built in a p–n junction, for example, p-i-i-n structure, provides highly efficient conversion of solar energy. Cascaded design could be applied to any heterojunction semiconductor material used in production of solar cells. In the current chapter, we present the design of corrugated surfaces applicable to common solar cells. Corrugation implies design of inverted pyramids on the surface of semiconductor solar cells. It is shown that a corrugated surface increases absorption of solar energy. Careful selection of anti-reflection coating (ARC), proper matching of refractive indices for semiconductor and ARC materials allows to significantly reduce the reflection of solar light. Combination of ARC with corrugated surfaces might be limited by properties of semiconductor materials and/or by the drawbacks associated with the production technology. In recent years, various research groups applied corrugation to surfaces of p-i-n solar cells. However, only researchers of Advanced Electronic Technology Center (AETC) at UMass applied ARC corrugation design to the cascaded Si solar cells. To allow solar cells to work longer hours under some illumination, we offer novel design of tracking/anti-tracking systems. Economic assessment of the system, which combines all three efficient factors, i.e., corrugation, ARC, tracking/ anti-tracking, is discussed at the end of the chapter.

Accumulation of dust (also known as soiling) on the surface of solar panels decreases the amount of sunlight reaching the solar cells underneath and thus the efficiency of the solar panel is severely impacted. To harness their designed capacity to its fullest, they need to be cleaned periodically, usually with water. Due to water scarcity in some area, cleaning becomes difficult, challenging and subsequently costly. Solar Photovoltaic conversion technique of is largely used as a pioneer and efficient conversion of solar energy. Many factors govern Solar Photovoltaic energy conversions efficiency like solar intensity, the area of the module, semiconductor, tracking mechanisms, dust, and dirt etc. Nowadays among these factors dust and dirt has become crucial for research since they have a significant effect on conversion efficiency. If proper cleaning mechanisms are used then, it may show about 25% improvement in output energy or about 15 to 20% enhancement in conversion efficiency. Hence, rigorous study of SPVC automated cleaning mechanism is vital. This paper discusses a comprehensive overview of dust problem and the recent developments made on automated cleaning system of solar photovoltaic modules which gives a brief overview of techniques like electrical, mechanical, chemical and electrostatic. The main objective of the study is to review the literature on solar photovoltaic module automated cleaning techniques for identifying research gaps in the automated cleaning systems.