Nanocrystalline solar cells

The quality of human life depends to a large degree on the availability of energy sources. The present worldwide energy consumption exceeds already the level of 6000 Gigawatt. It is expected to further increase sharply from the rising demand of energy in the developing countries. This implies enhanced depletion of fossil fuel reserves. leading to further aggravation of the environmental pollution exerting adverse effects on the well being of man kind. Adding the dangers arising from the accumulation of plutonium fission products from nuclear reactors, the quality of life on earth is threatened unless renewable energy resources can be developed in the near future. Photovoltaics is expected to make important contributions to identify environmentally friendly solutions of the energy problem. One attractive strategy discussed in this lecture is the development of systems that mimic natural photosynthesis in the conversion solar energy for the fixation of carbon dioxide. The task to be accomplished by these systems is to harvest sun light to produce electricity or drive an uphill chemical reaction, such as the cleavage of water into hydrogen and oxygen. The hydrogen can be subsequently employed to reduce carbon dioxide to produce fuels and chemical feed stocks. Learning from the concepts used by green plants we have developed a molecular photovoltaic device whose overall efficiency for solar energy conversion to electricity has already attained 10%.. The system is based on the sensitization of nanocrystalline films by transition metal charge transfer sensitizers. In analogy to photosynthesis, the new chemical solar cell achieves the separation of light absorption and charge carrier transport. Extraordinary yields for the conversion of incident photons into electric current are obtained, exceeding 90% for transition metal complexes within the wavelength range of their absorption band. Conventional photovoltaic cells for solar energy conversion into electricity are solid state devices do not economically compete for base load utility electricity production. The low cost and ease of production of the new nanocrystalline cell should be benefit large scale applications in particular in underdeveloped or developing countries. These regions of the earth benefit from generous sun shine rendering the availability of a cheap solar cell technology important in view of improving the quality of life and preserving natural resources. Quite aside from its intrinsic merits as a photovoltaic device, the nanocrystalline films development opens up a whole number of additional avenues for energy storage ranging from intercalation batteries to the formation of chemical fuels. These nanocrystalline systems will undoubtedly promote the acceptance of renewable energy technologies, not least by setting new standards of convenience and economy.     

Analysis of solar hydrogen production in Algeria: Case of an electrolyzer-concentrating photovoltaic system

The use of renewable energy and more particularly solar energy in hydrogen production is considered the most viable and the most environment protective. Electricity is required for water electrolysis to produce hydrogen. As photovoltaic modules enable the direct conversion of solar energy into electricity, photovoltaic systems are then the most indicated systems for this task.     

Integrated hydrogen production options based on renewable and nuclear energy sources

Due to varied global challenges, potential energy solutions are needed to reduce environmental impact and improve sustainability. Many of the renewable energy resources are of limited applicability due to their reliability, quality, quantity, and density. Thus, the need remains for additional sustainable and reliable energy sources that are sufficient for large-scale energy supply to complement and/or back up renewable energy sources. Nuclear energy has the potential to contribute a significant share of energy supply with very limited impacts to global climate change. Hydrogen production via thermochemical water decomposition is a potential process for direct utilization of nuclear thermal energy. Nuclear hydrogen and power systems can complement renewable energy sources by enabling them to meet a larger extent of global energy demand by providing energy when the wind does not blow, the sun does not shine, and geothermal and hydropower energies are not available. Thermochemical water splitting with a copper–chlorine (Cu–Cl) cycle could be linked with nuclear and selected renewable energy sources to decompose water into its constituents, oxygen and hydrogen, through intermediate copper and chlorine compounds. In this study, we present an integrated system approach to couple nuclear and renewable energy systems for hydrogen production. In this regard, nuclear and renewable energy systems are reviewed to establish some appropriate integrated system options for hydrogen production by a thermochemical cycle such as Cu–Cl cycle. Several possible applications involving nuclear independent and nuclear assisted renewable hydrogen production are proposed and discussed. Some of the considered options include storage of hydrogen and its conversion to electricity by fuel cells when needed.     

Synergistic roles of off-peak electrolysis and thermochemical production of hydrogen from nuclear energy in Canada

Hydrogen as a clean energy carrier is frequently identified as a major solution to the environmental problem of greenhouse gases, resulting from worldwide dependence on fossil fuels. However, most of the world's hydrogen (about 96%) is currently produced from fossil fuels, which does not address the issue of greenhouse gases. Although there is a large motivation of the “hydrogen economy”, for improvement of urban air quality, energy security, and integration of intermittent renewable energy sources, CO₂ free energy sources are critical to hydrogen becoming a significant energy carrier. Two technologies, applied in tandem, have a promising potential to generate hydrogen without leading to greenhouse gas emissions: 1) electrolysis and 2) thermochemical decomposition of water. This paper will investigate their unique complementary roles to reduce costs of hydrogen production. Together they have a unique potential to serve both de-centralized hydrogen needs in periods of low-demand electricity, and centralized base-load production from a nuclear station. Thermochemical methods have a significantly higher thermal efficiency, but electrolysis can take advantage of low electricity prices during off-peak hours, as well as intermittent and de-centralized supplies like wind, solar or tidal power. By effectively linking these systems, water-based production of hydrogen can become more competitive against the predominant existing technology, SMR (steam-methane reforming).     

Appropriate technologies for large-scale production of electricity and hydrogen fuel

Appropriate technology for energy supply requires the use of the most effective energy resources and conversion technologies that will also result in the minimum acceptable impact upon the environment. A useful parameter for evaluation of energy resources for large-scale production of electricity and hydrogen fuel is the specific energy of the appropriate energy resources. Available resources for such large-scale applications must come from some mixture of renewable, fossil, and nuclear energy. Analysis is made of the appropriate use of solar energy, chemical combustion fuels, and nuclear energy on the basis of their specific energy. The results show that the most appropriate resources for large-scale production of electricity and hydrogen are low-specific solar photovoltaic and wind turbine energy for large numbers of distributed small-scale applications and high-specific nuclear energy for smaller numbers of large-scale applications.     

Electrolyser-based energy management: a means for optimising the exploitation of variable renewable-energy resources in stand-alone applications

Electrolyser-based energy management (EBM) offers a versatile means for optimising the process of harnessing energy supplies derived from variable and/or intermittent renewable resources, e.g. solar (photo-voltaic), wind, wave and tidal. In general, EBM systems consist of an electrolyser, water and gas (hydrogen and, optimally, oxygen) storage and management systems and a means of (re-) generating electricity, e.g. a fuel cell. Such systems achieve their management via energy conversion and storage, this operational principle being referred to as electricity supply-and-demand management (ESDM). Implementation of this principle offers significant advantages in the utilisation of variable and/or intermittent renewable resources, as it permits electricity generated during periods of high-availability/low-demand to be “time-shifted” for subsequent re-supply during periods of low-availability/high-demand. Furthermore, EBM systems have the important advantage over other ESDM systems that the stored form of energy is readily utilisable as a pollution-free gas supply for thermal end-uses. This reconversion route significantly enhances the overall energy-conversion efficiency. Electrolyser and fuel cells based upon proton-exchange membrane technologies are preferred because these afford considerable operational advantages over any alternatives. In this paper these advantages are expanded upon and preliminary data based on these ideas are presented.     

Hydrogen production through solar energy water electrolysis

Various methods of making hydrogen from water have been proposed, but at the present time the only practical way to make hydrogen from water without fossil fuel is electrolysis. The development of a new, advanced, water electrolyser has become necessary for use in hydrogen energy systems and in electricity storage systems. All the new possible electrolysis processes, suitable for large-scale plants, are being analysed, in view of their combination with solar electricity source. A study of system interactions between large-scale photovoltaic plants, for electrical energy supply, and water electrolysis, is carried out. The subsystems examined include power conditioning, control and loads, as they are going to operate. Water electrolysis systems have no doubt been improved considerably and are expected to become the principal means to produce a large amount of hydrogen in the coming hydrogen economy age. Thus, the present paper treats the subject of hydrogen energy production from direct solar energy conversion facilities located on the earth's oceans and lakes. Electrolysis interface is shown to be conveniently adapted to direct solar energy conversion, depending on technical and economical feasibility aspects as they emerge from the research phases. The intrinsic requirement for relatively immense solar collection areas for large-scale central conversion facilities, with widely variable electricity charges, is given. The operation of electrolysis and photovoltaic array combination is verified at different insolation levels. Solar cell arrays and electrolysers are giving the expected results during continuously variable solar energy inputs. Future markets will turn more and more towards larger scale systems powering significantly bigger loads, ranging from hundreds of kW to several MW in size. Detailed design and close attention to subsystem engineering in the development of high performance, high efficiency photovoltaic power plants, are carried out. An overall design of a 50 MWp photovoltaic central station for electricity and hydrogen co-generation is finally discussed.     

Nuclear power, coal and energy conservation (with a note on the costs of a nuclear moratorium)

A programming model is used to explore some of the options by which the United States may realistically move away from its present heavy dependence on oil and gas to a more diversified energy economy, based on nuclear power and/or coal. The model incorporates both own- and cross-price elasticities. In this way it allows for price-induced interfuel substitution and price-induced energy conservation.Among the supply options considered are: the direct combustion of coal to generate electricity; the conversion of coal to synthetic fuels; the limited petroleum, natural gas, and shale oil resources; nuclear energy from light water reactors and, later, from fast breeder reactors; hydrogen via electrolysis; and such distant future technical options as central station solar power and fusion (aggregated and described only as “advanced technology”).Each of these energy sources is discussed in terms of its own costs and the probable date of its commercial introduction. We then quantify the sensitivity of the benefits from research and development to assumptions with respect to: the discount rate; the future (undiscovered) domestic resource bases of oil, gas and low-cost uranium; and the cost at which large future supplies of coal can be utilized.Under a plausible set of assumptions (the base case), we find that the present value of the benefits from both the fast breeder and coal-based synthetic fuels well exceeds their anticipated research and development costs. In an optimum mix, the combined benefits would be nearly $50 billion (in 1975 dollars) discounted at 10% annually over the 75-year span of our study, and $450 billion at a 5% annual discount rate. Under the same conditions, we also find that if a nuclear moratorium prohibiting the construction of additional plants throughout the country were to come into effect, the direct cost to the United States economy would be approximately $300 billion at a 10% discount rate and $2500 billion at a 5% rate.     

Hydrogen production at hydro-power plants

Hydroelectric power has the advantage of being a clean resource that is perpetually renewable. Alternative sources of energy such as thermal plants are becoming less attractive because of public opposition, spiraling costs, and excessive delays. Many utilities have actively explored the possibilities of increasing output at existing hydroplants by replacing or supplementing existing generating units. But hydroelectric plants are still utilizing only a portion of the river's hydraulic energy due to hydrologic and economic restraints. One possibility for increasing the efficiency of hydropower plants is the conversion of water to hydrogen through electrolysis by using the excess energy or wasted energy not yet utilized, and then conversion of hydrogen to electricity via a gas turbine or fuel cells. The electricity produced in the off-peak or no-demand time, or at the time of huge river flows in the spring can be stored in the form of hydrogen, and later, when the peak energy is needed, the hydrogen converted to electricity. One of the advantages of the proposed system is that the resource for production of hydrogen (the water) is available directly at the site. It appears that the conversion of electricity at hydro-power plants to hydrogen, and its utilization via a gas turbine, is technically and economically feasible.It is desirable to locate the electrolyzer near the hydro-plant if hydrogen is used only to generate electricity. The concept described in this paper would improve the economy of the project and generate additional revenues to the owner.     

Technoeconomics of large-scale clean hydrogen production – A review

Hydrogen is widely used in many industries, yet its role in the clean energy transition goes beyond being an element of these industries. Near-term practical large-scale clean hydrogen production can be made available by involving nuclear, solar, and other renewable energy sources in the process of hydrogen production, and coupling their energy systems to sustainable carbon-free hydrogen technologies. This requires further investigation and assessment of the different alternatives to achieve clean hydrogen using these pathways. This paper assesses the technoeconomics of promising hydrogen technologies that can be coupled to nuclear and solar energy systems for large-scale hydrogen production. It also provides an overview of the design, status and advances of these technologies.     

Prospects of hydrogen production potential from renewable resources in Algeria

Hydrogen production from renewable energies is a key part in the energy transition to realize a sustainable energy economy for both developed and developing nations. For Algeria, successful energy transition toward a hydrogen economy will require the establishment of its potential. This study was conducted to estimate the potential for producing hydrogen from renewable resources in Algeria. The renewable energies considered are: solar photovoltaic and wind. To accomplish this objective, first, we analyzed renewable resource data both statistically and graphically using Geographical Information System (GIS), a computer-based information system utilized to create and visualize the spatial distribution of the geographic information. Then, the study will evaluate the availability of renewable electricity production potential from these key renewable resources. The potential for the hydrogen production, via the electrolysis process with wind and solar photovoltaic electricity, is described with maps showing it per unit area in each region. Finally, the results of the estimated hydrogen potential from both resources for each region are compared and significant conclusions are drawn.     

RENEWABLE ENERGIES IN EUROPE : STATISTICS AND THEIR PROBLEMS

Eurostat official figures for 1991 show that renewable energy contribution to primary production in the European Union (12) was 7% and to gross consumption 3.7%. These figures were calculated by a methodology which takes into account the actual energy content of renewable electricity from water, wind and other sources in terms of oil equivalent as for nuclear energy, a 3 times higher value is calculated by applying a Carnot conversion efficiency of 33%.

In this paper, corresponding figures of 10.16% for primary production and 5.6% for gross consumption are calculated by applying equivalent Carnot efficiency of 38½ % for all non fossil electricity. With the addition of Austria, Finland and Sweden into the energy mix of the European Union, the renewable energy contribution for 1991 would have been 14.4% of.primary production and.7.8% for gross consumption.     

Methylcyclohexane production under fluctuating hydrogen flow rate conditions

Energy storage using liquid organic hydrogen carrier (LOHC) is a long-term method to store renewable energy with high hydrogen energy density. This study investigated a simple and low-cost system to produce methylcyclohexane (MCH) from toluene and hydrogen using fluctuating electric power, and developed its control method. In the current system, hydrogen generated by an alkaline water electrolyzer was directly supplied to hydrogenation reactors, where hydrogen purification equipment such as PSA and TSA is not installed to decrease costs. Hydrogen buffer tanks and compressors are not equipped. In order to enable MCH production using fluctuating electricity, a feed-forward toluene supply control method was developed and introduced to the system. The electrolyzer was operated under triangular waves and power generation patterns of photovoltaic cells and produced hydrogen with fluctuating flow rates up to 7.5 Nm³/h. Consequently, relatively high purity of MCH (more than 90% of MCH mole fraction) was successfully produced. Therefore, the simplified system has enough potential to produce MCH using fluctuating renewable electricity.     

Hybrid systems to address seasonal mismatches between electricity production and demand in nuclear renewable electrical grids

A strategy to enable zero-carbon variable electricity production with full utilization of renewable and nuclear energy sources has been developed. Wind and solar systems send electricity to the grid. Nuclear plants operate at full capacity with variable steam to turbines to match electricity demand with production (renewables and nuclear). Excess steam at times of low electricity prices and electricity demand go to hybrid fuel production and storage systems. The characteristic of these hybrid technologies is that the economic penalties for variable nuclear steam inputs are small. Three hybrid systems were identified that could be deployed at the required scale. The first option is the gigawatt-year hourly-to-seasonal heat storage system where excess steam from the nuclear plant is used to heat rock a kilometer underground to create an artificial geothermal heat source. The heat source produces electricity on demand using geothermal technology. The second option uses steam from the nuclear plant and electricity from the grid with high-temperature electrolysis (HTR) cells to produce hydrogen and oxygen. Hydrogen is primarily for industrial applications; however, the HTE can be operated in reverse using hydrogen for peak electricity production. The third option uses variable steam and electricity for shale oil production.     

Critical assessment of the production scale required for fossil parity of green electrolytic hydrogen

Hydrogen produced from renewable electricity through Power-to-Hydrogen can facilitate the integration of high levels of variable renewable electricity into the energy system. An electrolyser is a device that splits water into hydrogen and oxygen using electricity. When electricity is produced from renewable energy sources, electrolytic hydrogen can be considered to be green. At the same time, electrolysers can help integrate renewable electricity into power systems, as their electricity consumption can be adjusted to follow wind and solar power generation. Green hydrogen then also becomes a carrier for renewable electricity. Key green hydrogen production technologies, mostly PEM and alkaline electrolysers, are still further maturing, both in technical (efficiency), economical (CAPEX) and durability (lifetime) performance. Nonetheless, we will show in this contribution how fossil parity for green hydrogen, i.e. a Total Cost of Ownership (TCO) similar to grey H₂ coming from todays CO₂ intensive SMR processes, can already be achieved today. Moreover, this can be realised at a scale which corresponds to the basic units of renewable electricity generation, i.e. a few MW.     

An analysis of hydrogen production from renewable electricity sources

Three aspects of producing hydrogen via renewable electricity sources are analyzed to determine the potential for solar and wind hydrogen production pathways: a renewable hydrogen resource assessment, a cost analysis of hydrogen production via electrolysis, and the annual energy requirements of producing hydrogen for refueling. The results indicate that ample resources exist to produce transportation fuel from wind and solar power. However, hydrogen prices are highly dependent on electricity prices. For renewables to produce hydrogen at $2 kg⁻¹, using electrolyzers available in 2004, electricity prices would have to be less than $0.01 kWh⁻¹. Additionally, energy requirements for hydrogen refueling stations are in excess of 20 GWh/year. It may be challenging for dedicated renewable systems at the filling station to meet such requirements. Therefore, while plentiful resources exist to provide clean electricity for the production of hydrogen for transportation fuel, challenges remain to identify optimum economic and technical configurations to provide renewable energy to distributed hydrogen refueling stations.     

非化石能源制氢技术综述

在现今的经济社会和未来的低碳经济中H2将发挥重要作用.非化石能源制氢是化石能源短缺和温室气体排放等约束下的可持续制氢路径.综述了可再生电力电解制氢、核能制氢、太阳能制氢和生物质能制氢等四种非化石能源制氢技术的工作原理、流程设备和技术特点,最后对我国未来非化石能源制氢的路线选择进行了评论.     

Development of a renewable hydrogen economy: Optimization of existing technologies

There is an increasing need for new and greater sources of energy for future global transportation applications. One recognized possibility for a renewable, clean source of transportation fuels is solar radiation collected and converted into useable forms of electrical and/or chemical (hydrogen) energy. This paper describes methods for utilizing and combining existing technologies into systems that optimize solar energy collection and conversion into useful transportation fuels. Photovoltaic (PV)-electrolysis (solar hydrogen) and PV-battery charging systems described in this paper overcome inefficiencies inherent in past concepts, where DC power from the PV system was first converted to AC current and then used to power electrical devices at the point of generation, or fed back to the grid to reduce electricity costs. These past, non-optimized concepts included efficiency losses in power conversion and unnecessary costs. These drawbacks can be avoided by capitalizing on the unique feature of solar photovoltaic devices that match their maximum power point to the operating point of an electrolyzer or a battery charger without intervening power transformers. This concept is illustrated for two systems designed, built, and tested by General Motors for fueling a fuel cell electric vehicle and charging an automotive propulsion battery. Based on this research, we propose a scenario in which individual home-owners, businesses, or sites at remote locations with no grid electricity, can capture solar energy, store it as hydrogen generated via water electrolysis, or as electrical energy used to charge storage batteries. Such a decentralized energy system provides a home refueling option for drivers who only travel limited distances each day.     

The potential of hydrogen production from high and low-temperature electrolysis methods using solar and nuclear energy sources: the transition to a hydrogen economy in Brazil

Brazil has great potential for diversification and decarbonization of its energy matrix, with the insertion of a clean and renewable energy source such as hydrogen. This paper seeks to evaluate the surplus energy potential of solar and nuclear plants installed in the country for the production of green and purple hydrogen using high and low temperature electrolysis methods. Based on official reports and databases of energy production and demand, the results indicated that the total potential of surplus solar energy is equal to 4.29E+07 (kWh.d^?1). Further, the total potential of electricity production from the hydrogen obtained through surplus solar energy was equivalent to1.87E+07 (kWh.d^?1); and the total cost of producing solar hydrogen is equal to 1.07E+03 (USD.kWh^?1). In conclusion, the study contributed to demonstrate the pathways to the establishment of strategies that assist the transition to a hydrogen economy in Brazil.     

Integration and economic viability of fueling the future with green hydrogen: An integration of its determinants from renewable economics

The volatility of fossil fuel and their increased consumption have exacerbated the socio-economic dilemma along with electricity expenses in third world countries around the world, Pakistan in particular. In this research, we study the output of renewable hydrogen from natural sources like wind, solar, biomass, and geothermal power. It also provides rules and procedures in an attempt to determine the current situation of Pakistan regarding the workability of upcoming renewable energy plans. To achieve this, four main criteria were assessed and they are economic, commercial, environmental, and social adoption. The method used in this research is the Fuzzy Analytical Hierarchical Process (FAHP), where we used first-order engineering equations, and Levelized cost electricity to produce renewable hydrogen. The value of renewable hydrogen is also evaluated. The results of the study indicate that wind is the best option in Pakistan for manufacturing renewable based on four criteria. Biomass is found to be the most viable raw material for the establishment of the hydrogen supply network in Pakistan, which can generate 6.6 million tons of hydrogen per year, next is photovoltaic solar energy, which has the capability of generating 2.8 million tons. Another significant finding is that solar energy is the second-best candidate for hydrogen production taking into consideration its low-cost installation and production. The study shows that the cost of using hydrogen in Pakistan ranges from $5.30/kg to $5.80/kg, making it a competitive fuel for electric machines. Such projects for producing renewable power must be highlighted and carried out in Pakistan and this will lead to more energy security for Pakistan, less use of fossil fuels, and effective reduction of greenhouse gas emissions.