Biomass: A modern and environmentally acceptable fuel

The energy of the sun and carbon dioxide from the atmosphere are captured by plants during photosynthesis. Plant biomass can be used to absorb carbon dioxide emissions from fossil fuels, or it can be converted into modern energy carriers such as electricity, and liquid and gaseous fuels. Biomass supplies 13% of the world's energy consumption (55 EJ, 1990), and in some developing countries it accounts for over 90% of energy use. There is considerable potential for the modernisation of biomass fuels through improved utilisation of existing resources, higher plant productivities and efficient conversion processes using advanced technologies. The interest in bioenergy is increasing rapidly, and it is widely considered as one of the main renewable energy resources of the future due to its large potential, economic viability, and various social and environmental benefits. In particular, biomass energy is among the most favourable options for reducing carbon dioxide emissions. Most of the perceived problems such as land availability, environmental impact, economic viability, and efficiency can be overcome with good management. The constraints to achieving environmentally-acceptable biomass production are not insurmountable, but should rather be seen as scientific and entrepreneurial opportunities which will yield numerous advantages at local, national and international levels in the long term.     

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.     

CO2-free hydrogen production via microwave-driven methane pyrolysis

Hydrogen will play an integral role in achieving net-zero emissions by 2050. Many studies have been focusing on green hydrogen, but this method is highly electricity intensive. Alternatively, methane pyrolysis can produce hydrogen without direct CO₂ emissions and with modest electricity inputs, serving as a bridge from fossil fuels to renewable energies. Microwaves are an efficient method of adding the required energy for this endothermic reaction. This study introduces a new method of CO₂-free hydrogen production via non-plasma methane pyrolysis using microwaves and carbon products of this process. Carbon particles in the fluidized bed absorb microwave energy and create a hot medium (>1200 °C) in contact with flowing methane. As a result, methane decomposes into hydrogen and solid carbon achieving over 90% hydrogen selectivity with ∼500 cumulative hours of experiments This modular pyrolysis system can be built anywhere with access to natural gas and electricity, enabling distributed hydrogen production.     

Redox-flow battery design for a methane-producing bioelectrochemical system

Methane production at biocathodes is an innovative approach of storing renewable electrical energy in chemical energy via the biological conversion of carbon dioxide. Methane-producing microorganisms use electricity to catalyze the conversion of carbon dioxide into methane; a form of carbon-neutral natural gas. However, the rates of methane production remain too low for practical application. To improve performance, high area-to-volume ratio with good mass transfer is required. In this study, we used the design of redox flow-batteries with a high area-to-volume ratio of 2.0 cm²/cm³ and an external capillary manifold for flow distribution. Current densities up to 35 A/m² were applied, resulting in volumetric methane production rates of up to 12.5 L CH₄/L/d, three times higher than rates reported so far. The highest energy efficiency of 30% was obtained at 25 A/m². Even with a low relative abundance of methanogens in the microbial community (20%), dense biofilm growth was observed on the outer surface of the biocathode. Flow-battery cell design shows promising performance for application of methane-producing biocathodes.     

Applying ex-post index decomposition analysis to primary energy consumption for evaluating progress towards European energy efficiency targets

Monitoring the progress of the European Union and its Member States towards the EU’s energy efficiency target is a crucial part of the mandatory process as defined in the Energy Efficiency Directive 2012/27/EU. In this paper, we conduct index decomposition analyses to show the effects of both policies and autonomous developments driving the changes of primary energy consumption for the European Union (EU28) and its Member States for the time period of 2000 to 2014, with a comparative analysis of Germany and Poland. These analyses are based on the logarithmic mean Divisia index methodology and primarily on data compiled by Eurostat. They are carried out on two levels, i.e. on the level of total primary energy consumption as well as on the level of primary energy consumption related to electricity generation. The first level examines the influences of changes in final energy consumption and changes within the energy conversion sector on primary energy consumption. With the second level, we provide insights into the effects of changes in electricity consumption and production. According to our first-level analysis, the consumption of primary energy in the EU28 is primarily influenced by an increased share of electrical energy and the counteracting effect of rising efficiency in electricity generation, induced by an increasing share of renewable energies. Furthermore, the reduction of final energy consumption had a significant decreasing influence on primary energy consumption in the European Union. The second level of our analysis regarding electricity generation shows that the increasing effect on primary energy consumption due to the rising consumption of electricity was mainly compensated by substituting nuclear and thermal power plants by renewable energy technologies.     

Solar methanol synthesis by clean hydrogen production from seawater on offshore artificial islands

Synthetic fuel production from renewable energy, water, and anthropogenic carbon resources offers a promising alternative to fossil fuels by reducing the consumption of nonrenewable resources and greenhouse gas emissions. This article presents a case study of a solar‐based methanol plant that derives hydrogen and carbon dioxide material inputs from seawater on an offshore artificial island. Photovoltaic cells generate electricity for an electrolytic cation exchange membrane (E‐CEM) reactor that simultaneously produces hydrogen and carbon dioxide, with freshwater for electrolysis via seawater reverse osmosis. Carbon dioxide hydrogenation in a low‐pressure isothermal cascade‐type reactor system produces methanol as a liquid fuel product. Thermodynamic assessment of the integrated system indicates solar‐to‐methanol energy and exergy conversion efficiencies of 1.5% and 1.3%, respectively, with the most significant losses occurring in the offshore concentrator photovoltaic (CPV) and E‐CEM reactor unit.     

An assessment of the use of fuel chemicals synthesized from captured carbon dioxide for renewable electricity storage

本文介绍了国际上利用可再生能源结合捕集CO₂制燃料的最新技术进展。以化学合成的反应热力学为基础,通过分析计算与流程模拟,得到捕集CO₂制燃料化学品储电的能耗与?流,初步评估了甲醇作为储存电能介质的能效,并与氢储能及甲烷储能进行了比较分析。比较结果表明,氢储能流程最短,效率最高,但是没有固碳的作用。对于实现储能与固碳,甲醇的氢原子经济性较好。甲烷产物热值与反应热都较高。甲醇储能效率损失主要由前端电解制氢环节造成。     

Modeling & optimization of renewable hydrogen production from biomass via anaerobic digestion & dry reformation

There is a growing interest in the usage of hydrogen as an environmentally cleaner form of energy for end users. However, hydrogen does not occur naturally and needs to be produced through energy intensive processes, such as steam reformation. In order to be truly renewable, hydrogen must be produced through processes that do not lead to direct or indirect carbon dioxide emissions. Dry reformation of methane is a route that consumes carbon dioxide to produce hydrogen. This work describes the production of hydrogen from biomass via anaerobic digestion of waste biomass and dry reformation of biogas. This process consumes carbon dioxide instead of releasing it and uses only renewable feed materials for hydrogen production. An end-to-end simulation of this process is developed primarily using Aspen HYSYS® and consists of steady state models for anaerobic digestion of biomass, dry reformation of biogas in a fixed-bed catalytic reactor containing Ni–Co/Al₂O₃ catalyst, and a custom-model for hydrogen separation using a hollow fibre membrane separator. A mixture-process variable design is used to simultaneously optimize feed composition and process conditions for the process. It is identified that if biogas containing 52 mol% methane, 38 mol% carbon dioxide, and 10 mol% water (or steam) is used for hydrogen production by dry reformation at a temperature of 837.5 °C and a pressure of 101.3 kPa; optimal values of 89.9% methane conversion, 99.99% carbon dioxide conversion and hydrogen selectivity 1.21 can be obtained.     

中国中长期碳减排战略目标初探(Ⅱ)——中国煤炭消费过程的碳排放及减排措施

中国能源领域排放的二氧化碳主要来自煤炭,因此煤炭消费过程中的碳减排措施尤为重要。煤炭的主要用户是发电部门,基于应对气候变化的需要,煤电行业的低碳途径不得不考虑采用CCS技术。不论是新建燃煤电厂,还是今后在传统电厂改建过程中增设CCS设施已是大势所趋,预计多数仍将采用MEA法脱除烟气中二氧化碳这一成熟技术。由于MEA法技术经济指标不够先进,估计10~20年内必将出现更先进的脱二氧化碳工艺技术。传统的燃煤锅炉增加CCS的经济效益已经逊于IGCC-CCS,预计2020年后IGCC电厂将成为新建煤电厂的首选方案。20年后采用临氢气化炉与燃料电池FC发电相结合、把高温的热能和甲烷的化学能直接转化为电力的IGFC高效燃煤电厂或将成功应用,IGFC综合能量转化效率比IGCC相对高出1/2~3/4,发展前景不可低估。钢铁、水泥和化工等高耗煤工业部门可通过节能和采用CCS技术降低碳排放,其余用煤的工业部门和分散用户则应考虑节能或用天然气等低碳燃料替代,间接起到减排效果。预计2050年燃煤发电和高耗煤工业总计将排放二氧化碳4.6Gt,如果二氧化碳捕集量是2.9Gt,则净排放量为1.7Gt。加上其他难以捕集二氧化碳的工业、部门及民用煤排放二氧化碳1.0Gt,合计二氧化碳净排放量为2.7Gt(情景A)。如果采用更先进的技术和严格的节能减排措施,可减少煤炭消耗0.31Gt标煤,减少二氧化碳排放0.5Gt,使煤源二氧化碳净排放量减少到2.2Gt(情景B)。无论哪种情景,实施CCS的任务都十分艰巨。     

Farm-scale bio-power-to-methane: Comparative analyses of economic and environmental feasibility

Power-to-gas technologies are considered to be part of the future energy system, but their viability and applicability need to be assessed. Therefore, models for the viability of farm-scale bio-power-to-methane supply chains to produce green gas were analysed in terms of levelised cost of energy, energy efficiency and saving of greenhouse gas emission. In bio-power-to-methane, hydrogen from electrolysis driven by surplus renewable electricity and carbon dioxide from biogas are converted to methane by microbes in an ex situ trickle-bed reactor. Such bio-methanation could replace the current upgrading of biogas to green gas with membrane technology. Four scenarios were compared: a reference scenario without bio-methanation (A), bio-methanation (B), bio-methanation combined with membrane upgrading (C) and the latter with use of renewable energy only (all-green; D). The reference scenario (A) has the lowest costs for green gas production, but the bio-methanation scenarios (B-D) have higher energy efficiencies and environmental benefits. The higher costs of the bio-methanation scenarios are largely due to electrolysis, whereas the environmental benefits are due to the use of renewable electricity. Only the all-green scenario (D) meets the 2026 EU goal of 80% reduction of greenhouse gas emissions, but it would require a CO₂ price of 200 € t⁻¹ to achieve the levelised cost of energy of 65 €ct Nm⁻³ of the reference scenario. Inclusion of the intermittency of renewable energy in the scenarios substantially increases the costs. Further greening of the bio-methanation supply chain and how intermittency is best taken into account need further investigation.     

The resource of biomethane,produced via biological,thermal and electrical routes,as a transport biofuel

Biomethane is an energy vector suitable for renewable transport fuel which may derive energy through three different methodologies: thermal gasification; biological anaerobic digestion; and conversion of electricity to hydrogen (via electrolysis) and on to methane as described by the Sabatier Equation. Thermal gasification to produce methane (based on “hard” feed stock) tends to require significant scale, of the order of 400 MW. Biological anaerobic digestion (based on “soft” feed stock) is typically of scale less than 1 MW. Systems based on the Sabatier Equation convert hydrogen to methane exothermically and sequester carbon. The resource is assessed at 19% of energy in transport in Ireland. Adopting the approach of the EU Renewable Energy Directive (for example double credit for biofuels from residues and lignocellulosic feed stock) biomethane can supply 40% renewable energy supply in transport (RES-T). The resource is sufficient to supply 30% of the private transport fleet with indigenous sustainable gaseous biofuel.     

Interactions and implications of renewable and climate change policy on UK energy scenarios

As a response to the twin challenges of climate change mitigation and energy security, the UK government has set a groundbreaking target of reducing the UK’s economy-wide carbon emissions by 80% from 1990 levels by 2050. A second key UK energy policy is to increase the share of final energy consumption from renewables sources to 15% by 2020, as part of the wider EU Renewable Directive. The UK’s principle mechanisms to meet this renewable target are the Renewable Obligation (RO) in the electricity sector, the Renewable Transport Fuel Obligation (RTFO), and most recently the Renewable Heat Programme (RHP) for buildings. This study quantifies a range of policies, energy pathways, and sectoral trade-offs when combining mid- and long-term UK renewables and CO₂ reduction policies. Stringent renewable policies are the binding constraints through 2020. Furthermore, the interactions between RO, RTFO, and RHP policies drive trade-offs between low carbon electricity, bio-fuels, high efficiency natural gas, and demand reductions as well as resulting 2020 welfare costs. In the longer term, CO₂ reduction constraints drive the costs and characteristics of the UK energy system through 2050.     

Techno-economic evaluation of medium scale power to hydrogen to combined heat and power generation systems

The European Hydrogen Strategy and the new « Fit for 55 » package indicate the urgent need for the alignment of policy with the European Green Deal and European Union (EU) climate law for the decarbonization of the energy system and the use of hydrogen towards 2030 and 2050. The increasing carbon prices in EU Emission Trading System (ETS) as well as the lack of dispatchable thermal power generation as part of the Coal exit are expected to enhance the role of Combined Heat and Power (CHP) in the future energy system. In the present work, the use of renewable hydrogen for the decarbonization of CHP plants is investigated for various fossil fuel substitution ratios and the impact of the overall efficiency, the reduction of direct emissions and the carbon footprint of heat and power generation are reported. The analysis provides insights on efficient and decarbonized cogeneration linking the power with the heat sector via renewable hydrogen production and use. The levelized cost of hydrogen production as well as the levelized cost of electricity in the power to hydrogen to combined heat and power system are analyzed for various natural gas substitution scenarios as well as current and future projections of EU ETS carbon prices.     

Three options to calculate the percentage renewable energy: An example for a EU policy debate

The European Commission proposed a renewable energy directive with binding targets for the percentage renewable energy, usually calculated with the primary energy method. This method has the disadvantage that for hydro and wind electricity production is counted, whereas for thermal electricity the higher input to power plants is counted. Therefore, the Commission looked for an alternative: the final energy method. Also this method has disadvantages. Firstly, electricity consumption is weighed equally to fuel consumption for heat and transport, neglecting higher primary energy demand for electricity. Secondly, non-energy consumption of energy commodities is neglected, artificially raising the percentage renewable energy. Therefore, I introduce a simple substitution method, which measures renewable energy by comparison with hypothetical equivalent conventional energy. Calculations for EU-27 show that the method strongly affects the contributions of different sectors (electricity, heat and transport), sources and countries. Concluding, any credible calculation method should reflect the trade off between conventional and renewable primary energy. A simple substitution method fulfills this condition, contrary to the primary and final energy method. Using these biased methods may result in policies that are inefficient in terms of saving conventional fuels and avoiding CO₂ emissions, the main underlying goals of the proposed directive.     

Looking into the Danish energy system: Lesson to be learned by other communities

Industrialization, development and social transformation has brought together issues of over exploitation of limited energy resource base (e.g. fossil fuel), accelerated threats of energy insecurity, and liberation of greenhouse gas emissions across the continents. The global challenge for the 21st century and way ahead is to find other means of satisfying energy needs, diversifying the energy supply, up-scaling the make-up of renewable energy to a greater extent, optimization of energy consumption and supply system. Denmark has been continuously moving towards optimization of energy production, usage and its overall management, during and even after the first global oil crisis. The country has been delivering its priority in the development of renewable energy and standing the country an energy self sufficient from last three decades. Country's overall consumption of energy has decreased than that of the decades of 1980 and 1990s, with wider range of energy mix and saving options. The Danish government has strategized to make the country fossil fuel free by 2050, where special attention and interventions is required to boost up its development of renewable energy in the country. The past efforts of the Danish government in the energy development has helped not only making the country ‘energy self sufficient’, but also lowering the level of carbon dioxide in the atmosphere. Danish energy policy and strategies have been found more conducive and reflective of the joint EU priorities on the matter of dealing with climate change and energy security. All the past progress and its allied policies seem to be quite supportive in fulfilling its strategies for greener future. This review paper will discuss on the past efforts of Danish government in energy management and highlights on some political initiatives, which have been realised to support the country moving towards clean and green energy future.     

Heat Roadmap Europe: Combining district heating with heat savings to decarbonise the EU energy system

Six different strategies have recently been proposed for the European Union (EU) energy system in the European Commission's report, Energy Roadmap 2050. The objective for these strategies is to identify how the EU can reach its target of an 80% reduction in annual greenhouse gas emissions in 2050 compared to 1990 levels. None of these scenarios involve the large-scale implementation of district heating, but instead they focus on the electrification of the heating sector (primarily using heat pumps) and/or the large-scale implementation of electricity and heat savings. In this paper, the potential for district heating in the EU between now and 2050 is identified, based on extensive and detailed mapping of the EU heat demand and various supply options. Subsequently, a new ‘district heating plus heat savings’ scenario is technically and economically assessed from an energy systems perspective. The results indicate that with district heating, the EU energy system will be able to achieve the same reductions in primary energy supply and carbon dioxide emissions as the existing alternatives proposed. However, with district heating these goals can be achieved at a lower cost, with heating and cooling costs reduced by approximately 15%.     

Basic concepts for designing renewable electricity support aiming at a full-scale transition by 2050

Renewable electricity supply is a crucial factor in the realization of a low-carbon energy economy. The understanding is growing that a full turn-over of the electricity sectors by 2050 is an elementary condition for avoiding global average temperature increase beyond 2 °C. This article adopts such full transition as Europe's target when designing renewable energy policy. An immediate corollary is that phasing-in unprecedented energy efficiency and renewable generation must be paralleled by phasing-out non-sustainable fossil fuel and nuclear power technologies. The double phasing programme assigns novel meaning to nearby target settings for renewable power as share of total power consumption. It requires organizing in the medium term EU-wide markets for green power, a highly demanding task in the present context of poorly functional markets in brown power. The EU Commission's 2007/2008 proposals of expanding tradable certificates markets were not based on solid analysis of past experiences and future necessities. The keystone of sound policies on renewable electricity development is a detailed scientific differentiation and qualification of renewable electricity sources and technologies, for measuring the huge diversity in the field. We provide but structuring concepts about such qualification, because implementation requires extensive research resources.     

Electricity produced from renewable energy sources—What target are we aiming for?

In 2001, the European Commission (hereafter “EC”) formulated an ambitious target of 21% of total community electricity consumption to be generated with renewable energy sources by 2010. Moreover, national indicative targets per Member State were specified. In practice, the latter are implemented in all Member States as national production targets, achievable exclusively through an increase of the domestic production of electricity produced from renewable energy sources (hereafter “RES-E”). However, in this article it will be shown that this is not in line with the EC's intent. Looking at the legislative process resulting in the Directive on the promotion of RES-E, it is demonstrated that instead the EC aimed for European trade in renewable electricity through national consumption targets.     

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.     

Renewable energy sources in Turkey for climate change mitigation and energy sustainability

In Turkey, there is a much more potential for renewables, but represent about 37% of total energy production and 10% of total energy consumption. This share is not enough for the country and the governments should be increase to this situation. Renewable energy technologies of wind, biomass, hydropower, geothermal, solar thermal and photovoltaics are finally showing maturity and the ultimate promise of cost competitiveness. With respect to global environmental issues, Turkey's carbon dioxide emissions have grown along with its energy consumption. States have played a leading role in protecting the environment by reducing emissions of greenhouse gases. In this regard, renewable energy resources appear to be the one of the most efficient and effective solutions for clean and sustainable energy development in Turkey. Turkey's geographical location has several advantages for extensive use of most of these renewable energy sources. Certain policy interventions could have a dramatic impact on shaping the relationship between geological, geographic and climatic conditions and energy production. This study shows that there is enough renewable energy potential in Turkey for fuels and electricity. Especially hydropower and biomass are very well.