Biogas production from catch crops: Increased yield by combined harvest of catch crops and straw and preservation by ensiling

The combination of catch crop cultivation with its use for biogas production would increase renewable energy production in the form of methane, without interfering with the production of food and fodder crops. The low biomass yield of catch crops has been shown as the main limiting factor for using these crops as co-substrate in biogas plants, since the profit obtained from the sale of methane barely compensates the harvest costs. Therefore, a new agricultural strategy to harvest catch crops together with the residual straw of the main crop was investigated, in order to increase the biomass and the methane yield per hectare. Seven catch crops harvested together with stubble from the previous main crop were evaluated. The effects of stubble height, harvest time and ensiling as a storage method for the different catch crops/straw blends were studied. Biomass yields as TS ranged between 3.2 and 3.6 t ha⁻¹ y⁻¹of which the catch crop constituted around 10% of the total biomass yield. Leaving the straw on the field until harvest of the catch crop in the autumn could benefit methane production from the straw both due to increased biomass yield and an increased organic matter bioavailability of the straw taking place on the field during the autumn months. Ensiling as a storage method could be feasible in terms of energy storage and guaranteeing the feedstock availability for the whole year. This new agricultural strategy may be a good alternative for economically feasible supply of catch crops and straw for biogas production.     

Socio-economic impacts of energy crops for heat generation in Northern Greece

Bioenergy is considered to be an attractive option mainly due to driving forces of an environmental nature (e.g. climate change and sustainability issues). This is particularly the case for energy crops, which show higher productivity per land unit than their conventional counterparts. In addition, by comparison, such crops are more homogeneous in terms of their physical and chemical characteristics than residual resources that are often described as the biomass resource of the future. However, despite the long-term research and the considerable efforts to promote them, implementation is still rather slow across Europe. In this paper, two perennial energy crops, cardoon and giant reed, are evaluated in Rodopi, northern Greece, as alternative land use, through comparative financial appraisal with the main conventional crops.

Based on the output of this analysis, the breakeven for the two energy crops is defined and an economic and socio-economic evaluation of a biomass district heating system is conducted.

Results prove that energy crops can be attractive alternatives if they are properly integrated into existing agricultural activities and complement the current cropping options. As such, they provide raw material for local heat applications, thus resulting in increased income for the region and an increase in the number of jobs.     

Interest in energy wood and energy crop production among Finnish non-industrial private forest owners

EU targets and regulations regarding energy production and the reduction of greenhouse gas emissions have been tightening in the 2000s. In Finland the targets are planned to be achieved mainly by increasing the use of biomass. Wood already accounts for a marked proportion of Finnish energy production, but additional reserves are still available. Energy crop production also has considerable potential. Practically all Finnish farmers are also forest owners. Therefore, private forest owners are in a decisive position regarding the supply of energy wood and crops in Finland. In this paper the future supply of biomass is examined according to their past behaviour, intentions and attitudes. Finnish forest owners have a positive attitude towards the use of wood and crops in energy production. Price is becoming more critical as a motive for the supply of energy wood. Recreation and nature conservation play a smaller role than factors related to wood production and forest management as for motives for harvesting energy wood. However, almost a half of forest owners in this study were uncertain of their willingness to supply biomass. This is partly due to limited knowledge of the issues involved in energy wood and agricultural energy crop production and the underdeveloped markets for energy biomass. In order to achieve the targets, supply should be activated by further developing market practices, information, guidance and possibly other incentives for landowners. In general, there is interest among landowners in increasing the supply of energy biomass. However, the growth of supply presumes that production is an economically attractive and competitive alternative, that the markets are better organized than at present, and that more comprehensive information is available about bioenergy and biomass markets and production techniques.     

Steam gasification of selected energy crops in a fixed bed reactor

The increasing world's energy demand and environmental concerns related to GHG emissions as well as depleting fossil fuel resources and unstable prices of crude oil and natural gas have caused a renewed interest in renewable energy sources, and in particularly in biomass, as an alternative to fossil fuels. In the paper the results of steam gasification of Salix Viminalis, Miscanthus X Giganteus (MXG), and Andropogon Gerardi in a laboratory-scale fixed bed reactor in the temperature range of 650–900 °C are presented as well as the procedure and results of biomass chars reactivity testing in the process of steam gasification. The highest reactivity R₅₀ in the whole temperature range was observed for MXG. Hydrogen content in the synthesis gas was comparable for MXG and Andropogon Gerardi and lower for Salix Viminalis, while the volumes of the synthesis gas and hydrogen were highest for MXG at all temperatures.     

Energetic density of different forest species of energy crops in Cantabria (Spain)

This article is the result of an analysis into the behavior of several forest species that could be used as energy crops in Cantabria. The species studied belong to several botanical genera. The study was conducted in several stages: firstly, the species was introduced to explore growth data and discard those species of slower growth. Once the genus maximising the biomass production was determined, several species of it were studied from the energy perspective. This combination of both allows the energy density for each species to be obtained, therefore making it possible to determine how big a cultivation area is required for a specific thermal power plant. Thus, for a power plant of 10 MWe, between 15,451 and 24,578 ha of Eucalyptus would be necessary, depending on the species chosen, at an approximate age of 4 years.     

Global warming and renewable energy sources for sustainable development in Turkey

Turkey, with its young population and growing energy demand per person, its fast growing urbanization, and its economic development, has been one of the fast growing power markets of the world for the last two decades. It is expected that the demand for electric energy in Turkey will be 300 billion kWh by the year 2010 and 580 billion kWh by the year 2020. Turkey is heavily dependent on expensive imported energy resources that place a big burden on the economy and air pollution is becoming a great environmental concern in the country. 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. This article presents a review of the potential and utilization of the renewable energy sources in Turkey.     

Yield of perennial herbaceous and woody biomass crops over time across three locations

The use of perennial biomass crops is expected to increase and will likely be part of a diversified approach to cropping system design that focuses on multiple economic, ecological, and environmental benefits. Field experiments were conducted from 2006 to 2011 at three locations in Minnesota to quantify biomass production across a diverse set of perennial herbaceous and woody crops. Herbaceous crops were harvested annually in the fall while the woody crops were harvested once following five years of growth. Willow produced more total biomass than all other woody and herbaceous biomass crops across all locations. However, miscanthus biomass yield was similar to ‘SX67’ willow at St. Paul and Waseca, but was dependent on the cultivar of miscanthus. Prairie cordgrass cultivars were among the highest and most consistent yielding herbaceous biomass crops across locations. Miscanthus cultivars produced the highest annual dry matter yield of 35 Mg ha⁻¹ yr⁻¹ biomass, but only during the final year of the study. Other herbaceous crops such as switchgrass performed well in certain locations and may offer flexibility in cropping choice. This unique information on comparative biomass yield across a diversity of perennial crops will inform the overall decision-making process in a way that reduces risk and optimizes productivity in specific environments. This study shows that several biomass crop species can be successfully grown as part of a diversified biomass cropping enterprise.     

Economic assessment and comparison of acacia energy crop with annual traditional crops in Southern Europe

In several policy documents bioenergy is recognized as an important renewable energy source in Italy. The increase in energy prices represents an opportunity for lignocellulosic energy crops such as acacia and poplar.     

Hydrogen production by biomass gasification in supercritical water using concentrated solar energy: System development and proof of concept

A novel system of hydrogen production by biomass gasification in supercritical water using concentrated solar energy has been constructed, installed and tested at the State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The “proof of concept” tests for solar-thermal gasification of biomass in supercritical water (SCW) were successfully carried out. Biomass model compounds (glucose) and real biomass (corn meal, wheat stalk) were gasified continuously with the novel system to produce hydrogen-rich gas. The effect of direct normal solar irradiation (DNI) and catalyst on gasification of biomass was also investigated. The results showed that the maximal gasification efficiency (the mass of product gas/the mass of feedstock) in excess of 110% were reached, hydrogen fraction in the gas product also approached to 50%. The experimental results confirmed the feasibility of the system and the advantage of the process, which supports future work to address the technical issues and develop the technology of solar-thermal hydrogen production by gasification of biomass in supercritical water.     

Energy and CO2 analysis of poplar and maize crops for biomass production in north Italy

The rising price of fossil fuel and the increasing environmental concern encourage the use of biomasses as energy sources. Aim of this study was to compare two poplar SRC and vSRC (6 and 3 years rotation cycle) with an annual crop (maize), used for biomass production in north Italy.The average of the biomass production was 13.9 Mg DM ha⁻¹ per year for the SRC and vSRC poplar and 19.2 Mg DM ha⁻¹ for the maize.The energy consumption for the poplar cultivations was about 15 GJ ha⁻¹ per year, which represented only the 6% of the energy biomass product (about 257 GJ ha⁻¹ per year).The input value of the maize was higher (26.8 GJ ha⁻¹ per year). In this case, the input value was about the 7% of the energy content in the biomass product (about 370 GJ ha⁻¹ per year).During the vSRC cultivation an amount of 8090 kg CO₂ eq ha⁻¹ was emitted, 6420 kg CO₂ eq ha⁻¹ for the SRC and 26,370 kg CO₂ eq ha⁻¹ for the maize.Compared to the maize, the poplar SRC (or vSRC) crops are interesting from an energetic point of view, while maize requires less manpower, but it has major problems related to the landscape biodiversity.     

Optimization-based planning of a biomass to hydrogen (B2H2) system using dedicated energy crops and waste biomass

The utilization of biomass for hydrogen production is one of the promising options for a sustainable energy system. In this paper, we develop a new optimization-based approach for design and analysis of the B2H2 system including production, storage, and distribution using dedicated energy crops as well as various resources of waste biomass. To achieve this goal, we first develop an optimization model using mixed-integer linear programming technique that includes practical variables and constraints for decision-making about the usage of dedicated energy crops. We then conduct a case study of the B2H2 system for the road transportation sector of future Korea. As a result, we identify an optimal system configuration that includes the utilized biomass types, occupied land sizes, the number and location of facilities, and the biomass and hydrogen flows between regions. We also analyze the cost distributions and the sensitivity of the main cost drivers on the total annual cost (TAC). The results reveal that the proposed B2H2 system is economically competitive with some of the other renewable-based hydrogen supply systems (wind and solar) in Korea.     

A new integrated renewable energy system for clean electricity and hydrogen fuel production

In this paper, a new renewable energy-based cogeneration system for hydrogen and electricity production is developed. Three different methods for hydrogen production are integrated with Rankine cycle for electricity production using solar energy as an energy source. In addition, a simple Rankine cycle is utilized for producing electricity. This integrated system consists of solar steam reforming cycle using molten salt as a heat carrier, solar steam reforming cycle using a volumetric receiver reactor, and electrolysis of water combined with the Rankine cycle. These cycles are simulated numerically using the Engineering Equation Solver (EES) based on the thermodynamic analyses. The overall energetic and exergetic efficiencies of the proposed system are determined, and the exergy destruction and entropy generation rates of all subcomponents are evaluated. A comprehensive parametric study for evaluating various critical parameters on the overall performance of the system is performed. The study results show that both energetic and exergetic efficiencies of the system reach 28.9% and 31.1%, respectively. The highest exergy destruction rates are found for the steam reforming furnace and the volumetric receiver reforming reactor (each with about 20%). Furthermore, the highest entropy generation rates are obtained for the steam reforming furnace and the volumetric receiver reforming reactor, with values of 174.1 kW/K and 169.3 kW/K, respectively. Additional parametric studies are undertaken to investigate how operating conditions affect the overall system performance. The results report that 60.25% and 56.14% appear to be the highest exergy and energy efficiencies at the best operating conditions.     

Energy and exergy analyses of hydrogen production via solar-boosted ocean thermal energy conversion and PEM electrolysis

Energy and exergy analyses are reported of hydrogen production via an ocean thermal energy conversion (OTEC) system coupled with a solar-enhanced proton exchange membrane (PEM) electrolyzer. This system is composed of a turbine, an evaporator, a condenser, a pump, a solar collector and a PEM electrolyzer. Electricity is generated in the turbine, which is used by the PEM electrolyzer to produce hydrogen. A simulation program using Matlab software is developed to model the PEM electrolyzer and OTEC system. The simulation model for the PEM electrolyzer used in this study is validated with experimental data from the literature. The amount of hydrogen produced, the exergy destruction of each component and the overall system, and the exergy efficiency of the system are calculated. To better understand the effect of various parameters on system performance, a parametric analysis is carried out. The energy and exergy efficiencies of the integrated OTEC system are 3.6% and 22.7% respectively, and the exergy efficiency of the PEM electrolyzer is about 56.5% while the amount of hydrogen produced by it is 1.2 kg/h.     

Assessment of potential biomass energy production in China towards 2030 and 2050

The objective of this paper is to provide a more detailed picture of potential biomass energy production in the Chinese energy system towards 2030 and 2050. Biomass for bioenergy feedstocks comes from five sources, which are agricultural crop residues, forest residues and industrial wood waste, energy crops and woody crops, animal manure, and municipal solid waste. The potential biomass production is predicted based on the resource availability. In the process of identifying biomass resources production, assumptions are made regarding arable land, marginal land, crops yields, forest growth rate, and meat consumption and waste production. Four scenarios were designed to describe the potential biomass energy production to elaborate the role of biomass energy in the Chinese energy system in 2030. The assessment shows that under certain restrictions on land availability, the maximum potential biomass energy productions are estimated to be 18,833 and 24,901?PJ in 2030 and 2050.     

Production and quality analysis of pellets manufactured from five potential energy crops in the Northern Region of Costa Rica

Modifications to a pellet manufacturing process must be made based on the characteristics of raw material used. The purpose of this work was to determine the alternations required to a wood pellet manufacturing process and the quality of the pellets produced using this process from five energy crops. Quality measurements include: the caloric value, the loss of moisture content in each production stage, the efficiency index of particle-pellet, ash content and quality as defined using the quantity of cracks and the transversal density and longitudinal density determined using X-ray radiography. The crops analyzed were rhizomatous plants, with caloric values ranging between 17.1 and 20.3 MJ kg⁻¹. This work determined that it was possible to produce pellets with Gynerium sagittatum and Phyllostachys aurea using the same production process for wood; however, Arundo donax and Pennisetum purpureum needed pre-air-drying and the Sorghum bicolor required mechanical dewatering before drying. A. donax, P. purpureum and G. sagittatum provided the highest efficiency index. When evaluating the pellet quality P. aurea and G. sagittatum hard a large quantity of cracks, unlike A. donax, P. purpureum and S. bicolor. The transversal and longitudinal pellet density varied from 1129 to 1294 kg m⁻³. The highest values of bulk density were obtained in A. donax and P. purpureum, followed by G. sagittatum and P. aurea, and the lowest bulk density was obtained in S. bicolor. Althogh out, some species produced cracks and high ash content, this work demonstrated that it is possible to produce pellets with moderate quality.     

A comprehensive comparative energy and exergy analysis in solar based hydrogen production systems

In the presented paper, energy and exergy analysis is performed for thermochemical hydrogen (H₂) production facility based on solar power. Thermal power used in thermochemical cycles and electricity production is obtained from concentrated solar power systems. In order to investigate the effect of thermochemical cycles on hydrogen production, three different cycles which are low temperature Mg–Cl, H₂SO₄ and UT-3 cycles are compared. Reheat-regenerative Rankine and recompression S–CO₂ Brayton power cycles are considered to supply electricity needed in the Mg–Cl and H₂SO₄ thermochemical cycles. Furthermore, the effects of instant solar radiation and concentration ratio on the system performance are investigated. The integration of S–CO₂ Brayton power cycle instead of reheat-regenerative Rankine enhances the system performance. The maximum exergy efficiency which is obtained in the system with Mg–Cl thermochemical and recompression S–CO₂ Brayton power cycles is 27%. Although the energy and exergy efficiencies decrease with the increase of the solar radiation, they increase with the increase of the concentration ratio. The highest exergy destruction occurred in the solar energy unit.     

Steam gasification of energy crops of high cultivation potential in Poland to hydrogen-rich gas

In the paper energy crops of considerable cultivation potential in Poland, namely: Salix viminalis, Helianthus tuberosus, Sida hermaphrodita, Spartina pectinata, Andropogon gerardi and Miscanthus X giganteus were tested in terms of steam gasification reactivity of biomass chars, as well as yields and composition of product gas in steam gasification and lime-enhanced steam gasification in a laboratory scale fixed bed reactor at 650 °, 700 ° and 800 °C.The highest value of reactivity for 50% of carbon conversion, R₅₀, was observed for Sida hermaphrodita, regardless the process temperature.Application of CaO for in-situ CO₂ capture in steam gasification of biomass chars resulted in hydrogen content increase at 650 °C to the levels comparable with the ones reached at 800 °C without carbonation reaction. Also hydrogen and total gas yields increased in tests of lime-enhanced gasification.     

A novel combined biomass and solar energy conversion-based multigeneration system with hydrogen and ammonia generation

In the present study, an innovative multigeneration plant for hydrogen and ammonia generation based on solar and biomass power sources is suggested. The proposed integrated system is designed with the integration of different subsystems that enable different useful products such as power and hydrogen to be obtained. Performance evaluation of designed plant is carried out using different techniques. The energetic and exergetic analyses are applied to investigate and model the integrated plant. The plant consists of the parabolic dish collector, biomass gasifier, PEM electrolyzer and hydrogen compressor unit, ammonia reactor and ammonia storage tank unit, Rankine cycle, ORC cycle, ejector cooling unit, dryer unit and hot water production unit. The biomass gasifier unit is operated to convert biomass to synthesis gaseous, and the concentrating solar power plant is utilized to harness the free solar power. In the proposed plant, the electricity is obtained by using the gas, Rankine and ORC turbines. Additionally, the plant generates compressed hydrogen, ammonia, cooling effect and hot water with a PEM electrolyzer and compressed plant, ammonia reactor, ejector process and clean-water heater, respectively. The plant total electrical energy output is calculated as 20,125 kW, while the plant energetic and exergetic effectiveness are 58.76% and 55.64%. Furthermore, the hydrogen and ammonia generation are found to be 0.0855 kg/s and 0.3336 kg/s.     

Solar hydrogen production and its development in China

Because of the needs of sustainable development of the mankind society and natural environment building a renewable energy system is one of the most critical issues that today's society must address. In the new energy system there is a requirement for a renewable fuel to replace current energy carrier. Hydrogen is an ideal secondary energy. Using solar energy to produce hydrogen in large scale can solve the problems of sustainability, environmental emissions, and energy security and become the focus of the international society in the area of energy science and technology. It has also been set as an important research direction by many international hydrogen programs. The Ministry of Science and Technology of China supported and launched a project of National Basic Research Program of China (973 Program) – the Basic Research of Mass Hydrogen Production using Solar Energy in 2003 for R&D in the areas of solar hydrogen production. The current status of solar hydrogen production research is reviewed and some significant results achieved in the project are reported in this paper. The trends of development and the future research directions in the field of solar hydrogen production in China are also briefly discussed.     

Impact of solar energy cost on water production cost of seawater desalination plants in Egypt

Many countries in North Africa and the Middle East are experiencing localized water shortages and are now using desalination technologies with either reverse osmosis (RO) or thermal desalination to overcome part of this shortage. Desalination is performed using electricity, mostly generated from fossil fuels with associated greenhouse gas emissions. Increased fuel prices and concern over climate change are causing a push to shift to alternative sources of energy, such as solar energy, since solar radiation is abundant in this region all year round.