Flexible power generation scenarios for biogas plants operated in Germany: impacts on economic viability and GHG emissions

Biogas plants enable power to be generated in a flexible way so that variable, renewable energy sources can be integrated into the energy system. In Germany, the Renewable Energy Sources Act promotes flexible power generation in biogas plants. Two existing biogas plants in flexible operation were analyzed with respect to economic viability and greenhouse gas (GHG) emissions to assess the feasibility of flexible operation. To do this, a biogas technology simulation model was developed to reproduce the technical design of both biogas plants and to link this design with twelve flexibilization scenarios. The evaluation of the economic viability is based on a discounting method of investment appraisal. For assessing the level of GHG emissions, the life cycle assessment method has been applied. The results show that the profitability of flexibilization is contingent upon premium payments promoting flexibility and direct sales resulting from a higher electrical efficiency of new or additionally installed combined heat and power units. Overall, with respect to profitability, the results of the flexible power generation scenarios are dependent upon the properties of the technical plant, such as its power generation and gas storage capacities. Relative GHG emissions from flexible biogas plants show significantly lower values than for referenced fossil gas–steam power stations. Among the various scenarios, the results reveal that the level of GHG emissions especially depends on the number of operating hours of the additional combined heat and power unit(s). The results of the analyzed biogas plants showed no direct correlation between GHG emissions and the economic benefits. Overall, a flexible power generation of biogas plants may improve the economic viability as well as result in lower GHG emissions in comparison with a conventional base load operation. © 2016 The Authors. International Journal of Energy Research published by John Wiley & Sons Ltd.     

Biomass energy in organic farming—the potential role of short rotation coppice

One of the aims of organic farming is to “reduce the use of non-renewable resources (e.g. fossil fuels) to a minimum”. So far, however, only very little progress has been made to introduce renewable energy in organic farming. This paper presents energy balances of Danish organic farming compared with energy balances of conventional farming. In general, the conversion to organic farming leads to a lower energy use (approximately 10% per unit of product). But the production of energy in organic farming is very low compared with the extensive utilisation of straw from conventional farming in Denmark (energy content of straw used for energy production was equivalent to 18% of total energy input in Danish agriculture in 1996).Biomass is a key energy carrier with a good potential for on-farm development. Apart from utilising farm manure and crop residues for biogas production, the production of nutrient efficient short rotation coppice (SRC) is an option in organic farming. Alder (Alnus spp.) is an interesting crop due to its symbiosis with the actinomycete Frankia, which has the ability to fix up to 185 kg/ha nitrogen (N₂) from the air. Yields obtained at different European sites are presented and the R&D needed to implement energy cropping in organic farming is discussed.Possible win–win solutions for SRC production in organic farming that may facilitate its implementation are; the protection of ground water quality in intensively farmed areas, utilisation of wastewater for irrigation, or combination with outdoor animal husbandry such as pigs or poultry.     

Prospective application of farm cattle manure for bioenergy production in Portugal

Biogas is a promising renewable fuel, which can be produced from a variety of organic raw materials and used for various energetic purposes, such as heat, combined heat and power or as a vehicle fuel. Biogas systems implementation are, therefore, subjected to several support measures but also to several constraints, related with policy measures on energy, waste treatment and agriculture. In this work, different policies and policy instruments, as well as other factors, which influence a potential expansion of Portuguese biogas systems are identified and evaluated. The result of this analysis shows that the use of the cattle manure for biogas production is still far from its potential. The main reason is the reduced dimension of the Portuguese farms, which makes biogas production unfeasible. Various options are suggested to increase or improve biogas production such as co-digestion, centralized plants and modular plants. Horizontal digesters are the most suitable for the typical Portuguese plant size and have the advantage of being also suitable for co-digestion due to the very good mixing conditions. Mesophilic anaerobic digestion due to a more robustness, stability and lower energy consumption should be the choice. The recent increase in the feed-in tariffs for the electricity production based on anaerobic digestion biogas is seen as a political push to this sector.     

Upgrading biogas produced at dairy farms into renewable natural gas by methanation

Renewable natural gas can be produced from raw biogas, a product of the anaerobic decomposition of organic material, by upgrading its CO₂ content (25‐50%) via thermocatalytic hydrogenation (CO₂ methanation). The H₂ needed for this reaction can be generated by water electrolysis powered by carbon emission‐free energy sources such as renewable or nuclear power, or using surplus electricity. Herein, after briefly outlining some aspects of biogas production at dairy farms and highlighting recent developments in the design of methanation systems, a case study on the renewable natural gas generation is presented. The performance of a system for renewable natural gas generation from a 2000‐head dairy farm livestock manure is evaluated and assessed for its economic potential. The project is predicted to generate revenue through the sale of energy and carbon credits with the payback period of 5 years, with a subsidized energy price.     

A GIS-based approach for evaluating the potential of biogas production from livestock manure and crops at a regional scale: A case study for the Kujawsko-Pomorskie Voivodeship

In Poland, the promotion of the development of biogas plants was intensified under legal regulations. The potential expansion prompts the need for the assessment of a variety of environmental and geographical constraints as well as technical and economic factors, which ensure socio-economically and ecologically sound biogas development. In this paper, both spatial and non-spatial data were integrated to the GIS model to help determine the optimal sites for installing anaerobic digesters (AD). The focus was placed on animal manure (from cattle and pig populations), and co-substrates such as crop silage. Furthermore, the paper provides insight into the structure of cost and benefits in order to examine what incentive measures suffice to force biogas development and how much biogas feedstock could cost to make investments viable. The techno-economic assessment was carried out for combined heat and power generation and bio-methane injection into the gas grid. The methodology was applied to Kujawsko-Pomorskie Voivodeship.     

What type of digester configurations should be employed to produce biomethane from grass silage?

Grass is an excellent energy crop; it may be classified as a high yielding, low energy input, perennial crop. Over 90% of Irish agricultural land is under grass; thus farmers are familiar with, and comfortable with, this crop as opposed to a “new energy crop” such as Miscanthus. Of issue therefore is not the crop, but the methodology of generating energy from the crop. Numerous farmers across Europe (in particular Germany and Austria) use grass silage as a feedstock for biogas production; in a number of cases the produced biogas is scrubbed to biomethane and used as a transport fuel or injected into the natural gas grid. Many Irish farmers are considering converting from conventional farming such as beef production to grass biomethane production. Numerous technologies and combinations of such technologies are available; from one-stage batch dry systems to two-stage wet continuous systems; from one-stage continuous wet systems to two-stage systems incorporating a batch dry reactor coupled with a second stage high-rate reactor. This paper reviews work carried out both in the scientific literature and in practice at commercial scale.     

Multi-objective optimization of biogas systems producing hydrogen and electricity with solid oxide fuel cells

The design of solid oxide fuel cells (SOFC) using biogas for distributed power generation is a promising alternative to reduce greenhouse gas emissions in the energy and waste management sectors. Furthermore, the high efficiency of SOFCs in conjunction with the possibility to produce hydrogen may be a financially attractive option for biogas plants. However, the influence of design variables in the optimization of revenues and efficiency has seldom been studied for these novel cogeneration systems. Thus, in order to fulfill this knowledge gap, a multi-objective optimization problem using the NSGA-II algorithm is proposed to evaluate optimal solutions for systems producing hydrogen and electricity from biogas. Moreover, a mixed-integer linear optimization routine is used to ensure an efficient heat recovery system with minimal number of heat exchanger units. The results indicate that hydrogen production with a fuel cell downstream is able to achieve high exergy efficiencies (65–66%) and a drastic improvement in net present value (1346%) compared with sole power generation. Despite the additional equipment, the investment costs are estimated to be quite similar (12% increase) to conventional steam reforming systems and the levelized cost of hydrogen is very competitive (2.27 USD/kgH₂).     

Environmental systems analysis of biogas systems—Part II: The environmental impact of replacing various reference systems

This paper analyses the overall environmental impact when biogas systems are introduced and replace various reference systems for energy generation, waste management and agricultural production. The analyses are based on Swedish conditions using a life-cycle perspective. The biogas systems included are based on different combinations of raw materials and final use of the biogas produced (heat, power and transportation fuel). A general conclusion is that biogas systems normally lead to environmental improvements, which in some cases are considerable. This is often due to indirect environmental benefits of changed land use and handling of organic waste products (e.g. reduced nitrogen leaching, emissions of ammonia and methane), which often exceed the direct environmental benefits achieved when fossil fuels are replaced by biogas (e.g. reduced emissions of carbon dioxide and air pollutants). Such indirect benefits are seldom considered when biogas is evaluated from an environmental point of view. The environmental impact from different biogas systems can, however, vary significantly due to factors such as the raw materials utilised, energy service provided and reference system replaced.     

Impact of single versus multiple policy options on the economic feasibility of biogas energy production: Swine and dairy operations in Nova Scotia

The economic feasibility of on-farm biogas energy production was investigated for swine and dairy operations under Nova Scotia, Canada farming conditions, using net present value (NPV), internal rate of return (IRR), and payback period (PP) economic decision criteria. In addition, the effects of selected environmental and “green” energy policy schemes on co-generation of on-farm biogas energy production and other co-benefits from anaerobic digestion of livestock manure were investigated. Cost-efficiencies arising from economies of scale for on-farm anaerobic biogas production were found for swine farms, and less so for dairy production systems. Without incentive schemes, on-farm biogas energy production was not economically feasible across the farm size ranges studied, except for 600- and 800-sow operations. Among single policy schemes investigated, green energy credit policy schemes generated the highest financial returns, compared to cost-share and low-interest loan schemes. Combinations of multiple policies that included cost-share and green energy credit incentive schemes generated the most improvement in financial feasibility of on-farm biogas energy production, for both swine and dairy operations.     

Use of waste for heat,electricity and transport—Challenges when performing energy system analysis

This paper presents a comparative energy system analysis of different technologies utilising organic waste for heat and power production as well as fuel for transport. Technologies included in the analysis are second-generation biofuel production, gasification, fermentation (biogas production) and improved incineration. It is argued that energy technologies should be assessed together with the energy systems of which they form part and influence. The energy system analysis is performed by use of the EnergyPLAN model, which simulates the Danish energy system hour by hour. The analysis shows that most fossil fuel is saved by gasifying the organic waste and using the syngas for combined heat and power production. On the other hand, least greenhouse gases are emitted if biogas is produced from organic waste and used for combined heat and power production; assuming that the use of organic waste for biogas production facilitates the use of manure for biogas production. The technology which provides the cheapest CO₂ reduction is gasification of waste with the subsequent conversion of gas into transport fuel.     

Experimental investigation on the production of biogas from waste food

The production of biogas has been a substantial target to be utilized globally, especially in the agricultural sector. Most organic waste that is being produced from other forms of renewable energy systems is mainly used to reduce greenhouse emission (GHG), which as well reduces the daily consumption of fossil fuels. Anaerobic Digestion (AD) has been studied widely in recent years where its implementation in the industry has seen a mitigating impact on greenhouse gases. Unrestricted discharge of the big amount of waste food (WF) has become the main effect of severe environmental pollution worldwide. Among the various treatment methods, anaerobic digestion (AD) of waste food allows its valorization and the biogas produced can be used as biofuel enhancing the gas supply. In this study, a mechanical pre-treatment with Hollander beater has been applied to break down the particle size of waste food in the way to increase feedstock specific surface areas in other to enhance biogas production. Following, the pre-treatment of waste food during 30 min beating time, the biogas yield achieved a value of about 610.33 ml/gTS. Accordingly, a response surface methodology (RSM) can be used to critically evaluate the effects of process parameter (beating time and temperature) to the output response (biogas production). Pre-treated waste food by Hollander beater at beating time of 30 min enhances biogas production by 80%. An optimum biogas yield was achieved with pre-treatment of waste food at a beating time of 30 min.     

Analysis of small-scale biogas utilization systems on Ontario cattle farms

The production of biogas through the anaerobic digestion of cattle manure and its subsequent use in the generation of electricity on larger farms in Ontario is currently economically attractive. This is a result of the Ontario Feed-In Tariff (FIT) program, which provides incentivized rates for the production of electricity from biogas. Although larger farms can take advantage of the higher rates for electricity, there are substantially more smaller farms for which individually designed and engineered biogas systems would be prohibitively expensive. By employing the concept of modular biogas plants, this analysis evaluates the economics of small-scale biogas utilization systems. Dairy farms with at least 33 animals and beef farms with at least 78 animals can operate economically attractive biogas systems. This analysis shows that approximately 9000 additional Ontario cattle farms would be able to take advantage of the FIT program, which would add 120 MW_e of renewable energy capacity to the Ontario electrical grid.     

Sustainable biogas energy in Poland: Prospects and challenges

The article investigates prospects and challenges for expanding of sustainable biogas energy in Poland. The number of Polish biogas fuelled power plants and installed electrical power during the 2001-2010 decade is presented. Current economical incentives for biogas energy are discussed. It is emphasized that some revisions to the Polish tradable certificate system are urgently needed in order to encourage energy crop cultivation and the use of best available power technologies. Further, promising, but mostly unexplored feedstocks, such as energy crops, grasses and sorted municipal organic wastes are analyzed. It is also revealed that agrobiogas is characterized by a unique feature of ‘negative net’ CO₂ atmospheric emissions and thus the role of agrobiogas in solving Polish CCS dilemmas is discussed. In regard to biogas energy systems it is stressed, that the cost of electricity from biogas is almost independent on the size of agrobiogas CHP power plants in the range of 0.2-5 MW_e. Therefore agrobiogas energy is well suited for distributed energy systems involving small-scale agrobiogas power plants offering more green jobs and improved local waste management characteristics. Finally, reliable technologies suitable for biogas energy conversion and upgrading of biogas fuel to marketable gaseous fuels are briefly characterized.     

Intensification of biogas production using various technologies: A review

Anaerobic digestion (AD) is an organic matter conversion technology which offers a wide range of options for production of biogas from organic biomass, providing an excellent opportunity to convert abundant bioresources into safe, eco-friendly, renewable energy. Important factors in the process of AD are the biodiversity of microorganisms, chemical load of oxygen demand, and content of water and total solids. A challenge for the future is to find technologies that will maximally enhance biogas production and to find pathways for biogas to supersede well-established technologies and practices in the contemporary heavily fossil fuel-based energy system. Current studies on technologies of biogas production indicate a number of possibilities of using appropriate biological and physicochemical additives, like added enzymes or fruit pomace, as well as immobilizing microorganisms on biofilters. Anaerobic biorefinery is an emerging concept that generates not only bioenergy but also high-value biochemical products from the same feedstock. This study is a review of articles describing the intensification of biogas production by using various technologies.     

Techno‐economic assessment for energy generation using bagasse: case study

Bagasse is selected as the biomass source that is studied because of its annual significant rate production in Iran and potential for energy generation. Bagasse has been as an energy source for the production of energy required to run the sugar factory. The energy needed by factories was supplied by burning bagasse directly inside furnaces, which had an exceptionally low output. To this end, today, a secondary use for this waste product is in combined heat and power plants where its use as a fuel source provides both heat and power. In addition, low efficiency of traditional methods was caused to increase the use of modern methods such as anaerobic digestion, gasification and pyrolysis for the production of bio‐fuels. In this paper, the energy conversion technologies are compared and ranked for the first time in Iran. Therefore, the most fundamental innovation of this research is the choice of the best energy conversion technology for the fuel production with a higher efficiency. To assess the feasibility application and economic benefit of biogas CHP plant, a design for a typical biogas unit is programmed. The results show the acceptable payback period; therefore, economically and technically, biogas CHP plant appears to be an attractive proposition in Iran. Copyright © 2012 John Wiley & Sons, Ltd.     

Economical – environmental evaluation of natural gas and renewable energy systems

Although the energy crisis has been slightly abated in the recent times, the possibility of a crisis caused by extremely high oil prices is still imminent. Simultaneously, the environmental crisis represented by climate change is further the major concern which requires an immediate solution. Hence, in this research, economical and environmental assessment of utilizing renewable energies in comparison with natural gas have been investigated which resulted to choose the best economically–environmentally alternative for power generation. Equivalent uniform annual value and scaling‐weighting check list with experts' comments through analytical hierarchy process have been applied for economical and environmental assessment, respectively. Afterward, the results of normalized economical and environmental assessment have been coalesced to gain a combined economical–environmental perspective. As economical surveys, four scenarios have been considered. The results reveal that the best choices are conventional steam cycle, combined cycle, and biogas if power is sold to consumer (other technologies have negative net present value in this scenario), respectively, without considering the social costs and the emission reduction. If power is sold to government, biogas, conventional steam cycle, combined cycle, and wind are technological priorities. In case of considering social costs and emission reduction incomes, the best choices are biogas, combined cycle, and conventional steam cycle, respectively, if power is sold to consumers. If not, the priorities are biogas and wind. Furthermore, environmental surveys have indicated that wind is the most applicable environmentally friendly energy to produce electricity with negative impact magnitude (NIM) of 1.3 (out of 10). In addition, photovoltaic, biogas, and hydropower remain at the next levels with NIM of 1.6, 1.7, and 3.2 (out of 10), respectively. While conventional steam cycle has 6.2 of NIM. Eventually, the combination of economical and environmental evaluation reveals that wind farms and biogas plants with normalized weight of 3.10 (310%) and 2.34 (234%) are the best choices of electricity generation method, respectively. Moreover, the least applicable one is conventional steam cycle with normalized weight of 0.63 (63%). To sum it up, wind farms and biogas plants are about five and four times more economical–environmental beneficial than conventional steam cycle power generation. Copyright © 2012 John Wiley & Sons, Ltd.     

The economics of hybrid power systems for sustainable desert agriculture in Egypt

Egypt has embarked on an ambitious desert land reclamation program in order to increase total food production. Energy planners for these desert agriculture locations have chosen diesel generation power technology because minimization of the initial capital cost of a power supply system is their top priority. This heavy reliance on diesel generation has negative effects on the surrounding environment including soil, groundwater, and air pollution. Although good solar and wind resource prospects exist for the use of cleaner hybrid power systems in certain desert locations, little research has been done to investigate the economic potential of such systems in Egypt’s desert agriculture sector. Using optimization software, we assess the economics of hybrid power systems versus the present diesel generation technology in a remote agricultural development area. We also consider the emission reduction advantages of using hybrid systems. Interestingly enough, optimization results show that hybrid systems are less costly than diesel generation from a net present cost perspective even with the high diesel fuel price subsidies. Since hybrids are also more environmentally friendly, they represent a strong step towards achieving sustainable desert agriculture.     

Energetic and economic investigation of Organic Rankine Cycle applications

The use of organic working fluids for the realization of the so called Organic Rankine Cycle (ORC) has been proven to be a promising solution for decentralized combined heat and power production (CHP). The process allows the use of low temperature heat sources, offering an advantageous efficiency in small-scale applications. This is the reason why the number of geothermal and biomass fired power plants based on this technology have been increased within the last years. The favourable characteristics of ORC make them suitable for being integrated in applications like solar desalination with reverse osmosis system, waste heat recovery from biogas digestion plants or micro-CHP systems. In this paper, the state of the art of ORC applications will be presented together with innovative systems which have been simulated in a process simulation environment using experimental data. The results of the simulation like efficiencies, water production rates or achievable electricity production cost will be presented and discussed.     

Biogas derived from municipal solid waste to generate electrical power through solid oxide fuel cells

Depleting fossil fuels and the pollution resulting from their consumption indicate an urgent need for clean and dependable alternatives such as renewable energies. Biomass is a free and abundant source of renewable energy. Municipal solid waste (MSW) as one of the main categories of biomass has always been an issue for metropolitan cities. It has, however, a high potential for biogas production. In this study, the technical and economic aspects of generating electrical power through solid oxide fuel cells (SOFCs) powered by injecting biogas derived from Tehran's MSW, as a case study, are investigated. The main objectives of the current study are to identify the power generation capability of the process and find out if it can result in a competitive energy resource. The total amount of obtainable methane through anaerobic digestion of MSW and then the achievable power generation capacity by using the obtained biogas are computed using the electrochemical relations inside the SOFC. The economic calculations are carried out to estimate the final price of the generated electricity, taking into account the major capital and ongoing costs of the required equipment. The effect of variations of MSW composition on the power generation capability and final electricity price is also studied. Moreover, the application of a gas turbine (GT) with the SOFC as a hybrid SOFC–GT system to recover the produced heat by SOFC and its effect on the power generation capability and the final electricity price are investigated. Results indicate that around 997.3 tons day^?1 biomethane can be generated using Tehran's MSW. By using the SOFC, the produced biogas can generate 300 MW_AC electrical power with a final cost of Depleting fossil fuels and the pollution resulting from their consumption indicate an urgent need for clean and dependable alternatives such as renewable energies. Biomass is a free and abundant source of renewable energy. Municipal solid waste (MSW) as one of the main categories of biomass has always been an issue for metropolitan cities. It has, however, a high potential for biogas production. In this study, the technical and economic aspects of generating electrical power through solid oxide fuel cells (SOFCs) powered by injecting biogas derived from Tehran's MSW, as a case study, are investigated. The main objectives of the current study are to identify the power generation capability of the process and find out if it can result in a competitive energy resource. The total amount of obtainable methane through anaerobic digestion of MSW and then the achievable power generation capacity by using the obtained biogas are computed using the electrochemical relations inside the SOFC. The economic calculations are carried out to estimate the final price of the generated electricity, taking into account the major capital and ongoing costs of the required equipment. The effect of variations of MSW composition on the power generation capability and final electricity price is also studied. Moreover, the application of a gas turbine (GT) with the SOFC as a hybrid SOFC–GT system to recover the produced heat by SOFC and its effect on the power generation capability and the final electricity price are investigated. Results indicate that around 997.3 tons day^?1 biomethane can be generated using Tehran's MSW. By using the SOFC, the produced biogas can generate 300 MW_AC electrical power with a final cost of $0.178 kWh^?1. By using the hybrid SOFC–GT, the electrical power capacity is increased to 525 MW_AC, and the final electricity cost drops to $0.11 kWh^?1, which indicates its competitiveness with other common energy resources in the near future, especially by considering different governmental subsidy policies that support renewable energy resources. The considerable environmental benefits of the proposed procedure, from both MSW management and CO₂ emission reduction points of view, make it a promising sustainable energy resource for the future. Copyright © 2016 John Wiley & Sons, Ltd.     

Pretreatment of lignocellulosic biomass for enhanced biogas production

Lignocellulosic biomass is an abundant organic material that can be used for sustainable production of bioenergy and biofuels such as biogas (about 50–75% CH₄ and 25–50% CO₂). Out of all bioconversion technologies for biofuel and bioenergy production, anaerobic digestion (AD) is a most cost-effective bioconversion technology that has been implemented worldwide for commercial production of electricity, heat, and compressed natural gas (CNG) from organic materials. However, the utilization of lignocellulosic biomass for biogas production via anaerobic digestion has not been widely adopted because the complicated structure of the plant cell wall makes it resistant to microbial attack. Pretreatment of recalcitrant lignocellulosic biomass is essential to achieve high biogas yield in the AD process. A number of different pretreatment techniques involving physical, chemical, and biological approaches have been investigated over the past few decades, but there is no report that systematically compares the performance of these pretreatment methods for application on lignocellulosic biomass for biogas production. This paper reviews the methods that have been studied for pretreatment of lignocellulosic biomass for conversion to biogas. It describes the AD process, structural and compositional properties of lignocellulosic biomass, and various pretreatment techniques, including the pretreatment process, parameters, performance, and advantages vs. drawbacks. This paper concludes with the current status and future research perspectives of pretreatment.