Smart Bioenergy

Biomass is the most relevant renewable energy source, with a wide range of possible and established methods to apply biomass for energy generation. In regards to the supply of sustainable energy, not only the provision of technology but also the integration of this technology into the system will be considerably important. This demands a change in bioenergy provision which is comparable to the transition from traditional to modern biomass use. The need for further development in the provision of bioenergy is also underlined by the challenges affecting the biomass resource base, including increasing demands for biomass for food, feed, materials and fuel. Furthermore, this is underlined by the major concerns surrounding factors relating to the land such as soil, nutrients and biodiversity.

Germany has implemented an active policy for the transition of the energy system towards greater use of renewable energy sources more than a decade ago, which has led to a strong increase in the amount of biomass used for electricity, heat and the provision of transport fuel. With relevant shares of electricity from wind and solar the need for better system integration is on the agenda. The situation in Germany can therefore provide interesting insights into the challenges and opportunities of using bioenergy in its new role. This will be elaborated on step by step in this book, starting with issues relating to the market and resource base, then moving on to analysis of the technical options, followed by the modeling of the effects on the German energy system in a case study and in conclusion focusing on the most promising fields as well as the missing elements for a successful transition.

Today bioenergy is the most important renewable energy carrier in Germany and yet it is mostly provided constantly as a base load, for example most biogas plants are in constant production at full load. In numerous ways, bioenergy could be a flexible option to satisfy the fluctuating demand for electricity, heat and transport fuels. In the power sector, biomass is a short-term option to meet the increasing need for flexible power generation, while wind or solar power are characterized by an alternating feed-in. Biogas plants in particular are ideal for providing power on demand for a stable electricity provision with a high percentage from renewables. The heat sector is well established for heat only provision, but has to integrate future combined heat and power concepts. Therefore, an optimal alignment between heat and power generation is required, if a high overall performance is to be achieved. Furthermore, the general decrease in heat through efficiency measures will change the way in which heat will be generated with more versatile load curves where flexible energy provision is favoured. In the transport sector flexibility is necessary in the form of a varying feedstock basis for consistent liquid biofuel products. For example, bioethanol could be made from sugar beets or cereals, where sugar, or starch converted into sugar, is processed by fermentation into alcohol. Second generation bioethanol is based on cellulose enzymatic split into single sugar molecules. Additionally, biomethane as a potential substitute for natural gas can be applied in different sectors and is predestined for flexible energy provision. A local and temporal decoupling of energy source generation, the well-established gas grid and the interchangeability with natural gas are all aspects that support this. It is expected that the different markets for power, heat and fuels will be more closely linked by the mid term. Here, some additional combinations of bioenergy with other renewables (i.e. power-to-gas) can provide flexible energy in different sectors additionally.

Biomass available for the flexible provision of bioenergy is a major factor in discussing the potential contribution flexible bioenergy systems could make to the overall energy system. Even though the quality of the biomass used has an impact on the potential availability of biomass, it might not be the most decisive factor. More important is the origin of the biomass since the production of biomass has a complex impact on land and land use and can also provoke change in land use. Many studies have been carried out to estimate future biomass potentials. Their results differ greatly, due to different methods, definitions and assumptions regarding the scope of the studies. Sustainable provision of biomass is a precondition for smart bioenergy supply. With liquid biofuels as a starting point, a number of certification schemes have been developed over recent years and recognised by the European Commission. The future development of these schemes and possible expansion to the whole agricultural or forestry sector will also influence the future biomass potentials of energy crops. This underlines the uncertainty surrounding the future potential of energy crops. In regards to smart bioenergy provision, one possible option is to make (existing) larger production units using energy crops more flexible by widening their product portfolio. To satisfy the specific technical demands of flexible provision greater quantities of feedstock will be required.

Flexible and demand-based production of electricity and heat (combined heat and power – CHP) from solid biomass is an extremely interesting concept for a renewable energy system as the used fuel shows excellent storability. However, conversion and power generation technology limit flexibility for several reasons.

Combined heat and power plants for the production of solid biomass are today designed for base load operation. The most common systems are steam cycles, organic Rankine cycles (ORC) and combinations of gasification and gas engines. Other available technologies include Stirling engines, fuel cells and thermoelectric generators (TEGs). Some technologies are already able to provide flexibility in power production. Extracting turbines, for example, are able to change the power-to-heat ratio of the system. It is possible to increase flexibility by using additional or upgraded units such as heat or gas storages, new steam turbines or new control systems. Potential solutions for increasing flexibility in combined heat and power production from solid biomass are expected to include micro-CHP systems and gasification units with high flexibility and high power-to-heat ratio. Larger plants may show less flexibility due to their thermal inertness (which sometimes has been part of the design, e.g. to stabilize combustion of fuels with low heating values).

The number of plants producing biogas and in particular the technology for converting energy crops and agricultural residues has been increasing substantially in Europe over recent years. The conversion process as well as the utilization of the produced biogas has been designed for a constant operation to allow for maximum capacity utilization. However, a certain degree of flexibility is part of the daily routine operation and in general biogas plants are able to vary their output. Flexibility requires in comparison to steady state operation some additional hardware such as increased gas conversion capacity (e.g. CHP units), a well-adjusted control of gas production and gas storage. This chapter discusses the technical requirements for flexible production and utilization of biogas.

Heat demand in households always depends on the building, the behavior of the inhabitants, the weather conditions as well many other factors. Therefore, there is always a fluctuating and often not very predictable need for heat. As heating systems have solved this problem for some time now, all heat generators are basically demand-based. Depending on the technology, heat buffering systems are sometimes required. Generally speaking, improved efficiency and low emissions were often achieved in the past by reducing start and stop procedures and applying some kind of base load heat generation. These kind of systems are very commonplace, providing the majority of renewable heat – not only in Germany but also in many other countries. In the future, heat from biomass will have to compare with other renewable heating options and will assume the role of securing heat provision at those times when temperatures fall considerably, when there is limited electricity available in the grid from renewables or when solar thermal systems are not working. This means that the biomass heat generators have to become more flexible in load changes over the total load range without increasing emissions and without significant efficiency losses. Basically, an appropriate design of the conversion system and its conceptual integration will enable a flexible heat supply through solid biomass. The available technologies and concepts for heat supply from solid biomass can be optimized by improved control units, automatic feeding, as well as additional heat storage systems. Consequently, there are a number of options to support the transition to a more renewable-based energy supply, also taking into account better insulation and a fall in the demand for heat in the housing sector. Nevertheless, this transition is more of a vision for decades to come and is still only just emerging in Germany.

In regards to a demand-oriented biofuel supply for the transport sector, this chapter considers the most relevant technologies and concepts for the production and supply of the most important liquid and gaseous biofuels and their current status quo. The limits of and opportunities presented by flexible biofuel production are considered. It has to be noted that flexible or part load operation of biofuel plants is not common. This also applies for most engineering plants in the chemical industry. Today biofuel plants are most commonly constructed as multiproduct plants such as bio refineries. Since the most inflexible step has an effect on the general system flexibility, intermediate storage, raw materials and various products are utilized in order to increase the system flexibility. Flexible management (i) of raw material and other input streams such as auxiliaries (reaction media, catalysts) and (ii) of plant operation in terms of main and by-products including the provision of products with high flexibility in application, is much more common than part load. In the article these opportunities are discussed for existing and new biofuel concepts. Furthermore, general issues of costing and environmental impact are considered.

As the previous book chapters concluded, the future bioenergy provision concepts for power, heat and transport fuels are characterised by more complex demands. A future energy market is characterised by the need for a sustainable flexible energy carrier with homogeneous properties for application in the fields of CHP, heat and fuel. To some extent these energy carriers are already available today (see Chaps. 4, 5, 6 and 7). However, in many cases untreated biomass cannot fulfil the requirements of existing and future conversion processes or demands respectively. As far as solid biofuels are concerned, the high moisture content of untreated biofuels coupled with a low energy density and high biological activity require the development of often costly storage, transport and conversion techniques. Various research activities are still ongoing to improve the utilisation of biofuels in existing and future technologies, available infrastructure and therefore also in logistic and storage issues. A similar development can be observed regarding the biogenic substitutes for natural gas (biomethane, bio-SNG). Such upgraded “new” – or rather “advanced” – solid and gaseous biofuels are high energy value products for gasification and combustion in industrial conversion plants as well as for domestic applications with excellent advantages in flexible energy provision. The amount of advanced solid biofuels in the markets of heating and power or combined heat and power systems will increase, as will the share of the biogenic substitutes for natural gas with further development and process optimisation.

This chapter reviews the current developments in selected biomass pretreatment processes and their intermediate biofuel products that have the potential to increase flexible bioenergy production in the short and mid-term. On the one hand, these include biomass densification without thermal treatment as well as torrefaction and hydrothermal treatment for producing intermediate solid biomass. On the other hand, technologies for biogenic substitutes for natural gas are evaluated. The focus lies on the surplus value of the technologies in terms of flexibility during energy production or use of the advanced solid biofuels or biogenic substitutes for natural gas as intermediate bioenergy carriers.

Energy scenarios and roadmaps indicate that intermittent renewable energy sources such as wind power and solar photovoltaic (PV) will be crucial to the power supply in the future. However, this increases the demand for flexible power generation, particularly under conditions of insufficient wind and/or solar irradiation. Among the renewable energy sources, bioenergy offers multiple end-use in the form of power, fuel or heat. Biomass-based power combines the advantages of being renewable, exceptionally CO₂ neutral and supporting demand-oriented production.

This chapter analyses four energy scenarios for Germany, focusing on the relevance of flexible bioenergy therein. Depending on how the scenarios are constructed, the range of biomass potential in the energy system is 1,180–1,700 PJ/a. The following sections of the chapter investigate the potential of flexible power generation from biomass on a regional scale (50 Hertz grid) starting with a description of the current state of bioenergy generation in the region and its potential for supplementary heat provision. We model the contribution of flexible biogas and solid biomass power using a minimization of daily residual load variance as a goal function. Two points in time are modeled – 2011 and 2030 to include the current and projected installed capacity from wind and solar PV. The results indicate that depending on the framework conditions, flexible bioenergy inclusion can reduce the daily variance in the residual load by >50 % compared to a non-flexible system. We conclude that flexible bioenergy has significant potential to contribute to balancing the power system with increasing shares of intermittent sources such as wind and solar PV.

In a nutshell, smart bioenergy can be described as the process of optimizing individual technologies and plants to an optimized contribution of bioenergy technologies to the overall energy system and infrastructure with the benefit of providing additional services from bioenergy. The focus of this book is on the conceptual approaches and the technical potential for developing different biomass provision routes towards more flexibility. This requires conversion plants with units that can be controlled with precision and well adapted to short reaction times, with a partial load function of the conversion process and additional storage facilities.

Power provision from biomass is one application, where increasing flexibility can be expected in Germany over the next 5 years when electricity from wind and photovoltaic will become more important. Due to the specific frame conditions of power provision, the demand for flexibility in this sector is expected to be very challenging, requiring reaction times of only a few minutes to provide positive or even negative energy to balance grid stability. Beside the specific German case, flexible power to increase the grid stability can be necessary due to different reasons and is required in many countries of the world. Highly flexible heat provision in small scale combustion units is not so much an issue at the moment, but is expected prospectively to be due to an increasing supply of heat from solar systems and/or heat from excess energy from wind and photovoltaic (power to heat). Fuels for transportation are also expected to change in the years to come. Furthermore, the increased availability of fluctuating wind and solar power will provide excess energy during certain periods. Basically speaking, the excess electrical energy can be converted into thermal or chemical energy and meet some of the demand for heat or fuel consumption. As a result, some of the flexibility needs can be shifted between the different sectors. To enable technologies to fulfil the additional demands for smaller and more flexible bioenergy provision, the availability of advanced intermediates is a core issue. This includes further development and market implementation of advanced solid biofuels as well as biomethane.

Challenges on the road to becoming more flexible do not only occur from the technical options and limitations but also from the elements of the supply chain, including sustainable feedstock provision, the implementation of flexible conversion concepts and the demand from the renewable energy market. With regard to the holistic system approach, three pillars for smart bioenergy systems can be identified: (i) an additional demand for smaller application units in terms of energy provision from biomass, (ii) the necessity to have improved technologies providing the desired products in small units and (iii) and new concepts of system integration – including the energy system but the coupled production of materials energy carriers from biomass as well.

It is only through the combined actions of different stakeholders that flexible bioenergy can be implemented successfully. A stepwise approach to achieving flexibilisation has to be designed and a careful consideration of the directed transition of the related energy systems is imperative. The bigger picture of such an upcoming energy supply system is the combined provision of heat, power and fuels based on different renewable energy carriers. Moreover, smart bioenergy needs to be coupled with future bio-economy approaches, providing materials and energy from the limited feedstock. The book does not go into detail here but many of the elaborated technical and managing elements, such as the sustainable feedstock base, designed intermediates and controlled conversion processes in production networks are necessary for flexible bioenergy provision and for advanced bio-based material production within a future bio-economy.