Today bioenergy plays a major role in the renewable energy provision, for heat and power and for liquid biofuels as well. With an increasing share of renewables on the one hand side and a limited availability of biomass on the other hand, the provision of bioenergy has to consider the demands of the future energy system with high shares of fluctuating wind and solar power. This includes new and improved technologies and concepts for biogas, biomethane, and liquid and solid biofuels, which are discussed in the following, while for the electricity sector, the demand for more flexible provision might take place in the years to come; for more flexible heat provision, the transition is expected in a longer time frame. For their market implementation adopted regulatory framework and price signals from electricity markets are necessary.
Review
Background: With wind power and photovoltaics, volatile renewables have emerged as central pillars of the energy transition. This increases the demand for flexibility options to compensate fluctuations in power generation. Focussing on the role of bioenergy as a renewable flexibility option, this article seeks to address two questions. The first is whether there is an option value of bioenergy as a provider of low-carbon flexibility in a future power system, which might justify continued technology-specific deployment support. The second question is whether existing market and policy incentives are effective in activating flexibility potentials, and what perspectives exist for increasing flexibility incentives. Methods: The article follows an interdisciplinary approach. First, technical potentials for flexible bioenergy plants and potential systemic contributions are examined. This is followed by an economic assessment of what flexibility incentives are provided by relevant market and policy framework conditions. Findings: Power from biomass can be well suited to provide flexible generation for grid stabilisation and residual load balancing. Biogas plants require an increase of nominal power over rated power, whereas the technical flexibilisation potential of solid biomass plants depends on specific technologies. Particularly, small-scale combined heat and power systems can deliver fast responses. For existing biogas plants, the Renewable Energy Sources Act's (EEG) flexibility premium and balancing market revenues have incentivised some changes in the production behaviour and investments in plant flexibilisation. However, decreasing spot market price levels and decreasing price variance reduce incentive strength. This also limits flexibilisation incentives for solid biomass plants. For new biogas plants, the EEG's remuneration rules set effective flexibility incentives, but 2014 reductions in remuneration rates have significantly slowed down the expansion. Conclusions: Given high technical potentials for flexibility provision, there is an option value of keeping bioelectricity in the technology mix until more is known about its future competitiveness with other low-carbon flexibility options. To maintain this option value, there is a case for setting policy incentives in a way that continued technological development remains possible. A stringent climate policy could accelerate structural change in the electricity sector, to allow for market price signals which incentivise low-carbon flexibility provision.
The production of synthetic natural gas (SNG) from renewable sources in cases requires a dynamic and intermitted operation of the methanation reactors. This may lead to catalyst damage. Therefore, the present work is aiming at identifying restrictions and optimization approaches of the start‐and‐stop operation of fixed‐bed methanation reactors. 2D modeling and simulation work is conducted and the warm‐start behavior of a fixed‐bed reactor after one to four hours operation intermittence is analyzed. The result reveals the possibility for an operation interruption of up to four hours without high adaptation effort to restart the reactor. After approximately four hours, the catalyst bed at the inlet part of the reactor reaches a temperature that provokes problems for a subsequent warm start.
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