Increasing shares of variable renewable electricity (VRE) generation are necessary for achieving high renewable shares in all energy sectors. This results in increased excess renewable electricity (ERE) at times when supply exceeds demand. ERE can be utilized as a low-emission energy source for sector coupling through hydrogen production via electrolysis, which can be used directly or combined with a carbon source to produce electrofuels. Such fuels are crucial for the transport sector, where renewable alternatives are scarce. However, while ERE increases with raising VRE shares, carbon emissions decrease and may become a limited resource with several usage options, including carbon storage (CCS). Here we perform a model based analysis for the German case until 2050, with a general analysis for regions with a high VRE reliance. Results indicate that ERE-based electrofuels could achieve a greenhouse gas (GHG) abatement of 74 MtCO₂eq yearly (46% of current German transport emissions) by displacing fossil fuels, at high fuel-cell electric vehicle (FCEV) shares, at a cost of 250–320 € per tCO₂eq. The capital expenditure of electrolysers was found not to be crucial for the cost, despite low capacity factors due to variable ERE patterns. Carbon will likely become a limiting factor when aiming for stringent climate targets and renewable electricity-based hydrocarbon electrofuels replacing fossil fuels achieve up to 70% more GHG abatement than CCS. Given (1) an unsaturated demand for renewable hydrocarbon fuels, (2) a saturated renewable hydrogen demand and (3) unused ERE capacities which would otherwise be curtailed, we find that carbon is better used for renewable fuel production than being stored in terms of overall GHG abatement.

Wind and solar PV have become the lowest-cost renewable alternatives and are expected to dominate the power supply matrix in many countries worldwide. However, wind and solar are inherently variable renewable energy sources (vRES) and their characteristics pose new challenges for power systems and for the transition to a renewable energy-based power supply. Using new options for the integration of high shares of vRES is therefore crucial. In order to assess these options, we model the expansion pathways of wind power and solar photovoltaics (solar PV) capacities and their impact on the renewable share in a case study for Germany. Therefore, a numerical optimization approach is applied on temporally resolved generation and consumption time series data to identify the most efficient and fastest capacity expansion pathways. In addition to conventional layouts of wind and solar PV, our model includes advanced, system-friendly technology layouts in combination with electric energy storage from existing pumped hydro storage as promising integration options. The results provide policy makers with useful insights for technology-specific capacity expansion as we identified potentials to reduce costs and infrastructural requirements in the form of power grids and electric energy storage, and to accelerate the transition to a fully renewable power sector.

Wind and solar PV have become the lowest-cost alternatives for power generation in many countries and are expected to dominate the renewable power supply in many regions of the world. The temporal volatility in power production from these sources leads to new challenges for a stable and secure power supply system. Possible technologies to improve the integration of wind and solar PV are electrical energy storage and the flexible power provision by bioenergy. A third option is the system-friendly layout of wind and solar PV systems and the optimized mix of wind and solar PV capacities. To assess these different options at hand, a case study was conducted covering various scenarios for a regional power supply based on a high share of wind and solar PV. State-of-the-art concepts for all the stated technologies are modelled and a numerical optimization approach is applied on temporally-resolved time series data to identify the potential role of each option and their respective interactions. Power storage was found to be most relevant in solar dominated systems, due to the diurnal generation pattern, whereas bioenergy is more suitably combined with high wind power shares due to the less regular generation pattern. System-friendly wind and solar power can reduce the need for generation capacity and flexible options by fitting generation and demand patterns better.

Background The transition towards a renewable based power system in Germany largely depends on variable renewable energy sources (vRES) like wind power and solar PV. Their high variability over time poses new challenges for power system stability. Bioenergy as a renewable source has already been established in recent years and has the capability to offset fluctuations from wind and solar PV and can therefore play a new role in coming years. Methods This paper describes how existing bioenergy plants can be operated in order to offset fluctuations in power systems, performing a power system modelling based on time series data. As sample transmission system (TS), TransnetBW has been chosen, one of the four German transmission systems. We modelled two different types of bioenergy plant clusters, one including solid biomass plants and the other cluster covering biogas plants and other plants with comparable characteristics. For the modelling of the operation of these clusters, we used registered time series of the years 2011 and 2012 for a total load and feed-in from wind and solar PV, which were projected for the year 2022. The flexible bioenergy clusters are operated in order to minimize fluctuations in residual load (RL). This approach served as the basis to assess how concepts for flexible bioenergy provision can contribute to the task of balancing future power systems based on vRES. Results Bioenergy plays an important role in the renewable power supply of the TransnetBW TS, as it holds a share of 23.3% among the renewables projected for 2022. A flexible bioenergy (BE) provision allows for a reduction in daily residual load fluctuations by 30% compared to the non-flexible power generation from BE. Flexible BE effectively offsets high fluctuations originated from the feed-in of the substantial solar PV installations in the TS and also contributes to serve the peak load. But in contrast to regions with higher renewable shares from vRES, the amount of avoided BE power production in times of negative RL (excess power from renewables) is still negligible for the 2022 time frame investigated and thus reducing the immanent requirement for flexible BE. Conclusions In line with existing studies, the results show that bioenergy is already a valuable asset to achieve the targeted REN shares and can support the integration of the large vRES capacities in coming years, if produced flexibly. Operating biomass installations in a flexible manner effectively reduce daily fluctuations in RL, allow for a better integration of vRES and contribute to cover peak power demand. But from the findings of this case study, we conclude that the focus in the near-term should be on the efficient utilization of BE as the top priority until the demand for flexible BE provision is progressively increased with rising shares of vRES. Giving the regional differences, it should be stressed that the regional context, the relative share of wind and solar PV in the power system and therefore the investigated time horizon are important for defining the role of flexible bioenergy in the years to come.

In this paper we investigate the effectiveness of the auction scheme for onshore wind energy in Germany. Auction schemes were introduced across Europe in order to support cost effectiveness, i.e., achieving low awarded prices while achieving the set expansion targets for renewables. In Germany, with more than five years of experience and 24 auction rounds already held since the introduction of auctions in 2017, the results can be analyzed and compared to the effectiveness of the former feed-in tariff or feed-in premium scheme (FIT/FID) which was abandoned after 2017.