Dispatchable RES and flexibility in high RES penetration scenarios: solutions for further deployment

1. Introduction

Through the Paris Agreement, Parties to the UNFCCC have reached a landmark to fight climate change. Aligned with this, the European Union has set itself an ambitious long-term goal of reducing greenhouse gas emissions by 80–95% (in comparison to 1990 levels) by 2050. Combating climate change within the above framework calls for a wide-scale deployment of renewable energy technologies (RETs).

Although the contribution of renewable energy sources (RES) in the electricity mix has significantly increased, the focus has been on intermittent RETs, whereas the required system flexibility is (mainly) provided by conventional power plants. The transition toward a more sustainable energy supply, and in the case of the European energy system, the decarbonization of the electricity sector through the deployment of renewable energy technologies, is an issue of high interest among policymakers and researchers.

With high shares of renewable energy, electricity system flexibility gains importance. The in-feed of variable RES-electricity (RES-e) can be balanced by energy storage and dispatchable electricity generation technologies, significantly increasing the market value of RETs combinations. Such currently available RETs include (among others) Concentrated Solar Power (CSP) with thermal energy storage (TES), solar photovoltaic (PV) with storage (electrochemical storage or electrical thermal energy storage (ETES)), hydropower, hybrid power systems, and biomass. All these technologies can provide dispatchable power, as they have some kind of energy storage, e.g. dam, battery or thermal storage. However, dispatchable RES-e face significant challenges in high RES penetration scenarios, which originate from the fact that the increased electricity system services offered (e.g. intraday, balancing, ancillary services, etc.) are not fully taken into account in their revenue streams.

In this framework, market and regulatory adaptations could drive the market uptake of dispatchable RETs. More specifically, collaborative efforts could play an important role in achieving the European energy transition at lower cost than purely national approaches, as renewable sources could be exploited at locations that require low support costs by offering high potential (good renewable resources), thus leading to lower overall system costs. In particular, the establishment of the ‘enabling framework’ as defined by the recast RES Directive 2018/2001 (Art. 3(5)), and especially the cooperation mechanisms (joint projects, statistical transfers, joint support schemes) that support regional development of RETs projects, could be a key element for collaborative CSP projects (Boie and Del Rio 2021).

This Special Issue aims to contribute to the better understanding of the importance of dispatchability and flexibility, and to highlight the policy and regulatory conditions needed in order for dispatchable RETs to be further deployed, supporting a fully decarbonized energy supply.

2. Delving into the special issue

The Special Issue opens with a study by Thonig et al. (2021), who analyze the influence of ideology on the ambition level of climate and renewable energy policy, as well as technological preferences for power system flexibility in four European countries. These policies and programs are compared with citizen poll data, to check how citizens are influenced in these topics by their general political preferences/ideology. It seems that ideology-driven political positions are not related to very different preferences regarding target ambition for climate and energy policy and that increasing the power system flexibility will be a major energy political challenge in the coming decade.

Lilliestam et al. (2021) investigate past trends in the global CSP market and their implications for the future outlook of CSP, on a national, regional and global scale, building on concepts from different streams of research. Two separate but related sets of literature are being used: the industrial life-cycle (ILC) and the technological innovation systems (TIS) literature, with the results focusing on the formative phase of a technology and its industry and innovation system. The results demonstrate that although CSP is becoming a cost-attractive technology, not only compared with other dispatchable renewables but also with fossil power, the outlook for CSP is very uncertain and entirely depends on action taken by national policymakers. Rapid action is necessary to support the technology in the short and middle terms.

Acknowledging the importance of dispatchability, Kiefer, Caldés, and Del Rio (2021) investigate through a survey targeting stakeholders in Spain and Germany and an expert elicitation, whether the greater need for dispatchable RETs can be a driver for the use of the EU cooperation mechanisms, focusing on the case of CSP. The analytical framework utilized takes into consideration drivers and barriers for the use of cooperation mechanisms, as well as the assessment of the drivers and barriers to the deployment of CSP in the EU. The results demonstrate that dispatchability is the most influential factor for the use of cooperation mechanisms for CSP in the future, and that the dispatchability of CSP could be rewarded through design elements in feed-in tariffs (FITs) and feed-in premiums (FIPs), whether set administratively or in auctions.

In an effort to evaluate alternative dispatchable solar power technologies, namely CSP with Thermal Energy Storage (TES) and PV with ETES or utility-scale Li-Ion batteries, Schöniger et al. (2021) investigate the competitiveness of each of the three options as a function of current and future investment costs and the desired storage duration. The energy system model Balmorel is used for the modeling of specific costs in a closed model setup. The key conclusion of the analysis is that PV+battery is most competitive for short storage durations, while CSP+TES is more economic for longer storage periods. To enable future electricity systems to cover short-term as well as long-term flexibility needs, it is advisable to further develop and support deployment of both options in the electricity market.

The role of demand response on joint allocation of wind and solar-based distributed generations to optimize network losses is the multi-constraints optimization problem the next study focuses on. Rawat et al. (2021) formulate the problem as a mixed-integer second-order cone programming (MISOCP) problem to minimize energy losses. Their analytical framework is investigated under different case studies to evaluate the impact of integrating demand response on the allocation of distributed generations. The simulation results show that integrating demand response with planning of distributed generations leads to more energy savings and improvements in voltage profile. It is observed that joint allocation of wind turbines and PV will minimize energy losses significantly as compared to allocation of wind turbines/PV alone.

The analysis of Koltsaklis, Dagoumas, and Mladenov (2021) combines three alternative algorithms for the electricity market clearing process to optimally determine the annual energy mix of a power system. The whole framework and model’s effectiveness is stress-tested with an illustrative case study of the Bulgarian power system. Several model formulations for exploring the effects of different market clearing algorithms on the resulting energy mix, as well as on the economic aspects of the studied power system, are thus provided. Flexible services, such as those offered by hydropower plants, become of top priority in the operation of electricity markets, considering the penetration level of variable RES.

3. Conclusions

A lesson emerging from this Special Issue is that alternative approaches for recognizing the importance of dispatchability and flexibility in the further deployment of RETs toward a more sustainable energy supply are needed by several stakeholders, primarily policymakers, but also utilities, investors and technology companies, in order to comprehend the emerging dynamics in the field. Due to the complexity of the issue, a number of parameters should be taken into consideration.

The articles in this Special Issue are delving into these parameters, focusing not only on the pure technical/modeling approaches adopted but also on the complementarity with socioeconomic data and political preferences, as well as policy tools, such as the cooperation mechanisms, in order to provide a comprehensive picture of the current situation and the existing potential to act as a valuable driver for dispatchable RETs.

Therefore, in order to further support the promotion of RETs, and CSP in particular, not only the technological maturity and competitiveness of the technology has a role but also the public support of the citizens (expressed also through political preferences), and the recognition of the role of dispatchability and flexibility through specific auction design.

Acknowledgments

The Editors would like to express their sincere thanks and gratitude to the authors who submitted papers to this Special Issue, and, especially, the reviewers, who spent their valuable time on providing their detailed feedback. Without their help, it would have been impossible to prepare this Special Issue in line with the high standards set from the beginning.

The Editors would also like to acknowledge the support received from the MUSTEC project (https://mustec.eu), which provided the analytical framework for many of the papers included in this Special Issue. MUSTEC receives financing under the European Union’s Horizon 2020 research and innovation program, under the grant agreement No. 764626. The content of this Special Issue is the sole responsibility of its authors and editors and does not necessarily reflect the views of the European Commission.