Plummeting costs of renewables - Are energy scenarios lagging?

Wind and solar energy play a pivotal role in deep decarbonization pathways for the future. However, energy scenario studies differ substantially in the contribution of these technologies, as the technology selection in models strongly depends on the choice of techno-economic parameters. In this article, we systematically compare the cost assumptions for solar and wind technologies in global, regional and national energy scenario studies with costs observed in reality and with recent remuneration from market auctions. Specially, we compared the capital expenditure (CAPEX) and the levelized cost of electricity (LCOE) towards the year of 2050 when available with historical market prices and auction prices. Our results indicate that the trend of rapid cost declines has been structurally underestimated in virtually all future energy scenario analyses and suggest that even the most recent studies refer to obsolete or very conservative values. This leads to underestimating the future role and level of deployment of renewable technologies. We recommend an open database for costs of renewable technologies to enhance the accuracy and transparency of future energy scenarios

Commentary and critical discussion on ‘Decarbonizing the Chilean Electric Power System: A Prospective Analysis of Alternative Carbon Emissions Policies’

This paper is a commentary on ‘Decarbonizing the Chilean Electric Power System: A Prospective Analysis of Alternative Carbon Emissions Policies’ –an article published by Babonneau et al. in the Energies Journal. On the one hand, our aim is to point out and discuss some issues detected in the article regarding the literature review, modelling methods and cost assumptions, and, on the other hand, to provide suggestions about the use of state-of-the-art methods in the field, transparent and updated cost assumptions, key technologies to consider, and the importance of designing 100% renewable multi-energy systems. Furthermore, we end by highlighting suggestions that are key to modelling 100% renewable energy systems in the scientific context to contribute to expanding the knowledge in the field

Renewable energy in copper production: A review on systems design and methodological approaches

Renewable energy systems are now accepted to be mandatory for climate change mitigation. These systems require a higher material supply than conventional ones. Particularly, they require more copper. The production of this metal, however, is intensive in energy consumption and emissions. Therefore, renewable energy systems must be used to improve the environmental performance of copper production. We cover the current state of research and develop recommendations for the design of renewable energy systems for copper production. To complement our analysis, we also consider studies from other industries and regional energy systems. We provide six recommendations for future modeling: (a) current energy demand models for copper production are overly simplistic and need to be enhanced for planning with high levels of renewable technologies; (b) multi-vector systems (electricity, heat, and fuels) need to be explicitly modeled to capture the readily available flexibility of the system; (c) copper production is done in arid regions, where water supply is energy-intensive, then, water management should be integrated in the overall design of the energy system; (d) there is operational flexibility in existing copper plants, which needs to be better understood and assessed; (e) the design of future copper mines should adapt to the dynamics of available renewable energy sources; and (f) life cycle impacts of the components of the system need to be explicitly minimized in the optimization models. Researchers and decision-makers from the copper and energy sector will benefit from this comprehensive review and these recommendations. We hope it will accelerate the deployment of renewables, particularly in the copper industry

Bridging granularity gaps to decarbonize large-scale energy systems - The case of power system planning

The comprehensive evaluation of strategies for decarbonizing large- scale energy systems requires insights from many different perspectives. In energy systems analysis, optimization models are widely used for this purpose. However, they are limited in incorporating all crucial aspects of such a complex system to be sustainably transformed. Hence, they differ in terms of their spatial, temporal, technological, and economic perspective and either have a narrow focus with high resolution or a broad scope with little detail. Against this background, we introduce the so- called granularity gaps and discuss two possibilities to address them: increasing the resolutions of the established optimization models, and the different kinds of model coupling. After laying out open challenges, we propose a novel framework to design power systems in particular. Our exemplary concept exploits the capabilities of power system optimization, transmission network simulation, distribution grid planning, and agent- based simulation. This integrated framework can serve to study the energy transition with greater comprehensibility and may be a blueprint for similar multi-model analyses

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Optimal planning of hydropower and energy storage technologies for fully renewable power systems

Greenhouse gas emissions need to stop shortly after mid-century to meet the Paris Agreement of keeping global warming well below 2°C. Fully renewable energy systems arise as a clear solution. To cope with their highly fluctuating power output (wind and solar photovoltaic), power systems need to become more flexible than they are today. Energy storage is one source of flexibility and is widely esteemed as a key-enabler for the energy transition. Hydropower often has storage, and can also help in this task. To assess how much energy storage is needed, expansion planning tools are commonly used. In general terms, they aim to minimize system-wide investment and operational costs, while meeting a set of techno-economic constraints. In the task of quantifying the need for energy storage, the present thesis makes four contributions, related to the overarching research question: how to plan the optimal energy storage mix for fully renewable power systems with important shares of hydropower? These contributions aim to assist the energy transition and to be relevant for energy system modelers, energy policy makers, and decision makers from ecohydrology, storage companies, and the renewable industry. - First contribution: The last couple of years have seen a particularly strong enrichment of such expansion tools. In response, the first contribution of this thesis is to provide a comprehensive review of the existing models, including a clear classification of the approaches and derivation of the current modeling trends. This review culminates by identifying the following open challenges for storage planning. First, the many available storage devices are quite diverse in their technical and economic parameters (including efficiency and lifetime), and this must be considered in the models. The tools also need to count with a high resolution of space and time to adequately capture the challenges of integrating renewable generation. Second, the many services that storage technologies can provide (beyond energy balancing, such as power reserves) need to be acknowledged. And third, the different energy sectors (electricity, heat, transport) all have sources of flexibility; thus, planning has to become multi-sectoral. - Second contribution: Many storage expansion studies have been produced within the last 5 years, but these resulted in a very broad range of storage requirements. To shed light on their recommendations, the second contribution systemizes over 400 scenarios of these studies for the U.S., Europe, and Germany. This exercise revealed that, as the share of renewable generation grows, the power capacity (e.g. GW, in pumped hydro, related to the number of turbines) and energy capacity (e.g. GWh, in pumped hydro, related to the water held by its reservoir) of storage systems increase linearly and exponentially, respectively. As grids become highly renewable, especially when based on solar photovoltaic, the need for storage peaks. The power capacity is around 40-75% of the peak demand, and the energy capacity 10% of the annual demand. A final finding of this analysis is that assumptions on electrical grid modeling, grid expansion, and energy curtailment have strong impacts on the found storage sizes. - Third contribution: Developing a new optimization tool for storage expansion planning in the power sector is the third contribution: LEELO (Long-term Energy Expansion Linear Optimization). LEELO extends the available models by including further services in the planning approach: power reserves and energy autonomy. A further novelty of LEELO is a detailed representation of hydropower cascades, which is a convenient source of flexibility in many regions of the world. A case study about Chile for the year 2050 assesses the impact of including these multiple services in the planning stage on the final storage recommendations. Indeed, the found deviations in total power capacities and energy capacities of storage are large; up to 60% and 220%, respectively. Moreover, the resulting storage mix (i.e. the sizes of the individual storage technologies) is also strongly affected. Lastly, planning with such services revealed a 20% cost increase that would otherwise remain hidden to the planners. Overall, modeling multiple services in expansion planning is relevant when designing fully renewable systems, as controllable (dispatchable) generators disappear. - Fourth contribution: In the final contribution, two optimization-objectives are added to LEELO. The first one relates to reducing hydropeaking, a highly fluctuating operational scheme of hydropower reservoirs that threatens the downstream river ecology. The second objective minimizes new transmission lines, as they have numerous externalities that result in delays and social opposition. Multi-objective LEELO is able to find the Pareto Front of these three dimensions (costs, hydropeaking, new transmission). In a case study, again about Chile, the found trade-offs are assessed from the perspective of the involved stakeholders. It found that the minimum cost solution requires doubling the existing transmission infrastructure while operating at severe hydropeaking. Avoiding all transmission projects will cost between 3 and 11% (depending on the allowed level of hydropeaking). In other words, the upside of new transmission is rather limited. As transmission is avoided, the generation turns significantly more solar while investments in wind decrease. At the same time, and to support a solar grid, the requirements for storage technologies grow. Demand for storage also grows when hydropeaking is constrained, as a direct response to the missing flexibility from hydropower. Severe hydropeaking can be mitigated for as little as 1% of additional costs (if new transmission is installed), which is good news to environmental organizations. Completely avoiding both hydropeaking and new transmission lines is the most extreme scenario, costing an additional 11% and requiring about 20% more storage power capacity. In short, cheap storage and solar technologies emerge as key-enablers for reaching such attractive solutions that can avoid both externalities (transmission and hydropeaking). A clear investment strategy for these technologies is needed and, if done right, can make the generation more sustainable and socially acceptable. When comparing the storage requirements for Chile to those for Europe and the U.S., it becomes clear that the storage power capacities needed for Chile are on the higher end (>70% of peak demand). This is related to the fact that Chile’s power system is about 20 times smaller and has highly correlated energy resources. The needed energy capacities are also on the higher end (9-13% of annual demand). Here, however, the existing hydropower park already provides a buffer of 6%, making the remaining demand much lower (3-7%). If new transmission projects are to be avoided, the need for storage increases very strongly in terms of power capacity (adding 5 to 30 percentage points) and only slightly in terms of energy capacity (adding 1 percentage point). Mitigating hydropeaking also increases the need for power capacity but without exceeding the range above. The strongest storage requirements arise from the multi-service simulations; in particular for meeting high levels of energy autonomy, the (storage) energy capacity needs to be doubled. Relating back to the main question on how to plan the mix of energy storage systems, it became evident that multi-service, multi-sector, and multi-objective approaches are needed. This thesis took a first step in that direction. Two detailed extensions (multi-service, multi-objective) for storage planning determined a higher need for these technologies in a case study on Chile, where the future for storage looks promising. In general, the performed case study provides the first 100% renewable scenarios for Chile. Altogether, the gained insights showed to be relevant for stakeholders from the energy and environmental sectors on the path to a zero-carbon energy supply

To prevent or promote grid expansion? Analyzing the future role of power transmission in the European energy system

Future energy-supply systems must become more flexible than they are today to accommodate the significant contributions expected from intermittent renewable power sources. Although numerous studies on planning flexibility options have emerged over the last few years, the uncertainties related to model-based studies have left the literature lacking a proper understanding of the investment strategy needed to ensure robust power grid expansion. To address this issue, we focus herein on two important aspects of these uncertainties: The first is the relevance of various social preferences for the use of certain technologies, and the second is how the available approaches affect the flexibility options for power transmission in energy-system models. To address these uncertainties, we analyze a host of scenarios. We use an energy-system optimization model to plan the transition of Europe’s energy system. In addition to interacting with the heating and transport sectors, the model integrates power flows in three different ways: as a transport model, as a direct-current power-flow model, and as a linearized alternating-current power-flow model based on profiles of power transfer distribution factors. The results show that deploying transmission systems contributes significantly to system adequacy. If investments in new power-transmission infrastructure are restricted—for example, because of social opposition—additional power generation and storage technologies are an alternative option to reach the necessary level of adequacy at 2% greater system costs. The share of power transmission in total system costs remains widely stable around 1.5%, even if cost assumptions or the approaches for modeling power flows are varied. Thus, the results indicate the importance of promoting investments in infrastructure projects that support pan-European power transmission. However, a wide range of possibilities exists to put this strategy into practice

Dynamic control strategy in partially-shaded photovoltaic power plants for improving the frequency of the electricity system

When large-scale photovoltaic power plants (PV-PPs) operate under partially-shaded conditions, their power output can be extremely fluctuating. This situation may compromise the energy balance of the electricity grid, which in turn threatens its secure operation from a frequency control viewpoint. In this context, the development of control strategies to reduce the variability of the power generated by PV-PPs is a key issue towards reaching sustainable electric systems. With this purpose, this paper proposes a novel control strategy to reduce the negative effects that PV-PPs operating under partially-shaded conditions may cause on the frequency control of electricity grids. The control operates the PV-PP in deload mode, i.e. keeping power reserves. The deload level of the PV-PP is set dynamically during the day considering a 10-min forecast of solar generation. The forecast is performed with artificial neural networks, first predicting the day-type (sunny, cloudy, overcast) and then the solar power. The controller continuously monitors the condition of the PV-PP: when the plant is under non-uniform shaded conditions, it deploys the power reserves to smooth the PV power. The proposed control was applied to a Chilean case study focused on the Atacama Desert, testing different control rules for the deload level. The obtained results show that the implementation of the proposed control considerably improves the frequency performance of the electricity grid. Although operating in deload mode implies energy losses in the PV-PP, the use of a dynamic deload level minimizes these losses when compared to a constant deload level. Altogether, the dynamic simulations show that such a control can play a relevant role for frequency control in electrical power systems with high shares of photovoltaic power. Our findings give important insights to electricity regulators about the technical requirements that they should impose to large-scale PV-PPs in electric power systems dominated by renewables energies

Challenges and trends of energy storage expansion planning for flexibility provision in low-carbon power systems - a review

Expansion planning models are often used to support investment decisions in the power sector. Towards the massive insertion of renewable energy sources, expansion planning of energy storage systems (SEP - Storage Expansion Planning) is becoming more popular. However, to date, there is no clear overview of the available SEP models in the literature. To shed light on the existing approaches, this review paper presents a broad classification of SEP, which is used to analyze a database of about 90 publications to identify trends and challenges. The trends we found are that while SEP was born more than four decades ago, only in the last five years increasing research efforts were put into the topic. The planning has evolved from adequacy criteria to broader targets, such as direct costs, mitigation of CO2 emissions, and renewable integration. The modeling of the network, power system, energy storage systems (ESS), and time resolution are becoming more detailed. Uncertainty is often considered and the solution methods are still very diverse. As outstanding challenges, we found that (1) the large diversity of ESS, in contrast to conventional generation technologies, and (2) the complex lifetime and efficiency functions need to be addressed in the models. (3) Only a high temporal and spatial resolution will allow for dimensioning the challenge of integrating renewables and the role of ESS. (4) Although the value of ESS lies beyond shifting energy in time, current SEP is mostly blind to other system services. (5) Today, many flexibility options are available, but they are often assessed separately. In the same line, although cross-sectorial (power, heat, transport, water) SEP is becoming more frequent, there are many open tasks towards an integrated coordination. The planning of future energy systems will be multi-sectorial and multi-objective, consider the multi-services of ESS, and will inherently require interdisciplinary efforts