Short-Term Operational Flexibility in Long-Term Generation Expansion Planning

In light of the European climate ambitions, there has been substantial growth in capacity of variable renewable energy sources in many Member States, with significant future growth expected. Such sources impact the operation of the power system by challenging its ability to maintain the short-term balance between supply and demand. Firstly, their output is variable and uncertain, increasing the need for short-term flexibility. Secondly, they displace part of the conventional flexibility providers, i.e. the dispatchable generation technologies, decreasing the supply of short-term flexibility. These sources also impact the planning of the power system by challenging its long-term ability to meet the aggregate demand for electricity. Firstly, only a limited share of their capacity can be called upon at any given time. Secondly, their impact on power system operation also has an impact on power system planning. The first aspect, related to \textit{firm capacity adequacy}, is well understood and is mostly dealt with adequately in planning models. The second aspect, related to \textit{flexibility adequacy}, has only recently emerged as an area of interest in planning. To study the importance of short-term flexibility adequacy in long-term power system planning, a high level of temporal and operational detail is needed, while managing the required computational effort. For that purpose, an alternative approach is developed for representing power system operation in planning: a clustered formulation of the unit commitment problem. Using this formulation, a planning model is developed which identifies the optimal investment portfolio, taking into account renewable energy objectives, and determines the scheduled production and consumption levels to deliver energy and reserve. The need for short-term flexibility is represented via the modeling of the day-ahead electricity market with an hourly resolution - to include the effects of variability, and operating reserve requirements following the guidelines of the European Network for Transmission System Operators for Electricity - to include the effects of uncertainty. The supply of flexibility is represented via mathematical models of dispatchable and variable generation, long-term demand response, re-electrifying and non re-electrifying storage, and flexibility through interconnection. First, the developed planning model is applied to a test system to assess the impact of short-term flexibility requirements on the cost and composition of the optimal investment portfolio. The supply of short-term flexibility is limited to the sources most commonly found in European power systems, namely dispatchable generation technologies and pumped hydro energy storage. Results show that renewable uncertainty is the most important driver of the short-term flexibility-related costs. Results further show that the way of handling this uncertainty, i.e. the adopted reserve sizing and allocation strategy, is decisive for the final impact of flexibility adequacy requirements. Based on the findings of this work it can be said that it will most likely no longer be cost-effective to centrally impose a level of reliability in a highly renewable power system. In a liberalized and decentralizing power system context, the value of reliability will also be something to be determined in a liberalized and decentralized way. Finally, it has to be noted that other elements than short-term flexibility requirements may have larger impacts on total system cost, and that it might therefore be more opportune for other planning models to dedicate additional computational resources to these issues, rather than to including the short-term flexibility constraints. This, naturally, depends on the goal of the research. Second, the planning model is used to assess the value of alternative sources of short-term flexibility, and the importance of the level of operational detail for assessing their impact. The supply of short-term flexibility is expanded to include a number of selected technologies of the three other types of flexibility sources: energy storage, demand response and interconnection. Results show that different technologies generate added value in different ways, but that they are also to a certain extent interchangeable. Results further show that the optimal level of investment depends on how well the technologies are able to compound different sources of added value, and that high operational detail in a power system planning model is therefore indispensable, as it enables the model to capture the total added value of the different technologies. The combined flexibility of the considered conventional and alternative flexibility providers allows to significantly reduce the cost of short-term flexibility requirements. Coupled to an ambitious operating reserve strategy, this flexibility could thus enable the integration of large shares of variable renewable energy sources without significant flexibility adequacy-related costs. One of the main challenges to be addressed is the remuneration of the flexibility providers for their added value. Regardless of the specific mechanism through which this will be realized, based on the findings of this work it can be said that such mechanisms should be technology-neutral and developed in an international context.status: publishe

The Impact of Long-Term Demand Response on Investment Planning of Renewable Power Systems

The increased penetration of intermittent renewable energy sources has an important impact on the operation and planning of power systems. On the one hand the short-term variability and limited predictability challenges system security, resulting in an increased need for operational flexibility. On the other hand the limited number of full load hours challenges system adequacy, resulting in an increased need for back-up generation capacity. When evolving towards a fully renewable power supply this back-up generation capacity can come from e.g. biomass technologies or a combination of power-to-gas storage and gas-fired power plants. An alternative is the use of the flexibility provided by long-term demand response. Such demand response can shift demand over longer periods of time, and as such is able to structurally lower demand during periods of low energy availability. This work quantifies the impact of such demand response on the investment planning of a conceptual power system following the integration of large shares of intermittent renewable generation. Simulations show that a limited amount of long-term demand response flexibility can have an important impact on the total system cost and the investments in generation and storage capacity. They also show the importance of the way in which the use of this flexibility is constrained in terms of the number of activations, the maximum activated power and the maximum duration of an activation.status: publishe

Evaluating the construction of prominent scenarios for a low-carbon European power system in 2050

Given the stringent climate constraints the European Union has put forward for the power sector, the European energy system will have to change drastically. Although presenting a great number of challenges, the necessary transformation of our energy system also presents us with the opportunity to move towards a more sustainable society. This means balancing economic and social development with environmental protection, known as the triple bottom line. This work will focus on scenarios for the future electric energy system with high levels of renewable energy to realise this transformation. To adequately evaluate the challenges this poses the modelling of the energy system has to be sufficiently detailed. The last few years a number of highlevel studies have been published exploring possible pathways for the evolution of national and regional energy systems towards a low-carbon 2050 energy system. Four prominent studies have been examined in detail as to how they model the operational aspects of the energy system, namely: Energy Roadmap 2050 by the European Commission, Power Choices by EURELECTRIC, Roadmap 2050 by the European Climate Foundation and Battle of the Grids by Greenpeace. They are compared in terms of how they model supply, demand and the flexibility options of an energy system. A number of opportunities are found for the improvement of the construction of roadmaps for a low-carbon European energy system. The main focus is on the assessment of the technical feasibility of the proposed supply side configurations.status: publishe

The Role of Long-Term Energy Storage in Investment Planning of Renewable Power Systems

The transition towards a decarbonized power system requires the integration of large shares of variable renewable energy sources. Their intermittent nature challenges the short-term ability of the power system to maintain the system balance, and its long-term ability to meet the peak demand. This results in an increased need for operational flexibility. Simultaneously, the availability of conventional dispatchable generation to provide such flexibility becomes less evident. Energy storage systems present an alternative source of flexibility. This paper focuses on the role of long-term storage, such as power-to-gas, which is able to also deal with seasonal variations in the output of renewables. It studies the impact of long-term storage on the investment planning of a conceptual power system following the integration of large shares of variable renewable generation. Simulations show that long-term storage reduces the need for installed renewable generation capacity to meet renewable objectives, and that it has a pivotal role in realising a fully renewable supply at a realistic cost. Results further show that the deployment of long-term storage depends greatly on the availability of biomass. If biomass is available, long-term storage investment only occurs at extremely high renewable penetrations.status: publishe

Operational flexibility provided by storage in generation expansion planning with high shares of renewables

The integration of variable renewable energy re-sources result in an increased need for operational flexibility. Energy storage is one of the alternatives to conventional genera-tion technologies to provide this flexibility. A generic model for energy storage is introduced into a generation expansion plan-ning model, considering operational constraints of power plants and system balancing requirements. Different targets for the final renewable electricity generation towards the future are imposed, quantifying the need for electricity storage and the impact on the electricity generation mix. When facing high renewable targets, storage is found to reduce the need for in-stalled generation capacity, both conventional and renewable, and reduce the electricity generation costs.status: publishe

Wage without Work

status: publishe

Quantifying the importance of power system operation constraints in power system planning models: A case study for electricity storage

The realized and expected growth of variable renewable energy sources challenges both power system operation and power system planning. A decreasing share of dispatchable generation technologies in electricity generation and an increasing need for short-term flexibility means that the added value of alternative short-term flexibility providers, such as electricity storage, becomes important. This paper studies the way in which alternative flexible resources, here storage technologies, generate added value by running various set-ups of a power system planning model with different levels of operational detail. Firstly, this allows to identify the different roles flexible technologies play in power system operation, and the subsequent impact on power system planning. Secondly, this allows to determine the importance of operational detail in power system planning models to accurately assess the value of flexibility. Results show that storage technologies have the technical ability to provide firm capacity, smoothen the residual load curve, manage the impact of hourly dispatch constraints and provide reserve capacity. Nevertheless, the extent to which this is translated into investment depends on how cost-effectively a technology can offer these services. Results further show that to fully capture the added value of flexibility providers high operational detail is needed in planning models.status: publishe

Benefits of a multi-energy day-ahead market

© 2018 Energy system integration can bring several benefits to energy systems, notably to those that are in transition to high shares of renewable energy. Strategies are needed to realize the theoretical benefits of this approach in practice. Therefore, this paper proposes the organization and mathematical formulation of a multi-carrier day-ahead market in which electricity, gas and heat are traded simultaneously. This market set-up is applied to a conceptual test case to identify how - compared to a reference set-up mimicking the current practice - the multi-carrier market is able to unlock the benefits of energy system integration. It is quantitatively shown that the multi-carrier market (1) eliminates the need for forecasts of prices on subsequent markets and the consequences of the related errors, (2) allows to use the flexibility available in one carrier to facilitate the balancing in another, e.g. using the flexibility of a heat system to help balance the electricity system, and (3) enables specific market outcomes, unachievable in a sequential set-up, which increase the optimality of the market outcome.status: publishe

Benefits analysis of voltage regulation on MV networks' investments

International audienc

Quantifying the Flexibility of Residential Electricity Demand in 2050: a Bottom-Up Approach

This work presents a new method to quantify the flexibility of automatic demand response applied to residential electricity demand using price elasticities. A stochastic bottom-up model of flexible electricity demand in 2050 is presented. Three types of flexible devices are implemented: electrical heating, electric vehicles and wet appliances. Each house schedules its flexible demand w.r.t. a varying price signal, in order to minimize electricity cost. Own- and cross-price elasticities are obtained through a regression analysis. Via a Monte Carlo approach-based method, the elasticities are scaled up to a country level. The results show that the electric energy demand will double and peak power demand can increase by a factor 5 to 8 compared to today. The elasticity matrices show that most flexibility is available in winter and least in summer.status: publishe