Sheila Samsatli

A general spatio-temporal model of energy systems with a detailed account of transport and storage

Abstract This paper presents a general spatio-temporal model of energy systems comprising technologies for generation/conversion, transport and storage and infrastructures for transport. The model determines the optimal network structure (e.g. location and size of technologies and their interconnections through transport infrastructures) and its operation (e.g. rate of utilisation of technologies and transport flows) considering simultaneously the short-term dynamics and a long-term planning horizon. Here, we address one of the main challenges of solving a large scale MILP model: tractability. This issue is mainly caused by the need to include a wide range of time scales in the model: yearly (or decadal) intervals to include investment decisions; seasonal intervals to account for e.g. seasonal variations in demand and availability of resources; and hourly (or shorter) intervals to model the dynamics of storage technologies and to account for intermittency of renewable resources and demand. To exacerbate the problem, the spatial aspects also need to be fine enough to locate and size the technologies properly and to model the transport of resources, which depend on the location of demand and availability of resources. The model uses an efficient representation of time that exploits periodicity in system properties via a non-uniform hierarchical time discretisation. A decomposition method is also proposed wherein the large problem is broken down into 3 sub-problems that are then solved iteratively until the objective function is no longer improved. These methods significantly improve the computational efficiency without sacrificing temporal and spatial detail. The applicability of the model is illustrated using a case study in which the least-cost design and operation of a hydrogen network is determined such that the hourly transport demand of the different regions of an island is met by the intermittent and remotely located wind energy.

Fower-to-hydrogen and hydrogen-to-X: Which markets? Which economic potential? Answers from the literature

With the expansion of renewable energys contribution to the energy mix, balancing the electricity grid is becoming increasingly challenging. Alongside other solutions, Power-to-Hydrogen concepts are gaining significant interest. In this paper, the “Task 38”, initiated by the Hydrogen Implementing Agreement of the International Energy Agency, presents the first of a two-step literature review regarding Power-to-Hydrogen and Hydrogen-to-X concepts with a focus on prospective market and economic potential. The study reveals a large scope of literature that shows a considerable variety of suggested implementation schemes. The transportation sector is identified as the most promising consumer market. Hydrogen-to-Gas pathways will require subsidies in order to be profitable. Hydrogen-to-Power becomes an economically promising option in the context of systems with high shares of renewables and a need for longer-term storages. Additionally, key enablers for Power-to-Hydrogen concepts are identified; namely support policies, concurrently with ongoing progress on the development and implementation of industry standard.

Fower-to-hydrogen and hydrogen-to-X pathways: Opportunities for next generation energy systems

Energy systems are evolving rapidly around the world, driven mainly by CO2-e reduction targets. This has led to opportunities for integrated low carbon electricity-and-fuel systems founded on large scale “Power-to-Hydrogen, Hydrogen-to-X” (PtH-HtX). Power-to-Hydrogen (PtH) refers to large scale electrolysis. Hydrogen-to-X (HtX) refers to a range of high value products and services. If these pathways start with low-carbon electricity, then the fuel consumed at the downstream end also low-carbon. Use of intermittently low valued power lowers all production costs. This paper specifically identifies the main pathways and interconnections in a way that overcomes the ambiguities inherent in the term “Power-to-Gas”. In turn, this provides solid and easier to understand foundations for building legal and regulatory frameworks for new business opportunities along the lengths of the numerous pathways from supply to consumption.

Optimal Design and Operation of Heat Networks Utilising Hydrogen as an Energy Carrier

Abstract Renewable hydrogen has been receiving much attention as a clean energy vector. This paper presents an mixed integer linear programming (MILP) model that was used to explore scenarios for decarbonising domestic heat demands in Great Britain (GB) using a network of hydrogen storage (underground and pressurised vessels); hydrogen pipelines and electricity transmission lines; (onshore and offshore) wind farms, electrolysers, fuel cells and hydrogen-fired boilers and combined heat and power (CHP) plants. GB is divided into 16 zones where different sizes of technologies were considered. The model determines the number, capacity and location of conversion and storage technologies as well as the structure and capacity of the hydrogen and electricity transmission networks, in order to maximise profit subject to the maximum available land area for onshore wind farms and maximum number of offshore wind turbines that can be installed in each zone. The model simultaneously determines the hourly operation of the whole network. Within the technologies and infrastructure considered in the case studies, which are all assumed to be new investments (i.e. existing assets are not considered), results indicate that the cost of avoided CO2 emissions by replacing natural gas with renewable hydrogen as the energy carrier to satisfy heat demands is £795/tCO2.

Whole-Systems Modelling of Alternatives for Future Domestic Transport

Two alternatives for future domestic transport, powered by renewable wind energy, were compared from a whole-systems point of view using a mixed-integer linear programming model that accounts for the pathways from the primary energy source to the end use. The model simultaneously determines the number, size and location of conversion and storage technologies and the structure of the transmission network, as well as their hourly operation over an entire year. The integrated wind-electricity-hydrogen network presented in Samsatli et al., 2015 (for hydrogen fuel cell vehicles only) was extended to include grid-scale batteries and electricity demands from electric cars, accounting for the aggregate charge state of the vehicles’ batteries. Two cases were considered: one where the electric vehicle batteries could only be charged overnight and one where some of the vehicles could also be charged in the afternoon (e.g. while the owners are at work). The former case results in a more expensive network due to the grid-scale battery storage required; both cases are cheaper than satisfying transport demand using fuel cell vehicles mainly because of the much higher cost of the hydrogen distribution network.

Renewable electricity integration at a regional level: Cantabria case study

Sustainability Energy Programs (SEPs) determine the operative way in which the different energy vectors must be provided to final industrial, domestic or transport customers, as target demands for each final form of energy. In order to reduce the current huge regional electric deficit of the Cantabria region (northern Spain) due to imports from neighboring regions, a restructured, integrated system based mainly on wind on-shore power for 2020 is envisaged by the SEP of Cantabria. In this work, results of a Resource-Task Network model for the electricity grid have been developed as a previous step to feed the STeMES model for a better temporal resolution that can consider energy storage. A MILP optimization problem is solved for the minimization of the total cost of the electricity network capable of supplying the electricity demand in Cantabria for the 2020 horizon, using as a starting point the 2014 generation, transformation and distribution structure.