Energy in the perspective of the sustainable development: The 2000W society challenge

As energy plays a central role in the world development, it represents as well a major challenge for sustainable development. Today, more than 80% of the primary energy consumption is based on fossil fuels and the share is likely to remain high in the future. Even if technology developments will reduce the specific consumption, the world energy demand is likely to increase in line with its population. Energy and material efficiency and the integration of the renewable resources will therefore have to play a major role for sustainable development. The challenge concerns not only the technologies at the conversion and useful energy level, but also the energy management and infrastructures. The 2000 W per capita society initiative launched by the Board of the Swiss Institutes of Technology targets the identification of the major technological breakthroughs to reduce the per capita primary energy use of Switzerland by two-thirds within five decades. This study examined the energy saving potentials in the complete conversion chain “from primary energy to energy services” in the main sectors of economy: buildings, transport and industry. The report highlights the possible benefits which could be obtained from new materials, new technologies and an intensification of product and capital use. The systems integration appeared to be of prime importance in order to valorise the exergy potentials of the energy resources. The report emphasizes the political responsibility of developing the enabling society infrastructure: not only for the energy distribution (electrical, gas or heating networks) but also for the information technology, the appropriate regulations, the education and for the necessary integration of the lifetimes of the manufactured artifacts in the pathway to the 2000 W per capita society.

Thermo-Economic Optimisation of Solar Tower Thermal Power Plants

James Spelling

Amidst a backdrop of rapidly increasing world-wide electricity demand, solar thermal power generation shows great potential for supplying the electricity needs of numerous countries in the Sun-belt regions of the world. In these regions, the absence of significant biomass, hydrological or geothermal reserves makes solar thermal power the most promising solution for meeting that most fundamental of demands: energy. Amidst the different options available for harnessing the Sun’s power, solar thermal technologies have been shown capable of producing electricity at the most economically viable rates [32]. However, all currently existing solar thermal power plants have been based around the use of Rankine, or steam turbine, cycles which are limited in the efficiencies they can achieve. In order to make better use of the Sun’s energy, higher efficiency cycles should be used. With their high concentration ratios, solar thermal power tower systems are amongst the best options for making use of the Sun’s potential. As the energy delivery temperature of central receiver systems is higher, they harness the solar radiation at a higher exergy level [4]. This higher temperature also opens the road to the use of more advanced thermodynamic cycles. Hybrid fossil-fuel – solar systems are also imaginable [13], as the energy delivery temperature is compatible with standard gas turbine cycles. Hybrid systems can help mitigate the requirements of thermal energy storage, as well as reducing the perceived risk when investing in new solar technology, which stimulates research and development, as well as providing employment. Recent developments in the field of high temperature volumetric receivers [10] along with rock- based packed-bed storage systems have opened up an interesting possibility. High temperature receivers allow the use of higher-efficiency combined-cycle setups, whereas packed-bed units offer the possibility of cheap storage. Larger storage volumes allow pure-solar systems to extend their power production into the night, making hybrid options less attractive. This is compounded by the common practice of guaranteeing a preferred tariff for electricity sales from pure-solar sources With this in mind, a complete dynamic model of a power plant based on the pure-solar concept has been elaborated. The performance of the setup is evaluated over a range of days, using solar insolation profiles obtained from satellite data. In order to examine different design options and their impact on the performance of the power plant, a multi-objective, thermo-economic optimisation of both the power plant superstructure and operating conditions was performed using the new, dynamic models. By means of an evolutionary algorithm [17], a family of Pareto-optimal points were obtained, representing the trade-off between increased power plant efficiency, and lower levelised energy costs. Through use of optimisation, it was shown that exergetic efficiencies in the region of 21-27% can be achieved, for relatively low power outputs of between 3 and 11 MWe. These configurations correspond with levelised electricity costs in the region of 14-21 UScts/kWhe. In most regions, the use of solar power is encouraged by the guarantee of a preferential tariff for electricity sales from renewable sources. Sale of electricity at a price of around 24 UScts/kWhe [32] should therefore be imaginable, ensuring the economic viability of solar thermal power tower systems. It can be concluded that, when properly designed, solar thermal power plants based on combined cycles are both economically and thermodynamically promising. By raising the efficiency of the plant, the size of the solar collector field is diminished, increasing the otherwise low energy densities of solar power systems. By reducing the levelised electricity costs, solar thermal power plants become more economically viable, accelerating their construction and thus, hopefully, reducing our dependence on fossil-fuels.

2009

Energy efficiency and conversion in complex integrated industrial sites

Zoé Périn-Levasseur

This thesis presents a methodology to analyse the integration of heat recovery energy conversion technologies and biorefinery concepts in existing pulp and paper facilities. By using innovative process integration techniques and thermo-economic optimisation tools, efficient energy saving opportunities can be obtained and guidelines can be applied to implement energy efficiency enhancing measures. The objective is to provide engineers a decision support tool for the design of heat exchangers networks. The system approach used in this work is based on the development of a framework that implements existing simulation tools and process integration methods. The first contribution of this work resides in the establishment of a reconciled model of a complex pulping facility where utility and process measurements are studied simultaneously. Derived operating nominal conditions are validated through a complete sensitivity analysis. The resulting base case model is considered to be representative of the original process and constitutes the basis of the process energy integration definition problem. The core of the methodology consists in the application of two successive approaches: the top-down and the bottom-up approach. The top-down approach allows to identify which sub-systems of the facility consume more energy and could eventually lead to large energy savings. Conversion technologies used to produce utilities and their distribution to the process are also identified. The bottom-up approach benefits from the results of the top-down approach in order to evaluate the energy saving potentials. Systematic definition of the process heat transfer requirement defined as hot and cold streams is obtained according to different heat-temperature profiles. The exergy concept is employed to explain how using different heat-temperature profiles of the same energy requirement is changing the perspective of the energy use in the facility and therefore make possible the identification of energy saving opportunities with different levels of process modifications. An innovative way of considering the steam producers using as a main feed process materials in the definition of the process integration problem is also presented. The development of scenarios using systematically all energy requirement definitions is done and allows the elaboration of a decision support tool that point out the critical process modifications necessary to achieve interesting energy savings. A detailed example of the complete methodology developed in this thesis is illustrated using the multi-effect evaporator. The optimal integration of combined heat and power production and heat pumps is also presented. Finally, the interest of using this methodology is demonstrated in the case of a biorefinery integration by the development of a trade-off between the conversion of lignocellulosic materials into bio-materials and energy.

EPFL2009

The digitalization of energy systems: towards higher energy efficiency

Marina Dorokhova

The energy industry is going through challenging times of disruptive changes caused by decarbonization, decentralization, and digitalization. As the energy value chain is restructuring itself to accommodate the growing penetration of renewables, increasing number of independent power producers, and augmented self-consumption, new energy management approaches are required to accomplish energy transition. With the Fourth Industrial Revolution underway, it becomes evident that digitalization is the key to increase energy efficiency and ensure stable, reliable, and secure operations of the electric grid. Due to the energy industry's massive inertia, most energy utilities are missing the real momentum for unleashing large-scale digitalization enabled by Information and Communication Technology (ICT). This thesis proposes a set of ICT-based software applications, models, and tools aiming to bridge the gap between strategic roadmaps focused on the energy industry's digitalization and their actual implementation in real-world scenarios through digital energy services. The research is conducted within the designed ICT-based smart building and smart community frameworks, the modular structure and scalability of which can serve as a backbone for future digital energy management solutions. The introduction of a novel unsupervised load disaggregation approach helps raise awareness of one's energy-related behavior and understand what drives the energy usage in residential households without compromising privacy and security. Showcasing algorithm's performance on real-world datasets from Norway and Germany highlights compliance with state-of-the-art disaggregation accuracy and reduced computational costs. The development of machine learning-based supervised and unsupervised building occupancy forecasting algorithms with prediction accuracies beyond 97% helps identify best-suited windows for energy-saving opportunities and deliver insights into one's presence and absence patterns. Built on top of that occupancy-centric rule-based heating and air conditioning automation algorithm strives to unlock the buildings' massive potential for energy savings without compromising the occupants' thermal comfort. Simulations on real-world datasets collected in Portugal demonstrate more than 15% potential energy savings. Zooming out from smart buildings towards smart communities, we focus on the important role of intelligent green mobility in supporting further digitalization of the electric power sector. To overcome the inconveniences posed by the sparsity of charging infrastructure and facilitate the adoption of Electric Vehicles (EVs), we present a reinforcement learning (RL)-based EV-specific routing method that guarantees paths' energy feasibility in a graph-theoretical context. Consequently, we propose several deep RL algorithms to control EV charging with the aim to increase renewables' self-consumption and EV drivers' satisfaction. Benchmarking against rule-based and model predictive control demonstrates RL's superior computational performance and better fitness for future mobility systems. Finally, we introduce an innovative decentralized blockchain-supported framework that enables secure and reliable accounting of energy exchanges within the smart community. Implementing it in a demonstration site in Switzerland shows blockchain's potential to reduce EV charging costs, transform the market's business model, and facilitate the large-scale deployment of EVs.

EPFL2021