Energy Savings Potential in Dual Smart Grid Solutions: Are there synergy effects to be found using a dual smart grid system for heat and electricity?

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Master of Science Thesis Department of Energy Technology

KTH 2020

Energy savings potential in Dual Smart Grid solutions

TRITA: TRITA-ITM-EX 2020:488

Matteo Giordano

Approved

Date: 08/09/2020

Examiner

Jörgen Wallin

Supervisor

Jean-Benoit LAFOND

Commissioner

Jörgen Wallin

Contact person

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Abstract

Smart cities and eco-districts will shape a new city landscape in the upcoming years, making renewables the only source of energy. They have the potential to cut greenhouse gas emissions up to 99 %, reaching the ambitious energy and sustainability goals set by Europe and the rest of the world.

Double smart grids is a 20^th-century concept aiming at connecting the current main energy networks as(electrical and thermal) into a unique mesh. It enables the exchange of energy and new options for storage, flexibility, and reliability.

The goal of this study is to show the potential energy savings captured by the implementation of a double smart grid on a district and city level, and to quantify energy savings on a European scale.

The first chapter of this work aims to clarify the objective of a smart grid, how it is composed, and why it is called smart. It implies a complete understanding of the history of the two grids, digging on the district heating concept as well as the fundamental of an electrical grid. Moreover, an overview of the major energy needs that usually exist in a district has been presented, to demonstrate what a double smart grid should meet in terms of energy demands.

Secondly, an exhaustive analysis has been carried out to point out the main technologies available on the market to meet these energy needs. It focuses on all major renewable heat sources and the upcoming technologies expected to help energy transition in reaching its ambitious goals. The same process is applied for the most mature renewable electricity sources, with a focus on decentralized and decentralized structures. Storage options and flexibility have been added at the list since their integration will drastically reduce energy production. This means that, before producing new energy, it is necessary to better consume the one already produced. It is always true that the greenest kWh is the one ever produced.

Lastly, double smart grid synergies have been evaluated through an exhaustive analysis of a smart renewable energy scenario, that includes a complete integration of the double smart grid concept, in the first step, and a triple smart grid concept as full-cycle scenario (including green gas networks).

Throughout the entire document, several project examples have been presented to complete the theoretical knowledge with concrete examples developed all over the world. Most of them have been developed by Dalkia Smart Building. The results show the necessity to boost innovation and pilot projects around double smart grids and in general smart energy systems, and it will require impressive efforts from government and private investors.

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Table of content

Abstract ...- 2 -

Table of figures ...- 5 -

Table of projects ...- 7 -

1 Introduction ...- 8 -

1.1 Background ... - 8 -

1.2 Objective ... - 8 -

1.3 Hypothesis ... - 9 -

1.4 Company - Dalkia Smart Building ... - 9 -

1.5 Limitations and Confidentiality ... - 9 -

1.6 Method of attack ... - 10 -

2 Literature review ... - 11 -

2.1 Climate Change ... - 11 -

2.2 Smart Grid Concept ... - 12 -

2.3 District heating framework ... - 12 -

2.4 Electrical Grid ... - 15 -

2.5 What makes a Grid “Smart” ... - 16 -

2.6 Energy demand ... - 16 -

2.7 Useful, final, primary energy ... - 17 -

2.8 Heating demand ... - 18 -

2.9 Cooling demand ... - 19 -

2.10 Domestic Hot Water ... - 19 -

2.11 Energy Efficiency and energy savings ... - 20 -

3 Double Smart Grid ... - 21 -

3.1 Configuration ... - 21 -

3.2 Thermal Smart Grid ... - 21 -

3.3 Energy production systems ... - 22 -

3.3.1 Biomass and Biogas... - 22 -

3.3.2 Geothermal ... - 30 -

3.3.3 Heat pump ... - 33 -

3.4 Seasonal Thermal Energy Storage (STES) ... - 45 -

3.5 Flexibility ... - 46 -

3.6 Thermal Smart Grid project innovations ... - 48 -

3.7 Double smart grid potential ... - 55 -

3.8 Electrical Smart Grid ... - 56 -

3.9 Electricity generation ... - 56 -

3.9.1 Mechanical to electrical energy ... - 56 -

3.9.2 Solar photovoltaic... - 57 -

3.10 Storage ... - 62 -

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3.11 Self-consumption... - 67 -

3.12 Flexibility (Demand-side flexibility)... - 69 -

3.13 Energy management ... - 74 -

4 Energy savings potential in Dual Smart Grid Solutions ... - 75 -

4.1 Synergic effects ... - 75 -

4.2 Smart energy system ... - 76 -

4.2.1 100 % renewable energy scenario ... - 79 -

5 Results ... - 82 -

5.1 Nanterre Coeur Universitaire ... - 85 -

6 Discussion ... - 88 -

7 Conclusion ... - 90 -

References ... - 94 -

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Table of figures

Figure 1: District heating evolution in France in the last century (Réseau de chaleur et territoires , 2018). _______________________ - 13 - Figure 2: District heating development in time (Euroheat & Power). _______________________________________________ - 13 - Figure 3: District heating and Cooling interconnections (Juutilainen, 2018). __________________________________________ - 14 - Figure 4: AC distribution system with associated voltages (Edison Tech Center, 2014). __________________________________ - 15 - Figure 5: Energy consumption repartition in frozen food retails (left) (Zoi Mylona, 2017) and in households (right) (Eurostat Statistic Explained, 2019). _______________________________________________________________________________________ - 17 - Figure 6: Primary energy consumption by sector in 2009 (UCLA, n.d.). ____________________________________________ - 17 - Figure 7: Building's thermal energy balance (H. Sarvelainen, 2019). _______________________________________________ - 18 - Figure 8: Chimal reaction in an anaerobic environment (Maji Solutions, 2019). _______________________________________ - 23 - Figure 9: From left to right, woodfuel (Gael woodfuel), charcoal (Blog.guideENR), wood chips (ITS WOOD), pellets (Alibaba.com). ____ - 23 - Figure 10: Heating value as the percentage of humidity varies (Wood Energy, 2019). ____________________________________ - 24 - Figure 11: Global waste composition (percentage) (The World Bank). ______________________________________________ - 24 - Figure 12: Biomass power plant in CHP mode (Salix Renewable). ________________________________________________ - 25 - Figure 13: Digester biogas principle (Maji Solutions, 2019). ____________________________________________________ - 26 - Figure 14: CHP from gas turbine schematic representation (Worl Alliance for Decentralized Energy) _________________________ - 26 - Figure 15: View from the top of the Camille Claudel eco-district (SeLoger, 2017). ______________________________________ - 28 - Figure 16: The biomass power system in its components (Camille Claudel Energies, n.d.). _________________________________ - 28 - Figure 17: Distribution system from the production to end-users (Camille Claudel Energies, n.d.). ____________________________ - 29 - Figure 18: Type of geothermal energy per temperature level and depth (Dr Anthony Budd). ________________________________ - 30 - Figure 19: Map of the exploitable geothermal resources per temperature in Europe (César R.Chamorroa, 2014). __________________ - 31 - Figure 20: Geothermal source for district heating applications (GeoPicta ). ___________________________________________ - 31 - Figure 21: Heat pump principle (Veolia Water 2 Energy). _____________________________________________________ - 34 - Figure 22: Temperature variation in the underground as a function of depth (Anya Seward, 2014). __________________________ - 35 - Figure 23: COP as a function of the temperature difference (left, (S. B. Riffat, 2014)) and COP as a function of the inlet temperature (cold source) (right, (Anita Sant'Anna, 2014)). ____________________________________________________________________ - 35 - Figure 24: Geothermal heat pump using probes (Energie Plus, 2014). ______________________________________________ - 36 - Figure 25: Eco-district located at Issy-Les-Moulineaux (UrbanEra, Bouygues Immobilier ). _______________________________ - 37 - Figure 26: Distribution network eco-district Issy-les-Moulinaux (Pôle Réseaux de Chaleur - Cerema, 2013). ____________________ - 37 - Figure 27: Decentralized production from the same water network (Geothermies) _______________________________________ - 39 - Figure 28: Eco-district ”Smartseille” located at Marseille (Canal+). _______________________________________________ - 40 - Figure 29: District heating and cooling network eco-district Smartseille (EDF). ________________________________________ - 40 - Figure 30: Eco-district ”Cap Azur ” in Roquebrune Cap Martin (EDF, 2020). _____________________________________ - 42 - Figure 31: Heat exchanger in the grey waters (left) (Dalkia Smart Building) and district heating and cooling network (right) (BouyguesDD, 2016). _______________________________________________________________________________________ - 43 - Figure 32: Energy efficiency of a heat pump in the simultaneous heat and cold production mode (SERM, n.d.). ___________________ - 44 - Figure 33: Example of a heat pump application on a district level, arranged from (SERM, n.d.). ____________________________ - 44 - Figure 34: Borehole Thermal Energy Storage in summer operation (charging, left) and winter operation (discharging, right) (Applied Hydrogeology Geothermal Innovation) ____________________________________________________________________________ - 45 - Figure 35: Aquifer Thermal Energy Storage in summer operation (charging, left) and winter operation (discharging, right) (Applied Hydrogeology Geothermal Innovation). ____________________________________________________________________________ - 46 - Figure 36: District heating demand using (a) linear regressions, (b) decision tree, (c) support vector machine, and (d) artificial neural network (Etienne Saloux, 2018). ___________________________________________________________________________ - 47 - Figure 37: Peak load management in the STORM project (The STORM). __________________________________________ - 47 - Figure 38: EctoGrid smart thermal grid concept (Ectogrid, 2020). ________________________________________________ - 49 - Figure 39: EctoGrid system at Medicon Village (Ectogrid, 2020). ________________________________________________ - 49 - Figure 40: LowExTra multi-conductor district heating system concept (LowExTra, n.d.). _________________________________ - 51 - Figure 41: Temperature ranges in LowExTra multi-conductor networks (Technische Universität Berlin, 2017). __________________ - 52 - Figure 42: Temperature ranges in LowExTra multi-conductor networks (Technische Universität Berlin, 2017). __________________ - 52 - Figure 43: Total annual costs (left axis) and average heat generation costs for the three scenarios evaluated (Elisa Dunkelberg, 2018). ____ - 53 - Figure 44: Thermal layer in a Smart City (Engie, 2013). _____________________________________________________ - 55 - Figure 45: Cooling network in a smart thermal grid (Engie, 2013). _______________________________________________ - 55 - Figure 46: Electricity generation in a Direct Current generator (Polytechnic Hub, 2018). _________________________________ - 56 - Figure 47: Example of solar irradiance depending on the location (Ahmad Siouti, Atef Belhaj Ali ” Evaluation of Solar Energy Potential for the Red Sea Project, Kingdom of Saudi Arabia”, 2019). _________________________________________________________ - 58 -

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Figure 48: Photoelectric cell (PVinsights, 2020). ____________________________________________________________ - 58 - Figure 49: Example of an off-grid (left) and a grid-tied solar system (Mep Cell, 2020). __________________________________ - 59 - Figure 50: View from the top of the project area in the French Riviera (Nice Grid, 2020). ________________________________ - 60 - Figure 51: Design scheme of the district involved in the project (Nice Grid, 2020). ______________________________________ - 61 - Figure 52: Main storage technologies ranged per power and discharge time (energy applicable) (David Sprake, 2017). _______________ - 62 - Figure 53: Lithium-ion battery diagram (sivVector/Shutterstock.com). _____________________________________________ - 63 - Figure 54: Processes used in the Jupiter 1000 demonstrator to convert electricity in hydrogen (Jupiter1000, n.d). ___________________ - 65 - Figure 55: Alkaline electrolysis (Hydrogenics, 2020). ________________________________________________________ - 65 - Figure 56: Proton Exchange Membrane electrolyzer schematization (ZBT, n.d). _______________________________________ - 66 - Figure 57: State-of-the-art of different storage solutions (IRENA, 2019). ___________________________________________ - 67 - Figure 58: Structure of the electricity network with self-consumers (Autoconsommation.cre.fr, 2020). __________________________ - 68 - Figure 59: Price development of residential PV systems in €/Wp (European Commission, 2019). ___________________________ - 68 - Figure 60: Net load curve profile of a power system integrating large solar photovoltaic sources (CAISO, 2019). __________________ - 69 - Figure 61: Power system evolution thanks to flexibility (IRENA, 2019). ___________________________________________ - 70 - Figure 62: Power-to-hydrogen end-use applications (IRENA, 2019). ______________________________________________ - 71 - Figure 63: Operation principle of V2V, V2H, and Pilot recharging (RTE). _________________________________________ - 72 - Figure 64: Power potential break down in peak shaving operation (Conseil Général de l’Economie, 2020). ______________________ - 73 - Figure 65: Summary table of the five key solutions to provide demand-side flexibility (IRENA, 2019). ________________________ - 73 - Figure 66: Flexibility impact on an energy system (IEA, 2020). _________________________________________________ - 74 - Figure 67: Typical present energy system based on fossil fuel-based technologies (D. Connolly, n.d). ____________________________ - 77 - Figure 68: Smart energy system with renewable energy integration (D. Connolly, n.d). ____________________________________ - 77 - Figure 69: Example of synergy in a double smart grid solution (D. Connolly, n.d). ______________________________________ - 78 - Figure 70: Projections of demand and supply in the EU28 Ref2050 scenario (D. Connolly, n.d). ____________________________ - 80 - Figure 71: "General consensus" scenario towards the 100 % renewable smart energy system (D. Connolly, n.d). ___________________ - 82 - Figure 72: Potential of reduction with heat pumps and district heating implementation (D. Connolly, n.d). ______________________ - 83 - Figure 73: Renewable electrofuels integration in the smart energy system (D. Connolly, n.d). ________________________________ - 84 - Figure 74: Total annual socio-economic costs of each step toward the Smart Energy Europe scenario (D. Connolly, n.d). _____________ - 85 - Figure 75: Mock concept of the eco-district in Nanterre, Paris (Demain La Ville, 2017). _________________________________ - 86 - Figure 76: Double Smart Grid principle diagram. The red and blue pipes represent the thermal smart grid, whereas the yellow line represents the electric smart grid (Dalkia, 2017). _____________________________________________________________________ - 87 - Figure 77. LCOE comparison for several energy production technologies (AMORCE, 2018). ______________________________ - 89 - Figure 78: Double smart grid interaction in centralized and decentralized systems (Andrea sBloess, 2018) ______________________ - 91 - Figure 79: Triple grid network. Adapted from (Energy PLAN, 2014) ____________________________________________ - 92 -

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Table of projects

Eco-district “Camille Claudel”, Palaiseau

Eco-district ” Fort – Issy-les-Moulineaux” in Hauts-de-Seine Eco-district ”Smartseille” in Marseille

Eco-district ”Cap Azur” in Roquebrune Cap Martin

“Ectogrid” by E.ON

“LowExTra project” in Germany

Intelligent solar district “Nice Grid” on the French Riviera Demonstrator project “Jupiter 1000” in France

Double Smart Grid on “Nanterre Coeur Université” in Nanterre, Paris

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1 Introduction 1.1 Background

“City: an inhabited place of greater size, population, or importance than a town or village” (Merriam-Webster, 2020).

A city is the main place, as underlined in the above definition, where the value is created. This is due to the concentration of people and power. Unfortunately, people and production create not indifferent wastes. It has been estimated that 2% of the entire world's surface is covered by cities (including towns and villages), and where more than half world population lives in (Karim Beddiar, 2015).

To slow down this skyrocketing trend, new goals and objectives are emerging inside the city, such as reduction of pollution, waste, inefficiency, an increase of transport networks, and, above all, reduction of energy demand and switching to green solutions. The answer to all of this is called Smart City, and the solution behind is called Double Smart Grid (Karim Beddiar, 2015).

On a personal level, I dedicated my last study cycles to the energy transition goal, and it has become a way of life before a profession. My educational background counts 5 years of high school in Building Plan Designer in which, for the first time, I asked myself the question “Why buildings consume so much energy, at how is it possible to reduce it?”. This first turning point helped me to make the best decision I ever made, to become an engineer, more precisely, energy engineer.

Consequently, I enrolled in Politecnico di Torino, in the Energy Engineering course, and in 2018 I got my graduation.

After those 3 intense years in Turin, I decided to move abroad for the Master, intrigued by the development of new technologies from other countries, and to enrich my background with new experiences. The Master I have chosen brought me to Paris (Ecole Polytechnique), Stockholm (KTH), and Barcelona (ESADE Business School), expanding my passion for the energy transition and, in particular, renewable energies.

The ambition to promote and force the energy transition opened me towards this new concept of Smart City and, behind it, the Smart Grids, where green technologies make this concept feasible.

1.2 Objective

This Master Thesis aims to analyze the energy systems within a Smart City and, more precisely, to investigate the Double Smart Grid solution, an innovative way of rethink an entire city.

The Double Smart Grid is a new millennial concept where the “conventional” smart grid (electrical) is associated with a thermal smart grid, contributing to the same ultimate goal of energy savings and zero carbon emission.

The objectives of the work are:

• Analyze and describe the Double Smart Grid concept, its evolution, implication in different levels, and future prospectives.

• To describe and critically analyze concrete examples of applications developed by Dalkia Smart Building.

The following research questions will be evaluated to meet the aims of this study:

• What does it mean, concretely, the term Smart City, and what are the existing energy systems that create it?

• What is a Double Smart Grid and how is it composed?

• What are the main sustainable energy production technologies to meet sustainability goals?

• What is the synergic effect of the Double Smart Grid referring to energy savings and what are the pros and cons?

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• How could you monitoring and govern all this energy system simultaneously without wasting energy?

• How could the 100% green energy production goal be implemented and what are the possible technological solutions?

1.3 Hypothesis

Evocating the name Smart City, the term city, of course, pops up. The development and concept of a smart city is linked to the evolution and design of a city from an urbanistic point of view. Urbanists and city planners are integrating more and more architectural and natural solutions with the citizens at the center. Furthermore, sustainability and biodiversity concepts are always at the core of every project and they are taking more importance as the awareness of climate change is penetrating in people’s minds.

Consequently, the hypotheses brought in this study refers to a durable and sustainable idea of the city, as it already is behind the Smart City concept.

1.4 Company - Dalkia Smart Building

In accordance with my study plan, I decided to perform my last internship in Dalkia Smart Building, a subsidiary of Dalkia, the energy efficiency branch of EDF (Electricité de France), the main electricity supplier in France.

This Master Thesis will be carried out in parallel with my internship in a more operational context more . That means the projects I will develop inside the company may be analyzed and taken as a reference during the drawing of this work and supported by technical knowledge from the appropriate department in Dalkia Smart Building (DSB).

Dalkia Smart Building combines within the same structure the functions of the design office and general contractor specialized in technical batches, in order to design and build tailor-made energy and digital solutions with guaranteed results. The main strategic axes are:

• Smart Building: integrating innovative solutions able to connect, optimize, and improve the performance of buildings. The main offers concern schools (universities, high schools), swimming pools and tertiary offices.

• Green Data Centers: integrating data security, promoting local renewable energies and waste heat recovery, reducing the energy bill.

• Double Smart Grid (electric & thermal): capitalizing the synergic effect of the double smart grid, high level of energy savings and renewable energy ratio can be achieved. Mainly developed inside smart cities or eco-districts, this solution is the most promising around the globe.

Being a design and realization company, the added value that links all together these offers is the Energy Performance Contract. This new vision of contracting is trending nowadays among the most important companies, especially the non-suppliers. The idea is to contract a certain level of energy efficiency (energy reduction) or a rate of renewable energies in the production between the company and the customer. All the investment cost is financed by the promoter of the project and it receives a monthly bill from each customer for the energy provided by its energy equipments. In this sense, it becomes a proper energy supplier. The feasibility and determination of the energy thresholds are analyzed in the proper paragraph in chapter three.

The last point, not for importance, is the exploitation of the project, including maintenance and monitoring.

Principally applied to Smart Cities, where Energy Performance Contracts requires meticulous accounting, the energy monitoring through Energy Management System opens the door to the next generation of data analysis.

1.5 Limitations and Confidentiality

Double Smart Grid solution is a multidisciplinary subject that includes several subcategories, such as commercial, juridical, financial and technical. In turn, the technical cluster includes several aspects to be taken into account,

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electrical knowledge and thermal expertise above all. This study aims to underline, from a general perspective, the functioning of the Double Smart Grid, analyzing the equipment that plays a leading role in the composition.

To emphasize the internship I am performing, diverse examples of projects will be described. This idea, better explained in the following paragraph, may result in confidentiality issues, principally in projects where the contract has not yet been signed. Moreover, projects in the developing phase may arise the same conflicts and, consequently, a confidentiality problem.

To overcome these problems, general references for the project will be deployed and, where impossible, a reference from other sources will be taken into consideration. This process will not change the final results of the analysis but will cover DSB from juridical problems.

Finally, confidentiality data may vary throughout the drawing of this study, according to the development phase of the project under consideration.

1.6 Method of attack

The objective of the study will be achieved developing in parallel two main clusters: literature review and project investigation. The first is essential to create the base for the core analysis of the Double Smart Grid, highlighting the main components and the key concepts. A historical flashback is also incorporated in the literature review, enabling the time travel of innovations in the sector and giving more structure for the understanding of the idea behind.

Furthermore, the literature review will be also present throughout the entire study where the necessity for a background is considered as necessary.

To show the benefits and drawbacks of this innovative and sustainable solution, real projects will be analyzed nearly always a theoretical solution is presented.

A big part of the projects presented has been developed by Dalkia Smart Building.

The combination of the literature review, as a “theoretical” background, and the project analysis, as “state of the art”, will enable the critical and objective investigation needed to answer the research questions previously mentioned. Finally, possible scenarios will be developed based on the study carried out, spacing from the technological point of view (reaching 100 % of renewable energy and safe supply) to the final consumer point of view (investment restraints). The final consumer (human centricity) is also taken into account throughout the entire document, being the crucial pillar for the development of the Smart City in the near future.

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2 Literature review 2.1 Climate Change

413.99. This is the incredible value of CO2 level in parts per million that has been detected in March 2020 (CO2 Earth, 2020). It is just a number, but if it is compared to the pre-industrial levels, hence around 172 – 300 ppm, it shows up how unbelievable the CO2 level has been grown in just half a century.

Even if, at this concentration, the CO2 does not directly affect the human being, it has disastrous effects for the environment, and consequently the people living on it. The effect created is called the greenhouse effect and it has the principle of blocking the heat from exiting the earth’s atmosphere, the same principle that happens in a greenhouse or a house with the windows closed and the sun’ rays directly entering in the room (NUNEZ, 2019).

Extreme weather, food supply disruption, and increased wildfires are only three of the catastrophic effects that are striking the Blue Planet (NUNEZ, 2019).

Thus, 2015 is a pivotal year for the environment. Firstly, with the sign of the Paris Agreement of 189 Parties out of 197 in the UNFCCC Convention (United Nations Climate Change, 2020) (United Nations Framework Convention on Climate Change) and, secondly, the instauration of the Sustainable Development Goals (SDGs) by the United Nations General Assembly.

The first has the main goal of limiting the increase of the Earth temperature above 2 °C (1.5 °C as a more ambitious goal) from the pre-industrial levels, throughout a path made of ambitious goals, financial flows, and a new technological framework. However, it has no bond targets with penalties, but instead National Determined Contributions (NDCs) delivered by each country based on their efforts and internal commitments (United Nations Climate Change, 2020).

The second is a collection of 17 goals to be reached by all United Member States in order to preserve and protect the environment from the pollution mainly derivated by human activities. Among them, the ending of poverty, affordable and clean energy for everybody, climate actions, and many more (Sustainable Development Goals, 2020).

More recent is the Green New Deal announced by the European Parliament and its president, Ursula Von der Leyen, in which Europe aims to become the first climate-neutral continent by 2050. The European Green Deal sets the roadmap to reach that courageous goal, spacing from different axes such as boosting the efficient use of resources by moving to a clean, circular economy, restoring the biodiversity and cutting the pollution, etc (European Commission , 2020).

The energy transition will be possible only with heavy investments and binding targets to be respected by each country. Moreover, energy is not the only one to be placed at the core, people have the priority. Thus, a massive reshaping of the entire economy and employment system must be taken into account.

Energy targets, so far proposed, aims “to increase the EU’s greenhouse gas emission reductions target for 2030 to at least 50%

and towards 55% compared with 1990 levels in a responsible way” (European Commission, 2019).

The main pillars where governments and industries must act are (European Commission , 2020):

• Energy Efficiency opportunities: the principle of “the greenest kilowatt-hour is the one that is not consumed”. Before producing energy, it is important to reduce the consumption of the one we have already produced. It can be fulfilled by new energy-efficient technologies (appliances, equipment, machinery, etc), building renovations, digitalization (enabling control and optimization through analytics and big data), industrial recycling, waste heat, etc;

• Energy Shifting: replacing fossil fuel production systems (or in general the highest CO2 emitters) with renewable energies, such as wind, solar, electricity hydrogen (if green), geothermal heat, biomass, biogas, etc;

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• CO2 reduction: implementing Carbon Capture, Utilisation, and Storage to capture the CO2 coming from fossil fuel generators, and negative carbon capture, capturing CO2 from the atmosphere (the principle of photosynthesis).

• Green Mobility: reshaping the conventional infrastructure system, by firstly replacing fossil fuel cars with electric or hydrogen ones, and secondly to promote transport-sharing, public transports, and green means (bike, scooter, etc).

• Smart City: integration of all solutions mentioned above but starting from a small scale to an entire country. This step is necessary to not break the conventional system incorporating disruptive solutions in everyday life. The Smart City concept has the Smart Grid approach as foundation.

2.2 Smart Grid Concept

The Smart Grid Concept has been defined for the first time by the Smart Grids European Technology Platform in 2006 labeling it as “an electricity network that can intelligently integrate the actions of all users connected to it - generators, consumers and those that do both - in order to efficiently deliver sustainable, economic and secure electricity supplies” (EARPA, 2020).

The double flux of information – from the network to the final user and vice-versa –, as well as communication technologies, are vital for adjusting electrical flows, hence where electricity is demanded.

Furthermore, the adjective “smart” has taken a remarkable deployment during the last few years, associating it with multiple concepts. One of the latest, widely deployed in France, is the term Smart Thermal Networks. It refers to another type of smart grid, not electrical but instead thermal. The concept derrière is the same: exchange of information in real-time enabling the district heating or cooling system to meet certain needs, while capitalizing renewable energy and waste energy sources (Dalkia, 2020).

Nevertheless, this smart revolution has been possible only thanks to the development of information technologies. This smart revolution is commonly called “Digitalization”.

Even if the term “Digitalization” has not a clear and well-defined definition, most of the time it is referred to “as the way in which many domains of social life are restructured around digital communication and media infrastructures” (Bloomberg, 2018).

At the same level, the Internet of Things (IoT) is a hot topic that is gradually penetrating in all social layers.

Defined as “the interconnection via the Internet of computing devices embedded in everyday objects, enabling them to send and receive data” (Lexico , 2020), these connected devices are essential to establish a real-time connection between the final consumer and the supplier.

Digitalization and IoT have made possible the Smart Grids breakthrough and they unlocked significant energy savings necessary to climb the energy transition targets. More interesting is the synergic effect in terms of energy savings and CO2 emission reductions through the combination of both smart grids (Double Smart Grid), and an exhaustive investigation will be addressed in the coming chapters.

In the following paragraphs instead, more details have been provided to understand the evolution of the thermal and electrical smart gird, cardinal step for the analysis of the synergic effects.

2.3 District heating framework

The first notion of district heating dates to the Roman Empire where the first central heating system, called the Hypocaust system, consisted of a central heating production (furnace) with circulating hot air under the floor and surrounding walls. Wealthy Roman houses and baths were the only ones to possess this advanced heating system due to the high costs, mainly because of the engineering skills required and the construction competences (Romae VItam).

Moreover, during the 14^th century, it appears the first conception of a geothermal heat network in Chaudes- Aigues, a small village in southern France. It consists of canalizing, through wood channels, the hot water coming

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from a geothermal reservoir, at around 80-82°C, feeding the network and regulating it with valves. The canalization was possible thanks to a pressure gradient strong enough to exploit the gravity phenomenon. Indeed, Chaudes-Aigues is placed in a geological region that allows this type of system, having an important geothermal flux with a high geothermal gradient (DHC.news, 2015).

During the last century, the district heating system (urban heating) has had a sharp development, starting from big cities to less dense urban areas (figure 1).

Figure 1: District heating evolution in France in the last century (Réseau de chaleur et territoires , 2018).

The first heating networks (around 1940) were feed-in by heat produced in centralized plants, mainly powered by coal, gas, and oil (figure 2). In the following years, the thermal power plants were replaced by cogeneration plants, the principle of producing at the same time heat and electricity, reducing the waste heat, and increasing the overall efficiency. Moreover, other forms of thermal injections were developed, such as waste-to-energy (recover waste heat from incinerators), biomass power plants, and industrial waste heat (heat surplus). Consequently, the overall system efficiency increased and the system progressively reduced the temperature circulating in the channels, gaining in fewer leaks while satisfying the current energy demands (Euroheat & Power).

Figure 2: District heating development in time (Euroheat & Power).

The last “revolution” named “4^th district heating revolution” and that is the one currently happening, involves the integration of all kinds of renewable energies and waste heat, thanks to the lower temperature (50 – 60 °C) of the

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circulating fluid. It includes geothermal, wind and solar surplus (in combination with large-scale heat pumps), solar thermal, CHP (biogas and biomass), and other energy sources (waste heat from sewage and wastewater, absorption chillers, etc) (Euroheat & Power) (United Nations Environment Program (UNEP), 2015).

The added value of 4^th generation district heating and cooling systems is the valorization of different energy sources that would be difficult to exploit on an individual scale, as well as renewable and local energies (figure 3) (Karim Beddiar, 2015).

Figure 3: District heating and Cooling interconnections (Juutilainen, 2018).

The framework of a district network is based on several components with specific tasks, engineering conceived to distribute heating and cooling in double way connections (Karim Beddiar, 2015).

• At the bottom of the chain, there is the production system (in the form of plural sources) necessary to produce and/or recovery the calories deficit/surplus from the demand side;

• Primary distribution network employed to conduct the calories from the production to the sub-station;

• Sub-station, an interconnection between end-consumers and production network, usually incorporates a heat exchanger;

• Local heating system, as a final vector to reply to the users’ heating/cooling needs.

Multiple benefits make the district heating and cooling (DHC) system exceptional (United Nations Environment Program (UNEP), 2015):

• Energy efficiency, due to the deployment of low-grade energy sources (waste heat, free-cooling) and the integration with big-scale power plants, making them economically affordable.

• Greenhouse gas emissions reduction.

• Use of local and renewable energy resources, otherwise difficult to integrate into an energy system.

In conclusion, district networks represent one of the finest renewable energy solutions to be exploited in all cities and it constitutes the skeleton for smart thermal grids, necessary to create the city of the future, also referred to as

“Smart City” or “Eco-district”.

The difference between the terms “Smart City” and “Eco-district” is very subtle, and it comes mainly from a different principle of the city (smart city referred to a smart environment concept, eco-district focused more on a sustainable environment) while, nowadays, the goals and objectives are relatively the same, hence sustainability and digitalization.

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However, the two terms can be used in different contexts when an inclination towards sustainability goals is accentuated (eco-district) over “smart” ambitions (smart city).

2.4 Electrical Grid

The development of the power grid started around the 1870s all over the world, to satisfy the electricity demand of industrials, especially for mining uses. However, at the time, only luxury houses, hotels, and businesses had a connection to the power system. This early system consisted of coal-fired steam engine generation plants and direct current (DC) transmission lines (unidirectional flow of an electric charge (Wikipedia, 2020)) (Edison tech Center, 2014).

More economically convenient were the hydroelectric power plants, but just the businesses placed nearby one of these generation plants were able to be connected with both direct or alternating current (electrical current which periodically reverses direction (Wikipedia, 2020)).

Therefore, several business people thought up to send the electricity produced by hydroelectric plants to cities, requiring high voltage transmission lines (Edison tech Center, 2014). Nowadays, it supplies buildings, industrial facilities, schools, homes, etc, every day, every minute (Union of Concerned Scientists, 2015).

Four main components constitute the electricity grid system (Union of Concerned Scientists, 2015) (figure 4):

• Individual generators: all facilities and power plants that transform primary energy to electricity. They can have different primary energy sources. Among them, coal and natural gas power plants, nuclear power plants, and all renewable energy technologies (hydroelectric dams, wind turbines, solar panels,

biomass plants, waste heat recovery, etc).

In terms of responsiveness, natural-gas-fired plants are quick to be at full capacity and they are usually designed to meet peak demand. Sometimes these back-up facilities are used a few times per year, increasing the price per kilowatt-hour (necessary to be rentable). Coal-fired and nuclear power plants have not flexibility at all, that is why have been always utilized to satisfy the big part of the electricity demand.

In contrast, renewable energies are used whenever they are available, due to the nature of intermittency (sun, wind).

• Transmission lines: briefly anticipated in the first lines of the chapter, transmission lines are necessary to transport electricity from individual generators to electricity consumers. The transmission can occur through overhead power lines or even underground power cables, and it depends on the distances and the nature of the ground.

• Transformers. In order to be transported with negligible losses, the electric power must be increased in voltage. This process is important to decrease the current circulating on the wire, the main responsible for heat losses (Joule effect). The voltage must be raised from tens of thousands of volts (V) (depending on the generator) to 110 000 V or even greater (345 – 765 kV). The same principle is applied in reverse when electricity approaches the end-user and it must be set up at 220/240 V.

Figure 4: AC distribution system with associated voltages (Edison Tech Center, 2014).

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• Distribution: the distribution network is the system that links the transformer to the end-user (load). It is just a wire connection that usually has a lower voltage than transmission and sub-transmission lines.

• Consumer use or “load”: the load is everything that consumes electrical energy. It is usually divided into homes, building, commerce, industries, etc.

Around the globe, electricity grids are reaching their capacity saturation, due to the increase in electrical demand (a consequence of electrification) and new sources of electricity that feed the current system. It has changed during the last years to meet the ultimate goals of urbanization and industrialization, but at present, it is necessary to rethink the electrical grid. It must be redesigned to incorporate the new digital devices and technologies, helping to meet the expanding 21^st Century electricity needs (Smartgrid.gov).

2.5 What makes a Grid “Smart”

The previous paragraphs have analyzed the current district networks and electrical grids, the base components of a double smart grid. In both cases, it showed up that the evolving world is requiring more and more energy (thermal and electrical), almost reaching capacity saturation, requiring innovative solutions to overcome the problem. The “easiest” way to integrate the system “as it is” with emerging Information and Communication Technologies (ICT), making them “Smart”. These digital devices will allow for two-way communication between the utility and its consumers, enabling the real-time adaptation at the fast-changing electrical demand that is ruling 24/7 (Smartgrid.gov).

All these digital technologies create, in turn, different layers of “smart” systems. Smart meters and smart appliances/equipment generate smart buildings/industries that, connected with distribution and generation facilities, results in smart grids. Finally, the integration of all infrastructure inside a city (public infrastructure such as street lighting and mobility) formulate the smart city concept (Karim Beddiar, 2015).

Going forward, a smart city can be seen as a juxtaposition of two separate layers: the energy network and the digital network. The exchange of information between them, namely big data, allows the energy system, simply composed of energy needs (electricity, heat, cold, domestic hot water), to quickly interact with supply facilities and better adjust the energy flux.

2.6 Energy demand

During the design phase of a project, the energy demand identification is a crucial part because it quantifies the size of the energy system, from the production equipment to the emitters in the end-consumers place.

Moreover, the thermal and electrical grids are drastically influenced by this energy demand identification due to the high system lock-in. Precisely, once the network is placed, such as pipelines for the thermal mesh, the maximum flow that can pass through it is fixed. Changing the entire system due to greater energy demand, it is a synonym of a new installation, with related costs.

Consequently, extreme accuracy is placed during an energy demand estimation for a city or a district. In fact, the three main energy needs, practically in every sector, are heating, cooling, and domestic hot water. However, the proportions can massively change between one sector to another due to different usages, for example between supermarkets and households where, in the first, refrigeration needs account for 60 % of the total energy demand (Zoi Mylona, 2017) whereas in the residential sector the space cooling accounts just for 0.3 % (dominated by space heating at 64.1 %, pictured in figure 5) (Eurostat Statistic Explained, 2019).

Figure 5: Energy consumption repartition in frozen food retails (left) (Zoi Mylona, 2017) and in households (right) (Eurostat Statistic Explained, 2019).

As represented in figure 6, buildings play a key role in primary energy consumption (values in 2009) reaching 40 % of the total and they are responsible for around 30 % of greenhouse gas emissions, almost equally divided between commercial and residential (UCLA, n.d.). Not enough, since the population is expected to keep growing (estimation sets around 8.6 billion by mid-2030 (United Nations Department of Economic and Social Affairs, 2019)), the floor area of buildings is attested to grow as well.

Figure 6: Primary energy consumption by sector in 2009 (UCLA, n.d.).

Since a smart city includes the three sectors, it is crucial to evaluate the energy needs from all prospectives and to incorporate renewable solutions to meet the energy transitions goals.

In the following paragraphs, a picture of the main influencing factors affecting the three energy needs, for the residential sector, is provided.

2.7 Useful, final, primary energy

Quite often, these three ways of measuring energy consumption create a lot of confusion, sometimes even in offices that treat energy-related topics. Before going on in the study, a concise explication has been provided to specify the differences inside a system (Karim Beddiar, 2015).

• Useful energy: it is the energy the consumer can “see”, for example, heat, light, powertrain, etc and it is delivered after the appliance. Generally, it is difficult to measure it.

• Final energy: it is the energy available in different forms directly usable. It is the one measured at the meter in m³ or kWh. It is the energy before the appliance and the difference between final and useful energy is the energy lost due to the appliance efficiency (washing machine, oven – electrical coils, etc).

• Primary energy: it is the energy needed from nature to provide the amount of useful energy for the final consumer. It includes all the heat losses (extraction, transportation, the efficiency of the appliance). It is expressed in kWh of primary energy.

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2.8 Heating demand

Heating demand represents one of the main sources of consumption in the residential and tertiary sector, especially in countries where the average external temperature is constantly below zero, and in building stocks not very well insulated (usually built before 1945).

Heating demand depends on several factors (Karim Beddiar, 2015):

• Age of the building correlated with the construction material used and level of isolation.

• Internal gains: occupants, lighting, equipment and appliances, office devices, etc

• External gains: direct solar gains, external temperature, etc

• Regulation of the system able to counteract the intermittency of the building (in terms of usage).

• User behavior: internal setpoint temperature, energy efficiency actions, etc

The goal of the heating system is to assure an internal setpoint temperature (for example 20 °C) during the coldest day that might be met during the year (depending on the geographical location). Moreover, it has been set another temperature by local design offices, named “temperature of non-heating”, that is the temperature in which is no longer necessary to heat the building. It depends on proper building characteristics such as isolation, the inertia of building components, internal and external gains. Usually, it is 2 or 5 °C lower than the internal temperature of the building (set-point).

Consequently, all these elements are taken into account during the sizing phase, where total heat losses must balance the internal gains, as represented in picture 7.

Figure 7: Building's thermal energy balance (H. Sarvelainen, 2019).

Main heat losses in a building are (Karim Beddiar, 2015):

• Thermal flow through the walls and windows: heat tends to move from higher temperatures to lower.

The coefficient of a material to allow this passage is called ”heat transfer coefficient”, expressed in W/m²k. The bigger it is, the greater the dispersion.

• Air renewal: air renewal (measured in Air Changes per Hour, m³/h) is necessary due to hygiene reasons and to prevent the formation of condensation (mold). A common ACH is around 0,5 – 1. Heat recovery systems can drastically reduce energy consumption to heat the new air from the outside.

• Thermal bridges (linear and punctual): every time that a discontinuity in material or in shape is present, the thermal resistance sharply decreases. Usually, they are responsible for 10 to 30 % of the total heat losses.

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Internal and external gains are difficult to measure, and usually, approximate values are taken during the thermal simulation of the building. For example, one person can emit between 100 and 250 thermal W, and office devices around 75-150 W/m² (Karim Beddiar, 2015).

The energy production system is then ready to be sized, considering all these factors. The useful power of the equipment, however, must also include the heat losses occurring during the production (efficiency of the generator) and transportation.

2.9 Cooling demand

When the summer comes, cooling demand for climatization becomes significant. As heating demand, cooling demand depends on multiple factors such as surface to cool down, the total surface of windows exposed to the sun (south), lighting, number of occupants, localization, the type of activity, the inertia of building materials, etc (Karim Beddiar, 2015).

In line with the concept above, a balance between cooling needs and the totality of internal and external gains is necessary to evaluate the power of generators.

However, unlikely heating needs, cooling needs are not really proportional to the external temperature since humidity (latent heat) is not taken into account, requiring additional calculation or hypothesis (Karim Beddiar, 2015).

2.10 Domestic Hot Water

Domestic Hot Water (DHW) refers to the water mainly used for cooking and washing, and for that reason, it is subjected to restrict regulations, such as the minimum temperature to prevent the proliferation of the legionella bacterium. In centralized production systems, it replaces the individual electric boiler.

While space heating is at the center of the new policy agenda regarding energy efficiency, especially regarding the reduction of energy consumption per meter square (Passive House, Green Building), domestic hot water (DHW) remains quite stable, taking the lead as the major source of energy consumption in the residential sector (Karim Beddiar, 2015).

Domestic hot water needs depend mainly on the type of building served and the number of people. A title of example, in one apartment the needs of DHW at 60 °C are around 35 – 50 liter per person per day. An external factor that influences the production system (efficiency and energy consumption) is the temperature of the cold water in the network, and it depends on the location (temperature higher in hot countries/cities) (Karim Beddiar, 2015).

A second factor that increases the energy consumption in collective buildings is the “looping”, term associated at the loop of water in the network to maintain the delivery temperature for 24/7. It can cause an increase as far as 50 % of the total (Karim Beddiar, 2015).

A city or a district is always composed of different buildings with similar usages, and during the system design, oversizing is constantly to be avoided (both for costs and for performances).

Thanks to the smart grid concept, all the buildings within the mesh can communicate, exchanging information about their energy demand, allowing a constant adjustment of the production.

Here comes the idea of synergies within a city. Since different buildings have distinct energy needs at various times, a shared network allows the exchange of electricity and thermal needs among the connected. Energy recovery is then the main actor together with electricity, and in the following paragraphs will be analyzed and underlined the benefits and synergies of this interconnected system (Karim Beddiar, 2015).

2.11 Energy Efficiency and energy savings

In order to evaluate the energy savings of double smart grid solutions and associated synergies, the definition of energy efficiency and especially energy-saving are presented, allowing a common and clear understanding of the theme.

Energy efficiency can be defined as the amount of output that can be produced with a given input of energy measured in percentage between 0% and 100% (Erbach, 2015). Strictly, according to the EU Energy Efficiency Directive (directive containing a set of binding measures to help the European Union reach its energy efficiency goals, set at 32.5% for 2030 (European Commission, 2020)), “energy efficiency’ means the ratio of output of performance, service, goods or energy, to input of energy”.

An example of performance is the thermal comfort in a building, transport as service, and smartphone as good (Erbach, 2015).

The efficient use of energy is the direct benefit of energy efficiency, meaning less energy consumed. Some examples of energy efficiency measure currently deployed:

• New high-performance appliances (refrigerators, engines, light bulbs, etc).

• Buildings renovation (isolation, systems regulation, etc).

• High-performance vehicles.

Energy savings is the reduction of energy use due to the application of energy efficiency measures. Its calculation derived from two different points in time, before and after the energy-efficient measure. Some examples can be found in energy production systems in which replacing an old and inefficient boiler with a new one, can bring important energy savings with the same amount of energy delivered.

Energy savings also indirectly reduce the greenhouse gas emission since the energy that is not consumed is not produced, cutting the associated GHG emissions.

In the present study, energy savings analysis linked to smart district heating and electrical smart grid will be addressed. Primary, referring to energy savings gained from the more efficient energy technologies deployed, secondly, the number of renewable energies sources that can be integrated into the system.

Consequently, it is important to define the ratio of renewable energy production (out of the total energy produced) into the system, called Ratio REN (referring to the French “TAUX ENR”). The Ratio REN includes all renewable energy sources such as wind, solar, biomass, geothermal, waste heat, etc.

This parameter is also critical for the Energy Performance Contracts development (EPC - the innovative business model of selling “useful energy” to the end-consumer taking care of the entire cost of installation and maintenance) since it is one of the main contractual engagement between the energy provider and the project management. This is done to meet the environmental and energy goals.

A title of example, below a common way to calculate the Ration REN for a network:

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅 𝑅𝑅𝑅𝑅𝑅𝑅𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛= 1 − 𝐶𝐶𝑅𝑅𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑅𝑅𝑅𝑅𝑅𝑅𝐶𝐶 𝐶𝐶𝑅𝑅𝐶𝐶 𝑅𝑅𝑅𝑅𝑅𝑅𝐶𝐶𝑝𝑝𝑅𝑅𝑝𝑝𝐶𝐶𝑝𝑝𝑅𝑅𝑅𝑅𝑅𝑅𝐶𝐶+ 𝐶𝐶𝑅𝑅𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝑅𝑅𝑅𝑅𝑅𝑅𝐶𝐶 𝑅𝑅𝐶𝐶𝑎𝑎𝑅𝑅𝑎𝑎𝑅𝑅𝑅𝑅𝑝𝑝𝑎𝑎𝐶𝐶+ 𝑃𝑃𝑝𝑝𝑅𝑅𝑝𝑝𝐶𝐶𝑝𝑝𝑅𝑅𝑅𝑅𝑅𝑅𝐶𝐶 𝑃𝑃𝑃𝑃 𝑇𝑇𝑅𝑅𝑅𝑅𝑅𝑅𝑎𝑎 𝑎𝑎𝐶𝐶𝑎𝑎𝑝𝑝𝑒𝑒𝑒𝑒 𝐶𝐶𝑎𝑎𝑎𝑎𝑝𝑝𝐶𝐶

Usually, the only energy needs taken into account are heating, cooling, and DHW delivered on the foot of the building because other types of energy needs such as private usages in households are complicated to simulate during the design phase and consequently it is hard to set a reference for the total energy need (Dalkia Smart Building, 2020).

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3 Double Smart Grid

Energy efficiency has been identified as the basis for the Europe 2020 strategy to meet the ambitious energy targets. Important directives have been published, such as the Energy Efficiency Directive (Directive 2012/27/EU) and the Directive on the Energy Performance of Buildings (Directive 2010/31/UE). This last aims at reaching “nearly zero-energy buildings” in all sectors by 2021.

According to article 2.2 of the Directive 2010/31/UE (Andreas Hermelink, 2013):

“‘nearly zero-energy building’ means a building that has a very high energy performance. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby”

Implementing the multiple measures tied with the Energy Directive, energy consumption in buildings is expected to decrease and, at the same time, energy production is expected to increase (both thermal and electrical). These new technologies implemented, such as solar thermal and solar photovoltaics, will allow the consumer to become a producer every time their consumption is lower than production. This new figure has been called “prosumer”

(STĂNIŞTEANU, 2017).

The shifting from consumers to prosumers implies the network will turn from a unidirectional network to a bidirectional network. In this way, when a building produces more energy than the demand, it can transfer the excess to another building connected at the same network, thus increasing the overall energy efficiency of the system. Nevertheless, advanced devices such as smart metering and controlling, and the complete environment of Information and Communication Technology are key to coordinate and to ensure a perfect synergy (STĂNIŞTEANU, 2017).

Integrated solutions such as the Double Smart Grid can ensure a perfect synergy in terms of energy efficiency between the thermal and the electrical grid.

3.1 Configuration

A Double Smart Grid is an innovative solution that valorizes renewable and local energy sources and integrates artificial intelligence intending to optimize the energy consumption of buildings connected (Dalkia Smart Building, 2020).

It includes:

• Smart thermal grids to valorize renewable energy and mutualize the energy needs of different sectors (commerce, residential, offices) reducing the environmental footprint and reducing costs. The interchange of energy flows in the network is key.

• Smart electrical grid to assure a 100% auto consumption of the entire network in the smart city/district (not only a building).

• Digital control to adapt, in real-time, energy production based on consumption (Dalkia Smart Building, 2020).

Before estimating synergic benefits in terms of energy savings, a deep investigation in each solution has been carried out.

3.2 Thermal Smart Grid

The smart thermal grid focuses on the efficient integration of renewable energy sources, distributed energy generation, and involvement of consumers’ interactions (STĂNIŞTEANU, 2017). The main advantage of smart thermal grids is their flexibility, their capability to accommodate any changes that occur in supply and demand for thermal needs in the short-, medium-, and long-term (Sullivan, 2016).

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To properly work and to be labeled as a green solution, the smart thermal grid must include renewable energies sources under different forms. In this context, various renewable energy production solutions are presented in the next paragraphs, accompanied by relevant project examples already exploited (where present) and followed by an analysis from an energy savings point of view, highlighting benefits and potential improvements.

3.3 Energy production systems

The amended Energy Performance of Buildings Directive (Directive (EU) 2018/844) introduced long-term renovation strategies. Under the directive, each Member State must establish a long-term renovation strategy to support the renovation of the national stock of residential and non-residential buildings, both public and private, into a highly energy-efficient and decarbonized building stock by 2050, facilitating the cost-effective transformation of existing buildings into nearly zero-energy buildings’ (Ciucci, 2020).

As previously mentioned, nearly zero-energy buildings reduce heat loads, which in turn can lower the temperature needed in the network, thus improving the overall energy efficiency and allowing renewable energy sources to become the main source of heat.

Several thermal renewable energy solutions are currently available, each one with its potential benefits and its limitations. Those renewable energy solutions are best suited for use in smart cities and eco-districts due to their technical characteristics, operational parameters, simplicity of integration, and reliability. Most of them can be exploited in stand-alone and individual solutions, while others are only deployed with a distributed network.

The following sections will analyze some of those renewable energy solutions currently available for deployment in thermal grids, underling the potential integration opportunities in a Double Smart Grid solution.

3.3.1 Biomass and Biogas

• Context

Biomass is one of the oldest materials used to produce heat throughout combustion. Still, worldwide in 2017, 55.6 EJ of biomass was utilized for energy purposes – 86% of the use was in the form of primary solid biofuels including wood chips, wood pellets, fuelwood for cooking and heating etc. 7% of the biomass was used as liquid biofuels. Biogas, municipal waste, industrial waste had almost equal share at 2 – 3% (Global Bioenergy statistics 2019, 2019).

Due to its characteristics and its easy deployment, biomass is one of the most widely used renewable energy sources for derived heating, with a 96% share in the global renewable heat market. The main sectors, where the heat produced is consumed, are residential and commercial establishments (space heating) and industries (heating demand for processes) (Global Bioenergy statistics 2019, 2019).

Moreover, the biomass chain can be considered as neutral from a greenhouse gas emissions point of view. The biomass combustion release to the atmosphere approximately the same quantity of CO2 absorbed during its growth, throughout the photosynthesis process. Nevertheless, a more meticulous carbon life cycle analysis will consider the CO2 emitted during the production and transportation phase, components non-negligible. These aspects must be carefully analyzed during the feasibility study of an energy production project (Karim Beddiar, 2015).

Recent studies have shown an interesting combination of biomass power plants and carbon captures and storage (CCS), also known as “Bio-Energy with Carbon Capture and Storage” (BECCS), that will provide one of the most viable and cost-effective negative emission technology to fight the increase of the Earth’s temperature (The History of BECCS, 2016). In practice, throughout the entire biomass life cycle, the CO2 extracted from the atmosphere will be drastically lower from the one released due to the combustion of the same quantity.

Biogas is a combustible product obtained from the decomposition of organic waste. When the organic matter, such as food scraps and animal waste, break down in an anaerobic environment (an environment absents of oxygen) they release a blend of gases, primarily methane and carbon dioxide. Because this decomposition happens

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in an anaerobic environment (lack of oxygen), the process of producing biogas is also known as anaerobic digestion (Homebiogas).

Figure 8: Chimal reaction in an anaerobic environment (Maji Solutions, 2019).

This degradation is only possible in the presence of fermentable materials: unstabilized sewage sludge, fresh fecal sludge, and other organic waste such as manure, plants or food waste (Maji Solutions, 2019).

• Characteristics

Thermal grids work successfully with a centralized power plant, due to the presence of a primary network that distributes the heat produced and, in certain cases, aggregates the heat issued by other energy production systems.

Additionally, the low cost of deployment makes it interesting as a feed-in solution.

Nevertheless, before selecting biomass as a production system in every project, a feasibility study must be carried out to evaluate each aspect individually. Major questions to pose are (Karim Beddiar, 2015):

- Availability of the bio source near the delivery station (silos for the storage) (approximately 80 km) to avoid an excessive weight of the transportation component in the total price.

- Warranties of supply all along the system lifetime.

- Energy needs to be satisfied. Due to the low efficiency of the boiler at non-nominal load, it is preferred to design the boiler for 80% of the total thermal needs and implement a secondary gas or electric boiler for the peak loads.

- Environmental impact, including transportation.

- Economical comparison between the price per kWh of the biomass solution and the conventional one, hence gas (CAPEX and OPEX).

There are multiple types of biomass products, each one as a result of different processes. The forestry sector is the largest contributor to the bioenergy mix globally. Forestry products, including charcoal, fuelwood, pellets, and wood chips, account for more than 85% of all the biomass used for energy purposes. One of the primary products from forests that are used for bioenergy production is woodfuel (Global Bioenergy statistics 2019, 2019).

Industrial waste from the wood sector is the second supplier of biomass products, where usually there are subjected to preliminary processing before being sold.

The most deployed in the residential sector is the woodfuel (figure 9), while pellet is constantly increasing due to the availability of small size boiler (around 4 kW) (Karim Beddiar, 2015).

Figure 9: From left to right, woodfuel (Gael woodfuel), charcoal (Blog.guideENR), wood chips (ITS WOOD), pellets (Alibaba.com).

The most important parameter to evaluate the effective heating capacity is the moisture content. The higher the percentage, the lower the heating value, and the heavier the matter (figure 10).

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Figure 10: Heating value as the percentage of humidity varies (Wood Energy, 2019).

Biogas produced by anaerobic digestion can be exploited in different production systems to produce separate energy vectors such as heat through combustion in a generator, electricity via a gas engine, simultaneously heat and electricity through cogeneration processes or in a form of biomethane injected in the gas grid or in form of fuel under pressure (Karim Beddiar, 2015).

Anaerobic digestion is seen as a proper “waste-to-energy” due to the conversion from waste to heat, electricity, or both. In general terms, 15 000 tons/year of waste (produced by 50 000 habitants) is capable of electrically power 1 300 dwellings and to provide domestic hot water to 2 000 households at the same time (Karim Beddiar, 2015).

According to The World Bank, the food and green waste represents the biggest portion (around 44%) of global waste each year (figure 11) (The World Bank). This amount is estimated, by the Food and Agriculture Organisation of the United States (FAO), as 1.3 billion tonnes per year (The World Bank). Moreover, more than one-third of the total solid waste is gathered in open dumps producing an important level of CO2 emissions. It is estimated that 1.6 billion tonnes of carbon dioxide (CO2) equivalent greenhouse gas emissions were generated from solid waste treatment and disposal in 2016 (globally), or 5 percent of global emissions. This is driven primarily by disposing of waste in open dumps and landfills without landfill gas collection systems. Food waste accounts for nearly 50% of emissions (The World Bank).

As this snapshot describes, a tremendous potential is hidden behind the biogas deployment. It could decrease waste from one side, and supply heat and/or electricity from the other. Nevertheless, the global installed biogas capacity accounts just for 15 GW in 2015, with 10.4 GW in Europe only, 2.4 GW in North America, 711 MW in Asia, 147 MW in South America and 33 MW in Africa (Nicolae Scarlat, 2018). Germany alone in 2017 counted 9331 anaerobic digestion plants, with a total of 4550 MW of installed power. Energy production in 2017 reached 32,48 TWh of electrical energy produced by biogas installations (DOUARD, 2018).

Figure 11: Global waste composition (percentage) (The World Bank).