1 Background
Among the scientific community, two things are widely acknowledged:
- The climate is changing at a very high rate, and its acceleration is mainly due to anthropogenic activities. Some gases, called greenhouse gases, trap the sun’s heat and prevent them from leaking back outer the atmosphere. They are the primary driver of climate change. The greenhouse gas emissions concentrations in the atmosphere have been increasing from human activities. CO\(_2\), the most significant contributor to climate change, had risen to 48% above its pre-industrial level (European Commission, no date).
- The consequences of this change are expected to be massive for both humans and ecosystems (IPCC, 2022).
From this start, key sectors where emissions should be attenuated must be identified. Figure 1.1 and 1.2 illustrate the demonstrated relation between CO2 emissions and energy consumption. From this statement, energy consumption must be reduced to diminish the emissions, either by shrinking the energy demand or by increasing the energy efficiency of the processes.
Figure 1.1: Global primary energy consumption by source.
Figure 1.2: Annual CO\(_2\) emissions from fossil fuels, by world region.
Looking at the energy consumption by sector, among all activities, residential buildings account for 20% of the energy use in selected IEA countries, as shown in Figure 1.3. Moreover, the global energy demand is still expected to increase by 50% between 2010 and 2050 in a business-as-usual scenario (IEA, 2013). Most of the consumption is related to space and water heating (Figure 1.4, 69% of residential consumption), meaning that trying to lower the residential buildings sector carbon emissions needs a comprehensive approach considering both electrical and thermal demand.
Figure 1.3: Largest end uses of energy by sector in selected IEA countries, 2019.
Selected IEA countries refers to 2019 data for nineteen IEA countries whose data are available for most end uses: Australia, Austria, Canada, Czech Republic, Finland, France, Germany, Hungary, Italy, Japan, Korea, Luxembourg, New Zealand, Poland, Portugal, Spain, Switzerland, the United Kingdom and the United States; Canada and Italy include 2018 data. Other industries include agriculture, mining and construction. Passenger cars include cars, sport utility vehicles and personal trucks.
Figure 1.4: Shares of residential energy consumption by end use in selected IEA countries, 2018.
Additionally, the world urban population represents 55% of the total one and is expected to grow to 6 billion people (World Bank, no date) (70%). Today, two-thirds of the global energy consumption come from cities, which emit more than 70% of the total greenhouse emissions (World Bank, no date).
Those considerations are pushing toward a high interest in Urban Systems.
The decarbonisation of energy systems in urban areas should be driven by high electrification. The use of electricity is expected to increase substantially as an alternative fuel. The conventional technologies for heating, such as boilers, would be replaced by ones that require renewable energy vectors (electrical heating, HVAC systems like heat pumps) (IEA, 2013).
Indeed, while technological development has been outstanding in the last decades, the penetration of the new technologies into the Swiss market is still quite poor. As an example, solar production represents less than 5% of the total electricity demand (OFEN, 2020). Furthermore, the 2020 production from solar installations represents 3.34TWh, while the sole potential of roofs and facades from residential buildings is estimated to 67TWh (OFEN, no date).
Consequently, the exploitation of local energy resources is expected to grow, shifting the current electrical grid to a more decentralised one; households or organisations consume energy from the grid at some times, while at others, they produce surplus energy that they can re-input into the grid. The concept of prosumers has been developed for this kind of interaction where one actor is both consumer and producer. The installation of energy devices must then be carefully done so that it answers the constraints of the grid. As a matter of fact, non-drivable energies put pressure on the electrical power grid. The grid must always be balanced, i.e. the production must be equal to the consumption. This is to ensure the stable operation of the grid at nominal frequency (50Hz in Europe). With the current system where few plants are responsible for the production, plant turbines can easily adapt so that the balance is kept, from the higher voltage level. With non-drivable inputs on the grid at the low-voltage level, it is much more difficult to reequilibrate the imbalances (Laugs, Benders and Moll, 2020). Moreover, high peak production power can also overload the transformers or cause transmission bottlenecks (Cao, Metzdorf and Birbalta, 2018).
Those constraints from the power grid means that when maximising the electricity generated locally (e.g., solar panels), the interaction of the building energy system with the grid should be lowered (Middelhauve, 2022). The grid restrictions make it challenging to determine what technologies should be installed for a building to meet its demand, as optimal solutions depend on the context. Thus, the energy problem must be solved on a case-by-case basis.
To enable good energy-wise policies to help the renewable technologies penetration, one must not only enhance the technologies but also provide efficient decision tools, able to propose a set of solutions to an energy demand.
References
© EPFL-IPESE 2022
Master thesis, Spring 2022
Joseph Loustau