1 Background
It is nowadays broadly acknowledged that the climate is changing at a very high rate due to anthropogenic activities. The consequences of such a rapid change represent a threat for both humans and ecosystems (Intergovernmental Panel on Climate Change (IPCC) 2023). As a matter of fact, \(CO_2\) emissions are positively correlated with the global primary energy consumption Ritchie, Roser, and Rosado (2022). As no promising technological perspective that would enable to decorrelate primary energy consumption and CO2 emissions exists, it is crucial to shrink the global primary energy consumption in order to slow down the climate change.This reduction can be achieved by diminishing energy demand, improving energy efficiency of energy conversion processes and by sector coupling, all simultaneously.
Among all human activity sectors, the buildings and construction sector accounted for 36% of the 2018 global final energy use (“2019 Global Status Report for Buildings and Construction” 2019). Regarding the residential sector specifically, it accounted for 20% of the final energy use in 2019 and in 19 selected IEA countries including Switzerland (IEA 2019). Besides electrical needs for lighting and appliances, most of this energy demand is to fulfill thermal needs: space heating (SH) and domestic hot water (DHW). A comprehensive, integrated, and multi-energy approach is thus needed to reduce the carbon emission of the buildings sectors.
The decarbonization of the building stock should be characterized by building refurbishment to reduce the heating demand but also by the electrification of the end-use together with a decarbonization of electricity. Switching to electrical heating, ventilation and air conditioning (HVAC) systems allows a higher conversion efficiency and improves the integration of locally generated renewable energy, such as by installing photovoltaic (PV) panels on rooftops Rüdisüli et al. (2022).
The building sector is thus expected to experience a high electrification rate together with a massive deployment of solar energy. However, while technological development has been outstanding in the last decades, the penetration of the new technologies into the Swiss market is still quite poor and the energy transition is yet to come. As an example, solar production represents less than 5% of the total electricity demand (Swiss Federal Statistical Institute 2022). Furthermore, the 2020 production from solar installations represented 3.34 TWh, while the sole potential of roofs and facades from residential buildings is estimated to 67 TWh (Office fédéral de l’énergie 2019).
The deployment of distributed renewable energy vectors such as solar technologies, raises indeed a double issue of its financing and its integration to the energy system. On one hand, whereas solar energy requires small operating cost, it necessitates important capital investments compared to a business-as-usual scenario where the already-existing fossil-energy infrastructure is exploited at the same current pace. One the other hand, as solar energy is a stochastic energy source, PV panels integration put pressure on the power grid which needs to be always balanced to ensure stable operation at nominal frequency. In a centralized energy-system with few big plants responsible of providing power to consumers, the balance of the grid is way more easily controllable than in a distributed energy system where consumers become also producers (Laugs, Benders, and Moll 2020). Moreover, high peak production power can also overload the transformers or cause transmission bottlenecks (Cao, Metzdorf, and Birbalta 2018).
These two issues could however be more easily manageable if the interaction between the power grid and the building energy system is limited by maximizing self-consumption and self-sufficiency (Middelhauve, n.d.). This two objectives allows to maximizes the PV potential. It is economically beneficial for the consumer since her power demand to the grid would decrease consequentially. It could therefore incite to increase the PV panels capacity. Maximizing the self-consumption together with the self-sufficiency also reduces the power stress on the grid since power needs and power injections are lowered. However, high self-consumption self-sufficiency is not that easily achievable for a single consumer since electrical needs and electrical production from PV panels are not so often in phase. For such a reason, self-consumption and self-sufficiency at the individual scale does not represent an answer ambitious enough to both questions raised earlier.
In order to mitigate this limitation, locally produced energy could be consumed at a higher but intermediary scale, the neighborhood scale. The different buildings of a same neighborhood could then benefit from synergies due to shared installations for instance or due to a more spread-out neighborhood demand along the day. The resulting neighborhood demand curve for a typical day would flatten compared to a single building demand curve. Such configurations, where energy exchanges between nearby buildings of a same neighborhood can occur, show a higher self-consumption rate, and more cost-effective energy system solutions than building energy system without exchange being possible (Middelhauve, n.d.).
This “Communauté Énergétique Local” (CEL), meaning local energy community, concept seems promising to start the energy transition. However, its implementation in Switzerland remains currently limited to RCPs (for Regroupement de Consommation Propre in French). A RCP allow to gather different producers and consumers in a single community where energy can be freely shared. The grouping can occur at the building scale, for big building with different households for instance. In this case it is a simple RCP, but it can also occur at a bigger scale with multiple buildings. This latter case is called RCP microgrid. It represents a first step toward the right to self-consume at a bigger scale than the individual scale, but its implementation remains difficult and its attractiveness is limited since it requires the installation of a private network (microgrid). Its operation is also determined by the lease that defines the relationship between all the stakeholders. This solution is more suitable to new neighborhoods about to be built, but for already existing ones, installing a private network is often expensive besides the high \(CO_2\)-emissions related to the fabrication and the installation of the microgrid.
In the context of the revision of the Federal Electricity Supply Act (LApEl) (Swiss Federal Assembly 2007) that should open the door for a fully liberalized electricity market, legal changes might allow for local energy exchanges using the public Distribution System Operator (DSO) network. Local energy communities using the public network could then be allowed and local energy market could flourish. But besides necessary institutional changes, the stakeholders of the current energy system need to fundamentally change their business model for the restructuration of the energy system and the CEL and local energy market implementation to happen. As a matter of fact, it appears that power utility owners and DSO are critical actors whose attitudes greatly influence the development of CEL (Warneryd, Håkansson, and Karltorp 2020). It is therefore crucial to identify what could be the economical consequences of CEL development for each stakeholder and if there are economically viable conditions for the DSO and power utility owners under which energy communities are beneficial for the energy transition.
In order to help decision-makers to design good energy-wise policies, engineers and scientists can provide decision tools. These tools should not only provide a set of technical solutions that answers to a local energy demand, but also model and optimize financial flux between each stakeholder. Indeed, it is important to remind that the energy transition wont happen without huge investments, and it is thus important to ensure the economical stability of each actor.