The two pillars of the decarbonisation of the buildings sector in Europe are a) improving energy efficiency and b) supplying with renewable energy sources both new and existing buildings. Recent developments show that energy developments at the neighbourhood or district scale can accelerate and improve the required quality to meet the requirements of the Paris agreement (1,2). Acting at the neighbourhood level permits to better consider the energy interactions between the buildings and the local energy system. The concept of zero-energy districts is based and benefits from highly energy efficient buildings and local generation and consumption of renewable and low carbon energy systems (3,4).
Figure 1: A building belonging to the ZERO-PLUS project settlement in Voreppe, France (20).
Positive Energy Districts (PEDs) are neighbourhoods with annual net zero energy import and net zero CO2 emissions, generating more renewable energy than they consume yearly. PEDs are characterized by a) net-positive renewable energy production on a yearly basis, b) high energy efficiency, c) flexibility d) diversified renewable energy technologies, and e) focus on providing inclusive, affordable, and sustainable lifestyles rather than on economic advantages. They usually include energy storage and EV charging solutions and require integration of different systems and infrastructures and interaction between buildings, the users and the regional energy, mobility and ICT systems.
Three categories of PEDs have been identified. The difference lies in the ability to interact with energy networks, consumers, and producers outside the geographical boundaries of the PEDs.
Figure 2: Plus energy settlement in Freiburg, Germany (21).
Autonomous PEDs have clear geographical boundaries and on-site renewable energy generation. They may not import energy from the external electricity grid and district heating/gas network but can export the excess renewable energy. Dynamic PEDs have clear geographical boundaries and annual on-site renewable energy generation and can furthermore interact with other PEDs, external electricity grids, and district heating/gas network. On the contrary, virtual PEDs allow the implementation of (virtual) renewable energy systems and energy storage solutions outside their geographical boundaries.
In a net-zero (NZED) or positive energy district, the central energy system should be completely based on renewable energy sources and should accommodate and provide the energy for the whole community. Further, community-level financial aspects and environmental impacts (including GHG emissions) should be critical parts of the decision process (6).
Figure 3: Net Zero Energy Buildings Cluster / retrofit projects. Renovated district in Bad Aibling, Germany (22).
NZEDs and PEDs present several important advantages compared to Net Zero Energy Buildings, (NZEBs):
They promote full sharing of energy needs, costs, and resources among the community buildings, that is very beneficial to a cost-effective management (7).
The potential mismatch between energy demand and energy generation, which is very common at the building scale, can be avoided at the neighborhood/district level as communities can ensure a more balanced management (8-9).
At the community level, oversizing of the energy system can be avoided by proper assessment and sharing of the total energy demand (10).
The management of the various available and used energy resources in a centralized energy system is more efficient and offers the flexibility to balance the demand and supply by using efficient energy storage systems (13). This offers more flexibility and a potential for more energy services like electric mobility.
the process of generation and distribution of energy runs in parallel, allowing the minimization of the distribution and surplus losses (11-12).
In high-rise buildings, NZEB concepts come with specific challenges that are much better addressed when the energy system is generated at the community level (14).
The implementation and use of a microgrid at community level can supply excess energy to the energy grid resulting in additional financial benefits for the tenants (15).
To realise the net-zero/positive concepts at the district level, three main energy components have to be optimized (Figure 1):
The thermal load of the building has to be minimized using energy conservation technologies at the building scale, to minimize the heating, cooling and lighting loads (16-17).
The energy generation and supply system have to be based on clean and renewable energy technologies to supply the whole district.
The outdoor climate has to be properly considered to achieve the best possible conditions during the whole year (18-19).
The main purpose of this document is to provide knowledge, information and a reference for the city authorities, building professionals and stakeholders to design and implement NZEDs/PEDs across different climatic and location-based conditions.
Figure 4: Portland Net Zero Energy Community (23).
PED establishment is in an early stage. A large number of PEDs are on their way to being established in Europe. However, PEDs integrate various decentralized and renewable energy sources that are at a mature stage (e.g. solar photovoltaics).