The 2030 Framework for climate and energy sets a 40% cut in Greenhouse Gas (GHG) emissions compared to the 1990 level as an EU-wide target for 2030. To this end, the European Union (EU) has established clear legislative frameworks to reduce its energy demand. The Energy Performance in Buildings Directive (EPBD, Directive 2010/31/EU amended by Directive 2018/844/EU) and the Energy Efficiency Directive (EED, Directive 2012/27/EU amended by Directive 2018/2002/EU) are set to decarbonise the building stock. These directives confirm the requirement of a target for nearly zero-energy buildings (NZEB), starting from January 2019 for new public buildings, and from January 2021 for all new constructions. Therefore, the NZEB target for new buildings will become common practice.
The general definition of NZEB was given by the EPBD 2010/31/EU as ‘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’. Following this initial statement, the EU Member States introduced their own specific definition and requirements according to their own context. A comprehensive overview at European level is given by this paper written by The European Commission’s Joint Research Centre (JRC) that reports the energy targets, balance of approaches and the main specificities of each country. Following the NZEB target, the paper introduces the definition of a Plus Energy Building (PEB) as ‘a building that produces more energy from renewable energy sources (RES) than it imports over a year’. This means that the building consumes an amount of delivered energy that is lower than the renewable energy exported to the grid. It is possible that in future a PEB target as a reference for new constructions could be included in EU legislation.
Although there is no definition of PEB at the EU level, there are several interpretations that derive both from EU research projects and from practical application.
Powerhouse, an organization that has built several PEB in Nordic climates, including the first Plus Energy Hotel in Europe, states that ‘a PEB is a construction that, in the course of a 60-year period, will generate more renewable energy than the total amount required to sustain daily operations and to build, produce materials as well as demolish the building’.
Another interesting definition is given by the Horizon 2020 project EXCESS that considers a PEB to be ‘an energy efficient building that produces more energy than it uses via renewable energy sources, with high self-consumption rate and high energy flexibility over a time span of one year’.
The forthcoming European Green Deal call under Horizon 2020 features topic “energy and resource efficient buildings” which refers to Energy Positive Buildings, defined as buildings ‘(producing electricity, covering their heating and cooling needs and contributing to the grid stability) with sustainable, renewable energy technologies’.
In Germany, the target of PEB represents a consolidated practice, especially in the case of residential buildings named Plus Energy Houses (PEH). The experience of recent years has been collected by the German Federal Institute for Research on Building and they have released the technical guidance called What makes an Efficiency House Plus? about the key aspects to be considered when designing and constructing a new PEH, with the scientific support of the Fraunhofer Institute for Building Physics.
The starting point is the definition of PEH, identified as a house with a positive yearly energy balance, in terms of both primary and final energy, considering the energy consumed for heating, cooling, domestic hot water production, lighting and appliances and the renewable energy generated. The energy balance in Germany is evaluated through a standardised calculation method as implemented in the publicly available tool Effizienzhaus Plus Rechner. The guideline presents an overview of the main technologies adopted in PEH, and performances and costs based on a set of exemplary case studies collected in the country. The added value of the guideline is the presentation of monitoring data from real building operation that highlights the energy consumed and generated from renewable sources and the personal experience of owners and designers.
The future implementation of PEB: the overview of the main European Projects
As analysed by the JRC, the implementation of the EU 2020 energy and climate targets is triggering the transition of Europe’s neighbourhoods towards net-zero energy districts, therefore PEB will play a significant role to reach this target. In fact, the surplus of energy that a PEB is able to produce from renewable energy can be supplied to the surrounding buildings and services such as public electric vehicle charging stations, minimising the energy demanded from the grid.
Plus Energy Buildings are already achievable but there is a need for an attractive business model ensuring reliability of the calculated performances, high indoor environmental quality, cost-effectiveness of the proposed solutions and reduced extra-over costs in comparison to a standard building available on the market. In this regard, the European Commission is supporting new solutions that aim to increase the viability of PEB, as demonstrated by the following EU research projects on the topic.
The ongoing CULTURAL-E project aims to define modular and replicable technology solutions for Plus Energy Houses (PEHs). In particular, CULTURAL-E will develop technologies that take into consideration the local climate and socio-cultural contexts. The analysis will be implemented by dividing Europe into climate-cultural geo-clusters, and the main specificities for each of them will be defined according to the analysis of the users’ energy practices, experience of local experts and designers. A special focus will be devoted to the comfort expectations of the users, with an analysis of the requirements and the definition of conditional rules for a comfortable PEH indoor environment. One of the key results will be an interactive atlas of the different European climate-cultural geo-clusters in combination with possible solutions to provide guidance for architects and designers interested in building PEHs.
EXCESS aims to demonstrate how nearly-zero energy buildings can be transformed into plus energy buildings through the use of key technologies developed within the project. The core of the project is the implementation in four demonstration cases in Nordic, Continental, Oceanic and Mediterranean climate zones, in order to assess the technologies in different contexts and so ensuring the replicability across Europe. In particular, the key aspects of the project will be i) to analyse challenges and opportunities associated with upgrading single technologies within existing building systems, ii) identifying enabling factors for local energy trading among buildings, and iii) defining new services to grid operators or utilities. The main technologies that will be implemented in the demonstration cases will be multi-functional façade elements with integrating photovoltaic and solar panels, geothermal heat pumps, heat flexible thermal storages and batteries.
Another interesting project is Syn.ikia, whose key concept is the interplay between novel technologies at the neighbourhood scale, energy efficiency and flexibility of the buildings, good architectural and spatial qualities, sustainable behaviour and citizen engagement. Starting from the single PEB, the project will expand the boundary towards the neighbourhood by aggregating buildings and including local storage systems and energy supply units. The users, buildings and technical systems within the neighbourhood will be connected via an integrated digital cloud (HUB) system that will be developed within the project implementation.
The abovementioned projects are also sharing the outcomes within Annex 83 Positive Energy Districts, an initiative of the International Energy Agency in the Energy in Buildings and Communities programme. This initiative aims to provide a clear definition and performance target of a Plus Energy District, meant as an area within the city boundaries capable of generating more energy than consumed and flexible enough to respond to the variation of the energy market. Moreover, Annex 83 will develop planning tools and decision-making processes related to positive energy districts.
Solutions for PEB at the neighbourhood scale are also investigated in the project ZERO-PLUS, started in 2016. In ZERO-PLUS, the main challenge is to increase the viability of NZEB and PEB through the implementation of three parallel strategies: i) increasing the efficiency of the building reducing the energy need, ii) reducing the construction costs through the introduction of modular solutions, and iii) reducing operational costs through better management of the loads and resources on a neighbourhood scale rather than on the scale of a single building.
At a larger scale, the project +CityxChange (Positive City ExChange) will introduce strategies that will foster the uptake of Positive Energy Blocks (PEBs) at urban level. In particular, the project will work on the definition of systemic solutions for implementing positive energy neighbourhoods, called building blocks in the project, and analysing the impact at urban scale within several European cities. The project will also work on the definition of recommendations for new policy interventions, market regulation and business models to foster the positive energy targets at building at neighbourhood scale. In particular, the project involves cities in Norway, Ireland, Romania, Czech Republic, Spain, Bulgaria, and Estonia that will implement the innovative technical and policy recommendations developed.
Conclusion and future outlooks
This article describes different NZEB and PEB definitions and collects best practices from practical implementations and Horizon 2020 projects, providing an overview on a complex and dynamic topic. NZEBs and PEBs will play a crucial role in the future energy system and will be essential to implement the European decarbonisation strategy. The definition of clear energy performance targets, the development of viable and efficient technological solutions and the implementation of effective policies represent the key challenges for enabling the replicability and the uptake at European level.