Can buildings become active players in the energy transition? By combining heat pumps, renewable energy and innovative thermal storage technologies, new solutions are transforming homes into flexible, efficient and low-carbon energy hubs for the future.
Marco Rocchetti, Thematic area leader, energy and technologies at Innovation Division at R2M Solution | LinkedIn profile
(Note: Opinions in the articles are of the authors only and do not necessarily reflect the opinion of the European Union)
The European building sector is undergoing a profound transformation, driven by the need to reduce energy consumption, phase out fossil fuels and increase the integration of renewable energy sources. Buildings are currently among the most energy-intensive sectors in Europe, with heating, cooling and domestic hot water accounting for a major share of residential energy demand. In this context, the transition towards zero-emission buildings requires not only the deployment of renewable energy systems but also the adoption of technologies that improve energy efficiency and enable more flexible demand management.
Heat pumps are expected to play a central role in this transition, as they can provide heating, cooling and domestic hot water with high efficiency while supporting the electrification of building services. When powered by renewable electricity, they can significantly reduce dependence on fossil-fuel-based heating systems and contribute to the decarbonisation targets set by the European regulatory framework. However, the increasing penetration of heat pumps also raises new challenges related to electricity demand peaks, grid stability and the mismatch between renewable energy generation and building energy needs. For this reason, the integration of heat pumps with advanced thermal energy storage systems is becoming increasingly relevant. Phase change materials and thermochemical storage solutions can separate energy production from energy use, support load shifting, increase renewable self-consumption and enhance building energy flexibility. This article explores how such integrated systems can contribute to a more resilient, efficient and decarbonised residential energy model, with particular attention to innovative solutions developed within the MiniStor European research project.
The growing deployment of heat pumps is strongly supported by the European policy framework for building decarbonisation. Recent legislation, including the revised Energy Performance of Buildings Directive (EPBD) and Renewable Energy Directive (RED III), promotes the electrification of heating and cooling, the integration of renewable energy sources and the development of flexible, low-carbon buildings. Within this context, heat pumps are increasingly recognised as a key technology for achieving both energy efficiency and decarbonisation objectives.
In line with the current regulatory framework, heat pumps represent a key technology that is economically sustainable for achieving the EU’s building decarbonisation goals, as set out in the REPowerEU framework. The European industry has set a target of installing around 60 million heat pumps by 2030, compared with an estimated European stock of approximately 25.5 million in 2024.
Figure 1. Potential stock growth scenario, based on 2015-2021 actuals. Source: 2025 European heat pump market report, published by EHPA.
As presented by European Heat Pump Association (EHPA) in the 2025 European Heat Pump Market report and illustrated in Figure 1, the market has experienced slower growth in recent years. The projected stock growth is lower by 15 million of installations, representing a 25% decrease. This is due to a combination of factors, such as increased electricity prices in the EU, a decline in the new construction sector and the conclusion of national incentive programmes.
Despite the recent slowdown, heat pumps remain one of the most promising technologies for residential decarbonisation. However, future market growth will increasingly depend not only on the deployment of heat pumps themselves but also on their ability to interact with renewable energy sources, storage technologies and smart energy management systems. This integrated approach is becoming essential to maximise efficiency, reduce operating costs and provide flexibility services to the grid.
Heat pumps play a dual role in a decarbonised building scenario: reducing primary energy demand and replacing fossil fuels currently used for heating, cooling and domestic hot water production.
Figure 2. Example of a heat pump installed in a family house.
Source: The global energy crisis is driving a surge in heat pumps, bringing energy security and climate benefits. Published by IEA 30 November 2022.
The primary building energy demand reduction is guaranteed by the fact that heat pumps work by transferring energy from a source (usually external air, water or ground) to the building interior through a cycle of expansion and compression that consumes electrical energy. During this process, the heat pump transfers more energy than it consumes. This aligns with the energy efficiency first principle of the Energy Efficiency Directive and the EPBD’s trajectory towards zero-emission buildings. Reducing building heating and cooling demand is highly efficient, especially when heat pumps are combined with building insulation and low-temperature distribution systems such as radiant floors and walls or low-temperature terminals. The heat pump efficiency is defined as the ratio of heat transferred to compression work. For this reason, the lower the temperature difference between the heat source and the supply temperature, the higher the heat pump efficiency, expressed as the Coefficient of Performance (COP). Common values for commercial COPs range from 3 to 5 for air-to-water heat pumps and from 4.5 to 6 for geothermal heat pumps. This aspect makes heat pumps the most efficient heating and cooling system for achieving EPBD energy performance requirements in new buildings and during deep renovation of existing buildings, where they are installed as replacements for gas boilers.
Heat pumps contribute to replacing fossil fuels and promoting building electrification by using electricity as the primary input. Although there is a niche market for gas-powered heat pumps, most of the market consists of electric heat pumps.
The increased use of renewable energy sources, mostly in the form of photovoltaic systems or thermal panels installed at building or district level, in turn makes the installation of heat pumps easier and economically attractive. The combination with RES reduces the purchase of electricity from the grid, and additional integration of energy storage systems can completely offset the environmental impact of nearly zero-energy buildings, enabling the concept of energy flexibility.
In the context of decarbonising buildings, the greatest benefits are achieved if heat pumps are integrated with:
Energy flexibility is the second key pillar for achieving the EU’s decarbonisation goals. According to the IEA EBC Annex 67 approach, it can be defined as the ability of a building to manage its energy demand and generation in response to local climate conditions, user needs and grid requirements, while maintaining indoor comfort, environmental quality and the proper functioning of its services.
Heat pumps can play a significant role in enhancing building energy flexibility, as they turn heating and cooling systems into controllable resources. By adjusting electricity consumption according to system needs, they enable buildings to respond dynamically without compromising indoor comfort. In this way, buildings are no longer passive energy consumers but can become active elements in grid management.
Within this framework, a flexible building can maximise the value of electricity generated by local renewable energy sources, particularly by increasing self-consumption and reducing reliance on the grid. Photovoltaic production, for example, is variable and often concentrated in the middle of the day, when local demand may be limited. Flexible buildings can absorb this surplus generation by activating heat pumps, storage systems or electric vehicle charging, thereby reducing unplanned electricity feed-in to the grid.
Table 1 lists some energy flexibility models that can be enabled by the installation of heat pumps, storage systems, RES or other flexible assets.
Table 1. Energy flexibility models applicable at building level with heat pumps.
The MiniStor project, concluded in June 2025 and co-financed by the EU, has been developed with the primary objective of providing an innovative, economic and sustainable solution composed of a heat pump combined with innovative thermal energy storage systems, aimed at maximising the penetration of renewable energy systems and supporting the decarbonisation of the residential sector.
The system can provide basic services such as heating, cooling and domestic hot water production, common to commercial technologies such as gas or biomass boilers, combined with additional innovative services such as short- and long-term energy storage, energy consumption and flexibility management, which are characteristics more closely related to smart technologies.
MiniStor can be considered composed of sub-systems not yet available from any other company in this unique form on the market. It is characterised by two different innovative thermal energy technologies, a thermochemical unit (TCM) and two units with phase change materials that provide high performance in terms of storage capacity. The ammonia-based TCM solution has high energy density, around ten times higher than that of water-based technologies currently available on the market, allowing it to store a high level of thermal energy in a small volume. This aspect makes it particularly interesting for the residential sector, where space for technological systems represents a limitation.
Figure 3. Overview of the MiniStor system. Source: MiniStor deliverable 3.1 ‘Initial dimensioning of the system according to general use typologies’.
The system can be easily integrated with thermal RES, such as photovoltaic-thermal panels, solar thermal collectors, as shown in Figure 3. This feature makes it a highly promising solution for market uptake in contexts increasingly oriented towards distributed energy configurations. The project has been demonstrated under five different conditions, varying both climatic zones and building typologies: a social housing building in Cork, Ireland; two student residence apartments, one in Santiago de Compostela, Spain, and one in Kimmeria, Greece; a nearly zero-energy private house in Sopron, Hungary; and a smart home in Thessaloniki, Greece.
To cover all European climatic zones, 15 additional cities were analysed through simulation, taking into consideration the most common building typologies and heating and cooling systems used in each city, with support from the Eurostat database.
To demonstrate the importance of combining heat pumps with thermal and electrical storage systems supported by renewable energy systems, Table 2 reports the results of the project simulations in five relevant European cities.
Table 2. Results obtained by MiniStor simulations. Source: MiniStor deliverable 7.7 ‘Costs and benefits assessment’.
The simulations show excellent results in countries with high solar radiation, where renewable energy (especially thermal) efficiently assists the heat pump. Under these conditions, the heat pump achieves a high COP using electricity produced by the PVT panels. Where solar irradiation is limited, efficiency is significantly reduced, and the heat pump relies on grid electricity instead.
Notably, the annual heating and cooling demands considered in the simulations are representative of the 1970s and 1980s building typologies. Modern construction standards, discussed at the beginning of this article, drastically lower energy consumption, making the MiniStor system economically viable in northern countries as well.
The simulation results were analysed to determine the maximum acceptable market price for the MiniStor system over a 10 to 15-year reference period. Even though the system's actual lifespan could exceed 15 years, this analysis assumes a 10-year period of guaranteed, steady performance. After 10 years, performance degradation becomes likely. This 10-year timeframe also matches the standard acceptable payback time for residential customers.
The estimated target market price was approximately €45,000, a value that is broadly aligned with the current cost of alternative heating and cooling systems combined with conventional storage solutions.
The simulation results did not include the additional benefits that the system could provide in terms of energy flexibility, particularly through its interaction with buildings at district level, nor did they account for potential national support schemes and incentives.
In conclusion, the decarbonisation of the building sector is increasingly driven by electrification. However, this process must consider not only energy generation from renewable sources but also the effective management of energy across daily and seasonal timeframes. A decarbonised scenario strongly focused on renewable energy sources alone cannot be considered fully sustainable unless it is supported by technological systems capable of enabling energy flexibility, such as energy storage solutions and sector-coupling technologies, including heat pumps. Heat pumps have achieved high levels of efficiency, but they cannot provide a complete solution on their own. Research demonstrates that innovative integrated solutions are emerging, attracting growing market interest and offering promising pathways to support the transition towards a more flexible and decarbonised building sector.
