Innovative energy solutions in plus-energy buildings

The municipal housing company Stockholmshem has built two plus-energy buildings in Stockholm Royal Seaport with occupancy from 2019. The two buildings with 43 rental apartments become net energy producers with the help of solar panels, geothermal heat, efficient insulation and ventilation, and recycling of excess heat from wastewater. The unique architecture features balconies in the façade and angled roofs with built-in solar panels to harness the sun as an energy source. This cutting-edge project combines an innovative set of about twenty forward-thinking energy solutions.

The buildings are designed for energy efficiency, producing more energy than they consume throughout the year. The focus is on minimising heat loss through an airtight building envelope and heat recovery from both ventilation and wastewater systems, while generating renewable solar energy on-site.

Implementation and technology choices

Stockholm Royal Seaport was identified in Stockholm's environmental programme in 2008 as the city's next sustainability-profiled area. In 2010, the overarching policy document was adopted by the City Council with objectives for the area to become an attractive, resource-efficient, fossil-fuel-free district and an international model in sustainable urban development where new innovative tools, methods, and working practices are tested for subsequent scaling up to the rest of the city.

Land allocation competitions are one of the innovation-driving tools for achieving these goals. In 2014, Stockholmshem won a land allocation competition in the Brofästet phase in Stockholm Royal Seaport. The focus of the competition was to create plus-energy buildings through smart energy solutions and a functional architecture. Out of 16 participating housing companies, Stockholmshem scored the highest overall points. The project was awarded for its “holistic approach to energy efficiency and good living environments with interesting and exciting architectural expression”.

The buildings are designed with angled roofs to maximize the benefits of the sun as an energy source, balconies that are built into the façade, and with cutting-edge energy solutions and environmental performance. Stockholmshem gathered experts from various fields and solutions from previous development projects, which have been further developed and combined in new ways to create synergies in a new comprehensive solution.

Stockholmshem has collaborated with, among others, the architectural firm Dinell Johansson, the energy engineer Incoord, the structural engineer Kåver & Mellin, and Tema landscape architects, focusing on sustainable building and good living environments.

To meet the requirements for a plus-energy building, the building's energy use needed to be minimised and the technology optimised. The measured energy use during 2024 shows that the building uses approximately 12.6 kWh/m² per year calculated according to the then-applicable Swedish Building Code Regulations, including heating, hot water and building electricity. According to Stockholm Royal Seaport's calculation method, where electricity for heating is weighted by a factor of 2, the energy performance is 26.8 kWh/m². The measured solar cell production is 20.6 kWh/m² per year. Over a full year, the building has an energy surplus of 1.8 kWh/m² and meets the definition of a plus-energy building.

Architecture and building design

The compact design of the plus-energy buildings with airtight building envelopes and adapted for a range of energy-technical solutions are fundamental for meeting the energy requirements. Together with a wastewater heat exchanger and geothermal heating, this forms a functional whole.

The buildings have an optimal shape factor with angled roofs with solar cells to maximize electricity production and small areas exposed to weather and wind, thereby minimising energy losses.

The exterior walls are straight without niches and angles. The buildings' roof ridges have been rotated to provide directly south-facing roof surfaces, optimised to capture the sun's rays. The roof angle of 30 degrees is within the optimal range for high-efficiency solar cells with silicon technology. On the opposite side, the roof is covered with sedum plants that delay stormwater flow to Husarviken through a so-called rain garden – a shallow depression in the landscape with a draining system and a filter material covered with plants.

Sun-facing gable façades are clad with solar cells using less shade-sensitive thin-film technology. North-facing gable façades have trellis panels for climbing plants.

The actively heated living area is minimised but supplemented with an unheated living zone in the form of glazed balconies along the long façades. This provides a compact, functional residence during the winter half of the year which is significantly expanded during the summer half with areas that are heated by natural means. By using sun protection in the form of curtains along the balconies, heat can be let in during the winter and stored in the balconies' concrete structure, but reflected away during the summer.

Plus-energy building energy production and usage

The installation consultant Incoord, who designed for Stockholmshem, primarily worked to minimise energy losses, secondly optimised internal heat loads, and finally solved the remaining energy needs with technically energy-efficient solutions. Detailed project engineering was required to minimise energy use.

The heat from cooling the space with the solar cells' rectifiers is used to preheat the heat pump and, in the best case, energy is stored in the bedrock.

The building produces its own energy

About 30 per cent of the solar cells' electricity production can be used directly for the building's electricity needs for lighting, heat pumps, and fans. The remaining electricity production is sold to the grid and balanced against purchased electricity during the cold season. Over the year, the solar cells produce more energy than the property needs.
The tenants' electricity subscriptions are initially signed by Stockholmshem with Bra Miljöval (Good Environmental Choice).

Heat storage

The internal heat loads have been optimised by utilising the heat generated by residents and technical equipment. Here, the heat storage capacity in the buildings' concrete structure is a good prerequisite.

Space-efficient apartments relative to the number of residents have been a goal in the effort to maximise the effect of internal heat loads. This has resulted in efficiently designed four-, three- and two-room apartments. Optimised airflow and thus smaller air volumes to heat make it easier to utilise internal heat sources.

Heat recovery

Heat exchangers for heat recovery from ventilation air and wastewater play an important role in utilising waste heat. Additionally, the glazed concrete balconies create a kind of "microclimate zone" where the concrete stores the heat energy from the sun's rays during the night.

Not just technology – tenants also need to know what to do

For a plus-energy building to function as intended, tenants must understand how to ventilate and what it means to be away during the cold season. Stockholmshem therefore maintains an active dialogue with its tenants about what is required to live in a plus-energy building.

Morten Johansson, architect at DinellJohansson, and Torbjörn Kumlin, project manager at Stockholmshem, discuss the plus energy buildings in Brofästet. (Swedish only)

Potential and future scaling opportunities

Building energy-efficient residential buildings that also produce large portions of or more than their own energy needs is a challenge. Experiences from this project can be shared and make it easier for other actors in similar upcoming projects. The plus-energy buildings are important milestones where energy-smart solutions are combined with an exciting architectural form.

Land allocation competitions where sustainability criteria are evaluated have proven to be an important tool for challenging developers to perform even better through collaboration of various disciplines at early stages. At least a hundred people within the contractor, consultant, and client sectors engaged creatively in developing good competition proposals.

The buildings' innovative character had already led to significant coverage in national media and trade press for urban development, construction, property management, and energy issues before occupancy.

The ambition for the plus-energy buildings is set high, and monitoring the energy performance is an important part to ensure they meet expectations and draw lessons for future development and requirements setting in Stockholm Royal Seaport and the City of Stockholm.

Article Published: 10/05/2023 Updated: 07/10/2026