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Solar energy and ground source heat pumps for Swedish multi-family housing (completed)

Ground source heat pumps (GSHP) are common in Sweden, but solar energy systems are not. GSHP could offer an ideal platform to integrate solar energy into the building and national energy systems towards meeting climate goals and increasing the share of renewable energy to 100%.


Ground source heat pumps (GSHP) are known as a renewable heating source and have the potential to be 100% renewable and sustainable when the electricity is generated from hydro, wind, or solar. While hydropower is well developed and wind installations are increasing rapidly, solar energy is the most practical source for integrating into the building and can play a significant role increasing renewable energy production in Sweden.

Multi-family houses are predominantly connected to district heating; not necessarily because they want to, but oftentimes have to. Their options are limited in part because in densely populated areas there is not enough space to drill a sufficiently sized borehole field. With an undersized borehole array, there is a risk that ground temperatures will decline over time, a significant problem considering that a reduction of only one degree reduces efficiency by 3%. Alternatively, if the temperatures can be increased there is a great opportunity for electricity savings; if all existing GSHP in Sweden had their boreholes increased by one degree, it would save 200 GWh of electricity per year. Regenerating, stabilizing, or increasing borehole temperatures can be accomplished sustainably using locally collected solar energy.

Background on solar energy in Sweden

As anyone who has spent time in the Nordics knows, the supply of solar radiation is greatly imbalanced from summer to winter which is also the primary cause of high energy demands in the winter. This has not stopped the exponential increase of solar photovoltaic (PV) installations, which have rapidly decreased in cost and are economically supported by the government. While this works as a way to initiate the market, the seasonal imbalance remains a challenge to the development of solar as an significant energy source for Sweden.

Graphs showing the rapid increase in solar PV installations in Sweden (from the IEA-PVPS national report for Sweden) and the demand/supply imbalance between buildings and solar

One challange for PV in buildings is increasing self-consumption, which is the electricity generated by the PV system used directly in the building. When there is more generation than is needed, called over-production, the excess can be sold to the network. Self-consumed electricity is more economically valuable than over-production, meaning an owner should increase self-consumption as much as possible. Additionally as more solar power is installed across the country, there is an increased liklihood that prices during the summer will be eroded and could even become negative. This is already happening in Germany and has negative consequences for PV owners and the electricity system at large.

A three year research project exploring technical and economic potential for solar PV technology in multi-family houses has been completed here at Energiteknik under 2016. Much more information is available at the following project page link:

Proposed solution: PV/thermal + GSHP

To increase the efficiency of solar collectors, self-consumption of PV generation, and heat pump efficiency, the integration of hybrid solar PV/thermal modules on the source-side of the heat pump can be interesting. A PV/thermal hybrid collector affixes a heat exchanger to the back of PV cells, which can increase electricity production by cooling the cells as well as capture thermal energy normally lost to the ambient air. Connecting on the source side of the heat pump will reduce the electricity needed for the compressor and also enable storage of excess heat in the boreholes. The stored heat increases the borehole temperatures such that the compressor runs more efficiently in winter as well. The configuration also opens up interesting possibilities for converting PV over-production into stored heat rather than dumping it to the network.

This is just an example of a potential system configuration, not one of the selected designs


This study focuses on the exploring the technical and economic potential of PV/thermal + GSHP system in Swedish multi-family houses. While not a new concept, much of the previous work has been focused solar thermal systems and the addition of PV can make for unique configurations and control strategies. Therefore the objective is to identify interesting and practical system configurations and optimize them for energy efficiency, profitability, and exergy efficiency.


The PV/thermal + GSHP concept is complex with many possible configurations and component sizings. The first step in the process is to make a comprehensive review of previous work considering not only PV/thermal but also solar thermal research to help identify configuration strategies. In conjunction with our project partners, we then aim to have three to five system configurations which can practically be implemented in either new installations or existing.

The next step, and the bulk of the project, will be carried out using extensive computer modeling validated with several sources of measured data. Models for each component will be tested to ensure good results when combined into the larger system simulations. Once the systems models are created, they will be validated agains project partner data from existing GSHP installations as well as several test sites around Sweden. With validated models, experiments can then be done to test component sizing and control strategies to meet the optimization objectives.


Spring 2016

Component models for PV/thermal collectors and bore holes are tested and the literature review performed. Preparations for test sites are also being performed.

Autumn 2016

System configurations are identified and models are created. Models include not only PV/thermal + GSHP systems, but also base cases which do not include solar or only have PV.

Spring 2017

Models are validated using existing GSHP data from project partners. PV/thermal models are validated as data becomes available from test sites.

Autumn 2017

Experiments are carried out to optimize the PV/t + GSHP systems and compare their performance to base case systems.

Spring 2018

Final results and conclusions are published


This project is financed by The Swedish Energy Agency (Energimyndigheten) under the Effsys Expand program.

Project Partners

BRF Moranvikan

BRF Timmermannen 2

Project Partner Documents Folder


For more information about the project or partnership opportunities, please contact:

PARMENIDES – Plug & plAy EneRgy ManagEmeNt for hybriD Energy Storage
HYSTORE - Hybrid services from advanced thermal energy storage systems
Open-source models for holistic building energy system design at scale
Tank to Grave Management of new Low-GWP Refrigerants (Hantering av nya låg-GWP köldmedier från installation till destruktion)
Novel tool and guidelines for designing ground source heat pumps (GSHPs) in densely populated areas
Data driven lab for building energy systems
Long-term performance measurement of GSHP systems serving commercial, institutional and multi-family buildings
Smart Control Strategies for Heat Pump Systems
Open-source models for holistic building energy system design at scale
Control systems for hybrid solutions based on biomass fueled Stirling engines, solar and wind for rural electrification
Prosumer-Centric Communication for Solar PV Diffusion (completed)
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Solar energy and ground source heat pumps for Swedish multi-family housing (completed)
Solar photovoltaic systems in Swedish cooperative housing (completed)
Smart Control Strategies for Heat Pump Systems (completed)
Creating and Understanding Smart Innovation in Cities
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High-Resolution GIS District Heating Source-Load Mapping
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Smart Renovation Strategies for Sustainable Electrification
Future Secondary Fluids for indirect refrigeration systems
Smart Fault Detection and Diagnosis for Heat Pumps
Performance indicators for energy efficient supermarket buildings
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High-Resolution GIS District Heating Source-Load Mapping
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Building state-of-the-art (SotA) supermarket: Putting theory into practice
Efficient utilization of industrial waste heat by low temperature heat driven power cycles – an integrated approach for Swedish Industry
Cooperation between Supermarkets and Real Estate Owners; Energy Efficiency and Business Models
Digitalization and IoT technologies for Heat Pump systems
Capacity control in Heat Pump systems
Alternative secondary fluids
Functional surface coatings for energy efficient heat pumps
Two-phase flow in flat channels
Two phase heat transfer & pressure drop with new environment friendly refrigerants in minichannels (completed)
Numerical Study on flow boiling in micro/mini channels (completed)
Distributed Cold Storages in District Cooling
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Simulation of temperature distribution in borehole thermal storages supported by fiber optic temperature measurements (completed)
Solar energy and ground source heat pumps for Swedish multi-family housing (completed)
Neutrons for Heat Storage, NHS, (completed)
4D Monitoring of BTES (completed)
Aquifer Thermal Energy Storage (completed)
Deep Borehole Heat Exchanger (completed)
Combined Heat and Power plants in combination with borehole thermal energy storage (completed)
Improved borehole technology for Geothermal Heat Pumps development (completed)
Compact Minichannel Latent Energy Storage for Air Related Cold Storage Applications
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Renewable Energy Park, RE-Park (completed)
Efficient use of energy wells for heat pumps (completed)
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