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Smart Solar Hybrid Solutions for Sustainable European Buildings (completed)

Achieving the ambitious national goals in the Swedish building sector are impossible without smart, cost-effective, scalable, and integrated solutions for heating, cooling and electricity. The goal of this project is to advance the development of an integrated heating, cooling and electricity system solution for European buildings using solar PVT technology and ground source heat pumps.

Funded by: Mistra Innovation

Time period: January 2020 – December 2023

Project partners:

KTH Energy Technology

Solhybrid i Småland AB

Bengt Dahlgren Stockholm Geo A

MegaWatt Solutions Nordic AB

Background

The combination of solar PV/thermal collectors and ground source heat pumps are a scalable sustainable energy alternative for not only Swedish Multi-family houses and micro-districts, but also other European residential districts.

A promising pathway to the electrification and decarbonization of buildings are solar heat pumps (SHP). There a numerous methods for combining the two technologies, however, one increasingly interesting approach is the integration of photovoltaic/thermal hybrid collectors (PVT) with ground source heat pumps (GSHP). The benefits from this approach are:

  • dramatic reduction of the amount of land needed for boreholes in new systems,
  • recovery of degraded boreholes without the need for additional drilling,
  • high thermal production from PVT due to the low temperatures in a borehole circuit,
  • seasonal storage of solar heat from summer to winter,
  • greater electricity production from PV also due to the low temperatures, and
  • lower costs than traditional solar thermal designs.

Recent cost reductions have dramatically increased the solar PV market in Sweden, but PVT collectors have virtually no market share in comparison in part because the PVT+GSHP concept is at a very early stage of commercialization. This project is motivated by the potential for smart solar hybrid concepts to scale and decarbonize the building sector in Sweden and Europe. Its foundation stems primarily from two previously completed projects – the small Mistra Innovation project “Sunhybrid” (number MI15.18) led by Solhybrid i Småland and the Effsys Expand research project “Ground Source Heat Pumps for Swedish Multi-Family Houses: Innovative Co-Generation and Thermal Storage Strategies[A1]” (number 40936-1) led by KTH.

Aim and Objectives

The overall objective of this project is to advance in the development of an integrated heating, cooling, and electricity system solution for European buildings using solar PVT technology and ground source heat pumps. The project focuses on component, system, and business development and optimization.

The project aims at investigating the methods and strategies to reduce both operational and capital cost of the system as well as increasing the system efficiency. A system pilot will be constructed and monitored with sustainable business models developed for diverse applications in domestic and export markets.

At a component level, the goal is to further develop a PVT module specifically for heat pump integration that improves thermal efficiency while reducing production costs. At a system level, the goal is to validate and optimize the PVT heat pump concept in an expanded range of applications and markets. At a business level, the project aims to create the necessary business models for deploying PVT collectors and PVT heat pump systems considering supply chains, component certification, systems integration, and installer qualifications.

Outcomes

The first part of the project focused on identifying and modeling novel PVT collector designs that increase surface area contact between the working fluid, PV module, and air using computational fluid dynamics, to identify optimal flow distribution patterns and heat flux potential. The influence of materials (i.e. metals vs polymers) on heat transfer was also tested with special consideration for manufacturing techniques and cost-effectiveness. From a techno-economic perspective, it arises that the optimal design is a function of the system's goals. An aluminum corrugated or box channel design with 20 or 30-mm fins is recommended to maximize thermal output. Conversely, to maximize energy per cost of material, a corrugated polycarbonate design without fins or forced convection proves to be the best alternative due to a 50% higher energy-to-cost ratio, despite a potentially lower thermal energy yield compared to its metallic counterparts.

The second part of the project included testing and benchmarking of different commercially available PVT collectors to identify optimal design features for ground source heat pump integration, alongside assessing a PVT collector prototype. The tests were conducted at a newly built outdoor testing facility at KTH, to validate the main findings from the numerical modeling work and inform new PVT models for systems simulation. The results show that a box-channel aluminum design with 20 mm fins is recommended for integration with ground source heat pump systems. It has a high annual thermal energy output and does so with good material efficiency at a thermal unit cost that is marginally higher than a reference sheet and tube PVT.

Smart Solar Hybrid Solutions for Sustainable European Buildings - 1

The final part of the project consisted of applying the different PVT collector designs in holistic optimizations. The simulations, made in TRNSYS, were dynamic and included all components in the system. Of the considered designs, the Box-channel Aluminum collector with 20 mm fins (BC-AL-20) is the recommended one when it comes to series/regenerative integration with ground source heat pumps, which confirms the conclusions of the first two parts of the project. On the technical aspect, it combines a high zero-loss efficiency, which allows it to capture more of the incoming solar irradiation, with a high U-value, that enhances heat capture from the air during times of low solar irradiation. On the economic aspect, it is on par with the sheet and tube (S&T) design with the lowest TLCC. It is also found that PVT collectors have a much higher potential in systems with degraded or undersized borehole fields than in new systems with a properly sized borehole field.

Smart Solar Hybrid Solutions for Sustainable European Buildings - 02

Academic Publications

Journal Articles

Beltrán, F., Sommerfeldt, N., Reichl, C., Madani, H. 2023. Techno-economic analysis of photovoltaic/thermal collector designs for integration with ground source heat pump systems. Under review at Solar Energy, 2023

F. Beltran, N. Sommerfeldt, J. Eskola, and H. Madani, Empirical investigation of solar photovoltaic-thermal collectors for heat pump integration. Under Review at Applied Thermal Engineering, 2023.

C. Pourier, F. Beltran, N. Sommerfeldt, “Solar photovoltaic/thermal (PVT) technology collectors and free cooling in ground source heat pump systems” Solar Energy Advances, Volume 4, 2024, 100050, ISSN 2667-1131

Conference Articles

Sommerfeldt, N., Beltran, F., Madani, H. 2020. Solar PVT for heat pumps: Collector development, systems integration, market potential, BuildSIM-Nordic, Oslo, Oct 13-14.

Sommerfeldt, N., Beltran, F., Madani, H. 2020. High Market Potential Applications for PVT with Heat Pumps. Eurosun 2020, Athens, Greece, Sept. 01-03.

Beltrán, F., Sommerfeldt, N., Madani, H. 2022. Empirical validation of low-temperature PVT collector for heat pump integration. EuroSun 2022, Kassel, Germany, Sept. 25-29.

Beltrán, F., Sommerfeldt, N., Madani, H. 2023. Experimental testing of solar photovoltaic/thermal collector as a heat pump source under outdoor laboratory conditions. IEA Heat Pump Conference 2023, Chicago, USA, May 15-18.

Master Theses

Ebrahim, M. (2021). Performance Evaluation of a Photovoltaic/Thermal (PVT) Collector with Numerical Modelling.

Olausson, H., & Wernius, E. (2021). Development of a Simulation Model for Combined PVT and Ground Source Heat Pump Systems : A TRNSYS Model Created for Commercial Use.

Courcault, M. (2023). Technical performance modelling and optimization of PVT collectors in ground source heat pump integration.

Dijak, D., & Torstensson, E. (2023). Solar photovoltaic-thermal collectors and ground source heat pumps for commercial buildings: Case study in Sweden.

Eskola, J. (2023). Experimental testing of solar photovoltaic-thermal collectors for low-temperature heat pump integration.

Pourier, C. (2023). Solar photovoltaic/thermal technology collectors and free cooling in ground source heat pump systems.

Project contact persons

Sustainable Geothermal Energy for the Future: AI in ATES
Warm water systems, losses and Legionella
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
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)
Towards Sustainable (Fossil-free) Heating System in Small Residential Buildings
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
Building heating solutions in China
Accelerating innovation in buildings
High-Resolution GIS District Heating Source-Load Mapping
Digitalization and IoT technologies for Heat Pump systems
Sustainable combined systems for heating of buildings (completed)
Cost- and Energy-Efficient Control Systems for Buildings
Situation of Opportunity in the Growth and Change of three Stockholm City Districts (completed)
Wuxi Sino-Swedish Eco-City Project (completed)
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
Magnetic Refrigeration
High-Resolution GIS District Heating Source-Load Mapping
Smart Solar Hybrid Solutions for Sustainable European Buildings (completed)
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
Integrating Latent Heat Storage into Residential Heating Systems
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
Building heating solutions in China
Toward Sustainable (Fossil-free) Heating System in Small Residential Buildings
Renewable Energy Park, RE-Park (completed)
Efficient use of energy wells for heat pumps (completed)
Efficient design of geothermal heating systems (completed)
SPF (completed)