Dr. Michel Haller

The "GreenHub" project is one of a total of eight large-scale flagship projects of the Swiss Innovation Agency (Innosuisse). Together with 16 research partners, the consortium led by OST is pursuing a clear goal: the development of systemic and innovative approaches for the production, conversion and storage of renewable energy into environmentally friendly liquid fuels using raw materials supplied, for example, by waste incineration plants.

Due to the necessary decarbonization of the heat supply, heat pumps are becoming increasingly important for domestic hot water preparation. However, the relatively high requirements for hot water preparation and distribution temperatures for hygiene reasons often cannot be met with current heat pump concepts without the additional use of electric immersion heaters, and the system efficiency of the heat pump and storage tank combination often falls well short of the technical possibilities in the field. This project compares different concepts for hot water preparation with heat pumps in multi-family houses. The focus is on hygiene requirements and efficiency. The aim is to develop and investigate new approaches to achieve significantly higher efficiency in apartment buildings with hot water circulation. Only natural refrigerants are to be used. The project is co-financed by the Swiss Federal Office of Energy (SFOE) and involves the Institute of Energy Systems (IES) at the OST, Lucerne University of Applied Sciences and Arts (HSLU) and various industrial partners.

What options are there for implementing well-integrated solar systems that are also suitable for listed buildings (special architecture or historic interest)? What technologies are available for this, what do they cost compared to "ordinary" solar energy systems, and do they deliver the same yield? These questions were investigated by SPF on behalf of the Office for Energy and Transport of the Canton of Graubünden. As a result, a catalog of available solar technologies was published, which is also made available online here (in German).

In this applied Research Project the SPF Institute for Solar Technology carried out a feasibility study for the storage of solar energy in an aluminum redox cycle. Alumina (aluminum oxide) can be converted to elementary aluminum with an electrolysis smelter process that consumes electricity from solar or other renewable sources, and this elementary aluminum can then be transported to the point of use where it is used for the production of heat and electricity in buildings or industrial processes.

A combination of measurements from seven field systems and simulations of systems with large thermal storage tanks was used in order to derive rules for the extrapolation of design rules that lead to good thermal stratification from small (800 l) sized tanks to large (up to 200 m³) tank sizes. In addition, a deflection relation was defined that allows for the prediction of the preservation of existing stratification depending on the distance to the next obstacle in the storage tank, when fluid is entering vertically or via an elbow pipe in the direction of the storage tank cover.

The installation of heat traps is state of the art for pipes that are connected to thermal energy storage units but that are not permanently operated, i.e. the fluid in the pipe is not flowing continuously. In this project, the SPF investigates on issues that created uncertainty within the planning and installation community, such as the question of the significance and effect of insulation in the region of the actual heat trap.

Thermal storage systems are increasingly being used to balance the production and demand for heat or cold. In combination with renewable energy systems such as heat pumps or solar heat, the temperature stratification of the thermal storage is a decisive factor for the efficiency of the systems. But also in combination with biomass heating plants, the advantages of good thermal stratification are great, since stratification achieves more constant supply temperatures to the network and more storage capacity can be used with the same storage volume, thus reducing the cycling of the heat generators. Inflow geometries play a special role here, both for the loading and unloading of water reservoirs. In the projects DiffStrat and DiffStrat 2, different inflow geometries were investigated for their stratifying effect, both by measurements in the test bench and, building upon these results, also by CFD simulations.

Solar assisted district heating networks are booming in Denmark and are also progressing in Austria, Germany and Sweden. With these large solar thermal systems, low heat production cost below 5 Rp/kWh are reached. In this project, SPF supports district heating operators to find possibilities for the integration of solar heat in their network and analyses how large solar thermal installations can be optimally integrated in biomass heating networks in the Swiss context.

A solar-ice heating system was designed and installed as part of a pilot and demonstration project. Since 2017, the heating system is supplying a residential and commercial building of 2050 m² of energy reference area with space heating and hot water. The main components of the heating system are 120 m² of unglazed, spectrally selective solar collectors, an ice storage tank with 210 m³ volume, and a two-stage brine-to-water heat pump with 45 kW thermal output (B0/W35). The heat exchangers in the ice storage tank are periodically de-iced in winter and could therefore be designed with a small transfer area.

Renewable Metal Fuels (ReMeF) are seasonal energy carriers which are able to enhance the energy security. We investigate the contribution that ReMeF can make as combined heat and power elements of the building stock a) to cover the local demand for electricity and heat and b) to feed electricity into the grid to support the energy system. In focus are metals as winter-energy suppliers based on their availability, cost, and chemical properties, which potentially can achieve greenhouse gas savings compared to import-options or natural gas based systems. PeakMetal is co-funded by the Swiss Federal Office of Energy (SFOE), and lasts from December 2022 to December 2023.

Thermal stratification is an important parameter in the energy evaluation of storage tanks. The electrical energy consumption in a heat pump system can be up to 40 % lower with a well stratified storage tank than with a poorly stratified thermal energy storage.

In the StorEx project, SPF introduced stratification efficiency as a key performance indicator and at the same time a method for measuring it, which has already become established in Switzerland.

An alternative to this is the measurement of the storage tank according to the EN 12977-3 standard with a subsequent simulation with a calibrated model.

In order for the «thermal stratification» to become a generally, or internationally, recognized characteristic value for thermal storage tanks with a clearly defined measurement procedure, it is important that these two procedures are investigated in a comparative measurement. This is the aim of this project.

SPF has the technical lead in the EU Horizon Europe project reveal. Within this project, a seasonal energy storage cycle is developed that is based on the oxidation and reduction of aluminum as an energy carrier. The main responsibilities of SPF, besides the technical lead, is the development of technologies for Alu-to-Energy conversion: the conversion of energy that is stored chemically within the aluminium into heat and power. This development is in close collaboration with the institute UMTEC of OST. REVEAL is co-funded by the European Unions Horizon Europe Programme and Swiss State Secretariate for Education, Research and Innovation (SERI), and lasts from July 2022 to June 2026.

SPF has analyzed in more detail the options for self-consumption of photovoltaic electricity for water heating and prepared a fact sheet for EnergieSchweiz. It has been shown that self-consumption through hot water production via heat pumps can be useful by making appropriate adjustments to the running times of the heat pumps. However, the use of electric heating rods to increase self-consumption must be discouraged, because this is extremely inefficient compared to the heat pump and thus leads not only to efficiency losses and waste of electricity, but also to financial losses.

Within this project the potential of large thermal energy storages to facilitate the decarbonisation and simultaneous expansion of thermal networks are analysed. Different techniques of short-, medium- and long-term heat storage are considered. The focus is on the replacement of fossil peak load, the increased integration of waste heat, the shift of energy from summer to winter, and innovative approaches of sector coupling to balance production and demand of electricity.

The analyses are carried out on the one hand using representative generic thermal networks, and on the other hand for specific case studies of the participating industrial partners. In this way, generally valid results can be achieved, as well as a high probability to induce real pilot and demonstration projects.

The seasonal storage of heat in 100 % solar thermal heated single and multifamily buildings has been implemented in a number of projects in Switzerland. The first multifamily building with seasonal thermal energy storage that uses a combination of PV and heat pump instead of a solar thermal system is currently being built in Benzenschwil (AG/CH). In this project, concepts with solar thermal, solar electrical and combined solutions for 100% solar heating are compared, wherefore the entire lifecycle (LCA) of the different system is considered.

Geothermal heat pumps are efficient heating systems and therefore they can provide a substantial contribution to the reduction of CO2 emissions of the Swiss building park. In reverse operation mode, they can also cover the increasing cooling demand of buildings. However, the SIA 180 standard asks for passive measures to prevent overheating of buildings, even though active cooling could be covered by large extents with pv-electricity. In this project we analyze, under which conditions active cooling is energetically and economically beneficial, assuming elevated borehole regeneration fractions under consideration of entire districts.

The storage of larger amounts of renewable energy over longer periods of time can be considered one of the last unsolved problems of the energy transition. In the HePostAl and HybridStock projects, it was shown that aluminium enables the seasonal storage of renewable energy by means of a redox cycle and that the annual demand for electricity and heat of a double detached house can be covered with approx. one cubic metre of aluminium. In principle, both primary aluminium from aluminium smelting and aluminium from recycled material streams can be used for the production of heat and electricity. In this project, the effects of the choice of material on energy use, the quality of the reaction products and their market value as well as the ecological life cycle assessment (LCA) are investigated.

In the project HpCosy the basics for a decentralized brine-water heat pump system for flats in

multi-family houses will be developed and investigated. This "Comfort System" includes the functions heating, cooling and domestic hot water preparation, whereby the latter can optionally be controlled with the consideration of availability of own photovoltaic electricity as an individual system or in a swarm (cooperation for self-consumption).

The project is being carried out on behalf of the Swiss Federal Office of Energy and in collaboration with other partners from industry and research.

Reducing heat losses from existing residential buildings by refurbishing the building envelope is an important step to reduce the heating demand of buildings. In the EU project PLURAL, prefabricated façade modules are being developed and tested, which enable novel possibilities for energy generation, heat/cold supply and ventilation with the façade. The prefabrication of the façade modules is intended to enable rapid and cost-effective refurbishment in an inhabited state. Three field installations will be used to demonstrate renovations in different European climates. Simulations will be used to analyse components and buildings, and a Big Data management platform and decision-making tool for component selection and integration will be developed.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 958218.

The SolResHC project addresses research questions related to IEA PVPS Task 16 regarding "Solar Resource for High Penetration and Large Scale Applications".

Specifically, impacts of different weather scenarios on solar heating and cooling are assessed. Simulations for various future scenarios are carried out to determine the impact of weather data on the energy efficiency of different systems providing heating, cooling, domestic hot water and partly electricity for a multi-family house.

Furthermore, the influence of large feed-in from PV and other renewable energies to the electricity grid in Switzerland is analysed with a particular focus on the electricity price.

In SolSimCC, the effects of climate change and user behaviour on the profitability of solar energy systems (photovoltaics and solar thermal) were investigated. The results show only a minor influence of climate change on the profitability of solar plants. However, two changes significantly increase the profitability of solar thermal systems: firstly, the replacement of natural gas with more expensive biogas or syngas, and secondly, the adoption of more realistic heat consumption profiles instead of the idealised profiles often used in simulations today.

Minergie 2017 and MukEn 2014 define framework conditions that lead to more solar collectors being installed or not. The project will clarify which factors are decisive for the choice and use of solar collectors. Based on the existing standards, fundamentals and tools are to be improved so that an increased use of solar heat can take place.

In the VenTSol project, the behaviour of residents with regard to window ventilation, shading and room temperature will be investigated by detailed monitoring of five apartment buildings. This study should help to create detailed user profiles, which can be used for simulations and energy calculations. User behaviour is compared to the prevailing external climate, internal climate and energy consumption. The project should contribute to a better understanding of the so-called «UserGap».

In the SFOE project ImmoGap it was found that the choice of the method for weather correction of the energy monitoring data can have a strong influence on the determination of the performance gap. For this reason, a literature study on different weather correction methods was done for the SFOE and further research needs were identified. The literature study shows that the current situation regarding the weather correction of energy monitoring data is not satisfying.

SPF has carried out three projects from 2017 – 2020 on the topic of Legionella in hot water systems. In the LegioSafe project (2018), a literature study was conducted on legionella, temperatures in drinking water systems, and the occurrence of legionella in systems with solar thermal water heating. In 2019, a field study was conducted including 110 buildings in «LegioSafeCheck». More than 300 shower water samples and over 100 samples from the lower area of heat water tanks were taken and analysed for Legionella. One year later, in the project LegioSafePlus, exclusively buildings in which legionella > 1000 CFU/L were found in at least one shower water sample in 2019 were further monitored and re-sampled. The results were made available for the standardisation work of SIA 385/1:2020 and are described in three final reports. Results of both field studies were summarised in an article published in «hk gebäudetechik». Due to installation deficiencies identified in the field, a leaflet on the correct combination of hot water circulation and central cold water admixture was produced with the help of suissetec, GKS and Swissolar as well as EnergieSchweiz.

Fully solar heated single and multifamily houses are already technically feasible. The seasonal storage in these systems is associated with corresponding investment cost and demand for storage volume. This project analyses whether cost and used storage volume can be reduced with the combination of solar thermal with a PV driven heat pump system. Therefore, an existing system will be monitored and new innovative concepts are simulated and optimized. The project is carried out in collaboration with Lucerne University of Applied Sciences (HSLU) and Jenni Energietechnik AG.

Seasonal energy storage is one of the largest challenges of the energy turnaround. In the project HybridStock, the seasonal storage of renewable energy in aluminium is investigated. At times of high availability of electricity from renewable sources, this energy is converted to chemical energy and stored in elementary aluminium. In winter, chemical energy from the oxidation reaction of aluminium is used to produce heat and electricity.

In this project the concept which was the subject of the feasibility study HePoStAl is further pursued through laboratory work and the construction of prototypes.

Requirements and possible sites in Switzerland

The Drake Landing Solar Community has raised worldwide attention, when covering 100% of space heat for an entire quarter of single family houses with a concept of solar thermal collectors and a central borehole storage. In this project it was analyzed weather a similar concept can be realized in Switzerland. Therefore the legal conditions were summarized and the economic requirements were evaluated. A GIS based analyze shows, which locatios are specially suited for such a concept based on solar irradiation and geological conditions.

This pilot and demonstration project shows new ways for the cost-efficient renovation of multifamily houses to «nearly zero energy» buildings. The core components are multifunctional facade elements which, in addition to thermal insulation and windows with integrated comfort ventilation, contain both power generation with photovoltaics and the distribution of space heating. In a first phase of the project, the building physics fundamentals are analyzed and the feasibility is demonstrated with a prototype and simulations. In a second phase, a multifamily building in Bern will be renovated with this new concept.

Studies on individual room control and the so-called self-regulating effect (ErrEnEff project) were extended from single-family houses to multi-family houses. Three different room temperature control variants were evaluated and compared in terms of final energy demand, living comfort and economic efficiency. For this purpose, a reference building that corresponds to an average Swiss apartment building, was designed in IDA ICE. Parallel to the room control, the differing heat demand of apartments at the top and on the ground floor compared to apartments in the middle was also investigated for the case that they have identical or differing room temperature set points.

OpEEr is supported by the Swiss Federal Office of Energy (SFOE).

For the new building of Oblamatik AG in Chur, a heating and cooling concept that is unique in Switzerland was developed. Using the foundation slab as a heat sink and heat source represents an alternative to the current heating systems for office buildings. The regeneration of the foundation slab in winter as well as in summer is mainly guaranteed by PVT collectors. The HVAC concept is designed to use as much of the internal heat (servers, commercial refrigeration, etc.) as possible directly for heating purposes.

This project analyses multifamily homes that show a large gap between the predicted and the achieved energy performance, and determines the cause for these performance gaps. The combined effects of user behavior and the building technology and control are analyzed. From this analysis, options for action for planers and pubic authorities are deduced.

ImmoGap is supported by the Swiss Federal Office of Energy (SFOE).

Solar assisted district heating is widely used in countries as Austria, Germany and Sweden and is booming in Denmark. Heat production costs below 0.05 CHF/kWh where recently reached. With this feasibility study district heating networks of the canton of St. Gallen are analyzed in terms of the feasibility and the cost-benefit ratio of an integration of large solar thermal collector field. A further goal is to make contact between collector manufacturers and network operators as well as to initiate the realization of several large collector fields.

SWSG is supported by the canton of St.Gallen and the Swiss Federal Office of Energy (SFOE).

In this P&D-project a highly efficient heat supply for residential buildings in Obfelden was realized with new technologies. The combination of a low-lift heat pump with a deep membrane geothermal probe and a new type of control of the heating distribution system enables efficient heating in winter and cooling in summer with the lowest electrical energy consumption. The evaluation of several years shows how important monitoring and operation optimization are to realize efficient systems in the field. In addition to many valuable field experiences, the project has shown that a holistic concept can make a significant contribution to the stabilization of the Swiss energy supply.

The stratification efficiency of heat storages has a decisive impact on the energetic efficiency of solar thermal systems as well as of heat pumps. In this project, a representative key figure for stratification efficiency and a cost-efficient test procedure for its determination are developed for combi-storages that provide space heat and domestic hot water. The procedure is applied to combi-storages of different manufacturers, and the results are compared with each other. In addition to this, CFD simulations are carried out for the determination of the impact of direct horizontal storage inlets on the stratification of the storage. Selected stratification experiments are also validated with measurements the laboratory. At the end of the project, recommendations are given for the geometry and maximum volume flow rate at which direct horizontal inlets can be used without disturbing an already existing stratification in the storage.

This project receives funding from the Swiss Federal Office of Energy SFOE.

The EU project MacSheep is coordinated by the Institut für Solartechnik SPF and deals with the development of heating systems which combine solar thermal energy with heat pump technologies. The ambitious goal is to reach a reduction of 25 % of the electric energy use of those systems in comparison to the state of the art of 2011/2012 within the four years of the project.

These research and development activities receive funding from the Seventh Framework Programme of the European Union under grant no. 282825. The project start was in January 2012.

The combination of solar thermal systems with heat pumps is used increasingly for space heating and domestic hot water preparation in the building sector. Both technologies are considered to be key-technologies for the abatement of green house gas emissions. The combination of heat pumps with solar thermal heat increases the system’s efficiency and thus the electricity demand. Possibilities for the combination are versatile, and the question arises under which circumstances it is advantageous to use solar thermal collectors also for providing heat for the evaporator of the heat pump.