Homepage SPF Institute for Solar Technology

A selection of completed SPF projects

Since its establishment in 1981 many projects have benefited from our institutes competence. An overview of our completed projects provides insight into key topics.

Please note that for confidentiality reasons only public projects are displayed. Generally, projects that are carried out for private clients are subject to non-disclosure or confidentiality agreements.

Return to current projects.

BioSolFer – Integration of solar thermal into biomass district heating networks

Source: a energie

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.

SPF contact person

FRESH NRG – Development of a cost-efficient, optimized Fresnel collector

In order to strengthen the status of solar process heat in industry the aim of the EU funded project FRESH NRG (Fresnel for Solar Heat with New Revceiver and Geometry) is to develop and optimize a low cost Fresnel collector with the target of an efficiency of over 50 % at 250 °C. The cost reduction of the collector will be achieved by a first-of-its-kind lean manufacturing system. By optimizing the geometry of the collector and the use of ultra-light mirrors the transport and installation using modular "plug-in" components will be simplified. The SPF tests the optical properties and durability of the collector components and the performance of the absorber tube up to 200 °C. Furthermore, within the framework of the project the newly developed Fresnel collector will be installed in Jordan for heating & cooling and it will be monitored and evaluated by SPF.

SPF contact person

HotSpot – Storage of solar heat at a directly usable temperature level in the ground

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.

SPF contact person

TARO – Low temperature district heating: Energetic optimization based on dynamic simulations

Low temperature district heating networks, in which borehole fields serve as seasonal storage on a low temperature level for efficient decentralized heat pumps, are emulated in dynamic simulations. Based on the analyses of existing networks, means for optimizing the energy efficiency by global regulation strategies or the use of new renewable energy sources will be proposed.

This project receives funding from the Swiss Federal Office of Energy SFOE and is carried out in cooperation with the industry partners Amstein+Waltert AG and Vela Solaris AG.

SPF contact person

Reflex – Glare from reflected sunlight

The are no universal guidelines or thresholds for reflected sunlight in the public space. In this project,  physical parameters for an objective description and quantification of a «discomfort glare» from reflected sunlight are elaborated. Furthermore, the scattered reflection (bidirectional reflectance distribution function, BRDF) of several glass types and other materials of the building envelope is measured in order to generate an extensive database. This database can help to evaluate the «discomfort glare» from solar installations and other surfaces of the building envelope already in the planning phase. New materials or surfaces can be compared with  standard materials of the database in order to  assess their effect concerning glare from reflected sunlight.

SPF contact person

High-Ice – System development for high solar thermal gains with ice storage and heat pump

The objective of the High-Ice project was to investigate a specific concept of a solar thermal and heat pump system with ice storage (solar-ice system). An ice storage design with heat exchangers that can be de-iced was studied. The dependence of the system’s electricity consumption on the sizing of the main components (collector field and ice storage) was analysed by means of simulations with the software TRNSYS. An important additional aim of the study was to analyse the system concept from an environmental and an economic point of view. Further, an elastic heat exchanger plate made of EPDM-rubber that can be de-iced mechanically by inflation, was developed on the laboratory scale.

High-Ice was supported by the Swiss Federal Office of Energy (SFOE).

SPF contact person

StorEx – Theoretical and experimental investigations on the stratification efficiency of heat storages

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.

SPF contact person

EU project MacSheep

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.

More information can be found on the project website.

SOL-HEAP – Combined solar and heat pump systems

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.

SPF is carrying out research in this field in the framework of the IEA-SHC Task 44 in international cooperation with other institutes and the industry. Our main focus is the development and evaluation of new system concepts with the aid of computer simulations and laboratory testing with the well-proven Concise Cycle Test.

SCOOP – Polymers in solar thermal systems

A fast-growing market for solar thermal systems combined with the constantly increasing prices of the relevant commodities urged for a reflection to be made on the existing architecture of solar systems. In this context the polymers, which have been considered of little importance so far, may take on a key role in the future. When speaking of large volumes these particularly cost-effective production methods seem to be posing interesting cost-saving potentials.

SPF is carrying out research in this field within the framework of the IEA-SHC Task 39 in close international cooperation with other research agencies and industry. Our main focus is on designing innovative collectors and carrying out durability tests on the polymers employed.

SPF contact person

Solar thermal cooling

Increasing requirements for building cooling (not only in the summertime) and the consequent overload of electrical networks is turning into a major challenge. In this context solar cooling in general and solar thermal cooling in particular may make for an attractive variant in the reduction of required electrical power.

The SPF institute is actively engaged in this field and contributes to development within the framework of the IEA SHC Task 38 «Solar Air Conditioning and Refrigeration». A technology involving the release of heat in a hybrid cooler can be used as an alternative to open cooling towers in the medium-temperature range. It is being tested and improved with the 10 kW LiBr-H2O STATC laboratory system. System simulations with Polysun 5 are validated with measurement results.

Performance analysis and improvement of a combined pellet-solar system for heating and hot water production

Both pellet heating systems and solar thermal systems are undergoing a current surgence in growth. The goal of this project is the energetic improvement of systems combining pellet boilers and solar systems. Pellet and solar heating systems are combined on our test rigs and specifically tested under realistic operating conditions for operation and efficiency. The 12-day test procedure employed in this context is a procedure developed by SPF that is able to cover the conditions (atmospheric conditions, hot water requirements, building load, etc.) typically occurring over a year. With the help of the recorded data we validated a simulation model that is later used to work out yearly sums.

Solar thermal treatment of drinking water in emerging and developing countries

1.8 million people die every year from diarrhoeal diseases; 90 % of them are children aged under 5 years. This is due to a lack of sanitary facilities, hygiene and, to a great extent, the consumption of contaminated water. The goal of this project is to develop drinking water treatment methods able to provide an added value with respect to existing technologies and therefore significantly contribute to improve the quality of drinking water in emerging and developing countries. A preliminary study allowed the identification of potential for solar thermal drinking water treatment at a small-scale municipal level (between 100 and 1000 litres a day).

At SPF work is currently focussing on the technical development of a solar water pasteurization system that is able to treat the largest possible amount of water with the lowest possible investment costs. The microbiological principles affecting the system design were identified within the framework of a sub-project carried out in partnership with EAWAG.

Have a look at the Factsheet for further information:

Investigation and evaluation of adjusted solutions for hot water supply

This research project is intended to work out the theoretical and experimental principles for a systematic comparison of domestic hot water modules (DHWM). At present the market offers a wide range of models with different performance indications that differ in the way they work and their efficiency and yet are able to provide very specific benefits. So far no systematic comparisons were carried out by an independent organisation resulting in the absence of clarity regarding testing parameters, assessment criteria and their evaluation. For this purpose comprehensive investigations were carried out at SPF on different performance parameters and their impact on problem areas such as power, comfort or energy efficiency. A representative number of different modules were tested and compared at a test rig build up during this project. A final report concerning test procedure and rating parameters can be downloaded here.

A module-test allows manufacturers to account for their products performance and efficiency. Performance parameter measurements and the investigation of their influence should, however, also enable end-customers to compare different modules and select the module that best fits their application.

Developement of an enegy efficient «solar-loading-unit» for large solar thermal installations and a «fresh-water-unit» for high domestic hot water loads in buildings

Large scale heat-exchange units are optimized in a development project in cooperation with the industry partner taconova group AG and another research Partner Zentrum für integrale Gebäudetechnik ZIG der Hochschule Luzern. Innovative «solar exchanger stations» for collector fields up to 400 m² and new domestic hot water exchanger station for tapping rates of up to 200 l/min are tuned for an optimal co-working in large solar thermal installations.  SPF institute supports the industry partner with by the development and  implementation of novel control strategies for the "solar exchanger stations" based on dynamic annual simulations. Both units are experimentally tested and analyzed at a test rig in the ZIG institute and supervised in monitored field Installations.

Improved calculation models for gas and oil burners

The incorporation of gas and oil burners into a solar system is a key issue. This project is intended to analyse how such components may be integrated appropriately. For this purpose a number of systems available on the market were set up and tested on the test rig. Measurement results clearly indicate how efficiently a system works or where improvement potentials are to be found. Aside from the measurements, evaluations and improvements, the project also yielded improved calculation models for simulation that may be used in Polysun.

These new improved calculation models allow for interaction between solar energy and auxiliary heating in a combined solar thermal system to be improved through simulation as early as in the development stage.

20 year atmospheric exposure test on collector materials

Long-term stability predictions based on laboratory tests are one thing; aging behaviours in actual operation are often quite another. To prevent such discrepancies, between 1985 and 2007 SPF carried out a project involving the atmospheric exposure of materials potentially used for collector covering purposes.

Forty-two different translucent plastic materials and 16 glass materials were selected for this project. To achieve realistic conditions these materials were installed on so-called mini-collectors and exposed at two Swiss locations with different climatic conditions. Complete series were taken from a total of 700 samples prepared according to a fixed schedule, optionally cleaned according to a defined procedure; any changes in their optical properties were measured and recorded.

Thanks to this, SPF can now rely on a unique fund of reference materials, e.g. for the development of accelerated aging methods. Evaluations carried out so far on the available data have often yielded surprising results.

Simulation of innovative tank concepts for solar combi systems

This project resulted in the generation of a simulation environment for a strongly simplified (maximum lean) solar combi system. Computer simulations carried out within the project were intended to acquire knowledge on the thermal behaviour of this system as well as on the possible effects of different control strategies; in particular on the thermal tank. The system’s distinctive feature consists of a unique combination of an unpressurized tank and the solar loop’s drainback technology as well as the heating loop’s control strategy. The objective was to obtain an appropriate sizing of the system and for that reason cost functions were calculated based on collector size and tank capacity.

Based on such cost functions no system configurations revealed any financial benefit with respect to non-solar systems. Therefore, a new objective function was defined according to the cost/benefit ratio and minimized by means of the GenOpt optimisation software.

Compact solar combi-systems on the test rig

Compact, extensively standardized, factory-made systems are increasingly being used for solar space heating and water heating purposes in single family homes. This trend promises to reduce costs and improve functionality. To check this on the test rig a new test method, the Concise Cycle Test (CCT) was developed within the framework of the Task 26 of the IEA’s Solar Heating & Cooling Programme. This method is based on two principles: first the marginal conditions of climate and load occurring during one year are summarized within a 12-day test cycle; secondly, the system is not interfered with by measurements.

A large number of compact solar combi-systems were tested at the SPF institute within the framework of a multi-year study titled «Kombi-Kompakt+». The study was completed with the publication of the related test reports.

Heat losses through in-pipe counter-current circulation

Hot water tanks show a particularly high heat loss at pipe connections. They should be regarded as thermal bridges in which heat losses occur due to convection and thermal conduction. Although the issue of high tank connection losses has been known to experts since the 1980s, this subject has been extensively ignored, at least in Europe, by manufacturers and installers. No systematic studies or well-established recommendations are available to date on the configuration of tank nozzles and connection lines. Only empirical values and rules are currently available as to the use of siphons, convection brakes and convection barriers. No principles are known for empirical rules.

The results of this project should serve as the basis of a reduction in tank heat losses:

New storage concepts for solar and low-energy buildings

To bridge gaps due to low radiation days and cover any thermal energy requirements this research work focuses on the theoretical and experimental investigation of new tank technologies for thermal energy storage in heating and cooling systems for solar and low-energy houses. Such activities aim to develop new storage systems for solar thermal systems that are able to provide buildings with a high solar fraction. At SPF we develop decision-making principles for the use of these new storage technologies not only in heating and cooling systems but also for heat pumps and boilers.

Within this context our focus is on the use of solar energy and on providing free-standing one-family houses and apartment blocks with appropriately sized tanks that are able to cover the required heating and cooling requirements. Conventional storage systems use thermally insulated water tanks with a volume ranging from 400 to 1000 litres.

The investigations we carried out within the framework of the IEA SHC Task 32 lead the way in the implementation of new storage concepts with higher efficiency and storage density.

Solar thermal driven thermo-chemical accumulator

Such that a solar-thermal driven cooling system may be appropriately dimensioned, the refrigerating machine’s coefficient of performance (COP) under load must be known in dependency on the collector, in the heat release system and the evaporator fluid temperatures. Besides the operating behaviour of the ClimateWell thermo-chemical accumulator (prototype), the COP at different cooling performances was determined from measurements and suggestions were discussed as to how to improve the machine.

The special measurements were carried out at the SPF institute on specially-adjusted laboratory system test rigs.

EINSTEIN goes Swiss: industry audits and solar heat simulation for process heat

The joint European project EINSTEIN is currently focussing on the development of an expert system working towards the improvement of energy consumption in industry processes. EINSTEIN is based on a database containing detailed information and data on a variety of industrial processes. These data were obtained through exhaustive audits carried out in 90 companies from 6 different countries by experts specially trained for this task and later incorporated into the expert system.

«EINSTEIN goes Swiss» provides the Swiss industry with an opportunity to benefit from the development and validation of EINSTEIN as well as from further opportunities and chances associated with EINSTEIN. For this purpose, SPF is currently carrying out 10 industry audits within Swiss companies and providing consultancy on subjects such as process improvement, efficiency enhancement through heat recovery and the integration of renewable energies.

Regarding in particular the incorporation of solar-energy, a method based on annual simulations is currently being developed within the framework of «EINSTEIN goes Swiss»; based on process data and information on location, etc. this method is able to define the amount of heat that may be incorporated into the process through solar-thermal technology. The technical implementation is carried out by means of a Polysun-based plug-in for the expert system.

SimPel: development of methods for the determination of the annual average efficiency of small-scale biomass boilers

The goal of this project is to develop a method for the determination of the annual average efficiency of small-scale biomass boilers. To this end an application-specific boiler model was parametrized and validated on the simulation software TRNSYS. The required measurement data were acquired through cooperation with Austrian partners. Marginal conditions (such as location, building type, heating load) defined together with our partners were later employed at SPF to carry out appropriate annual simulations aimed at determining the annual average efficiency. The newly developed method should promote the quality and efficiency of small-scale biomass boilers internationally.

Flow investigations on immersed heat exchangers

The choice of the correct construction and dimensioning parameters for immersed heat exchangers plays a key role in the charging and discharging of hot water tanks. The varying conditions associated with a charging via solar collector (volume flows, temperatures) have so far led to the use of semi-empirical functions for construction and design. Such empirical values may however only be relevant for dimensions and designs of hot water tanks that have in the meantime undergone further development. The new and powerful methods of Particle Imaging Velocimetry (PIV) and Laser Induced Fluorescence (LIF) allow flow and heat transfer processes occurring in hot water tanks to be imaged in detail here at SPF.

The current research project focuses on the experimental determination of ideal parameters for the construction and dimensioning of immersed heat exchangers. Results will subsequently be used for the validation of numerical models; by means of a CFD (Computational Fluid Dynamics) and transient system simulation (TRNSYS) softwares. Simulation allows construction and dimensioning to be optimized and new empirical formulas for application-dependant dimensioning to be deduced.

To investigate a representative cross-section of conventional heat exchangers a search is carried out for companies willing to provide products. Such companies shall receive detailed results on the performance of their specific test objects and involved in the dissemination process of the project findings.