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Solar energy conversion requires permanent outdoor operation of essential components such as photovoltaic modules, solar collectors, or reflectors. They are exposed to weathering stresses. The stress levels depend on the local climates. Monitoring of climatic properties and sample properties in different climatic zones (alpine, arid, maritime, moderate, and tropical) during several years provided the base for categorization of these climates. The local climate does not differ very much from year to year in terms of frequency distributions, but big differences are found for different regions or climatic zones. Especially, the solar irradiation is very location‐dependent. The alpine location shows the highest UV irradiation. The UV fraction of the solar irradiation is varying between 2.2% (tropics) and 4.7% (alps). The temperature histograms can be modeled by Gaussian distribution functions. The maritime histogram is very slim and high, showing the cooling by the sea and the wind. Several approaches for a categorization of these local climates can be applied: Mean temperatures, effective temperatures, or the corresponding constant testing time for fictive degradation processes with arbitrary activation energy. The categorization of the relative humidity revealed humid climates in the alpine and the tropical test site, when considering the time of wetness (rh > 80%). Obviously, the humidity stress or the corrosivity would be very different at those sites. Therefore, a more holistic approach considering more stress factors simultaneously would be more appropriate for the categorization. The interaction between the samples and the climate creates the so‐called micro‐climate which is the real stress on the samples, such as surface temperature, daily temperature cycles, surface humidity, or temperature‐enhanced photo‐degradation. The conditions for accelerated life testing (ALT) modeled on the base of monitored climatic data and sample temperatures are different for the different locations. They offer another possibility for categorization of the climatic stresses and the option for designing climate‐adapted components.

A design of a box-type solar cooker was modeled and tested in the region of Sfax-Tunisia. This solar cooker was designed to allow reaching relatively high temperatures during days with low solar radiation owing to four outer reflectors. A mathematical model, which is based on thermal balances, was developed and implemented in a Matlab program to predict the thermal performances of the solar cooker. Several tests were effectuated in order to validate the robustness of the mathematical model and to determine the thermal performance of the solar cooker. The obtained results showed an acceptable matching between the experimental temperature values and the computed temperature values with a maximum error inferior to 4%. It was also proven that the use of four outer reflectors improved the optical efficiency of the solar cooker. Indeed, the first figure of merit passed from 0.07 to 0.14 and the maximum temperature of the absorber plate passed from 81.3 °C to 133.6 °C. The sensible loading test revealed that the calculated second figures of merit for different water loads were in the range of 0.34–0.39. Finally, two real cooking process were carried out where 72 min and 107 min were required to fully cook rice and beans respectively.

Based on an analysis of building processes to date, this paper proposes two ways to make Building Information Modelling (BIM) and with it complex building processes less expensive and more reliable. First, existing experience with building processes that include building-integrated solar systems is analysed, as they are one example for buildings with high energy-saving goals. Based on the analysis, the authors propose to include a new property set and functions in machine code in the next version of the Industry Foundation Classes (IFC). For the machine-code functions, several formats are proposed and the advantages and disadvantages of the proposed IFC extensions are discussed. For simple conventional building components, the existing IFC version 4 seems appropriate. Buildings with innovations that add complexity to the building process can profit most by the savings generated by exchanging machine-code functions. In building processes to date, much information is not shared because of proprietary matters. Functions in machine code can provide the necessary confidentiality so that more capabilities can be exchanged between the stakeholders. Models based on machine-code functions can be updated much faster than detailed models with many parameters. With machine-code functions, advantage can be taken of the greater accuracy of detailed models, as long as they are fast and easy to use. The modularity of the functions stimulates competition between alternative approaches, which makes simulation models less expensive. Finally, exchanging a closed, validated simulation model in machine code introduces a much lower risk of error than exporting and importing complex simulation models.

Solar building envelopes are attracting increasing interest. Building-integrated solar thermal (BIST) systems are one of the subgroups of solar building envelopes. This paper summarizes the most important contributions of recent years and extends them. First, BIST elements are defined and available BIST elements are presented. Then, the general functions which BIST systems can provide are presented and the conflict between the constant U and g values of simple planning software and the variable g and U values of BIST elements is discussed. Measurements to characterize BIST elements are presented as well as a design parameter space in which the current BIST elements are located and which can be used when developing innovative new components. Methods to evaluate and compare BIST technologies are presented. The substantial cost savings which were achieved in three building projects between 2002 and 2009 are discussed. Roles within the building process are presented, as well as the general methods and challenges for economic BIST calculations and one economic calculation as an example. Based on existing building processes, a vision for future BIST building process integration is presented. Simple BIST models, which need no programming, are provided with easy-to-use equations. The challenges of standards and regulations are outlined and future research topics are presented. This paper summarizes important recent contributions to BIST research as a basis for future progress in building-integrated solar thermal systems. Instead of aiming to cover all recent BIST developments, the focus is on BIST research findings which are relevant for cost reduction of BIST components and therefore necessary for the economic success of BIST technology. These are discussed, together with proposals for future research.

A photochromic (PC) device comprising an electrochromic film (WO 3 ) together with a photoactive film (usually, dye sensitized TiO 2 ) coated on glass and a redox electrolyte (e.g., iodide/triiodide together with lithium salt) reduces the optical transmission under solar illumination and bleaches, again, in dark or at low intensity of light. This work reports, for first time, on an application of sputter coated TiO 2 and WO 3 films for this type of PC devices. The applicability of TiO 2 and WO 3 films in PC device is individually investigated in dye solar cells and electrochromic cells, respectively. A dye solar cell with 180 nm TiO 2 was shown to be sufficient for the charge generation for electrochromic coloration of the WO 3 . The compatibility of WO 3 and redox electrolyte was studied in electrochromic devices by considering their redox potentials. The bleaching of the PC device has to be adjusted by the so called “loss current”. To address this, a thin catalytic layer of platinum (Pt) is deposited in between the photoactive and electrochromic layers. The optimized PC device exhibits a visual (solar) transmission modulation from 74 (63) down to 30% (20%) in 40 min under 1.5 A.M. illumination, and the bleaching is regained in 45 min in dark.

Building-integrated solar thermal systems (BIST) outperform building-added solar thermal systems (BAST) due to smaller heat losses at the back of the collector. BIST offer economic advantages, too. The insulation behind the collector can be used to reduce the heating demand of the building as well as to increase the solar thermal yield. Therefore, less material and labour are needed. Of course, the energy flux to the building interior needs to be considered. This energy flux depends in general on the operation of the collector as well as on the irradiance. Several innovative solar thermal building skins have been modelled in detail to analyze this coupling between the active building skin and the building. However, planners need an easy approach to include BIST into their calculations. Often, there is not enough budget to measure and model the new facade. This paper presents several new and simple models which are more accurate than neglecting the coupling to the building and which are less complex than detailed physical models.

In the building sector there is a new tendency to integrate solar thermal technologies into buildings. These systems are known as Building-Integrated Solar Thermal (BIST) and offer several advantages in comparison with the Building-Added (BA) installations. The present study is a critical review on modelling of BIST systems and also covers other types of BI solar configurations such as Photovoltaic (PV) and Photovoltaic/Thermal (PVT) in order to provide a better view of the literature. For some instances where the model and/or the system are interesting, BA systems are also cited. The studies are presented into groups, depending on the type of modelling (energetic, thermal, optical, etc.) and based on the technical characteristics of each system (solar collector, skin facade, etc.). The present article is the first part of an investigation about BIST modelling and it gives emphasis on the studies which focus on the interaction between BIST and building (coupled building/system configuration). The study reveals that majority of the modelling are about BIPV and skin facades while there are very few studies on BIST systems. Thereby, more investigations on energetic, thermal, optical simulations for BIST installations particularly for active systems (e.g. active solar thermal collectors) are necessary. On the other hand, innovative ideas such as systems with phase change materials, nanofluids, concentrating solar thermal could also be examined as a future prospect for modelling/simulation. The study also shows that further development of environmental models on BIST systems is required.

As part of the Shagaya Renewable Energy Master Plan in Kuwait, the presented study describes the methodology developed and applied for the optimization of the technology mix for a 2̊GW, 1002km2 renewable energy park. Scenarios with different focuses for the technology mix were developed, selecting from 14 technology options (three wind, five PV and six CSP) and emphasizing either high peak load supply, high overall annual electricity production or low levelized cost of electricity. An optimization procedure that uses a general pattern search algorithm implemented in the software GenOpt was used to maximize a score calculated from eight criteria. These were determined in a social-techno-economic evaluation, which included performance simulations of every technology option for the allocated site in Kuwait. Besides the available land area, the capacity credit of the installed technology mix was included as an additional boundary condition. 2010 was selected as base year since it was the most recent year for which both high quality meteorological and electricity demand data was available. The results for all considered scenarios are presented in this paper, with the one that was chosen as final result of the master plan comprising 136̊MW wind power, 614̊MW of PV and 1250̊MW of CSP. Furthermore, the study showed that thermal storage is indispensable to serve peak demand hours and a diverse technology mix is important to achieve a high capacity credit.

Building-Integrated Solar Thermal (BIST) systems are a new tendency in the building sector and provide multiple advantages in comparison with the Building-Added (BA) installations. The present paper is a critical review about solar system modelling with emphasis on BIST configurations. The review includes also BI solar systems which produce electricity (Photovoltaic: PV) or both electrical/thermal energy (Photovoltaic/Thermal: PVT) in order to provide a more complete view of the current literature. For some cases where the system and/or the model are of great interest, BA configurations are also cited. The references are presented separated into groups, based on the model type (thermal, energetic simulation, etc.) and system characteristics (solar thermal collector, skin facade, etc.). The present review is the 2 nd part of an investigation about BIST modelling and it focuses on modelling studies about the solar system itself. The results reveal that most of the investigations about BI configurations refer to PVT, PV or skin facades while there are few studies about BIST systems. Thus, there is a need for more investigations about BIST installations, especially for active configurations which could provide thermal (or electrical/thermal) energy for building energy requirements. On the other hand, more optical simulations as well as more life-cycle analysis studies about BIST are also necessary. Taking into account the findings of the 1 st part of the present investigation, majority of the BIST modelling studies focus on the system itself; thereby, more investigations which examine the system in conjunction with the building are needed. Moreover, concepts such as BI concentrating solar systems could also be examined provided that the system is viable from technical/economic point of view.

In the process of improving the performance of concentrating solar collectors a variety of reflector materials are undergoing development. To allow comparable performance predictions, precise and replicable measuring methods are needed. In this paper we propose a measurement method and set-up (VLABS: very-low-angle beam spread) to determine the specular reflectance for variable angular acceptance. Our measurement set-up and method VLABS is advanced in measurement accuracy and speed, it gives as a result the specular reflectance for variable acceptance angles with an angular resolution of 0.03 mrad. We show exemplary results for a glass and an aluminum reflector and discuss the impact of acceptance angles up to 33 mrad on measured reflectance values at different wavelengths.

In the German national research and development project “HeizSolar” the building concept of Solar-Active-Housesis analyzed. The concept allows for a high fraction of solar thermal energyof more than 50% of the total heat supply. Within the project nine existing buildings have been monitored since the beginning of the heating period of 2011. The technology applied for this kind of supply concept has been introduced in [1,2]. Based on the data obtained from the in-situ monitoring, typical operation conditions have been identified and analyzed in [3]. The measured datawas also used to derive parameters to calibratea dynamic system simulation model for Solar-Active-Houses[4]. Theelaborated model focuses on the performance of the solar thermal collector as well as the solar circuit. What is more, the dynamic interaction between the solar thermal heat generator and the auxiliary heating systems as well as the heat distribution system are incorporated in detail. Finally the diffuse heat flux resulting of the integration of large hot water storage tanks into the building envelope is implemented to the model. This model is applied in the following to analyze the general thermal behavior of the supply concept and to derive optimization potentials. In detail the systems performance in regard to different types of heat transferal systems for space heating is demonstrated. Also the dimensioning in regard to the key parameters of collector area and the thermal capacity of the storage system consisting of a hot water storage tankare stated.

The paper presents investigations on the process performance of different membranes with and without backing structure in direct contact membrane distillation. Influences of backing structures and their orientation are identified. An integrated membrane and backing model was developed. Laminates with different backing designs were examined over a wide range of operating conditions and compared to results for the same membranes without backing. Experimental results and model predictions for flux and thermal efficiency are compared. The model predictions agree well with the experimental results. An influence on the effective area for diffusion, an increase in effective diffusion path length in the membrane and the formation of a complex network of thermal resistances are considered to be the main effects, leading to a significant reduction in process performance due to backing structures. The backing was identified to be one of the key components for further improvement in MD applications. An integrated assessment of membrane properties in combination with backing structures was carried out by analysing membranes with different thicknesses and different pore sizes. The experimental observations show good agreement with theoretical considerations. A combined analysis of specific flux and thermal efficiency leads to comprehensive understanding of the process and its potential for optimisation.

Different approaches have been studied to evaluate the efficiency of the photoactive layer in a photochromic (PC) device. The studied device combines materials typically used in dye-sensitized solar cell (DSSC) and an electrochromic (EC) layer of WO3. First, we examine if the dye could be attached directly to the EC layer forming an efficient photoactive layer to colour the PC device. Further, different TiO2 layers have been coated on the EC layer to enhance dye loading and two different sol-gel TiO2 layers and the post-treatment of the EC layer with a titanium(IV) chloride tetrahydrofuran complex have been studied. The dye loading of different photoactive layers and their efficiencies in DSSC have been evaluated and discussed with regard to the performance of the PC devices. The results confirmed that the dye could be attached to the WO3 layer, but that the voltage of the DSSC is too low to colour the device. To realize a functioning PC device, the addition of TiO2 is necessary. The best performance (deep and fast colouration) is obtained for a PC device with a TiO2 sol-gel layer; the solar transmittance of the PC device decreases from 57% to 7.5% in under three minutes. According to our knowledge, this is the first study of the impact of the photoactive layer on the photochromic glazing's response.

Photovoltaic-thermal PVT collectors generate solar electricity and heat in a single component. The annual electrical and thermal yields depend in particular on the efficiency of the PVT collector technology, climate, and the type of solar thermal system. This paper provides a systematic comparison of the performance of unglazed, glazed, and PVT collectors with low-emissivity coatings. The yields of these PVT technologies are assessed in four types of solar thermal systems including domestic hot water systems and combi systems in single and multi-family homes at four European locations. For this purpose, an empirical PVT performance model is presented, validated and implemented into TRNSYS. Analyzing the simulation results, the assessed PVT collector technologies reach either high electrical or high thermal yields. This compromise originates from the technological trade-off between a good optical efficiency versus a high level of insulation. Thermally optimized glazed PVT collectors with low-emissivity coatings achieve the highest overall yields and the best energetic utilization of the collector area. These collectors achieve up to three times the electrical output compared to a side-by-side installation of flat plate collectors and PV modules with equal thermal output. The variations between the investigated systems can be attributed to the governing operating temperatures of the PVT collector which are found to be of central relevance. A novel approach puts these temperatures into the focus and introduces the characteristic temperature Tchar as new indicator with a strong correlation to both electrical and thermal yields. This approach can be used to assess electrical and thermal yields of PVT systems and select a suitable collector technology for a given application.

A new multi-channel spiral-wound membrane distillation (MD) module with a membrane surface area of 27.5 m 2 was developed, constructed and characterized. For comparison, a set of different conventional single-channel direct contact membrane distillation (DCMD) module prototypes is introduced and experimentally evaluated, as well. Furthermore, a comprehensive assessment on DCMD module design and operation as well as methods for comparative thermodynamic MD module evaluation has been conducted. The methodical core of this work specifically addresses an integrative method for the derivation of the thermal energy demand of DCMD systems, comprising specifications of the external heat recovery system. A new strategy for the optimization of energy demand in DCMD is identified, which aims on the formation of parallel temperature profiles by adjusting the flow streams on the evaporator and the condenser channel. Suitable methods for a comparative analysis of different MD performance results are suggested and fundamental MD specifications are derived and applied to evaluate a set of different DCMD prototypes. The methods involve the analysis of the permeate output rate, flux and thermal energy consumption with respect to feed flow rate conditions. The optimization of flux and thermal energy consumption is identified to rely on conflicting requirements, which cannot be satisfied at the same time. The optimal combination of flux and thermal energy consumption depends on the projected scenario and may not be identified by a technical assessment alone. Economic considerations must be included. As final outcome, a method of specifying MD results by a representation of flux versus thermal energy consumption is suggested in order to allow a meaningful evaluation and to achieve global comparability among different MD configurations and other thermal separation technologies.

The Linear Fresnel Collector (LFC) technology is currently being commercialised by several companies for the application in solar thermal power plants. This study compares the electricity generation costs for LFC and Parabolic Trough Collector (PTC). PTC is the most commercial CSP technology to date and is therefore regarded as the benchmark. For reasons of comparability, direct steam generation is assumed for both LFC and PTC. For the LFC, cost data comparable to typical CSP plant sizes are hardly available. Therefore, the break even cost – referring to aperture-specific collector investment – is determined, where cost-parity of the electricity generation with a PTC reference plant is reached. This study varies the assumptions on collector performance and operation and maintenance costs to reflect different designs of LFC technologies. The calculations were carried out using cost and hourly simulation performance models. Depending on the assumptions, the costs for a linear Fresnel collector solar field should range between 78 and 216 €/m 2 to reach cost-parity at assumed reference solar field costs of 275 €/m 2 for the PTC. The LFC principle of arranging the mirrors horizontally leads to lower aperture-related optical efficiency which must be compensated by lower cost per m 2 of aperture compared to PTC. The LFC is a collector with significant cost reduction potential, mainly due to cheaper mirrors and structural advantages.The presented cost and performance targets shown in this study must be met by LFC technology developers to reach the PTC benchmark.

International audience; Photovoltaic-thermal collectors (or PV-T collector) are hybrid collectors where PV modules are integrated as an absorber of a thermal collector in order to convert solar energy into electricity and usable heat at the same time. In most of the cases, the hybrid collectors are made by the superposition of a PV module on the thermal absorber of a solar collector. In this paper, the approach is different and is to analyze thermal and optical properties related to both PV and solar thermal functions in order to identify an optimum combination leading to a maximum overall efficiency. Indeed, although these two functions do not exploit the same range of radiation wavelengths, thermal and PV functions are not so complementary due to photo-conversion thermal dependency. In this context, an alternative PV cell lamination has been developed with increased optical and thermal performance. The improvements were evaluated around 2 mA/cm2 in terms of current density in comparison to a standard module encapsulation. Based on this technique, a real size PV-T module has been built and tested at Fraunhofer solar test facilities. The results show a global efficiency of the PV-T collector above 87% (79% thermal efficiency plus 8.7% electrical efficiency, based on the absorber area).

Photovoltaic–thermal (PVT) collectors are hybrid collectors which make, in principle, optimal use of the solar resource by co-generating electricity and heat in a single module. Spectrally selective but transparent low-emissivity (low-e) coatings are a suitable measure to reduce thermal losses. In this paper the development of PVT collectors with low-e coatings by means of experiment and simulation is presented. A highly transparent low-e coating based on silver, specifically optimized for the application in PVT collectors, is developed. By combining layers of low-refractive SiO2 and high-refractive TiO2 a low emissivity of ɛ373K = 0.13 is achieved while maintaining high solar transmittance of τAM1.5 = 0.79. This coating is applied in a glazed, flat plate, liquid-type PVT collector. Thermal and electrical performance were tested and compared to a PVT collector with the same design yet without low-e coating. A numerical model of the PVT collector is presented showing good agreement of simulation and experiment. With this model the impact of low-e coatings on thermal and electrical performance is analysed and discussed. The newly developed low-e coating reduces the collector heat losses by 82% while the electrical efficiency drops by only 3%.

The water supply of many countries in the Middle East relies mainly on water desalination. In Qatar, the water network is completely fed with water from desalination plants. One of these power and desalination plants is located in Ras Abu Fontas, 20 km south of the capital Doha. The heat required for thermal desalination is provided by steam which is generated in waste heat recovery boilers (HRB) connected to gas turbines. Additionally, gas fired boilers or auxiliary firing in the HRBs are used in order to decouple the water generation from the electricity generation. In Ras Abu Fontas some auxiliary boilers run 24/7 because the HRB capacity does not match the demand of the desalination units. This paper contains the techno-economic analysis of two large-scale commercial solar field options, which could reduce the fuel consumption significantly. Both options employ parabolic trough technology with a nominal saturated steam output of 350 t/h at 15 bar (198°C, 240 MW). The first option uses direct steam generation without storage while the second relies on common thermal oil in combination with a molten salt thermal storage with 6 hours full-load capacity. The economic benefit of the integration of solar power depends mainly on the cost of the fossil alternative, and thus the price (respectively opportunity costs) of natural gas. At a natural gas price of 8 US-$/MMBtu the internal rate of return on equity (IRR) is expected at about 5%.

The European Union (EU) and the Hashemite Kingdom of Jordan are executing a project “Capacity Building for Wind Energy and Concentrating Solar Power in Jordan – WECSP”, financed by the EU under the ENPI and EuropeAid Program. Beneficiary is the National Energy Research Center NERC, Amman, Jordan. Within this project, testing facilities and pilot plants for both wind energy and concentrating solar power (CSP) will be established at a site owned by NERC. To support NERC, a Technical Assistance (TA) team led by the Fraunhofer Institute for Solar Energy Systems ISE has been contracted. We report on the execution of the TA contract and the resulting implementation of the WECSP project so far, including the legal framework and preparations for CSP installations in Jordan, requirements, grid connection, power purchase and experiences made. The assessment of solar resources at different sites as one main criterion in the site selection process is reported, including the actual resource information for the chosen site at Al Fujeij. The preparation of technical specifications for the CSP tender is reported, containing the CSP pilot plant the CSP test lab equipment. We describe the resulting tender and the evaluation procedure of the six bids that had been received. A supply contract was signed between the owner of the plant NERC and the technology provider Solar Euromed for the supply of a CSP pilot plant of 0.5 MWe capacity based on Linear Fresnel collector technology, the delivery of test equipment and training and capacity building activities. The pilot plant and test lab will be implemented during 2014/2015. Details on the actual status of implementation will be presented elsewhere.

Solar resource assessments use solar radiation data from past observations to estimate the average annual solar radiation over the expected lifetime for a solar energy system. However, solar radiation at the Earth’s surface is not stable over time but undergoes significant long-term variations often referred to as “global dimming and brightening”. This study analyzes the effect of these long-term trends on solar resource assessments. Based on long-term measurement records in Germany, it is found that the additional uncertainty of solar resource assessments caused by long-term trends in solar radiation is about 3% on the horizontal plane and even higher for tilted or tracked planes. These additional uncertainties are not included in most uncertainty calculations for solar resource assessments up to now. Furthermore, for the measurement stations analyzed, the current irradiance level is about 5% above the long-term average of the years 1951–2010. Since the direction of future trends in solar radiation is not known, different possibilities to estimate the future solar resource are compared. In view of long-term trends that could extend beyond the period of past observations and beyond the projected lifetime of a solar energy application, a paradigm shift is proposed: instead of using the longest possible period to calculate an average value, only the 10 most recent years should be used as the estimator for future solar irradiance.

International audience; Photovoltaic-thermal (PVT) hybrid collectors are co-generation components that convert solar energy into both electricity and heat and represent in principle one of the most efficient ways to use solar energy. The aim of the study presented in this paper is to assess the performance of this type of collector as part of a solar thermal system. First of all, the development and the test results of an experimental flat plate PVT collector are described. Then, in the second part, the performance of this hybrid collector being part of a solar thermal system in a building is determined and compared to that of systems operating with standard solar devices (i.e. solar thermal collector and PV panel), through simulations using TRNSYS. Comparisons according to various evaluation criteria were made assuming the same surface area and under the same climatic conditions. The results show that in configuration of limited available space for solar collector area, the use of efficient PVT collectors in the building envelop can be more advantageous than standard PV and solar thermal components, not only from an energetic point of view, but also considering the exergy and the primary energy saving.

New facades of high-rise buildings often include renewable energy converters to allow "green building" operation. At the same time, numerous tenants value visual transparency. Transparent solar thermal collectors (TSTCs) aim at decreasing the non-renewable primary energy demand and increasing the visual transparency at the same time. On the one hand, this paper presents the main modelling challenges that arise when considering building facades and especially integrated TSTC systems. New transient systems simulation (TRNSYS) [Beckman, W. A., L. Broman, A. Fiksel, S. A. Klein, E. Lindberg, M. Schuler, and J. Thornton. 1994. "TRNSYS The Most Complete Solar Energy System Modelling and Simulation Software." Renewable Energy 5 (1-4): 486-488] types have been especially developed for this purpose. A simplified model is presented for comparison purposes. On the other hand, the overall performance for a building with facade-integrated TSTC, as measured by its non-renewable prima ry energy demand, is treated. This is achieved by considering a complete simulation model coupling the TSTC, building and heating, ventilation and air conditioning operation. Possibilities for primary energy savings are investigated using the building mass as additional thermal storage.

The development of small to medium size, autonomous and robust desalination units is needed to establish an independent water supply in remote areas. This is the motivation for research on alternative desalination processes. Membrane distillation (MD) seems to meet the specific requirements very well. This work is focused on experimental studies on full scale demonstration systems, utilizing a parallel multi MD-module setup. Three different plant concepts are introduced, one of them is waste heat driven and two of them are powered by solar thermal collectors. Design parameters and system design are presented. After the analysis of plant operation a comparison among the plants as well as a comparison with laboratory experiments is carried out and discussed. Impact of different feed flow rates, salinities, operating hours and process temperatures are taken into consideration and put into relation. GOR values and specific thermal heat demand are derived and compared. Energy balances of all three plants are given, uncovering heat losses and identifying room for improvement.

A performance model is presented that enables yield predictions of hybrid photovoltaic and thermal (PVT) collectors. It applies for both non-concentrating (PVT) and concentrating (CPVT) systems. The model is based on considerations on energy balance, heat transfer and the dependence of the photovoltaic efficiency on absorber temperature. Similar to the quasi dynamic model for thermal collectors, linear parameterizations of both electrical and thermal power outputs are derived. The respective linear coefficients are obtained from multi-linear regression on solely standard measurement data. The model is applied to measurement data of a CPVT collector to exemplify the procedure and to validate the model. Good agreement of empirically determined collector coefficients with expectations from known parameters is achieved.

This paper deals with the design of a single glazed flat plate Photovoltaic–Thermal (PV–T) solar collector. First, the thermal and electrical performances of several single glazed flat plate PV–T concepts based on water circulation are investigated, using a simple 2D thermal model, then different ways of improvement are presented. It mainly consists in focusing on the heat transfer between PV cells and fluid, and also on the optical properties of materials. Thus, the most appropriate concept configuration has been identified and suitable material properties have been selected. A prototype collector has been designed, built and tested. A high thermal efficiency was reached at zero reduced temperature. For this level of thermal efficiency, the corresponding electrical efficiency has is lower than efficiency of a standard PV panel using the same technology. However, this solar PV–T collector is reaching, in these standard conditions, the highest efficiency level reported in the literature.

Transparent facade collectors can provide solar heating and cooling and lead to primary energy savings even compared to an opaque wall. They can be simulated with a detailed physical model based on laboratory measurements. The demonstration installation in Ljubljana will provide extensive measurement data of transparent facade collectors in an outdoor environment. This allows a comparison with simulations performed with the model validated by laboratory measurements. This paper presents the demonstration installation and the measurement system, which are based on the new modelling abilities and focused on the outdoor validation of such models.

Flexible perovskite based solar cells with power conversion efficiencies of 7% have been prepared on PET based conductive substrates. Extended bending of the devices does not deteriorate their performance demonstrating their suitability for roll to roll processing.