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Abstract: A clear consensus exists in German society that renewable energy resources have to play a dominant role in the future German energy supply system. However, many questions are still under discussion; for instance the relevance of the different technologies such as photovoltaic systems and wind energy converters installed offshore in the North Sea and the Baltic Sea. Concerns also exist about the cost of a future energy system mainly based on renewable energy. In the work presented here we tried to answer some of those questions. Guiding questions for this study were: (1) is it possible to meet the German energy demand with 100% renewable energy, considering the available technical potential of the main renewable energy resources? (2) what is the overall annual cost of such an energy system once it has been implemented? (3) what is the best combination of renewable energy converters, storage units, energy converters and energy-saving measures? In order to answer these questions, we carried out many simulation calculations using REMod-D, a model we developed for this purpose. This model is described in Part I of this publication. To date this model covers only part of the energy system, namely the electricity and heat sectors, which correspond to about 62% of Germany's current energy demand. The main findings of our work indicate that it is possible to meet the total electricity and heat demand (space heating, hot water) of the entire building sector with 100% renewable energy within the given technical limits. This is based on the assumption that the heat demand of the building sector is significantly reduced by at least 60% or more compared to today's demand. Another major result of our analysis shows that – once the transformation of the energy system has been completed – supplying electricity and heat only from renewables is no more expensive than the existing energy supply. [Copyright &y& Elsevier]

Abstract: A clear consensus exists in the German society that renewable energies have to play a dominant role in the future German energy supply system. However, many questions are still under discussion; for instance the relevance of the different technologies such as photovoltaic systems and wind energy converters installed offshore in the North Sea and the Baltic Sea. Also concerns exist about the cost of a future energy system mainly based on renewable energies. In order to be able to address the raised issues on a scientifically sound basis we have set up a new simulation model REMod-D (Renewable Energy Model-Deutschland) that models the energy balance of the electricity and heat sector including all renewable energy converters, storage components and loads for a future German energy system for a whole year based on an hourly energy balance. The target energy systems modeled use a high fraction up to 100% of renewable energies to cover the electricity and heat demand (heating and hot water). The model includes also energy retrofit of buildings as a measure to reduce future heat loads of the building sector. A mathematical–numerical optimizer is applied in order to identify system configurations with minimal overall annual cost. In this first part of a two-paper series we describe the methodology of the REMod-D model and discuss cost and performance values of all included components and in the second part we will discuss the results. [Copyright &y& Elsevier]

This numerical study evaluates and compares four different flexibility and storage options in building energy systems (batteries, fuel switch, water tanks, and thermal building mass) in terms of potential improvements in load scheduling and energy efficiency. Using a generic modern office building with concrete core conditioning as an example, two different supply concepts (one based on a heat pump, one based on a CHP unit) are considered. A novel hybrid control concept is applied which is designed to be compatible with state-of-the-art controllers implemented in the field. The results show that batteries are the most technically attractive options in terms of grid support, efficiency and ease of implementation. Fuel switch is comparably straightforward to implement, but provides significant benefits only for the considered CHP system. Water tanks with a capacity of about two full operation hours offer nearly the same flexibility as much larger tanks, but negatively influence the efficiency of heat pump systems. The thermal building mass can be used effectively and efficiently for thermal storage, particularly in the heating season, but this is technically challenging to realize. It is shown that current electricity prices do not offer sufficient variations to stimulate grid-supportive operation. [ABSTRACT FROM AUTHOR]

Zeolite coatings allow for process intensification in various fields. In the zeolite coating process, silicone polymers are well suited as binding agents due to their unique and outstanding properties like thermal stability and water vapor permeability. In this work, selected silicone binders were used to prepare zeolite coatings which were characterized subsequently for their thermal and mechanical properties and pore accessibilities. Thermogravimetrical analysis (TGA) and temperature-controlled diffuse reflection FT-IR spectroscopy (T-DRIFTS) were performed to assess the thermal stability. Cross-cut, bend, and impact tests were used to investigate the mechanical stability of the coatings. The accessibility of the zeolite pores in the coating was quantified by N2 porosimetry. Superior coatings could be obtained using Silres MP50 Binder and Silixan's W220, which had the least impact on the zeolite micropore volume while Silres REN 50 coatings showed the best mechanical stability and were very temperature stable at the same time. [ABSTRACT FROM AUTHOR]

Highlights: [•] 135 systems from 88 companies based in 11 countries were found. [•] We present detailed analyses of many system and component related characteristics. [•] We show that solar energy is widely used as energy source for heat pumps. [•] We present technical solutions for the combination of solar thermal and heat pumps. [Copyright &y& Elsevier]

Abstract: Summer air conditioning represents a growing market in buildings worldwide, with a particularly significant growth rate observed in European commercial and residential buildings. Heat-driven cooling technologies are available, which can be used in combination with solar thermal collectors to alleviate the burden caused by air conditioning on the electric utilities and the environment. Solar air conditioning has progressed considerably over the past years as a result of efforts toward environmental protection and new developments in components and systems, and significant experience has been gained from demonstration projects. The main obstacles for large scale application, beside the high first cost, are the lack of practical experience and acquaintance among architects, builders and planners with the design, control and operation of these systems. This paper describes the main results of the EU project SACE (Solar Air Conditioning in Europe), aimed to assess the state-of-the-art, future needs and overall prospects of solar cooling in Europe. A group of researchers from five countries has surveyed and analyzed over 50 solar-powered cooling projects in different climatic zones. The paper presents a short overview on the state-of-the-art and potential of solar-assisted cooling and air conditioning technologies. The results of the study, including a database of the surveyed projects, an evaluation of these projects on a uniform basis, an economic analysis tool, user guidelines and a multimedia tool—are presented. The potential energy savings and limitations of solar thermal air conditioning in comparison to conventional technologies are illustrated and discussed. [Copyright &y& Elsevier]

This paper describes the prototype of a small adsorption heat pump working on the adsorption pair silica gel-water. The developed system consists of two modules, each containing an adsorption reactor and a second heat exchanger for evaporation and condensation of the working fluid. The two modules are operated periodically in order to obtain a quasi-continuous heating or cooling output. A reliable control unit has been developed and implemented in the machine. Hot water provided at temperatures of 80°C to 95°C is used to drive the machine, and heat from the low-temperature heat source (10°C to 20°C) is upgraded to the intermediate temperature level of about 35°C to 45°C, which is suitable for low-temperature heating systems such as wall or floor heating installations. For cooling applications, chilled water of 10°C to 15°C is produced in an almost continuous mode. The first prototypes have been tested. Heating coefficients of performance (COPs) of more than 1.3 and cooling COPs for air-conditioning purposes (12°C to 15°C) of 0.5 have been achieved. The machine provided a mean heating power of up to 15 kW and a cooling power of up to 8 kW. [ABSTRACT FROM AUTHOR]

The energy transformation requires a shift in the energy sector from fossil fuels and their related technologies to carbon free technologies which are mainly renewable energy technologies. In addition to them, three key elements foster the realization of smooth and stringent transformation paths: coal phase out, energy efficiency, and electricity exchange. By applying the techno-economic energy system model REMod-D, the German case is analyzed in this paper with a focus on effects created by emphasizing these three elements in an energy transformation strategy. The analysis covers their impact on the power sector, heating sector, and transport sector which are influenced by the actual shaping of these elements. Overall, the model results show a shift in the German energy system towards a system using more electricity. This electricity is generated up to 85% from photovoltaics, wind power, and other renewable energy sources. Each of the three elements, if employed, leads by itself to a reduction of efforts on the level of developments such as the deployment of renewable energy and renovations, as well as the electrification of vehicles. In the case of combining the three elements, complementary effects can even be summed up. In the Active scenario with a joint use and implementation of the three key elements, this combination is analyzed as part of a cross-sectoral energy strategy for the transformation. Each element can reduce the total system cost by around 16 billion EUR per year. This paper concludes to prioritize these three key elements in the energy strategy in addition to the strong expansion of renewables and the change of heating systems and vehicle concepts. [ABSTRACT FROM AUTHOR]

• Novel methodology for calculating cost-optimized refurbishment roadmaps is presented. • Coupling of building model for refurbishment and system model for heating technologies. • Refurbishment roadmap include timing and refurbishment measures for specific buildings. • Applying the optimization achieves cost savings of 6–16 % and CO 2 savings of 6–59 % • Heat pumps play a central role in the context of CO 2 reduction. A novel methodology for calculating optimized refurbishment roadmaps is developed in this paper. The aim of the roadmaps is to determine when and how should which component of the building envelope and heat generation system be refurbished to achieve the lowest net present value. The integrated optimization approach couples a particle swarm optimization algorithm with a dynamic building simulation of the building envelope and the heat supply system. Due to a free selection of implementation times and refurbishment depth, the optimization method achieves the lowest net present value and high CO 2 reduction and is therefore an important contribution to achieve climate neutrality in the building stock. The method is exemplarily applied to a multi-family house built in 1970. In comparison to a standard refurbishment roadmap, cost savings of 6–16 % and CO 2 savings of 6–59 % are possible. The sensitivity of the refurbishment roadmap measures is analyzed on the basis of a parametric analysis. Robust optimization results are obtained with a mean refurbishment level of approx. 50 kWh/m2/a of the building envelope. The preferred heat generation system is a bivalent brine-heat pump system with a share of 70 % of the heat load being covered by the electric heat pump. [ABSTRACT FROM AUTHOR]

Separating dehumidification and cooling loads in air-conditioning systems has been proven to be a potential strategy to reduce electricity consumption if the dehumidification of air is mostly performed by heat-powered system components. Referring to experimental experiences in Singapore, this paper presents a novel electricity-efficient air-conditioning system consisting of a membrane unit, an evaporatively cooled sorptive dehumidification system (called ECOS system) and a high-efficient conventional cooling unit. The dehumidification of air is performed by a combination of the membrane unit and the ECOS system, and the sensible cooling of air is accommodated by a high-efficiency conventional chiller and in part by the membrane device. In order to find an optimized balance of the three air-conditioning components, an optimization-based simulation approach using a genetic algorithm is developed. The optimization is based on a simple objective function that comprises operating and investment costs. The optimization results reveal that an integration of a relatively large membrane unit, a small ECOS unit and a chiller operating at an elevated evaporation temperature is the most cost effective combination meeting comfort criteria. The resulting optimized combination has potential to save more than 50% of the system's lifetime operating cost compared to conventional systems supplying 100% fresh air. [ABSTRACT FROM AUTHOR]

A new method for assessing the grid interaction of a building’s electricity consumption and generation is presented. It consists of the Grid Support Coefficients GSC abs and GSC rel . GSC abs “weights” the electricity consumption profile with a time-resolved reference quantity which expresses the availability of electricity in the public grid (here: stock electricity price, residual load, cumulative energy consumption or fraction of wind and PV in the electricity mix). GSC rel relates GSC abs to the worst and best achievable values on a scale of −100 to 100 in order to increase the comparability of the results. The new evaluation method is applied to analyze the electricity consumption and/or production of 52 different energy supply systems in buildings, where detailed monitoring data are available. These examples include twelve heat pumps or chillers in office buildings, 38 heat pumps in residential buildings and two combined heat and power units (CHP) in multi-family buildings, all located in Germany. The in-depth analysis shows that the analyzed present-day buildings predominantly consume electricity at times with a low or average electricity availability. Optimal scheduling of all heat pumps could flatten the residual load significantly. In order to achieve this, thermal storages several times larger than the ones currently installed would be required. [ABSTRACT FROM AUTHOR]

The article discusses the annual potential of solar energy far exceeds the world's energy consumption. It talks about using the sun to provide a significant fraction of global electricity demand is far from being realized. Scientists from the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have assessed the recent trajectory of photovoltaics and outlined a potential worldwide pathway to produce a significant portion of the world's electricity from solar power.

Highlights: [•] An evaporatively cooled sorptive coated heat exchanger was experimentally tested. [•] The evaporatively cooled process outperforms the air cooled adsorption process. [•] Adsorbed water mass was increased by 46% and cooling capacity by a factor of 4.1. [•] Earlier research of air cooled adsorption was analysed with a dynamic model. [•] In comparison the evaporatively cooled prototype shows an enhanced performance. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Long-term transition pathways to a low-carbon energy system are analysed by applying the energy system model REMod. All in all, the paper contributes to the current research through an innovative scenario approach, using assumptions for societal trends and quantitative results for scenarios, analysing the paths towards climate neutrality and defossilization in 2050. In the case study of Germany, these trends and drivers influence the results and the technology composition in each consumption sector (buildings, transport, and industry). Across all scenarios, it can be observed that the electrification of all sectors is important for the defossilization of the energy system, as the direct use of electricity from renewable energy is more efficient than the consumption of carbon-neutral synthetic energy carriers. However, different consumer behavior (e.g., non-acceptance or resistance against specific technologies) influences not only the efficient use of (green) electricity, it also changes the optimal pathways of the transition to paths with greater efforts. One potential societal trend—sufficiency—could be an important cornerstone for reaching the targets, as the required expansion and exchange of technologies are lower and thus facilitate the transition. [ABSTRACT FROM AUTHOR]

The increasing installation numbers of ventilation units in residential buildings are driven by legal objectives to improve their energy efficiency. The dimensioning of a ventilation system for nearly zero energy buildings is usually based on the air flow rate desired by the clients or requested by technical regulations. However, this does not necessarily lead to a system actually able to renew the air volume of the living space effectively. In recent years decentralised systems with an alternating operation mode and fairly good energy efficiencies entered the market and following question was raised: "Does this operation mode allow an efficient air renewal?" This question can be answered experimentally by performing a tracer gas analysis. In the presented study, a total of 15 preliminary tests are carried out in a climatic chamber representing a single room equipped with two push-pull devices. The tests include summer, winter and isothermal supply air conditions since this parameter variation is missing till now for push-pull devices. Further investigations are dedicated to the effect of thermal convection due to human heat dissipation on the room air flow. In dependence on these boundary conditions, the determined air exchange efficiency varies, lagging behind the expected range 0.5 < ε a < 1 in almost all cases, indicating insufficient air exchange including short-circuiting. Local air exchange values suggest inhomogeneous air renewal depending on the distance to the indoor apertures as well as the temperature gradients between in- and outdoor. The tested measurement set-up is applicable for field measurements. [ABSTRACT FROM AUTHOR]

• Representation of BEV in a large scale energy system models. • Comparing constant and driving profile-based approach to model BEV energy demand. • Real driving profile-based BEV energy demand increases energy system costs. • FCEVs can substitute BEVs to avoid appearing peaks in power demand. • Energy system costs can be reduced by applying V2G technology. The transition of the motorized private transport sector from fossil fuel to electricity-based technologies is a widely discussed strategy that can contribute towards the achievement of the set climate protection targets. To accurately analyse the challenges and opportunities associated with this transition, the entire energy system needs to be considered in a holistic way. This study introduces two different methodological approaches for the assessment of battery electric vehicles. Both are implemented into the sector coupling, structure optimising model REMod and assessed for a future, nearly CO 2 neutral German energy system. The results show that realistic driving profiles could lead to simultaneous vehicle charging, which result in higher peak loads and eventually require an increase in power plant capacity. The model shows that once vehicles are charged irrespective of the residual load, electricity-demanding technologies throughout all sectors are progressively replaced by hydrogen or other gas-based technologies, as these options do not lead to an increase in electricity demand. This development negatively impacts the deployment of electric heat pumps and battery electric vehicles, which would play a major role otherwise. The cost-optimal system configuration can be achieved through implementation of a controlled charging strategy, shaving power load and supply peaks, integrating more power from variable renewable energy sources and reducing the yearly overall system costs by several billion Euros. [ABSTRACT FROM AUTHOR]