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Heat storages have become an increasingly important component of innovative energy systems on a district-level, characterized by a high share of renewable energy and/or a high degree of autarky. Large-scale thermal energy storages are required to compensate for the seasonal mismatch between demand and supply; they form a central junction in the distribution network of a district, linking the various sources and sinks.Established geothermal heat storage systems (Aquifer/borehole thermal energy storages) already show a high market availability. Based on a large number of customized implementations, substantial expertise and best practice is available in this sector. Additionally, closed systems based on artificial basins (Tank, pit, water-gravel thermal energy storages) were developed for site-independent implementation; they can be distinguished by different components, materials and construction methods. However, they still lack market maturity, with two key aspects as critical barriers: firstly, building complexity of such facilities is high, resulting in high investment costs. Secondly, planning processes are still subject to a significant degree of uncertainty. Consequently, such sophisticated and expensive projects are often contrasted with a high financial and technological risk.In order to tackle both of these key issues, we present two solutions within our study. We introduce an interesting alternative based on recycling. As high investment costs result mainly from excavations and expenses for structural components, we suggest the re-use of existing infrastructures and artificial basin installations. In our presentation, we estimate the potential of these technical conversions. From a conceptual perspective, we demonstrate the variety of possible types of infrastructures and analyze their suitability for being re-used as storage based on different requirements, e.g., accessibility, integrability, competing interests and legal constraints. From this, we derive an overall assessment with regard to the suitability of sites and highlight advantages and weaknesses of the various types of infrastructures.Still, any implementation can only be successful if the structure used shows sufficient performance. This is in high contrast to the usually considerable deviations from common design conventions for closed seasonal thermal energy storages, e.g., geometrically with respect to the surface/volume ratio. Here, the possible maximum storage capacity, charging/discharging power and efficiency of a re-used infrastructure after its conversion needs to be analyzed from a technical perspective. To address this suitability aspect, we use a recently developed simulation tool “STORE”, which allows versatile modelling and evaluation of storage design scenarios on a component level using a 2.5‑D approach. In our presentation, we employ “STORE” to a case study and examine a potential re-use of a former water-treatment basin. After applying common boundary conditions of an energy system and setting different design scenarios, we focus on performance indicators and reveal the best technical solution for this specific case study and discuss transferability of the results.Finally, we use our study to demonstrate, under which conditions the conversion and re-use of artificial infrastructures can be a promising approach: By reducing investment costs of large-scale, closed thermal energy storage systems, it can pave their way to full market availability.

open access article Insulating glass flat-plate collectors can save cost by being produced quickly and automatically in insulated glass production facilities, and they can be filled with argon to reduce heat loss. During its lifetime, the collector is likely to lose argon because of gradual material degradation of the sealing. However, information on the influence of the argon concentration on the collector efficiency is limited. Therefore, the objective of this research work was to analyse this effect. A theoretical material property calculation of argon-air mixtures was carried out to determine the convective losses with variable argon concentrations. Thermal collector performance was measured experimentally using an outdoor solar tracker test rig. The results strongly suggest, that the influence of argon concentration on both the convective losses and the thermal efficiency is non-linear. The measurements revealed that an argon concentration of 90 % can increase average thermal performance by percentage points. An increase in argon concentration from 0 % to 50 % has almost twice the effect on average thermal efficiency as an increase from 50 % to 90 %. Concluding from these results, an argon leakage threshold of 2.5 percentage points per year is proposed to avoid disproportionate loss of efficiency over time.

The floodplain areas along the Naryn River in Kyrgyzstan are essential as they hold the riparian (local) ecosystems because they provide firewood, pastureland, and areas for recreation and protection against erosion. Due to limited access to adequate, reliable, and sustainable energy services, the rural population usually derived their energy needs from multiple natural energy resources (i.e., firewood, charcoal, agricultural residues, animal dung, and wood branches). This is considered a common and predominant practice in rural Kyrgyzstan. This situation leads to a negative impact on local ecosystem services. In addition to that, the reliance on solid fuels contributes to indoor and outdoor air pollution, which is partially threatening the local ecosystem services. By contrast, the employment of renewable-based energy supply systems would substantially reduce the burden on the environment, which is mainly untapped. To integrate renewable energies, it is important to understand the energy behavior of floodplain communities. In that response, the presented article is the first attempt to capture the energy identity of the floodplain community of Kyrgyzstan based on a quantitative energy-based (on-site) household survey. Furthermore, the present research article synthesizes the driving factors that have a (direct or indirect) impact on the energy and local ecosystem services. In addition, the present article proposes a brief pathway for the sustainable energy transition. The article records the recommendation to integrate renewable energies to preserve the local ecosystems of Kyrgyzstan.

In both rural and urban areas, two-wheeler vehicles are the most common means of transportation, contributing to local air pollution and greenhouse gas emissions (GHG). Transitioning to electric two-wheeler vehicles can help reduce GHG emissions while also increasing the socioeconomic status of people in rural Kenya. Renewable energy systems can play a significant role in charging electric two-wheeled vehicles, resulting in lower carbon emissions and increased renewable energy penetration in rural Kenya. As a result, using the Conventional and Renewable Energy Optimization (CARNOT) Toolbox in the MATLAB/Simulink environment, this paper focuses on integrating and modeling electric two-wheeled vehicles (e-bikes) into an off-grid photovoltaic Water-Energy Hub located in the Lake Victoria Region of Western Kenya. Electricity demand data obtained from the Water-Energy Hub was investigated and analyzed. Potential solar energy surplus was identified and the surplus was used to incorporate the electric two-wheeler vehicles. The energy consumption of the electric two-wheeler vehicles was also measured in the field based on the rider’s driving behavior. The modeling results revealed an annual power consumption of 27,267 kWh, a photovoltaic (PV) electricity production of 37,785 kWh, and an electricity deficit of 370 kWh. The annual results show that PV generation exceeds power consumption, implying that there should be no electricity deficit. The results, however, do not represent the results in hourly resolution, ignoring the impact of weather fluctuation on PV production. As a result, in order to comprehend the electricity deficit, hourly resolution results are shown. A load optimization method was designed to efficiently integrate the electric 2-wheeler vehicle into the Water-Energy Hub in order to alleviate the electricity deficit. The yearly electricity deficit was decreased to 1 kWh and the annual electricity consumption was raised by 11% (i.e., 30,767 kWh), which is enough to charge four more electric two-wheeler batteries daily using the load optimization technique.

In an ongoing project, low-investment measures for the optimization of district heating systems are analyzed. The optimization strategies are collected in a catalog, which is the core of a guideline. The application of this guideline is demonstrated using two concrete district heating networks as examples. In this study, the improvement of an analog controlled district heating substation by an electronic controller is investigated. High supply temperatures and heat losses are often a challenge in district heating networks. The district heating substations have a major influence on the network return temperatures. The comparison of the two substation setups with analog and electronic controllers is carried out by laboratory measurement. It can be shown that the return temperatures can be reduced by an average of 20 K in winter and transition, as well as 16 K in summer. The district heating network losses are calculated for one of both specific district heating networks. They are calculated from the ratio of network losses to generated energy. The generated energy is the sum of network losses and consumer demand. The thermal losses of the network can be reduced by 3%. The volume flow in the heating network can be reduced to a quarter. Therefore, the pumping energy requirement drops sharply since these changes cubically affect the volume flow.

Kyrgyzstan is a high-altitude mountainous country situated in a cold climatic zone. The age of the residential buildings, poor housing conditions and the absence of proper thermal insulation result in high heat demand and low thermal comfort in Kyrgyz houses. To maintain thermal comfort, the rural residents use traditional heating stoves to burn solid fuels during the winter months. Overconsumption of natural resources is mainly responsible for deforestation, as well as indoor and outdoor air pollution. Implementation of building thermal insulation is considered as one of the potential measures for energy conservation. In regards to this, the presented research proposes the various thermal insulation structures developed from the locally available natural materials. Further to this, it identifies the effectiveness of various thermal insulation structures on the annual space heating demand of a highaltitude single-family house located in rural Kyrgyzstan. The results show that the insulation parameter helps to save a considerable amount of space heating demand by up to 30 % in the case of existing houses and up to 70 % for newly built houses in rural Kyrgyzstan.

A large part of the Kyrgyz territory is covered by mountain ranges which result in extremely cold winter periods. The cold climatic conditions of Kyrgyzstan define heating as an essential need for Kyrgyz people. The majority of the residential buildings are constructed with poor thermal insulation or none at all, which yields high energy consumption in buildings to maintain thermal comfort. Especially in rural households, the heat demand is usually covered by solid fuels (i.e. wood, branches, coal and other solid fuels) burned in traditional stoves / boilers. The intensive use of solid fuels contributes to indoor and outdoor air pollution. Hence, there is a substantial need to provide sustainable and adequate heating services for residential buildings, particularly for the rural population. In response to this, the presented research article describes an investigation of solar resources to support space heating and domestic hot water preparation for single-family homes in rural Kyrgyzstan. Besides that, it identifies the thermal performance of typical single-family houses by considering local boundary conditions such as cold climate, highaltitude and routine behavior of the inhabitants. The determination of fuel savings by implementing solar-thermal domestic heating systems helps to explain the positive impacts on the environment. The investigation shows a significant solar-thermal energy potential available for domestic space heating and hot water preparation in Kyrgyzstan.

The research work was funded by the Federal Ministry of Education and Research (BMBF) of the Federal Republic of Germany within the CLIENT II funding programme International Partnerships for Sustainable Innovations under the project “ÖkoFlussPlan” (Project ID 01LZ1802A-F). open access article The northern part of the globe is dominated by industrialisation and is well-developed. For many years, the southern part of the world (South Asia, Africa etc.) has been a target of research concentrating on access to energy (mainly electricity) in rural regions. However, the Central Asian region has not been a focus of energy research compared to South East Asia and Africa. Despite plentiful domestically available energy resources, the energy supply in Central Asia is very unevenly distributed between urban and rural areas. Almost half of the total population of Central Asia lives in rural areas and there is a lack of access to modern energy services to meet primary needs. To analyse the energy situation (i.e., electricity, heating, hot water consumption, cooking, etc.) in rural Central Asia, this paper reviews residential energy consumption trends in rural Central Asian regions as compared to urban areas. Furthermore, the paper illustrates the potential of renewable energies in Central Asia. To perform the study, a qualitative comparative analysis was conducted based on a literature review, data, and statistical information. In summary, the presented article discusses the rural energy situation analytically and provides in-depth insights of Central Asian energy infrastructure.