The Concentrated Solar Thermal Technologies (CST) sector has struggled with high-costs associated with Concentrated Solar Power (CSP) plants in Europe over the past decade. Moreover, CSP has largely been viewed only as a flexibility provider for electricity systems. To address these challenges, the CST4ALL project promotes a range of hybridization and cooperation initiatives at the intersection of CST and other renewable energy technologies, drawing on the work of various European Technology & Innovation Platforms (ETIPs). CST4ALL aligns closely with current EU priorities- such as Smart Sector Integration, Fit for 55, and Clean Energy Transition Partnership (CETP)-as well as national energy strategies. It seeks to offer solutions to pressing issues related to decarbonisation and energy security. The key outcome is a series of workshops engaging both industry and research and development (R&D) communities, fostering interaction among stakeholders at key technology interfaces with the CST sector. By analysing both industrial and R&D perspectives, CST4ALL aims to expand the network of active stakeholders in the CST Implementation Working Group (IWG) under the SET Plan and to raise awareness of CST’s potential role in sustainable energy mix. This paper outlines the project’s main activities to support the European Commission’s cross sector approach – encouraging public and private investment in R&D and establishing the political and regulatory framework needed to implement the new CST Implementation Plan (IP) from October 2022 to March 2024.

As a domestic and non-intermittent resource, geothermal energy offers countries a clean and sustainable energy option while setting their energy mix strategies. Turkiye, endowed with rich energy fields, stands out as one of the fastest-growing countries in geothermal energy. The dramatic installed power capacity increase and significant expansion in the geothermal energy market, particularly after 2010 following the initiation of the incentive scheme, are pretty remarkable. Nonetheless, it is also evident that geothermal energy investments in the country have shown a decreasing trend in recent years. At this point, this paper aims to reveal the opportunities and challenges in the development of geothermal energy as the first comprehensive qualitative analysis for Turkiye. Furthermore, it evaluates the diffusion of geothermal energy in Turkiye based on the Technological Innovation Systems (TIS) framework to gain insight into the Turkish geothermal sector. According to the interviewees, financial and political barriers such as high investor costs, insufficient incentives for power generation, and the lack of incentives for direct utilization, along with lengthy and exhausting permitting processes, still hinder the prevalence of geothermal energy utilization in the country. Respondents find that Geothermal suggests a huge opportunity for the Green Energy transition in Turkiye and aids economic development through increases in employment opportunities and household welfare using combined uses in district heating, electricity, and greenhouse usage.

The usage of fossil fuel in the energy sector is the primary factor for global GHG emissions, so it is crucial to better utilize RE sources. One way to do that is to hybridize RE technologies to make up for their deficiencies while enabling a more synergistic power production. This study utilizes such an approach to hybridize the KZD-2 Geothermal Power Plant (GPP) with CST and biomass in the southwest region of Turkiye. The main motivation is to address the two main issues of GPPs—excess turbine capacities happening over the operating years and decreasing performance during hot summer months—while also increasing the flexibility of KZD-2. A topping cycle of CST–biomass is added utilizing a PTC field as the CST technology and olive residual biomass combustion as the biomass technology. The hybrid plant is simulated on TRNSYS, and the energetic data show that it is possible to generate more than 20 MWe of additional power during sunny and clear sky conditions while also increasing the Capacity Factor (CF) from 69% to 74–76%. Moreover, the financial results show that the resulting LCOAE is 81.19 USD/MWh, and the payback period is five or nine years for using the YEKDEM incentive or the spot market prices, respectively.

While Geothermal Power Plants (GPPs) can be a reliable renewable energy source, this reliability can decrease over the years due to brine mass flow declining. This reduced mass flow causes extra capacity unused in the GPP turbines. This problem can be overcome by hybridizing GPPs with CST and biomass. These three thermal technologies can, in theory, complement each other if all the resources are present at the exact location. This is the scenario for this study, as the location for the case study is the Kızıldere 2 (KZD2) GPP in Denizli, Turkiye, operated by Zorlu Energy. This region has sufficient potential for all three technologies: CST, geothermal, and biomass. Furthermore, by building a topping cycle using CST and biomass, it is possible to generate additional power. This study utilizes a topping steam Rankine cycle run equally by CST and biomass, and, as a result, the 20% excess capacity in the GPP turbine is used while generating an additional 20 MWe of power.

The rising population and increasing thermal comfort expectations are expected to exacerbate the already high HVAC use in offices, which unavoidably places a strain on energy supply systems. Storing thermal energy by incorporating phase change materials (PCMs) is an effective method for improving the buildings' energy efficiency. Understanding how a PCM wallboard responds to climate change (CC) is crucial to maintaining its viability and effectiveness in achieving energy efficiency and sustainability goals during a building's lifetime. This study presents a methodological framework to assess the performance of a building utilizing PCM wallboards in terms of cooling/heating energy demand (and corresponding GWP and operation cost) and occupant thermal comfort considering the changing climate. As a case study, a hypothetical office building located in a cold semi-arid climate with high diurnal fluctuations was selected, and the performance of offices orienting in different directions was evaluated when PCM wallboards with different melting ranges were utilized. PCM19 with a melting range close to heating set point reduced the heating demand by 5.0-7.4% for 2020 and 7.8-9.2% for 2050; while PCM25 with a melting range close to cooling set point yielded cooling reductions of 1.9-4.3% for 2020 and 0.7-2.4% 2050. However, PCM19 and PCM25 were ineffective in cooling and heating, respectively, as they were not compatible with the chosen set points. Coupling PCM25 with night-ventilation (NV) significantly enhanced the cooling savings (NV: 23.2-25.7% for 2020; 13.9-15.7% for 2050; NV + PCM25: 29.4-30.6% for 2020; 16.6-17.5% for 2050); though, the effectiveness of NV was impaired with rising night temperatures due to CC. Hourly energy analysis demonstrated varying performance of wallboards based on the time of day, suggesting potential benefits in supply-demand dynamics and time-of-use energy pricing. In naturally-ventilated scenarios, PCM utilization was ineffective in reducing indoor overheating risk, even when night-ventilation was introduced. Results highlight that to effectively mitigate indoor overheating risk in office buildings, PCM wallboards should be coupled with air-conditioning and night-ventilation. Furthermore, for a comprehensive evaluation of the energy/GWP/cost saving potential of a PCM wallboard during a building's lifetime, not only the current but also the projected local climate should be considered given the shifting energy demand towards cooling due to climate change. Overall, this study provides valuable insights into effective PCM wallboard utilization and lays the groundwork for enhancing the resilience of built environments in the face of climate change challenges.

Many software have been developed to analyze buildings and renewable energy systems. Generally, more than one software is used for the visual interface, energy simulation, optimization, and modeling of renewable energy systems in energy analysis studies. In this study, a novel web-based green building energy modeling software with layered architecture is developed to estimate the energy demand of buildings, make passive house analyses, and model renewable energy systems in buildings. Requests and responses between the user and application programming interface communicate using JavaScript Object Notation format. For the web frontend, libraries with visualization are used together with React, which is a JavaScript library created by Facebook. The developed software is free, open source and has it own visual interface. The developed software eliminates the requirement for more than one software in the analysis of standard/passive buildings with low/zero energy consumption. The developed software was verified using electricity consumption and production data of a positive energy passive building located in Turkey.

Concentrating solar thermal power is an emerging renewable technology with accessible storage options to generate electricity when required. Central receiver systems or solar towers have the highest commercial potential in large-scale power plants because of reaching the highest temperature. With the increasing solar chemistry applications and new solar thermal power plants, various receiver designs require in micro or macro scale, in materials, and temperature limits. The purpose of the article is computing the geometry of the receiver in various conditions and provide information during the conceptual design. This paper proposes a surrogate based design optimization for a micro-scale volumetric receiver model in the literature. The study includes creating training data using the Latin Hypercube method, training five different surrogate models, surrogate model validation, selection procedure, and surrogate-based design optimization. Selected surrogates have over 98% R2 fit and less than 4% root mean square error. In final step, optimization performance compared with the base model. Because of the model complexity, surrogate models reached better objective values in a significantly shorter time.

A volumetric receiver design process is proposed to respond wide range of power, outlet temperature, or mass flow rate needs. In the receiver model, concentrated solar radiation hits the inner surface cavity and heats the gaseous fluid passing through the porous media assembled between the cavity and the insulator. Porous media properties and receiver geometry are coupled in the design process to determine the best possible option. A two-step process starts with a parameter sweep to create a surrogate model. Then, gradient-based design optimization is performed using two different surrogate models to maximize the outlet air temperature for bounded design variables in receiver volume and outer surface temperature constraints. The proposed design process has the advantage of exploring more design options faster using the surrogate model and more accurate results using the base model in the plant-level simulations. The methodology is discussed by comparing the surrogate models and the model validation shows that over 95% accuracy is obtained using both surrogate models. Surrogate-based design optimization is compared as in solution time and the final results are compared with respect to the base receiver model.

Large market opportunities exist for solar powered Reverse Osmosis (RO) desalination technologies in fertile but arid areas with large solar and sea water resources. A challenge to realizing these markets is the variable nature of solar resources, which for the desalination plant can lead to high water costs due to low capacity factors (CF) and increased maintenance costs due to repeated start-ups and shut-downs. A potential solution is to power RO plants using both PV and CSP with Thermal Energy Storage (TES) with an aim to reduce shut-downs, and increase CF. In this study, three solar energy systems to power RO are considered: 1) PV only; 2) CSP with central receiver (CR) and TES; 3) PV and CSP with CR and TES. Two RO operational strategies are considered: 1) nominal load only; 2) variable load between minimal and nominal. The performance of these systems is simulated for Mersin, Turkey, using TMY data. The PV and CSP with TES system and variable RO operation achieved the levelized cost of water (LCOW) 1.92 USD m-3 with an RO CF of 60.8%.

A novel methodology to design a micro-scale, solar-only, air-breathing, open Brayton cycle and assess its on- and off-design performance. The methodology is applied to generate and assess six thermodynamic layouts over a range of solar irradiation levels. All plants have the same on-design requirements to create a baseline to compare their off-design performance. PyCycle, a thermodynamic cycle modeling library to model jet engine performance, is revised to transform the jet engine performance modeling to solar thermal plant performance modeling and used to create a volumetric receiver component. A response surface surrogate model of the receiver is created for design optimization to maximize the component-level efficiency. The compressor and turbine maps are scaled for the balance of the plant. Off-design efficiency, mass flow rate, operation range, turbomachinery maps, and maximum power output are presented. Since the methodology can be adapted to all plant sizes, the results are normalized to on-design condition. The outcome of this study demonstrates the impact of the thermodynamic configuration on off-design performance and provides a methodology to design plants that are more robust across a range of solar irradiation levels and can be operated in a more flexible manner. Compared to single shaft configuration, solar radiation operation range is improved by 5%, with 6% less mass flow, and operates more efficiently than the benchmark case over 85% of the operating regime.

Copper (Cu) has been an essential ingredient in the production of silvered-glass reflectors used in the concentrated solar power (CSP) systems. However, due to added material cost and the environmental burden induced by Cu mining, researchers have started to look for ways to develop copper-free coating systems for reflectors used in solar thermal applications. In this study, we employed accelerated aging tests to obtain the aging characteristics of reflectors with and without Cu and exposed reflectors outside for natural aging. Samples were subjected to Copper Accelerated Acetic Acid Salt Spray (CASS), Ultraviolet-Humidity (UVH) and UV tests, and the changes in the hemispherical and specular reflectance were measured and compared.

This study focuses on the design optimization of a micro-scale pressurized volumetric receiver by changing geometry and flow rate constrained by the volume, outlet air temperature, and outer surface temperature. The pressurized volumetric receiver model is replicated from an existing model, which assumes constant air pressure and neglects the convection loss from the cavity. The existing model is revised from a solver to a design optimizer. The replicated model is restructured using OpenMDAO (Open-source MultiDisciplinary Analysis and Optimization) framework, and analytical derivatives are implemented for efficient derivative calculation to increase optimization performance. The replicated model is verified, and the maximum outlet air temperature difference is less than 0.05%. Optimization performance, selection of optimizers, the effect of the domain size, and radiative methods are discussed. The combined impact of the design variables is observed by selecting SLSQP (Sequential Least SQuares Programming) and trust-region optimizers. Optimization performance is tested in different domain sizes and compared with a design of experiments analysis. For testing the impact of radiative heat transfer methods to design optimization, the Rosseland approximation, and P1 method are selected. Depending on the design domain, a solution methodology is suggested for future receiver design optimizations applicable for macro-scale pressurized volumetric receivers.

Dense granular flows exist in many solid particle heat exchangers and solar receivers studied in the field of Concentrating Solar Power (CSP). By tracking particles individually with the Discrete Element Method (DEM), the details of particle friction, collisions, and mixing can be modeled accurately. An open source DEM-based code for modeling heat transfer in dense granular flows is presented, called Dense Particle Heat Transfer (DPHT). It uses one-way coupling, with DEM run first to find the particle positions and DPHT run second to calculate heat transfer between particles and any walls. Heat transfer is computed with six sub-models, including effects from contact conduction, conduction through the thin fluid gap between particles, and thermal radiation. Simulations are run to investigate particle-particle radiation, with DPHT matching a full Monte Carlo ray tracing simulation to within 1.6%, whereas the “local environment temperature” models from literature show physically unrealistic results. As a test of the accuracy of DPHT, a simulation is run to replicate published experimental work, and results in terms of total heat transfer are within 4%. Finally, a tubular heat exchanger is analyzed, and a “radial” mixer design is introduced, increasing heat transfer by 8%. Several DEM-based heat transfer codes have been described in literature, but they are often kept in-house. Some open source codes exist as well, but they generally have drawbacks including missing heat transfer modes, insufficient flexibility to make significant changes, and incomplete documentation. DPHT aims to simplify this modeling method by providing a flexible, open source solution.

A model to estimate radiative heat transfer in particle beds is developed for use in the Discrete Element Method (DEM). Monte Carlo ray tracing simulations are run to find the Radiation Distribution Factor (RDF) between pairs of particles and between particles and a wall, in particle beds with random packing. Curves are found to express the average RDF as a function of distance, and within DEM these curves are used to estimate particle-particle and particle-wall radiative transfer. The resulting Distance Based Approximation model is computationally efficient and simple to implement. RDF-distance curves are given as a set of tables covering two particle emissivities (0.65, 0.86), four wall emissivities (0.4, 0.6, 0.8, 1.0), and five solid fractions (0.25, 0.35, 0.45, 0.55, 0.64). The accuracy of the model is investigated, with accuracy sufficient for many engineering applications shown. An initial implementation is demonstrated for a heat exchanger with a dense granular flow.

This study investigates the hybridization scenario of a single-flash geothermal power plant with a biomass-driven sCO2-steam Rankine combined cycle, where a solid local biomass source, olive residue, is used as a fuel. The hybrid power plant is modeled using the simulation software EBSILON®Professional. A topping sCO2 cycle is chosen due to its potential for flexible electricity generation. A synergy between the topping sCO2 and bottoming steam Rankine cycles is achieved by a good temperature match between the coupling heat exchanger, where the waste heat from the topping cycle is utilized in the bottoming cycle. The high-temperature heat addition problem, common in sCO2 cycles, is also eliminated by utilizing the heat in the flue gas in the bottoming cycle. Combined cycle thermal efficiency and a biomass-to-electricity conversion efficiency of 24.9% and 22.4% are achieved, respectively. The corresponding fuel consumption of the hybridized plant is found to be 2.2 kg/s.

A method is described to find the effective thermal conductivity due to radiation (k(rad)) for groups of particles at packed and less than packed states. Unlike most previous studies, the method does not rely on the assumption of a unit cell or absorption and scattering coefficients to derive k(rad). In this method, radiation is modeled with a 3D Monte Carlo ray tracing code, steady state particle temperatures are found with a particle-particle heat exchange simulation, and k(rad) is found with a comparison to heat conduction in an isotropic solid of the same geometry. This leads to the dimensionless Exchange Factor (F-E), allowing k(rad) to be calculated at any temperature and particle radius. The key result is a model for F-E over the entire range of emissivities from 0.3 to 1 and solid fractions from 0.25 to the fully packed state of 0.64. F-E results are compared to previous models, with agreement shown in some cases but a large disagreement found for low solid fractions. The k(rad) results are combined with the Zehner and Schlunder model for solid and fluid conduction, providing an equation for the full effective thermal conductivity. (C) 2020 Elsevier Ltd. All rights reserved.

For investigating the system response of parabolic trough collector heat generating system, a plant with parabolic trough collector field and two-tank molten salt thermal energy storage model with component-level control algorithm is developed for managing various working conditions. The model is transient inside the components and responds with hourly weather and demand data. The main purpose of this work is providing an alternative design methodology that focuses on the collector field, and storage size by investment, location, and load type. Using a simple economic model, the plant parameters are calculated, which contains only initial investment costs of the parabolic trough collector field and thermal energy storage costs. Depending on the economic model, various sizes of collector field and storage combinations are created at fixed initial investment costs in the mathematical model. A parametric study is performed by using the economic model simulating at several initial investment costs, two different locations in Turkey, and four different load profiles. As a result of the parametric study, maximum solar fraction cases are selected and the generalized trend is observed. The effect of thermal energy storage on the solar fraction is discussed and the change in thermal energy storage with optimum plant size is investigated. After the optimum investment, the linear increment trend of dispatchability is disappearing and increases asymptotically by increasing the plant and/or storage size. Later in this work, the significance of the load profile is emphasized, which should be one of the major design parameters for solar-powered energy systems.