The focus of this project is to conduct original research to improve the fundamental understanding of the performance of sCO₂ cycles and the design aspects of the key components, namely compressors, expanders and heat exchangers. Computational and experimental methods will be used to investigate the performance and design characteristics across a wide range of operating conditions. The results from these studies will improve existing scientific understanding and will facilitate the development of new performance prediction methods for the cycle and components. Understanding these aspects will not only lead to improved performance prediction but could also lead to improved component design in the future. Within this project the new prediction methods will be used to investigate and compare the performance of different cycle architectures and component designs. The results from these comparisons will enable the identification of the optimal systems that can operate across a wide range of heat input and load conditions, and therefore best facilitate improvements to sCO₂ systems.

Concentrated Solar Power (CSP) plants are set to play an important role in the energy supply mix in the twenty first century. Unfortunately, the Levelized Cost of Electricity (LCoE) of CSP (currently about 150 €/MWh1) has not attained the level targeted (100 €/MWh) except for few installations in exceptionally good locations. As of today, many ongoing research projects aiming at enhancing the efficiency of the power block and reducing the associated costs are based on supercritical CO₂ technology. However, relatively high ambient temperatures, typical in regions characterized by high solar irradiation, remain the Achilles heel of supercritical CO₂ cycles as the efficiency of these systems drops dramatically in warm environments where ambient temperature is close to or higher than the critical temperature of CO₂ (31°C), hence not allowing to adopt condensation (Rankine) cycles with expectedly higher efficiencies. This issue stems as an intrinsic critical hurdle for the future commercialization of CSP plants, which may be difficult to overcome by any means with the technology currently in use or with standard supercritical CO₂ technology. To address this limitation, this project proposes a modified working fluid whereby carbon dioxide is blended with certain additives to enable condensation at temperatures as high as 60°C whilst, at the same time, still withstanding the required peak cycle temperatures. This presents a major breakthrough in CSP technologies as it increases the thermomechanical conversion efficiency from the current 42% to above 50%, bringing about large reductions in LCoE. There are two main areas of research in this project: the first is the identification of the optimal additive which would reduce the size and increase the efficiency of the power block. The second is the development of tailored heat exchanger designs, particularly for the air-cooled condenser, to operate with the innovative fluid as these are key enabling components for the proposed technology. Both actions will lead to a significant reduction of CAPEX and OPEX with respect to conventional CSP technologies.

Commercial steam power plants pressurise and heat water to produce steam which is then expanded to produce electricity. However, using an organic fluid permits low temperature heat sources, typically between 80 and 350°C, to be converted into mechanical power more economically than steam. Organic Rankine cycles (ORC) have a great potential to contribute to the UK’s mix of low-carbon technologies with promising applications such as combined heat and power, concentrated-solar power and waste-heat recovery from reciprocating engines and other industrial processes with waste heat streams. However, despite successful commercialisation of ORCs for industrial-scale applications, more development is required at the commercial and domestic scales before its potential can be realised. More specifically, at these small-scales, the challenge lies in the design of systems that are efficient but are also low cost. One approach to achieving this is to develop systems that operate efficiently over a range of different conditions. This will enable the high-volume, low-cost production of ORC systems, enabling significant improvements in the economy-of-scale. Furthermore, at this scale, different expander technologies, such as turbo and screw expanders, and system architectures can be considered. However, it is not clear which expander technology or system architecture is the optimal choice to achieve the desired improvements in the economy-of-scale. To answer this question, it is important to improve the understanding of how different ORC expanders perform across a wide range of operating conditions, and to investigate how these systems respond to changes in the working fluid.

Excess heat from certain industrial processes represents a valuable resource for energy intensive industries (EII). However, technical and non-technical obstacles prevent industrial waste heat recovery. The EU-funded CO₂OLHEAT project intends to valorise waste heat even at a significant temperature of 400 °C if compared with the traditional steam/ORC solutions. The project will demonstrate the operation of a 2 MW waste-heat-to-power skid based on a 2MW-sCO₂ cycle in the CEMEX cement manufacturing plant in the Czech Republic. CO₂OLHEAT, relying on previous sCO₂ turbomachinery design experience and EU funded projects on industrial waste heat valorisation, will strengthen the EU industrial leadership in EII and turbomachinery sectors.

In the envisaged solar-Brayton cycle, supercritical carbon dioxide (sCO₂) is used as working media. Concentrated solar radiation is absorbed and stored in solid particles until the heat is transferred to the sCO₂. Unique properties of sCO₂ (such as high density and low viscosity) allow reaching high efficiency of the energy conversion and very compact design of the components compared to conventional Rankine steam cycle. The EU-funded COMPASsCO₂ project will integrate solar energy into sCO₂ Brayton cycles for electricity production. The project will design, test and model tailored particle-alloy combinations able to face the extreme operating conditions regarding temperature, pressure, abrasion, oxidation and corrosion during the plant lifetime. Testing of the particle-sCO₂ heat exchanger will validate the innovative materials developed.

Generating sustainable sources of power and fresh water is a challenge. Desalination plants are energy-consuming and have a high environmental impact. The EU-funded project DESOLINATION will develop an innovative desalination system coupling concentrated solar power (CSP) and forward osmosis, for a simultaneous production of green electricity and low-impact fresh water. Focusing on the Gulf Cooperation Council region, the project will test the developed technology for one year at the existing CSP plant of King Saud University in Riyadh. The desalination technology will first be coupled with an existing solar air Brayton cycle and then to a new power block operating with CO₂ blends with a net power output of around 1.7 MW.

In light of the EU’s commitment to remove carbon emissions from the energy system, the market for concentrated solar power (CSP) is growing. With improvements in CSP technology advancing rapidly, an estimated 11 % of the EU’s electricity may be produced by CSP by 2050. Countries with huge solar resources in the south, like Spain, could export CSP electricity to northern countries, such as Germany. The EU-funded SOLARSCO₂OL project will present sCO₂ cycles as a key enabling technology to facilitate a larger deployment of CSP in the EU. Led by an industry-oriented consortium, the project aims to be fully marketable by 2030.

HYBRIDplus:Advanced HYBRID solar plant with PCM storage solutions in sCO₂ cycles. HYBRIDplus aims to pioneer the next generation of CSP with an advanced innovative high-density and high-temperature thermal energy storage (TES) system capable of providing a high degree of dispatchability at low cost and with much lower environmental burden than the State of the Art. This thermal storage is based in the Phase Change Material (PCM) technology in a cascade configuration that can reproduce the effect of a thermocline and integrates recycled metal wool in its nucleus that provide hybridization possibilities by acting as an electric heater transforming non-dispatchable renewable electricity such as PV into thermal stored energy ready to be dispatched when needed. HYBRIDplus proposes a novel approach to concentrated solar power with a PV+Cascade PCM-TES CSP configuration based on a high temperature supercritical CO₂ cycle working at 600 ºC. This new plant is called to form the backbone of the coming energy system thanks to a higher efficiency and lower LCoE than state-of-the-art technology, and in addition to other benefits such as full dispatchability reached with the hybridization in the storage that allow higher shares of variable output renewables in the energy system and environmental friendliness (lower CO₂ emissions, minimum water consumption, enhancement life cycle impact).

SHARP-sCO₂ addresses key technological challenges to enable the development of a new generation of highly efficient and flexible CSP plants. Keeping on working with CSP-sCO₂ power cycles and investigating how to exploit air as operating fluid, SHARP-sCO₂ will develop and validate novel enabling technologies in EU top level labs. SHARP-sCO₂ will attain high temperatures and cycle efficiency, while guaranteeing reliable and flexible operation. Introducing a smart hybridization with PV by means of an innovative electric heaters, SHARP-sCO₂ will maximize sCO₂ operation and remuneration, exploiting PV affordability while counting on the unique energy storage capabilities of CSP.

sCO₂ as working fluid for innovative power plants Commercial facilities usually generate electrical energy by open, direct heated Brayton or Joule processes (gas turbines) and closed, indirect heated Rankine processes (steam circuit). Instead, a novel and innovative concept suggests supercritical carbon dioxide (sCO₂) as a working fluid for the Brayton process. Thereby, the low fluid viscosity at high density enables compacter components and small plant foot prints. Furthermore, numerous studies underline the potential and higher efficiency of sCO₂ power cycles in comparison to conventional energy conversion units.
In the frame of the CARBOSOLA project the design and commissioning of an operating technical scale facility with sCO₂ as a working fluid was performed at the Helmholtz-Zentrum Dresden-Rossendorf. Temperatures up to 600 °C and 650 °C at 300 bar and mass flow rates of 1.32 kg/s and 3.3 kg/s are possible.

The aim of the project is to design a flexible and efficient system for the storage of thermal energy and its reuse for the production of electricity and possibly also heat. The project will develop and produce working samples of key components on a model scale and verify their functionality. This will demonstrate the feasibility of the final energy system. Due to the novelty of the subject of the project, the validation of the key components and the acquisition of operational experience is necessary for the techno-economic study and the demonstration of the competitiveness of the solution. Due to the use of a very compact heat store and heat cycle, a very positive result of the economic study can be expected. In terms of time, all applied outputs will be achieved in 2021 and testing and verification of functionality will take place by mid-2023.

In the TOPCSP project, the overall research objective is to improve the design of the different systems of a CSP plant to increase its cost-competitiveness, reliability, environmental profile, and operational safety through:
1. Improving molten salt-based technology which has the lowest costs and higher capacity factors and the direct steam generation plants that are suitable at a lower scale,
2. Developing a high-temperature liquid receiver and the sCO₂ power block of the next generation of CSP plants and proposing new systems to contribute to enhancing the flexibility of CSP plants using molten salt reservoirs and solar fuels, and
3. Developing computational tools to improve the analysis and design of the systems considered.

Current fossil-fuel power plants have been designed to operate in base-load conditions, i.e to provide a constant power output. However, their role is changing, due to the growing share of renewables, both in and outside the EU. Fossil-fuel plants will increasingly be expected to provide fluctuating back-up power, to foster the integration of intermittent renewable energy sources and to provide stability to the grid. However, these plants are not fit to undergo power output fluctuations.
In this context, sCO₂-Flex consortium addressees this challenge by developing and validating (at simulation level the global cycle and at relevant environment boiler, heat exchanger(HX) and turbomachinery) the scalable/modular design of a 25MWe Brayton cycle using supercritical CO₂, able to increase the operational flexibility and the efficiency of existing and future coal and lignite power plants.
sCO₂-Flex will develop and optimize the design of a 25MWe sCO₂ Brayton cycle and of its main components (boiler, HX, turbomachinery, instrumentation and control strategies) able to meet long-term flexibility requirements, enabling entire load range optimization with fast load changes, fast start-ups and shut-downs, while reducing environmental impacts and focusing on cost-effectiveness. The project, bringing the sCO₂ cycle to TRL6, will pave the way to future demonstration projects (from 2020) and to commercialization of the technology (from 2025). Ambitious exploitation and dissemination activities will be set up to ensure proper market uptake.
Consortium brings together ten partners, i.e academics (experts in thermodynamic cycle/control/simulation, heat exchanging, thermoelectric power, materials), technology providers (HX, Turbomachinery) and power plant operator (EDF-coordinator) covering the whole value chain, constituting an interdisciplinary group of experienced partners, each of them providing its specific expertise and contributing to the achievement of the project’s objectives.