Supercritical CARbon dioxide/Alternative fluids Blends for Efficiency Upgrade of Solar power plants

Project Information

SCARABEUS

Grant agreement ID: 814985

DOI

10.3030/814985

Project closed

EC signature date 28 March 2019

Start date 1 April 2019

End date 31 January 2024

Funded under

• SOCIETAL CHALLENGES - Secure, clean and efficient energy

Total cost

€ 4 950 266,25

EU contribution

€ 4 950 266,25

Coordinated by

POLITECNICO DI MILANO
Italy

Periodic Reporting for period 3 - SCARABEUS (Supercritical CARbon dioxide/Alternative fluids Blends for Efficiency Upgrade of Solar power plants)

Reporting period: 2021-10-01 to 2024-01-31

Summary of the context and overall objectives of the project

The Levelized Cost of Electricity (LCoE) of CSP (currently about 150 €/MWh ) has not attained the level targeted (100 €/MWh) except for few installations in exceptionally good locations. 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, penalize the sCO2 cycle efficiency. SCARABEUS 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. The adoption of blenbded CO2 increases the thermomechanical conversion efficiency from the current 42% to above 50%, bringing about large reductions in LCoE.
The aim of the SCARABEUS project is to demonstrate that the application of supercritical CO2 blends to CSP plants has the potential to reduce CAPEX by 30% and OPEX by 35% with respect to state-of-the-art steam cycles, thus exceeding the reduction achievable with standard supercritical CO2 technology. This translates into a LCoE lower than 96 €/MWh, which is 30% lower than currently possible. The project will demonstrate the innovative fluid and newly developed heat-exchangers at a relevant scale (300 kWth) for 300 h in a CSP-like operating environment.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main results of SCARABEUS can be summarized as follow:
i) an innovative cycle concept was developed with a thermal efficiency above 51% assuming a maximum temperature of 700°C;
ii) The effect of CO2 blends on turbomachinery design was assessed with turbine efficiency up to 93.0%;
iii) Innovative heat exchangers were designed and tested with enhanced performance with respect to conventional ones by 24%;
iv) A CSP designed with SCARABEUS technology can reduce the LCOE down to 95 €/MWh with conventional solar tower technology and 89 €/MWh with third generation solar receivers (LCOE calculated assuming Seville as plant installation site);
v) the CO2-C6F6 blend was validated in TUW test rig for 150 hrs. The blend was tested up to a maximum temperature of 500°C and condensing at 52°C.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

CAPEX will be reduced: SCARABEUS designed an innovative power block with higher performance, smaller turbomachinery and enhanced heat exchangers. All these aspects reduced the CAPEX with respect to conventional steam cycles by 16%; When integrated in a CSP plant, the optimal design of the system lead to a CAPEX between 4800 and 5000 €/kW depending on receiver technology, which is between 10 and 15% lower than the state of the art technology. Cheaper plant can be designed but would lead to higher LCOE
OPEX will be reduced: the higher efficiency and smaller equipment lead to an OPEX reduction which is between 17% and 26% for the conventional solar salt receiver and third generation receiver technology with respect to the state-of-the-art.
Affordable and integrated energy storage solutions will be developed: SCARABEUS has a large impact on the design and cost of the thermal energy storage (TES) system which is included in the reference CSP plant. The new working fluid (CO2-blend) allows for a significant reduction of the inventory of heat transfer fluid in the TES system thanks to the much higher efficiency of the power block (lower thermal energy reserve for the same storage of equivalent-electricity)
Technology performance will be increased: The adoption of SCARABEUS in solar tower plants will yield higher conversion effiencies than commercial technologies both at design and off-design operating conditions. The calculated design efficiency is >50% compared to 47% for sCO2 Cycles and 43% for steam power plants, and this advantage is confirmed also at part load;
Innovation capacity will be improved: The key enabling innovation in SCARABEUS is a new working fluid (blended CO2) used in the power block. Along with this, a second significant innovation is the development of innovative (from a conceptual standpoint) air-cooled condenser and recuperative heat exchanger designs which will be optimized for each particular working fluid and demonstrated experimentally.

SCARABEUS Concept