Innovations

Enhancement of high-flux solar concentrator

The existing high-flux solar concentration subsystem will be enhanced with respect to heliostats pointing accuracy and spatial stability of spot centroid to reduce spillage and provide the most suitable testing conditions throughout the day at average concentration ratios exceeding 2,500 kW/m² average on aperture for at least 7 hours per day in summer and 5 hours per day in winter. At present, that challenging irradiance can only be guaranteed for 5 hours in summer and 3 hours in winter, with significant decrease as we move out from solar noon.

Given the ambitious targets in terms of solar reactor efficiency, SUN-to-LIQUID II will develop a high-accuracy flux measurement system that might guarantee a low level of uncertainty in the measurement of power inlet.

Development of tailored porous redox materials

Novel redox materials will be developed, able to achieve significantly higher energy conversion efficiencies. To this end, a dedicated computational model of the heat and mass transfer characteristics of redox materials with different structures will be created. With the help of this model, advanced structures will be designed, fabricated and tested on a 5 kW-level before the structures are scaled up to the power level of 50 kW and tested at the unique research facility in Móstoles, Spain, maturing the technology up to validation in relevant environment.

Possibilities for recycling the redox materials are investigated as well. As material recycling is a crucial issue for the viability of the production pathway, this task will deliver important information for the analysis of economic and environmental performance of the fuel pathway.

Receiver-reactor with sensible heat recuperation

SUN-to-LIQUID II will revise the basic design of the solar receive-reactor system developed in the preceding project SUN-to-LIQUID extending its capabilities, by integrating a thermal energy storage and further components, to improve the overall performance. The improvements are linked to:

• Heat recuperation: development and implementation of a thermal energy storage system, using an inert heat storage material and a heat transfer fluid to recover sensible heat of the solar receiver-reactor.
• Highly integrated design: the integrated design reduces heat losses and thermal inertia in the system. It will be crucial for recovering sensible heat.
• Advanced flow control: the cyclic process requires a temporal reduction of the total pressure followed by an oxidation at ambient pressure and the intermediate application of a heat transfer fluid to move sensible heat between the receiver-reactor and the thermal energy storage. An advanced flow control strategy will enable the additional functionalities.
• Limiting radiative heat losses: when operated with a thermal energy storage, solar radiation is only used as an energy input for the receiver-reactor during one step of the cycle. During the other steps of the process, the aperture is causing significant radiative heat losses. An aperture cover is considered to minimize such losses.
• Advanced cavity design: 3D printed redox structures with improved properties will be distributed within the cavity to optimize the system performance by taking the actual flux profile of the solar concentrator into account and by tailoring the properties of the redox structures to their location within the cavity.

Gas-to-liquid plant

The existing gas-to-liquid conversion unit from the preceding project SUN-to-LIQUID will be adapted to the syngas production volumes expected in the SUN-to-LIQUID II project:

• Significantly higher reactor efficiencies and the coupling with heat storage and recuperation will require the redesign of several parts of the system, optimizing the solar gas inlet configuration to the buffer tank and improving the product separation system to increase the product yield.
• The control strategy for start/stop and normal operation will be improved to ensure more stable and longer production of hydrocarbons.
• The decoupling of syngas production from its conversion through gas storage offers the possibility to optimize the gas-to-liquid plant separately from the thermochemical subsystem. By operating the gas-to-liquid facility around the clock, a day-and-night production of solar fuels can be realized.

System analyses and business case study

SUN-to-LIQUID II will evaluate key performance indicators of the project and support the innovation process with guidance from an economic and sustainability perspective. Informed recommendations and a roadmap will be derived with the aim to communicate future implementation perspectives of SUN-to-LIQUID II to various target groups.

• An integrated system model will be developed to quantify the performance of future commercial solar fuel refineries. It will deliver a systemic constraint analysis to identify critical steps within the process chain. The integrated system model and its mass and energy balances will be the basis for the evaluation of KPIs of future commercial solar fuel production, which are evaluated by life-cycle analysis, socio-economic and techno-economic analyses.
• This holistic assessment will be further exploited for a comparative analysis with Power-to-Liquid and algal fuel production (at a common baseline case location) and for a parametric business case study.
• Key results from the SUN-to-LIQUID II system analyses will contribute to a roadmap towards commercial solar fuel production.