The Gen 3 Particle Pilot Plant (G3P3): Integrated High-Temperature Particle System for Concentrated Solar Power project aims to design, construct, and operate a multi-MWt falling particle receiver system that can operate for thousands of hours, provide six hours of energy storage, and heat a working fluid (e.g., sCO2 or air) to ≥ 700 °C while demonstrating the ability to meet SunShot cost and performance goals.
G3P3 development is taking place at the National Solar Thermal Test Facility, the only test facility of its type in the United States. Our team consists of the Georgia Institute of Technology, King Saud University, Australian Solar Thermal Research Initiative (CSIRO, U. Adelaide, Australian National University), CNRS-PROMES, German Aerospace Center, EPRI, Bridgers & Paxton, Bohannan Huston, Inc., SolarDynamics, Carbo Ceramics, Solex Thermal Science, Vacuum Process Engineering, FLSmidth, Materials Handling Equipment, Allied Mineral Products, Matrix PDM Engineering, and Saudi Electricity Company.
Unlike conventional CSP receivers that use fluids flowing through tubes, the proposed particle-receiver system uses solid particles (ceramic or sand) that are heated directly as they fall through a beam of concentrated sunlight. Once heated, the particles are stored in an insulated bin before passing through a particle-to-working-fluid heat exchanger to power a high-efficiency Brayton cycle (e.g., sCO2 or air). The cooled particles are collected and then lifted back to the top of the receiver. Aside from the particle lift, the entire process is based on gravity-driven flow of the particles through each component.
Project research will advance novel particle-based technologies to address key risks, such as particle attrition and wear; dust formation, heat loss (receiver, storage, heat exchanger, lift), particle-to-working-fluid heat transfer, thermomechanical stresses, and materials erosion.
Component Design and Development
The major G3P3 components include:
CARBO Ceramics will provide new formulations for particles that have improved particle durability and maintain desired optical properties after long-term exposure to high temperatures (in-kind). KSU and Adelaide will investigate alternative cost-effective particles that can significantly reduce costs, especially when the temperature is only ~200 °C. ASTRI will carry out a sensitivity study on particle source/material (natural or synthesized) and properties (different sizes and density) in relation with falling particle hydrodynamics/heat transfer and durability/degradation. KSU will investigate other minerals such as red sands and olivine sands as well as other minerals found to be promising low-cost alternative to current bauxite-based products. We’ll investigate the physics of dust formation and particle attrition using high-resolution imaging methods under different particle conditions. Models will be developed using first principles or empirical correlations to predict particle attrition as a function of operating conditions in the G3P3 system.
A ≥1 MWt particle receiver is situated on top of a tower to heat the particles to nearly 800 °C in a single pass. The baseline design to accommodate required heating and mass flow rates is a directly-irradiated falling particle receiver system, but additional novel designs (centrifugal, obstructed, fluidized) and innovative patent-pending features (aperture covers, baffles, suction/recirculation, multistage release) will be considered in Phases 1 and 2 through partnership with international team members to reduce risks associated with achieving a 90% receiver thermal efficiency (commercial scale) at particle temperatures between ~570 and 775 °C. We will also implement automated particle mass-flow control methods to maintain constant particle outlet temperature and address risks associated with temporally and spatially varying solar flux.
Particle Receivers in Action
Videos courtesy of Jin-Soo Kim, CSIRO
Candidate particles include commercial ceramic particles from Carbo Ceramic, but alternatives will also be considered to reduce costs and improve optical/thermal/mechanical properties. Scalable particle storage systems will be designed and engineered in Phases 1 and 2, working with industry partners. Our previous studies have investigated both steel and non-steel structures to reduce costs and risks associated with erosion and heat loss.
Small-scale moving-packed-bed and fluidized-bed particle heat exchangers that can operate at >700 °C and >20 MPa have been designed and studied by the team. Larger-scale (≥ 1 MWt) systems that meet performance requirements will be evaluated to reduce cost and performance risks based on lessons learned from these previous studies. Low particle-side heat transfer, material erosion, and high-temperature creep/fatigue are risks for the high-pressure tubes or plates that will contain the working fluid flowing through the heat exchanger. Component testing and analysis will be performed to better understand and mitigate these risks. We will also design and fabricate a ≥ 1 MWt sCO2 flow loop using lessons learned from the design of Sandia’s 100 kWt sCO2 loop to provide high-pressure sCO2 to the heat exchanger.
Our team has demonstrated the use of screw-type (Olds) elevators to lift high-temperature particles for previous on-sun testing, but the lift efficiency was low (~5%) due to friction, which likely caused significant particle abrasion and attrition. We will work with industry to consider alternative designs studied by the team such as mine hoists and bucket elevators to reduce risks of particle attrition and meet the desired performance requirements.
Technoeconomic Analysis and Scale-Up
Preliminary models of a commercial 100 MWe particle power-tower system using the System Advisor Model (SAM) and EES have shown that particle-based CSP systems can meet the SunShot goal of $0.06/kWh using recently published capital costs for particle-based components with a receiver efficiency as low as 85% if the storage costs are reduced from $22/kWht to $15/kWht. In addition, results show that the G3P3 technology can be used as a peaker plant with three to six hours of storage and LCOE < $0.10/kWh. Cost advantages in the particle receiver and storage can result from eliminating costly high-temperature metal alloys to hold and convey fluids. Direct storage of the particles also provides cost advantages over gas-based systems, which require additional heat exchangers and storage media. Sandia and ANU will develop technoeconomic analyses for the G3P3 system based on findings from Phases 1 and 2, and EPRI will lead market adoption studies of particle-based CSP systems. By the end of Phase 2, we will have a detailed design of the G3P3 systems with updated technoeconomic analyses for both the pilot-scale and commercial-scale systems.
The end goal of this project is to have completed > 2000 hours of combined testing of the G3P3-USA and G3P3-Saudi integrated particle-receiver systems that meet desired SunShot metrics and demonstrate a thermal duty ≥ 1 MWt for the receiver and heat exchanger, which heats a working fluid (sCO2 and air for G3P3-USA and G3P3-Saudi, respectively) to >700 °C. Steady-state and transient operations will be demonstrated with inclusion of start-up and shut-down procedures, as well as deferred energy delivery with 6 hours of storage. Key results and findings (except for specific intellectual property) will be published in conference papers or journal articles. A clear path towards commercialization will be identified, if not demonstrated, through our international development efforts.
This work is funded by the U.S. Department of Energy Solar Energy Technologies Office as part of Gen 3 Concentrating Solar Power initiative. To learn more about the initiative, visit Generation 3 Concentrating Solar Power Systems (Gen3 CSP). The U.S. Department of Energy’s Solar Energy Technologies Office supports early-stage research and development to improve the reliability and performance of solar technologies. Learn more at the Solar Energy Technologies Office.