Gen 3 Particle Pilot Plant (G3P3)

The Department of Energy (DOE) recently announced a Phase III, $25 million award to Sandia National Laboratories to build, test and demonstrate a next-generation Concentrating Solar Thermal Power (CSP)  plant at the National Solar Thermal Test Facility (NSTTF) in Albuquerque, New Mexico. The award was announced on March 25 during a “100% Clean” webinar by DOE Secretary Granholm, and is part of a $70 million multi-year DOE Generation 3 CSP Systems (Gen3 CSP) program that began in 2018. Watch the DOE CSP video Secretary Granholm introduced during the webinar.

The objectives of the Gen 3 Particle Pilot Plant (G3P3) project are to design, construct, and operate a multi-MWfalling 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.

Project Overview

Component Design and Development 

In Phases 1 and 2, we successfully de-risked key elements of the proposed Gen 3 Particle Pilot Plant (G3P3) by improving the design, operation and performance of the G3P3 system through both modeling and testing of critical components (Figure 2).  Modeling and test results have led to optimized designs of each component that meet desired performance metrics.  Detailed drawings, piping and instrumentation diagrams, and process flow diagrams were generated for the integrated system, and structural analyses of the assembled tower structure were performed to demonstrate compliance with relevant codes and standards.  Instrumentation and control systems of key subsystems were also demonstrated.

The major G3P3 components include:


Particle Receiver

Storage System

Heat Exchanger and sC02 Flow Systems

Particle Lift

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.

Phases 1 and 2 Risk Reduction

  • CARBO HSP 40/70 selected for G3P3-USA based on demonstrated solar absorptance, durability and flowability at high temperatures
  • CARBO HSP 40/70 particles were exposed to 10,000 irradiance cycles reaching 1000°C per cycle which resulted in a 1% decrease in absorptivity. Particles held at a constant temperature of 800°C for 400 hours also resulted in a 1% decrease in absorptivity.
  • Particle flow processes and alternative low-cost particles were evaluated
  • Impact of particle properties on LCOE and other solar thermal applications were evaluated

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.

Phases 1 and 2 Risk Reduction

  • Advective losses and wind were found to be the primary loss mechanisms in lowering thermal efficiencies in our previous receiver designs
  • Seven new features (hood, quartz aperture covers, active airflow, multistage release, reduced volume receiver, SNOUT, and chimney) were simulated and/or tested in Phase 1 to reduce heat loss, mitigate wind impacts, reduce particle emissions, and minimize damage from high fluxes. Of these, three features (multistage release, reduced volume, and SNOUT) were shown to have significant impact (increasing receiver efficiency by over 10 percentage points in some cases) and are being implemented in the G3P3-USA receiver design.
  • Rigorous optimization was applied to a 2 MWt G3P3-USA receiver geometry; simulated efficiencies expected to approach ~85 – 90%
  • Over 250 hours of on-sun and ground-based testing were performed to investigate the impact of multistage release, reduced volume receiver, and automated particle flow control (PID) to regulate the particle outlet temperature
    • Receiver efficiencies up to ~80 – 90% were achieved with new features
    • PID controls were effective at maintaining particle outlet temperatures up to ~780 °C
    • Multi-stage release was effective at cooling backwall temperatures
    • Reduced cavity volume was effective at reducing advective heat loss
    • Emission of particle dust was below EPA and NIOSH standards
  • 100 MWe three-receiver tower design simulated with good wind resilience and efficiencies (> ~80%)
  • Watch our new particle receiver video clips

    Particle Receiver Video 1

    Particle Receiver Video 2

    (Videos courtesy of Brantley Mills, Sandia.)

    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.

    Phases 1 and 2 Risk Reduction

    • Flat-bottomed G3P3 storage bins were designed to induce funnel flow, reducing wall erosion and heat loss via stagnant self-insulating particles
    • Small-scale tests were performed to validate particle flow and heat-transfer models
    • Pre-cast refractory liner materials were tested for erosion and thermal expansion; shotcrete application methods were investigated and tested
    • Methods for cooling of concrete slab were investigated
    • Tower-integrated and ground-based storage bins designs were evaluated for commercial systems with capacities from 10 – 100 MWe with consideration of heat loss (<1%) and the structural limitations of tower-integrated systems in regions with high seismicity
    • Cost models for ground-based and tower-integrated storage were developed

    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.

    Phases 1 and 2 Risk Reduction

    • Simulations and testing of 100 kWt SuNLaMP HX and shell-and-tube KSU heat exchanger provided lessons learned and informed design of G3P3 HX
    • Shell-and-plate G3P3 HX design with integral headers, closer plate spacing (~3 mm), and counterflow design provided >300 – 400 W/m2-K with <2% (500 kPa) pressure drop based on modeling
    • Subscale (20 kWt) prototype was manufactured from stainless steel with novel design features to understand manufacturing steps and verify performance
    • Subscale prototype was tested up to 500 °C at 17 MPa, which yielded overall heat transfer coefficients of >300 W/m2-K and pressure drop <7 kPa (0.04%)
    • Particle flow testing was performed at 650 °C with varying plate spacing (1.5-6 mm) to demonstrate reliable and uniform particle flow in narrow vertical channels at operating temperature
    • Bonding, brazing, and chemically etching of IN740H was conducted, but bond strength has not yet met ASME code requirement. Parallel efforts provided the bond, braze, and etch development for constructing the heat exchanger from IN617 and HR230
    • sCO2 corrosion of 800H was larger than expected; corrosion testing is being planned for 800H, 740H, IN617, and/or HR230

    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.

    Phases 1 and 2 Risk Reduction

    • Bucket elevator selected for G3P3-USA due to excessive costs for small-scale skip hoist; skip hoist was designed and evaluated for 100 MWe plant
    • Heat loss from the G3P3 bucket elevator was modeled, and insulation was designed to minimize heat losses and particle temperature drops to < 3 °C
    • Transient heat loss and costs were evaluated for commercial-scale skip hoist

    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. You can also visit Sandia CSP projects or view the DOE CSP G3P3 profile page.

    Particles in Action

    Click to see the Free Falling_CSP Particle Receiver video.

    Click to see the Staged Falling_CSP Particle Receiver video.

    (Videos courtesy of Jin-Soo Kim, CSIRO)

    Cliff Ho