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Publication Name: Supercritical CO2 Brayton cycles for solar-thermal energy
Original File Name Searched: IversonArticle3.pdf
Page Number: 001

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Applied Energy 111 (2013) 957–970

Contents lists available at SciVerse ScienceDirect Applied Energy

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Supercritical CO2 Brayton cycles for solar-thermal energy Brian D. Iverson a,b,⇑, Thomas M. Conboy b, James J. Pasch b, Alan M. Kruizenga b

a Brigham Young University, UT 84602, United States

b Sandia National Laboratories, Albuquerque, NM 87185, United States


Modeling and experimental data are presented and compared.

Results include transient response of a sCO2 Brayton to reduced thermal input. Benchmarking data for steady state operation is tabulated.

Areas of necessary research for successful implementation of sCO2 Brayton.

article info

Article history:

Received 6 March 2013

Received in revised form 9 June 2013 Accepted 11 June 2013


Supercritical CO2


Solar-thermal Concentrating solar power Energy

1. Introduction

It is recognized that solar-thermal energy can play a useful role in generating electrical power despite concerns regarding cost, as the thermal source is accessible and ubiquitous. One platform to produce power from a solar resource is using the point-focus, power-tower system in which the solar-thermal energy is concen- trated thereby elevating the working temperature and associated efficiencies. Solar assisted power production to offset carbon emis- sions [1] and thermal storage for grid stability [2–4] remain strong motives for utilizing this approach. Cost-reduction efforts have been implemented to improve solar-thermal power production [5] with more aggressive efforts being supported by the U.S.

⇑ Corresponding author at: Brigham Young University, UT 84602, United States. E-mail address: (B.D. Iverson).

0306-2619/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.


Of the mechanisms to improve efficiency for solar-thermal power plants, one of the most effective ways to improve overall efficiency is through power cycle improvements. As increases in operating tempera- ture continue to be pursued, supercritical CO2 Brayton cycles begin to look more attractive despite the development costs of this technology. Further, supercritical CO2 Brayton has application in many areas of power generation beyond that for solar energy alone.

One challenge particular to solar-thermal power generation is the transient nature of the solar resource. This work illustrates the behavior of developmental Brayton turbomachinery in response to a fluctuating thermal input, much like the short-term transients experienced in solar environments. Ther- mal input to the cycle was cut by 50% and 100% for short durations while the system power and condi- tions were monitored. It has been shown that despite these fluctuations, the thermal mass in the system effectively enables the Brayton cycle to continue to run for short periods until the thermal input can recover. For systems where significant thermal energy storage is included in the plant design, these tran- sients can be mitigated by storage; a comparison of short- and long-term storage approaches on system efficiency is provided. Also, included in this work is a data set for stable supercritical CO2 Brayton cycle operation that is used to benchmark computer modeling. With a benchmarked model, specific improve- ments to the cycle are interrogated to identify the resulting impact on cycle efficiency and loss mecha- nisms. Status of key issues remaining to be addressed for adoption of supercritical CO2 Brayton cycles in solar-thermal systems is provided in an effort to expose areas of necessary research.

Ó 2013 Elsevier Ltd. All rights reserved.

Department of Energy [6]. High-efficiency power cycles is a critical component in achieving the cost reduction goals and may require temperatures that reach above 600 °C to obtain cycle efficiencies in the 50% range.

The supercritical carbon dioxide (sCO2) Brayton cycle has emerged as a promising avenue for high-efficiency power produc- tion. With growing interest in renewable energy sources, cycles with high efficiency are critical to achieving cost-parity with non-renewable sources. Convergence on sCO2 Brayton is occurring from the nuclear [7–9] and geothermal [10] fronts, in addition to solar-thermal [11–13]. Turbomachinery for sCO2 Brayton is in the development phase [14–19] and is gaining momentum as interest grows and technical risks are reduced. However, adaptation of the cycle to interface with various heat sources will be imperative for its adoption as an industry- manufactured technology.

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