Research Papers

Renewable Hydrogen From the Zn/ZnO Solar Thermochemical Cycle: A Cost and Policy Analysis

[+] Author and Article Information
Julia F. Haltiwanger1

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55407haltiwan@me.umn.edu

Jane H. Davidson

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55407haltiwan@me.umn.edu

Elizabeth J. Wilson

Humphrey Institute of Public Affairs, University of Minnesota, Minneapolis, MN 55407ewilson@umn.edu

Efficiency is defined as the fraction of the solar energy reaching the heliostats that is stored in the hydrogen, based on the LHV in Ref. 5 and the HHV in Ref. 22.

An 11MWe installed capacity solar concentrating power plant that went on line near Seville, Spain in 2007.

Based on 2000 full power h/year.


Corresponding author.

J. Sol. Energy Eng 132(4), 041011 (Oct 12, 2010) (8 pages) doi:10.1115/1.4002511 History: Received March 29, 2010; Revised April 23, 2010; Published October 12, 2010; Online October 12, 2010

Flexible energy carriers are a crucial element of our energy portfolio. In a future in which a significant fraction of our energy comes from renewable sources, renewably produced fuels will be vital. The zinc/zinc-oxide thermochemical redox cycle is one approach for producing hydrogen using solar energy. This paper explores the level of carbon taxation necessary to make the cycle competitive with hydrogen production via methane reforming. In addition, the time frame for economic viability is assessed through the use of experience curves under minimal input, midrange, and aggressive incentive policy scenarios. Prior work projects that hydrogen produced by the zinc/zinc-oxide cycle will cost between $5.02/kg and $14.75/kg, compared with $2.40–3.60/kg for steam methane reforming. Overcoming this cost difference would require a carbon tax of ($119987)/tCO2, which is significantly higher than is likely to be implemented in most countries. For the technology to become cost competitive, incentive policies that lead to early implementation of solar hydrogen plants will be necessary to allow the experience effect to draw down the price. Under such policies, a learning curve analysis suggests that hydrogen produced via the Zn/ZnO cycle could become economically viable between 2032 and 2069, depending on how aggressively the policies encourage the emerging technology. Thus, the Zn/ZnO cycle has the potential to be economically viable by midcentury if incentive policies—such as direct financial support, purchase guarantees, low interest rate loans, and tax breaks—are used to support initial projects.

Copyright © 2010 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 1

Time line for implementation of Zn/ZnO cycle technology under the three policy scenarios

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Figure 2

Learning curves for the production of hydrogen via the Zn/ZnO cycle assuming progress rates (PR) of 0.87, 0.82, and 0.77 and an initial cost of $14.75/kg and initial batch size of 100,000 kg.

Grahic Jump Location
Figure 3

Assumed cumulative H2 production under an aggressive policy scenario, a midrange policy scenario, and a minimal policy scenario for the Zn/ZnO cycle technology assuming PR=0.82. Curves extend up to 5 years after initiation of the last assumed plant.

Grahic Jump Location
Figure 4

The cost of hydrogen produced via the Zn/ZnO cycle (assuming PR=0.82) under different policy scenarios and SMR with and without a carbon tax. The intersections of the cost curves for the two H2 production methods indicate the year in which solar H2 becomes competitive for each policy scenario.

Grahic Jump Location
Figure 5

The sensitivity of the predicted “break even” year to the five major assumptions




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