Formation of Synthesis Gas Using Solar Concentrator Photovoltaics (SCPV) and High Temperature Co-electrolysis (HTCE) of CO2 and H2O
Authors: Frost Lyman Joseph , Hartvigsen Joseph , Elangovan S. 
Published: July 2010

Carbon dioxide is considered a greenhouse gas (GHG) that traps reflected solar energy and consequently increases the temperature of the earth. Many countries are now considering putting a tax on CO2 emissions that will increase the cost of products that are associated with those emissions. The most common method currently considered for dealing with CO2 emissions is the capture of the gas, pressurization, and then sequestration in either rock formations or saline aquifers. This is relatively costly in both capital investment and operation of the equipment. Also, there is the possibility that this CO2 will escape at some point in the future subjecting the company in question to an uncertain risk.

Ceramatec has been investigating an alternative approach that converts the CO2 into a useful product that can then be sold. Using solid oxide fuel cell materials in conjunction with a non-carbon source of energy it is possible to generate synthesis gas (CO and H2) and oxygen from CO2 and H2O. SCPV (Solar Concentrator Photovoltaic) systems are the most efficient generators of solar electricity and generate high quality heat at the same time. HTCE (High Temperature Co-electrolysis) uses both the solar electricity and the heat to electrolyze the CO2 and H2O at twice the total cycle efficiency of traditional electrolysis. The synthesis gas that is produced can be converted to synthetic fuels such as synthetic natural gas or Fischer Tropsch liquid fuels, or chemicals.

This paper will discuss this alternative approach to the disposal of CO2. This approach has the following advantages: permanent disposal, usable product, storage of solar energy in fuel, reduction of GHG, reduction in reflected solar radiation, and no additional GHG. The paper will discuss the application of the technologies, results of tests conducted to date, and the economics of the technology.

Introduction

The system described in this paper combines two complimentary technologies (i.e. a solar concentrator photovoltaic system and high temperature co-electrolysis) to turn water and carbon dioxide into a useful industrial input (i.e. synthesis gas). The process in effect provides a method to store the energy from sunlight in a form that is easily transported and can be used at any time rather than just when the sun is shining. At the same time, these technologies present a pathway to converting a greenhouse gas into useful product (i.e. synthetic natural gas, liquid hydrocarbons, or industrial chemicals).

Much debate on global warming has occurred but it is generally accepted that greenhouse gases (GHG) trap infrared radiation from the earth that would otherwise be radiated into space and thus retain heat within the atmosphere. In effect, GHG change the radiation balance by trapping some of the infrared heat associated with sunlight within the biosphere of the earth. The proposed technology attacks this problem in several ways.

(1) The SCPV system captures the heat associated with solar radiation and passes that heat to the HTCE system where the heat energy is used to increase the efficiency of the electrolysis process. Thus, the combined technologies will store not only the electrical energy from the SCPV but also the heat component of solar energy. This significantly increases the captured solar energy and thus, the efficiency of the total system.