Synergy with carbon capture and storage
The various endothermic reactions that have been discussed that potentially convert hydrocarbons to H2 and CO2 are also those that are proposed for potential CO2 emission-free processes. In this scenario, some of the fossil fuel itself is oxidized to provide the heat input for the reactions. CO2 is then scrubbed from the product gas for sequestration. The challenge in CO2 emissions is currently focused on finding storage sites capable of hosting quantities reaching annually 25 billion tons (‘Basic Research Needs for Solar Energy Utilization’, 2005). Such sinks, which could be geological formations, the ocean, saline aquifers, terrestrial ecosystems, etc., in order to be effective should provide extremely low leakage rates, since only 1% leakage rate could result in reversing any sequestration effort in a period of only 100 years (Muradov and Veziroglu, 2008), Even by using the safest, long-term CO2 storage option, predictions concerning both security issues and investment costs cannot be defined precisely (Knight, 2010; IEA, 2009). In theory, storages sites are more than enough to satisfy global requirements for CO2 storage, but in practice it is estimated that a very small proportion of those sites could be utilized (IEA, 2009; Van Noorden, 2010).
Whilst such technologies can be considered as future commercial competitors of CST, there is the potential of combining solar-driven reactions with carbon capture technologies to produce the end products. In this scenario, the solar input will significantly reduce the amount of CO2 per unit of H2 that must be separated and stored.