Abstract
The utilization of the captured CO2 as a carbon source for the production of energy storage media offers a technological solution for overcoming crucial issues in current energy systems. Solar energy production generally does not match with energy demand because of its intermittent and non-programmable nature, entailing the adoption of storage technologies. Hydrogen constitutes a chemical storage for renewable electricity if it is produced by water electrolysis and is also the key reactant for CO2 methanation (Sabatier reaction). The utilization of CO2 as a feedstock for producing methane contributes to alleviate global climate changes and sequestration related problems. The produced methane is a carbon neutral gas that fits into existing infrastructure and allows issues related to the aforementioned intermittency and non-programmability of solar energy to be overcome. In this paper, an experimental apparatus, composed of an electrolyzer and a tubular fixed bed reactor, is built and used to produce methane via Sabatier reaction. The objective of the experimental campaign is the evaluation of the process performance and a comparison with other CO2 valorization paths such as methanol production. The investigated pressure range was 2–20 bar, obtaining a methane volume fraction in outlet gaseous mixture of 64.75% at 8 bar and 97.24% at 20 bar, with conversion efficiencies of, respectively, 84.64% and 99.06%. The methanol and methane processes were compared on the basis of an energy parameter defined as the spent energy/stored energy. It is higher for the methanol process (0.45), with respect to the methane production process (0.41–0.43), which has a higher energy storage capability.
Highlights
The environmental and economic sustainability of future energy systems needs to deal with several challenges and technical aspects
The results show that the ratio between the spent energy and the stored energy is higher for the methanol process (0.45)
Energy storage systems have gained high interest in research since they are a promising approach to address the challenge of intermittent generation from renewables on the electric grid
Summary
The environmental and economic sustainability of future energy systems needs to deal with several challenges and technical aspects. The increase of the share of Renewable Energy Sources (RES) overcame 25% of energy generation, implying new issues related to balancing, security, and production-consumption profiles matching [1]. While the existing electricity network results were largely unchanged, solar and wind power have seen a large expansion during the last decade. This means that the current electrical energy system is un-optimized and needs adjustments. The electricity transmission system needs to be adapted from the large scale production facilities used today to smaller and locally distributed energy production sites. Energy storage solutions are Energies 2017, 10, 855; doi:10.3390/en10070855 www.mdpi.com/journal/energies
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