# On the use of CO2 for the integration of Renewable energy in the energy system.

Abstract

In the context of the energy transition, efficiency and renewable energy integration are identified as having the highest potential for mitigating the $$CO_{2}$$ emissions . From the energy system engineering point of view, this means that not only one has to convert renewable energy resources into distributed energy but also to make it available to supply the energy services when they are needed. In this paper, we demonstrate the role of process system engineering for designing the future energy systems and we explore the possible role that $$CO_{2}$$ could play as a material to help the energy transition. Considering $$CO_{2}$$ as a carbon support, we show on the one hand the possible role of $$CO_{2}$$ in the energy system : as an energy carrier in district energy systems or as a possible carbon source for long term renewable energy storage when considering power to gas concept. We also highlight the importance of understanding the carbon cycle, considering the $$CO_{2}$$ in the atmosphere and the possible ways to replace fossil fuel produced $$CO_{2}$$ by the one harvested in the atmosphere.

## Introduction

In the context of the energy transition, the energy efficiency and the integration of renewable energy resources are identified as having the highest potential for mitigating the $$CO_{2}$$ emissions. According to the energy technology perspective report of the International Energy Agency (Agency 2014), it corresponds to more then 65% of the contribution to the $$CO_{2}$$ mitigation effort needed to limit the temperature increase to 2°C. This leads to a considerable effort of the research community to propose new advances for the energy usage and conversion using bio-chemical, thermo-chemical or photo-chemical or physical concepts. For the engineers who will be responsible of designing the future energy system, the goal is today to integrate these new technologies in the energy system and to create innovative new smart multi-energy infrastructures that will allow the penetration of these technologies and to operate them with a maximum of efficiency. The role of the process and energy system design is to calculate the equipments to be considered to supply the products and the services required by the community (being a household, a district, a city or a country). This means defining the most attractive technologies to be used and their corresponding sizes and location, the way they are interconnected and the way they will be operated over their life time. It is also important to consider how they will be manufactured and dismantled or recycled at the end of their lifetime. The systems have therefore to be assessed with respect to different criteria like thermodynamic, economic or environmental. They have also to be assessed considering not only the existing technologies but also to show the potential role of the future technologies. It comes from this analysis a definition of the possible role of the energy policy as well as of the need for infrastructure development in particular considering multi-energy networks like electrical, gas or heat and information. For the engineers and the policymakers it is therefore important to define in a systematic way the most important competing system design scenarios and to define in a comprehensive way the performance indicators that will allow to compare them.