International Journal of Earth & Environmental Sciences Volume 2 (2017), Article ID 2:IJEES-139, 11 pages
Review Article
Exergy as Measure of Sustainability of Energy System

Peter Novak

Faculty for Technologies and Systems, Novo mesto, Slovenia
Prof. Peter Novak, Faculty for Technologies and Systems, Novo mesto, Slovenia; E-mail:
14 August 2017; 24 October 2017; 26 October 2017
Novak P (2017) Exergy as Measure of Sustainability of Energy System. Int J Earth Environ Sci 2: 139. doi:


Exergy is a measure of energy quality. The amount of exergy in energy carriers is very different. Normally the price includes only the value of quantity and not the quality of energy. Exergy is the only part of energy available to do work. For different purposes we need energy with different amounts of exergy: for heating and cooling the energy mixture between small amount of the exergy and large part anergy is needed. Transition to sustainable energy system, without GHG emissions, based on RE, open the questions how to evaluate exergy from solar energy. Solar energy in all form (irradiation, water flows, wind, and biomass) consists of nearly 100% of exergy. Solar energy is free, conversion systems are not. To exploit at maximum the solar exergy we need a sustainable energy system using in great amount the present infrastructure and existing or new developed energy conversion technologies. There is common agreement that we need four main presently used energy carriers: electricity, gaseous, liquid and solid fuels.

Our vision is the new Sustainable Energy System (SES) based on the use of solar and planetary energy for production of renewable electricity as a base for production of hydrogen. Hydrogen is a raw material for carbon recycling from biomass, making synthetic methane and methanol. The proposed SES is based on the existing infrastructure and known chemical processes. With regard to availability of renewable energy resources (RES) it is unrestricted and harmless in comparison to present fossil fuels use. The proposed SES consists of the three main exergy carriers: solar electricity, synthetic methane (CH4) and synthetic methanol (CH3OH).