Renewability Index of energy systems. The case of the global electricity with focus on its infrastructure between 1900 and 2050.

The Renewability Index (RI) of energy systems indicates the amount of net renewable exergy captured from nature for each unit of non-renewable exergy invested in the infrastructure of the technology and their utilization. This RI builds on the concept of exergy cost since it considers the non-renewable exergy sources used in energy production, both direct (fuels) and indirect (infrastructure, measure through exergy cost) use. Indirect use includes the extraction and refining of the materials used in the infrastructure. Therefore, conventional power plants present a RI below zero, since no net renewable exergy is captured and non-renewable exergy is destroyed in the production process. In the case of renewables, the RI would be greater than zero in case it captures more renewable exergy than the non-renewable exergy invested in its infrastructure. Thus, this study applies this concept to the global electricity system between 1900 and 2050, photovoltaics and wind technologies to study the role of its infrastructure. From 2017 onwards, the IEA’s Net-Zero Emission (NZE) scenario is used. The results show that, until 2028, the global electrical system is not renewable, as its RI is less than zero. From this point onward, it begins to increase rapidly, reaching 7 MJ/MJ by 2050. On the other hand, wind technology shows an RI of up to 14 MJ/MJ by 2050, while photovoltaic technology reaches 3.4 MJ/MJ by the same year. These results indicate that, despite accounting for a significant penetration of renewable technologies, efforts must be increased to reduce the non-renewable exergy cost of renewable infrastructures. The concept of the RI provides a metric to quantify the actual amount of exergy captured by an energy system and could be extended to assess the degree of renewability of society.