*Article* **Carbon Emissions Constrained Energy Planning for Aluminum Products**

**Rok Gomilšek 1,2, Lidija Cuˇ ˇ cek 2,\*, Marko Homšak 3, Raymond R. Tan <sup>4</sup> and Zdravko Kravanja <sup>2</sup>**


Received: 26 April 2020; Accepted: 22 May 2020; Published: 1 June 2020

**Abstract:** The production of primary aluminum is an energy-intensive industry which produces large amounts of direct and indirect greenhouse gas emissions, especially from electricity consumption. Carbon Emissions Constrained Energy Planning proved to be an efficient tool for reducing energy-related greenhouse gas emissions. This study focuses on energy planning constrained by CO2 emissions and determines the required amount of CO2 emissions from electricity sources in order to meet specified CO2 emission benchmark. The study is demonstrated on and applied to specific aluminum products, aluminum slugs and aluminum evaporator panels. Three different approaches of energy planning are considered: (i) an insight-based, graphical targeting approach, (ii) an algebraic targeting approach of cascade analysis, and (iii) an optimization-based approach, using a transportation model. The results of the three approaches show that approximately 2.15 MWh of fossil energy source should be replaced with a zero-carbon or 2.22 MWh with a low-carbon energy source to satisfy the benchmark of CO2 emissions to produce 1 t of aluminum slug; however, this substitution results in higher costs. This study is the first of its kind demonstrated on and applied to specific aluminum products, and represents a step forward in the development of more sustainable practices in this field.

**Keywords:** CO2 emissions; electricity planning; CO2 Constrained Energy Planning (CCEP); approaches for CCEP; aluminum products
