“Yes, producing aluminium requires lots of energy. And yes, CO2 is indeed an inherent by-product of the electrolysis process. But to make any sense of aluminium's impact on the climate, we need to apply a life-cycle perspective on our metal. And what we then realize is that this metal and material has the potential to be climate-positive.”

Svein Richard Brandtzæg
President & CEO
Norsk Hydro ASA

Smelter Energy Statistics (1980-present)

Refinery Energy Statistics (1985-present)

The high value of aluminium products is a function of their unique properties and these unique properties are realised through the input of significant quantities of energy in the smelting process.

All steps in the aluminium production process, as with all industrial processes, consume energy: fuel is combusted to mine, move and refine bauxite. Refineries may co-generated electricity for use or export in addition to producing the steam required for the Bayer process. Smelters combust fuel within the facility to generate heat for anode baking, casting and supporting operations and semi fabrication and fabrication facilities require heat and pressure to form the metal. The energy required by these processes, however, is relatively low compared to the electrical energy required by the reduction process:

The electricity imported to or generated within smelting facilities is in the form of Alternating Current (AC), but the Hall-Héroult process requires Direct Current (DC); therefore smelters transform AC power into DC power using rectifiers before transmission to the smelter potline. Some AC power (around 5% on average) is used by other processes and auxiliary services (such as fume treatment or heating & lighting) and the presence of these varies across smelters. Therefore a measure of the energy efficiency of smelters (the process energy) is better defined as the DC kilowatt hours (measured at point of rectification) consumed per tonne of aluminium produced than the AC kilowatt hours (measured at the point of import or generation) consumed per tonne of aluminium. The current mix of electricity sources worldwide is as follows:

Because of the high percentage of self generated and directly purchased electricity, the aluminium industry’s power mix does not necessarily match the grid mix found in aluminium producing regions/nations.

The global power mix of the industry is as follows –regional power mix data can be found on the website of the International Aluminium Institute, click on the link to left to view and download current and historical data.

For comparison, the non-aluminium global power mix is:

Average split of energy consumption by process in aluminium smelters:

Recent years have seen the industry move towards new centres of production, in part driven by the growth of new centres of consumption (such as China), but also due to changes in availability of reliable, long term and economical sources of power. Energy-rich countries and regions that are looking to diversify their economies or have stranded power (i.e. energy that is remote from consumer base), such as the GCC and Iceland are those which are seeing growth in aluminium smelting capacity and which are, in effect, exporting their excess energy in the form of aluminium or aluminium products.

The growth in smelting capacity worldwide, with new facilities tending to be the most energy efficient, has seen reduction energy consumption per tonne of aluminium fall by 10% over the last 20 years.

Due to the high power requirements of aluminium smelters, the aluminium and power generation sectors have a close developmental relationship. While new smelting capacity “follows” available energy, it also enables the development of power generation and distribution capacity in such areas, bringing reliable electrical energy to new areas, along with concurrent economic development, other industries and improved quality of life for residents.

A power station that is on constantly (base load) is more efficient than one that is used intermittently (peak load). Aluminium smelters, which require a constant source of power, play an important role in maintaining base load. Smelters can also modulate their power requirements to a certain degree, thus giving power generators and distributors a base load and allowing them to meet peak demands from other consumers, municipalities and other industries.

In some regions too another benefit of power generation is the by-production of fresh water. The power plant at DUBAL in Dubai, for instance, utilises its hot exhaust gases to drive a thermal water desalination plant, where up to 140 megalitres of fresh water can be produced per day from incoming seawater. This fresh water is used for the smelter’s on-site needs, with the excess being sold to a number of external customers, including the city of Dubai.