How Much Incremental Aluminum Capacity Does Grundartangi's Full Restoration Add to the Global Market?

Century Aluminum's (CENX) Grundartangi smelter in Iceland — one of Europe's largest primary aluminum facilities — suffered transformer failures in Q3 2025 that forced a temporary production halt on potline 2. Management now expects to return to close to full production by the end of July 2026, roughly 11–12 months after the outage began. The restoration raises a straightforward question: how much incremental metal does this put back into a global market already running tight?

Sizing the Grundartangi Gap

Grundartangi's nameplate capacity sits at approximately 310,000 metric tonnes per year across two potlines. With potline 2 offline since mid-Q3 2025, the smelter has been operating at roughly half capacity — removing an estimated 130,000–155,000 tonnes on an annualized basis from the market.

The impact is visible in Century's shipment figures. Consolidated quarterly shipments dropped from 176,000 tonnes in Q2 2025 to 162,000 tonnes in Q3, then fell further to approximately 140,000 tonnes in Q4. While other factors (Mt. Holly instability, Jamalco hurricane disruption) contributed, the Grundartangi outage was the dominant driver of the volume decline.

Full restoration by end of July 2026 would return roughly 130,000–155,000 incremental annualized tonnes to the global aluminum supply. Against a global primary aluminum production base of approximately 70–71 million tonnes per year, this represents about 0.18–0.22% of world output.

Small Number, Outsized Relevance

A fraction of a percent sounds trivial — but the global aluminum market has been operating near structural deficit for several years. The International Aluminium Institute has consistently reported that ex-China smelter utilization rates remain above 90%, and Western capacity additions have been virtually nonexistent outside of restart projects. In a market where surplus-to-deficit swings on the order of 500,000–1,000,000 tonnes move prices meaningfully, Grundartangi's 130,000+ tonne restoration is not negligible.

Moreover, Grundartangi produces value-added billet products for the European market. Century's Q2 2025 earnings call noted the ramp-up of billet casthouse production at the facility, and management guided for approximately $0.05/lb year-over-year increase in 2026 billet sales, generating an estimated $30 million of incremental EBITDA. Billet carries higher premiums than standard ingot, so the restoration's revenue impact exceeds what raw tonnage alone would suggest.

The Financial Picture for Century

Century's FY2025 quarterly results show the earnings drag from the outage clearly:

Q4 adjusted EBITDA of $171 million surged despite lower shipments, driven by higher realized aluminum prices and premiums. But management's Q1 FY2026 EBITDA guidance of $215–$235 million signals a step-change improvement, reflecting both the favorable price environment and initial volume recovery from Grundartangi.

For full-year FY2026, Century guided approximately 630,000 tonnes of primary aluminum shipments and $115–$125 million in total capital expenditure. The shipment figure implies a meaningful recovery from FY2025's outage-depressed run rate (annualizing Q4 shipments yields only ~560,000 tonnes). The gap between ~560,000 and 630,000 tonnes — roughly 70,000 incremental tonnes in the fiscal year — largely reflects the phased ramp of Grundartangi potline 2 through July plus contributions from the Mt. Holly restart.

Broader Industry Context

Century is not the only Western smelter adding supply. The Mt. Holly restart alone is expected to increase U.S. aluminum production by approximately 10%, adding over 75,000 tonnes per year once fully ramped. Combined with Grundartangi's restoration, Century is set to bring nearly 200,000 incremental annualized tonnes online across its portfolio by late 2026.

For peers like Alcoa (AA), which reported FY2025 quarterly revenue ranging from $3.0–$3.4 billion with EBITDA between $265–$869 million, the dynamic is complex. More Western supply theoretically pressures premiums, but the sheer scale of global deficit and tariff-driven regional dynamics (Section 232 tariffs have kept the U.S. Midwest premium elevated) suggest premiums remain structurally supported.

Norsk Hydro (NHY), with its own European smelting footprint, faces a similar setup — European billet premiums have been firm, and Grundartangi's restoration adds incremental supply into this high-premium market.

Investment Implications

For CENX bulls: Grundartangi's restoration is a near-term earnings catalyst. The combination of restored volumes, elevated LME prices (spot above $2,600/tonne in late 2025), and high Midwest/European premiums creates a setup where FY2026 EBITDA could meaningfully exceed FY2025 levels. The $215–$235 million Q1 EBITDA guide alone implies annualized earnings power well above FY2025's run rate.

For bears: Century trades at an EV/EBITDA of ~41x on trailing figures depressed by the outage. On normalized FY2026 earnings (if EBITDA reaches $800M+), the multiple compresses dramatically — but execution risk remains. Transformer repairs, insurance recovery timing (management noted potential lag in proceeds), and global recession risk could all delay or diminish the recovery.

What to Watch

1. Potline 2 restart milestones — Management targets end of July 2026; any slippage extends the volume drag.
2. Q1 FY2026 results — The $215–$235M EBITDA guide is the first real test of the recovery thesis.
3. European billet premiums — Grundartangi's value-add focus means premium trends matter as much as LME base prices.
4. Insurance proceeds — Century expects coverage for the transformer outage but timing remains uncertain.

Sources: Century Aluminum Q1–Q4 FY2025 earnings calls, CENX and AA financial statements via Diggr.