For most of the past decade, the flow battery conversation has been framed as a three-way race: vanadium versus iron versus zinc-bromine. By June 2026, that framing is outdated. The three chemistries are not at equivalent stages of commercial maturity, and the honest comparison looks very different from the one most buyer’s guides still present. Here is what the actual 2026 picture shows.

If you are evaluating a flow battery for a NZ or Pacific project, this is the comparison that matters. We will look at each chemistry honestly — what is deployed, what is in commercial supply, and what the manufacturer health actually looks like — and end with a practical recommendation for which one fits which use case.

Vanadium flow — the deployed incumbent

Vanadium redox flow is the chemistry with the longest operational track record and the largest global deployed capacity in 2026.

• Deployed scale: Rongke Power’s December 2024 completion of the 175 MW / 700 MWh Xinhua Ushi project pushed its global utility-scale fleet past 2 GWh — the largest installation footprint in the flow battery sector.
• Operational record: Sumitomo Electric’s Yokohama Works installation has demonstrated 24 years of continuous service on the same electrolyte (2001 to present, across two different battery systems).
• Peer-reviewed validation: a 2024 ScienceDirect study documented a 12-year commercial VFB with only ~5% capacity loss after a decade of service.
• Manufacturing pipeline: a 1.6 GW vanadium flow manufacturing complex is under construction in Baotou, China, backed by approximately CNY 11.5 billion in investment. China’s domestic 12 GWh VRFB mandate for 2027 ensures continued scaling.
• Cost trajectory: at sub-utility scale, vanadium flow currently sits at $800–$1,200/kWh installed. Manufacturing scale-up is expected to bring this down meaningfully through 2027–2030.
• The honest weakness: round-trip efficiency of 75–80% trails lithium and iron flow. Higher upfront capex than iron flow at small scale. Supply chain concentration in China.

Iron flow — promising technology, struggling manufacturer

Iron flow batteries are the second most-deployed flow chemistry globally, but the dominant manufacturer (ESS Tech) is in serious financial difficulty as of mid-2026.

• Technology validation: in May 2026, an American Public Power Association (APPA) report on Burbank Water and Power’s ESS deployment concluded that iron flow technology “works as intended” and “there is a place for this battery in a utility’s overall energy storage strategy” after a 21-month evaluation.
• Manufacturer status: ESS Tech disclosed in its Q1 2026 SEC filing that there is “substantial doubt about our ability to continue as a going concern” with $21.5 million cash on hand as of 31 March 2026. The company has acquired VoltStorage GmbH’s iron-salt battery IP to expand its platform.
• Active programmes: Project New Horizon with Salt River Project and Google (5 MW / 50 MWh, manufacturing 2026, delivery December 2027). Pipeline proposals exceeding 1.1 GWh by Q2 2025.
• Materials advantage: uses abundant iron and saltwater electrolyte. No supply chain dependence on critical minerals from China or anywhere else. Made-in-USA manufacturing model with 98% domestically sourced components.
• The honest weakness: limited deployment at scale, manufacturer financial uncertainty, lower deployed cycle data than vanadium, ongoing engineering challenges acknowledged by ESS in SEC filings.

Zinc-bromine — the chemistry without a major Western manufacturer

This is where the 2026 picture differs most sharply from older buyer’s guides. The most prominent commercial zinc-bromine manufacturer no longer exists.

• Redflow collapse: Australian zinc-bromine specialist Redflow Limited entered voluntary administration on 23 August 2024, ceased operations on 18 October 2024, and was liquidated in December 2024. The company had installations at 250+ sites across nine countries before closure.
• The reasons (Faraday Institute October 2025 report): “challenges in raising capital, high costs of producing components at small volumes and reliability issues leading to high repair costs under warranty.” Faraday noted these problems “do not appear linked to the format of the batteries” — meaning the technology itself may be sound, but commercial scale-up has not been achieved.
• Cycle life context: documented zinc-bromine cycle life sits at ~3,650 cycles, or 10 years at one cycle per day — half the lifespan of vanadium flow under comparable conditions.
• Other manufacturers: Primus Power offers a 25 kW / 125 kWh zinc-bromine system; e-Zinc has commercialisation funding for a different zinc chemistry; small Chinese manufacturers exist but at limited scale.
• The honest position for 2026 buyers: zinc-bromine is technically interesting but lacks an established Western manufacturer with proven utility-scale deployment after Redflow’s collapse. For a 25-year asset, treat the supply risk as substantial.

The fair comparison on the metrics that actually matter

Setting marketing aside, here are the four metrics that decide most procurement conversations.

• Round-trip efficiency: iron flow ~70–75%, vanadium ~75–80%, zinc-bromine ~70–80%. None match lithium’s 90–95%, but the long-duration use case is where these chemistries earn their place anyway.
• Cycle life: vanadium 15,000–20,000+ cycles, iron flow 10,000–25,000+ (manufacturer claims), zinc-bromine ~3,650 cycles. Vanadium wins on documented operational records; iron flow’s claims are real but less validated.
• Deployed evidence: vanadium has Ushi (700 MWh), Dalian (400 MWh Phase 1), Sumitomo Hokkaido (60 MWh). Iron flow has Burbank/APPA validation, Salt River Project pilot, Energy Warehouse deployments. Zinc-bromine has Redflow’s 250+ now-orphaned sites.
• Manufacturer durability: vanadium leaders (Rongke, Sumitomo) have decade-plus operating history. ESS Tech faces going-concern uncertainty. Redflow no longer exists.

Which chemistry actually wins in 2026

The verdict depends honestly on the use case, the location, and the buyer’s appetite for supply chain concentration.

• For NZ and Pacific utility-scale (1 MWh+): vanadium flow wins on deployed evidence, manufacturer continuity, and operational track record. Ushi, Dalian, and Hokkaido make it the only chemistry with proven 700 MWh-class deployment.
• For US buyers prioritising domestic supply: iron flow via ESS Tech is the chemistry to follow, with the going-concern caveat. Made-in-USA manufacturing matters for IRA-eligible projects and federal procurement.
• For zinc-bromine: hard to recommend for any new project commissioning in 2026, because the major manufacturer has been liquidated and the alternatives have not yet demonstrated equivalent scale. Existing Redflow installations need careful service planning.
• For NZ buyers specifically, the SPower Series brings Rongke’s Ushi-validated vanadium flow technology to utility and commercial-scale NZ deployments with local distribution and service.

Conclusion

The flow battery comparison conversation needs updating for 2026. Vanadium has decisively pulled ahead on deployed capacity, operational records, and manufacturer durability — Ushi is the proof point, Sumitomo Yokohama is the long-life evidence, and Rongke’s 2 GWh fleet is the supply chain reality. Iron flow is technically valid but commercially uncertain pending ESS Tech’s financial trajectory. Zinc-bromine, after Redflow’s liquidation, is currently without a major Western manufacturer suitable for utility-scale procurement. None of this means vanadium is the right answer for every use case. It does mean that the honest 2026 comparison looks much less like a three-way race and much more like one mature chemistry, one promising-but-fragile alternative, and one chemistry waiting for its next manufacturer.

For a tailored chemistry recommendation built around a specific NZ or Pacific project — including manufacturer due diligence and current lead times — the Zion Technologies team can put together a written summary within 48 hours.