Arbor reportedly readies roughly $250M Series B for on-site power

Arbor Energy is developing compact, modular power plants for data centers and other electricity-intensive sites that need power around the clock. Axios reported on Sept. 29 that the company is preparing to raise about $250 million in Series B funding. This is a proposed round, not a closed financing.

Rather than burn fuel in ambient air, Arbor’s system first removes nitrogen and burns natural gas—or eventually biomass-derived synthetic gas—with pure oxygen. The resulting carbon dioxide and steam drive a turbine; water then condenses, excess carbon dioxide goes to underground storage and the remainder recirculates through the closed loop, according to the company.

That design moves carbon capture into the power cycle instead of separating diluted carbon dioxide from conventional turbine exhaust. Arbor says each planned HALCYON module will produce 25 megawatts on roughly one acre, capture more than 98% of its carbon dioxide and begin delivering power in 2028. It lists AI data centers, microgrids, utilities and industrial sites as intended applications.

For now, Arbor points to a smaller pilot rather than an operating HALCYON fleet. The company says it built the 1-megawatt ATLAS pilot in 2025, delivered it to a San Bernardino test site and spun its turbomachinery above 35,000 revolutions per minute using cold carbon dioxide. Those are pilot and component milestones, not the full commercial output projected for HALCYON.

In March, Arbor announced an agreement with energy-project facilitator GridMarket to deliver up to 5 gigawatts of baseload power beginning in 2029. GridMarket works with data centers, manufacturers and logistics operators, but the announcement did not identify end customers or operating Arbor plants.

The proposed financing would be a sharp step up from Arbor’s last round. Axios reported in October 2025 that Arbor raised a $55 million Series A; the proposed Series B target is roughly 4.5 times as large. The new report comes while Arbor is still testing its pilot, roughly two years before its target for first HALCYON power.