Holmes Western

Executive Overview

Holmes Western is a 100 MWh Rondo Heat Battery (RHB) operating at Holmes Western Oil Corporation's facility in Kern County, California, which reached commercial operation in September 2025. The system is powered exclusively by a 20 MW on-site off-grid solar PV array and delivers continuous high-pressure steam at 100+ bar (1,450+ PSI) to the facility's industrial heat network 24 hours a day. After a ten-week commissioning period, the project achieved all milestones for daily automatic operation, efficiency, and reliability. It is the world's largest industrial heat battery in commercial operation, replacing one of the facility's natural gas-fired boilers.

How It Works & Differentiation

The Rondo Heat Battery uses surplus daytime solar electricity to resistively heat stacks of refractory bricks to storage temperatures exceeding 1,000°C. The stored thermal energy is dispatched on demand by passing air over the bricks, producing superheated steam that integrates directly into the facility's existing steam flanges and boiler systems without requiring facility modifications, new air permits, or combustion. Round-trip efficiency exceeds 97%. The storage medium — brick and wire — uses no scarce minerals, has no emissions, and is rated for a service life of 20-plus years. The off-grid solar configuration means the system charges during the lowest-cost hours of the day and delivers heat around the clock, decoupling generation from consumption with no fuel cost.

Commercialization & Traction

The Holmes Western project is Rondo Energy's most advanced commercial deployment and functions as the primary large-scale reference site for the company's global sales pipeline. Rondo has projects advancing across four continents and five industrial sectors, including chemicals, biofuels, food and beverage, and cement. The DOE Industrial Demonstrations Program selected Rondo and Diageo for up to $75 million in federal cost share for a comparable heat battery installation at Diageo's U.S. distillery facilities, validated in part by the Holmes Western operating record. The project was delivered with zero lost-time injuries and achieved all customer contract specifications.

Scalability & Strategic Context

Industrial heat accounts for approximately 25% of global final energy consumption, with the vast majority still supplied by fossil combustion. The Holmes Western deployment establishes that a 100 MWh heat battery can operate reliably at full industrial scale in a demanding continuous-process environment — the key commercial proof point for Rondo's broader market development. The system's drop-in compatibility with existing steam infrastructure removes the most significant adoption barrier for industrial operators, as no process interruption, new permitting, or facility redesign is required. Rondo's concurrent deployment at Heineken's brewery near Lisbon under an EDP heat-as-a-service contract demonstrates the model's applicability to the food and beverage sector on two continents simultaneously.