Energy Vault, a company developing grid-scale gravity energy storage solutions, has entered into an energy storage system agreement with DG Fuels, a developer of renewable hydrogen and biogenic-based, synthetic sustainable aviation fuel (SAF) and diesel fuel.

Under the terms of the agreement, Energy Vault agreed to provide 1.6 gigawatt hours (GWh) of gravity energy storage to support DG Fuels across multiple projects, with the first project slated for 500 megawatt hours (MWh) in Louisiana. DG Fuels expects to complete its Louisiana SAF project by mid-2022. This initial project will be followed by additional projects in British Columbia and Ohio.

Energy Vault’s advanced gravity energy storage solutions are based on the proven physics and mechanical engineering fundamentals of pumped hydroelectric energy storage, but replace water with custom-made composite blocks, or “mobile masses”, which do not lose storage capacity over time. The system uses proprietary technology to autonomously orchestrate the lifting and lowering of the bricks, storing the potential energy in the elevation gain, and generating then discharging electricity as the bricks are lowered.

The composite blocks can be made from low-cost and locally sourced materials, including the excavated soil at the construction site, but can also utilize waste materials such as mine tailings, coal combustion residuals (coal ash), and fiberglass from decommissioned wind turbine blades.

Additionally, the Energy Vault systems are intended to minimize environmental and supply chain risks, which was a critical factor in the final selection by DG Fuels. The systems are automated with advanced computer control and machine vision software that orchestrate the charging and discharging cycles while meeting a broad set of storage durations starting from 2 hours and continuing to 12 hours, or more.

DG Fuels (DGF) aims to develop several facilities in North America and Europe, designed to produce low-carbon sustainable aviation fuel by combining carbon from waste feedstock with green hydrogen from renewable sources. The Louisiana facility is the company’s first major project. Each facility will produce low-emissions fuel in a process that converts agricultural and timber waste feedstock into fuel with a carbon efficiency of approximately 93% or more—meaning that the project can produce more fuel with less feedstock than other processes.

DGF’s fuel production system better utilizes biomass feedstock over conventional biomass-to-liquids projects because of DGF’s use of waste CO₂ to make additional fuel. Depending on feedstock carbon content, DGF produces up to 3.6 barrels of biogenic blending component per ton of biomass feedstock compared to most other competitors who achieve about 1.1>1.3 barrel per ton of feedstock.

The basis of DGF’s integrated fuel and energy technology is the proven Fischer-Tropsch process, in use for more than 60 years. Existing plants around the world produce more than 170,000 BBL per day of synthetic fuel using Fischer-Tropsch. These facilities typically use approximately one ton of coal to produce one BBL of hydrocarbons, with a life cycle CO₂-emissions calculation that is slightly worse than equivalent fuels derived from conventional oil refining.

DGF’s method modifies the established Fischer-Tropsch system with several mechanisms that will decrease the CO₂-life-cycle emissions and reduce the quantity of feed-stock required. These changes eliminate the need for carbon sequestration and reduce the system’s feed-stock handling costs and complexity.

Additionally, DGF’s production method produces ASTM-certified direct replacement fuel with greater fuel density, lower particulate and NO_x emissions. The feed-stock reduction is achieved primarily by supplementing the process with oxygen and hydrogen produced by water electrolysis units that are powered by clean wind and solar generated electricity. DGF replaces the coal gasification used by others with biomass gasification and natural gas reforming. This simplifies implementation and further reduces new carbon emissions created in the process.

DG Fuels will deploy Energy Vault’s gravity storage systems to provide green electricity in conjunction with photovoltaic solar to firm and shape the renewable energy to match the demand load of the green hydrogen production. The renewable power will be used to power HydrogenPro water electrolysis for both hydrogen and oxygen feedstock production.

Energy Vault expects the agreement with DGF to provide up to $520 million in revenue across the three projects, the first of which expected to commence in mid-2022.